wastewater reclamation desalination technologies: a

WASTEWATER RECLAMATION DESALINATION TECHNOLOGIES: A TECHNO-ECONOMIC STUDY AT-SOURCE AND CENTRALISED TREATMENT OPTIONS

Thesis submitted in fulfillment of the requirements for the degree of

MASTER OF ENGINEERING

Mehdi Hedayati

School of Architectural, Civil and Mechanical Engineering Victoria University Melbourne, Australia February 2009

ABSTRACT

This research project was conducted to assist the Melbourne water industry decision makers to meet the Victorian State Government wastewater reclamation target of 20 per cent by 2010. The project focused on finding the best desalination technology for wastewater reclamation either at centralised wastewater treatment plants or at trade waste discharger sites, through development of a Decision Support Framework (DSF).

Although selecting of the best desalination technology is “site-specific”, the best desalination technology can be similar for a group of industrial facilities, if they have some common key parameters. This idea became the basis for the development of the DSF, considering several selection criteria including technical, cost, environmental, social and the commercial availability.

The DSF was demonstrated as an easy and practical tool through its application in several case studies including Western Treatment Plant (WTP), three trade waste facilities and a cluster of these facilities. The DSF selected desalination technology was also supported by further information about the desalination plant including cost, plant schematic, land and staff requirement, energy consumption and greenhouse gas emission.

This study recommends the Melbourne water planners to consider wastewater reclamation at the WTP as a short and medium term option for addressing the water shortage issue in Melbourne.

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DECLARATION

I, Mehdi Hedayati, declare that the Master by Research thesis entitled WASTEWATER RECLAMATION DESALINATION TECHNOLOGIES: A TECHNO-ECONOMIC STUDY AT-SOURCE AND CENTRALISED TREATMENT OPTIONS is no more than 60,000 words in length, exclusive of table, figure, appendices, references and footnotes. This thesis contains no material that has been submitted previously, in whole or in part, for the award of any other degree or diploma. Except where otherwise indicated, this thesis is my own work.

Mehdi Hedayati

Date 20/02/2009

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ACKNOWLEDGEMENTS

This project would not have been possible without the support and assistance of my supervisor Professor Chris Perera, Mr Nigel Corby from City West Water, and Dr. Simon Wilson from Melbourne Water Corporation. I would like to thank these gentlemen for their support.

City West Water provided funding as well as invaluable assistance including information and data. Victoria University also provided support, funding and resources, without which this project would never have proceeded. Again, thanks for invaluable support provided by Professor Chris Perera.

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TABLE OF CONTENTS

ABSTRACT………………………………………………………………………………………..i DECLARATION…………………………………………………………………………………..ii ACKNOWLEDGEMENTS……………………………………………………………………….iii TABLE OF CONTENTS………………………………………………………………………...iv LIST OF TABLES…………………………………………………………………………...…...X LIST OF FIGURES AND CHARTS..................................................................................Xii LIST OF ABBREVIATIONS……………………………………………………………….…..Xvi

CHAPTER 1 INTRODUCTION……………………………………………………………..1-1

1.1

BACKGROUND……………………………………………………………………..1-1

1.2

WASTEWATER RECLAMATION IN MELBOURNE……………………………1-2

1.3

AIMS OF THE PROJECT………………………………………………………….1-4

1.4

METHODOLOGY...........................................………………...…………………1-5

1.5

SIGNIFICANT OF THE RESEARCH…………………………………………..…1-5

1.6

OUTLINE OF THE THESIS……………………………………………………..…1-6

CHAPTER 2 MELBOURNE CURRENT WATER ISSUE………………………………..2-1

2.1

INTRODUCTION……………………………………………………………………...2-1

2.2

DEVELOPING ALTERNATIVE WATER RESOURCES FOR MELBOURNE.....2-2

2.3

MELBOURNE INDUSTRIAL WASTEWATER……….........................................2-4

2.4

WESTERN TRAETEMNT PLANT (WTP)……………………………………….....2-5 2.4.1

Loads of the Major Pollutants Discharged into WTP……………………..2-6

2.4.2

Wastewater Reclamation at the WTP……………………………………...2-7

2.4.3

Tackling the WTP Salinity Problem………………………………………...2-7

2.5 CLAENER PRODUCTION STRATEGY…………………………………………....2-8 2.5.1

Cleaner Production Opportunities……………………………………….....2-8

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2.5.2 2.6

CWW Cleaner Production Research and Development Program..........2-9

SUMMARY…………………………………………………………………………...2-9

CHAPTER 3

TECHNICAL ASPECTS OF DESALINATION PROCESSES……….....3-1

3.1

INTRODUCTION……………………………………………………………………3-1

3.2

WATER AND WASTEWATER IN INDUSTRY…………………………………..3-2

3.3

3.2.1

Desired Water Quality……………………………………………………….3-2

3.2.2

Generated Wastewater Quality……………………………………………..3-4

INDUSTRIAL WASTEWATER DESALINATION CONCEPT…………………..3-5 3.3.1

3.4

Desalination Train……………………………………………………………3-6

PRESSURE-DRIVEN DESALINATION TECHNOLOGIES……………….…...3-7 3.4.1

Technical Review…………………………………………………………….3-9 I.

Pre-Treatment…………………………………………………………..3-10

II. Membrane System Configuration…………………………………….3-11 III. Membrane Structure…………………………………………………...3-13 IV. Membrane Material Type……………………………………………...3-16 V. Operational Parameters……………………………………………….3-16 3.4.2

Practical Concerns………………………………………………………….3-17 I.

Fouling...................…………………………………………………….3-17

II. Scaling…………………………………………………………………..3-17 3.5

THERMAL (OR DISTILLATION) DESALINATION TECHNOLOGIES……...3-18 3.5.1

Technical Review…………………………………………………………...3-18 I.

Multi-Stage Flash (MSF)………………………………………………3-18

II. Multi-Effect Distillation (MED)…………………………………………3-20 III. Vapour Compression (VC)…………………………………………….3-21 3.5.2

Practical Concerns………………………………………………………….3-22 I.

Scaling…………………………………………………………………..3-22

II. Corrosion………………………………………………………………..3-22 3.6

OTHER DESALINATION TECHNOLOGIES…………………………………...3-22 3.6.1

Electrodialysis (ED) and Electrodialysis Reversal (EDR).....................3-23 I.

Advantages and Disadvantages……………………………………...3-24

II. Practical Concerns……………………………………………………..3-25 3.6.2

Ion Exchange (IX)…………………………………………………………..3-26

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Advantages and Disadvantages……………………………………...3-27

I.

II. Practical Concerns……………………………………………………..3-27 3.7

SUITABILITY OF TECHNOLOGIES FOR WASTEWATER RECLAMATION.............................................................................................3-28

3.8

SUMMARY…………………………………………………………………………3-29

CHAPTER 4 SUSTAINABILITY ASPECTS OF DESALINATION PROCESSES........4-1

4.1

INTRODUCTION……………………………………………………………………4-1

4.2

COST ASPECTS…..............................………………………………………......4-2 4.2.1

4.2.2

Cost Factors of Desalination...……………………………………………..4-3 I.

Quality of Feedwater…………………………………………………..4-3

II.

Plant Capacity………………………………………………………….4-5

III.

Site Characteristics……………………………………………………4-6

IV.

Cost Associated with Regulatory Requirements…….…………..…4-6

Cost Components of Desalination………………………………………….4-6 I.

Construction Cost……………………………………………………...4-6

II.

Direct Costs……………………………………………………...4-7

B.

Indirect Costs........................................................................4-7

Annual Costs................................................………………....……4-7

4.2.3

Cost Breakdown of Desalination...…………………………………..…...4-8

4.2.4

Hidden Costs of Desalination………………….........……………......….4-9

4.2.5

Future Costs of Desalination……………………………….....................4-9

4.2.6

Cost Estimating Methods....................................................................4-10

4.2.7

4.2.8 4.3

A.

I.

Cost-Chart Method...........................................….........................4-11

II.

Computer-Based Method……………………………………………4-11

Examples of Using Cost Estimating Methods…………………………...4-12 I.

Cost-Chart Method—Example 1…………….....…………………...4-12

II.

Computer-Based Method—Example 2……………………………..4-18

Cost Comparison of Desalination Technologies……………...…………4-22

ENVIRONMENTAL ASPECTS……………………………………….............…4-23 4.3.1

Concentrate Disposal………………………………………………….…4-23

4.3.2

Intensive Use of Energy…..……………………………………………..4-25

4.3.3

Greenhouse Gas Emission................................................................4-26

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4.4

SOCAIL ASPECTS……………………………………………………………….4-28

4.5

4.4.1

Noise Pollution……………………………………………………………4-28

4.4.2

Health Risks of Desalination Plant on Workers……………………….4-29

SUITABILITY OF TECHNOLOGIES FOR WASTEWATER RECLAMATION............................................................................................4-30

4.6

SUMMARY………………………………………………………………………...4-33

CHAPTER 5 DECISION SUPPORT FRAMEWORK...........…………………………….5-1

5.1

INTRODUCTION……………………………………………………………..........5-1

5.2

DECISION SUPPORT FRAMEWORK .................……………………………..5-2

5.3

5.2.1

Conceptual Idea......………………………………………………………....5-2

5.2.2

Developed DSF...................................................................................…5-3 I.

Cost…………………………………………………………………......5-5

II.

Technical Feasibility…….………………………………………….....5-5

III.

Records of Proven Commercial Practice.....………………….........5-6

IV.

Environmental Impacts………………………………………………..5-7

V.

Social Impacts….……………………………………………………...5-7

DSF ROUTES.......................................………………………………………….5-7 5.3.1

Thermal Desalination Technologies Route………………. ……………...5-8

5.3.2

Blending Viability Route..........................................................................5-9

5.3.3

EDR Application Route…………………………………………………….5-13

5.3.4

Raw Chemical Recovery and Reuse Route.......………………………..5-15

5.3.5

Residential Area Closeness Route....…………………………………….5-17

5.3.6

Water Softening Route……………………………………………………..5-18

5.4

FUTURE DEVELOPMENT OF DSF.....………………………………….……..5-20

5.5

SUMMARY…………………………………………………………………………5-21

CHAPTER 6 CASE STUDIES......................................................................................6-1

6.1

INTRODUCTION……………………………………………………………………6-1

6.2

WESTERN TREATMENT PLANT CASE STUDY………………………………6-1 6.2.1

Wastewater Treatment Train………………………………………………..6-3

6.2.2

Salt Reduction Demonstration Project……………………………………..6-4

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6.2.3

Feedwater Quality...................................................................................6-5

6.2.4

Desired Reclaimed Water Quality………………………………………….6-7

6.2.5

Site Infrastructure…………………………………………………………….6-7 I.

Land……………………………………………………………………….6-7

II. Energy…………………………………………………………………….6-9 III. Wastewater…………………………………………………………. …..6-9 6.2.6

Application of DSF...……………………………………………………….6-10

6.2.7

DSF Support Information…………………………..……………………...6-11 I.

Plant Schematic……………………………………………………….6-12

II. Land Requirements…………………………………………………....6-13 III. Staff Requirements…………………………………………………….6-13 IV. Costs………………………………………………………………….…6-14 V. Energy Requirement…………………………………………………...6-19 VI. Greenhouse Gas Emission...........…………………………………...6-20 6.3 TRADE WASTE FACILITY CASE STUDIES.................……………………...6-20 6.3.1

Application of DSF...……………………………………………………….6-22 I.

A Tannery Facility (Facility X)…………………………………..........6-22

II. A Fat and Oil Processing Facility (Facility Y)………………….........6-23 III. A Poultry Facility (Facility Z)…………………………………….........6-24 6.3.2 6.4

DSF Support Information……………………………..…………………...6-25

CLUSTER CASE STUDY………………………………………………………...6-30 6.4.1

Application of DSF....……………………………………………………….6-31

6.4.2

DSF Support Information…………………………………………………..6-32

6.5 COMPARISON OF SOME SELECTED INFORMATION OF CASE STUDIES.......................................................................................................6-36

6.6

6.5.1

Production Cost……………………………………………………………..6-36

6.5.2

Energy Requirement……………………………………………………….6-37

6.5.3

Greenhouse Gas Emission………………………………………………..6-38

SUMMARY…………………………………………………………………………6-38

CHAPTER 7 SUMMARY, CONCLUSION AND RECOMMENDATIONS……………...7-1

7.1

SUMMARY AND CONCLUSION………………………………………………….7-1 7.1.1

Literature Review…………………………………………………………….7-2

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7.1.2

Decision Support Framework……………………………………………….7-2

7.1.3

Demonstration of the Decision Support Framework……………………..7-3

7.2

RECOMMENDATIONS……………………………………………………………7-4

7.3

RECOMMENDATIONS FOR FUTURE WORKS………….....…………………7-5

REFERENCES……………………………………………………………………………..…R-1

APPENDIX A: MEMBRANE DESALINATION WATER CHEMISTRY…………………..A-1

APPENDIX B: DESALINATION PLANT COST ESTIMATING CHARTS……………….B-1 PPENDIX C: WTCost© SOFTWARE APPLICATION FOR THE VARIOUS..................C-1 PRE-TREATMENT SYSTEMS FOR THE WTP CASE

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LIST OF TABLES

Table 2.1

Major Sources of Pollutants Discharged into the WTP…………………..2-6

Table 3.1

Typical Quality Limits for the Selected Industries………………………...3-3

Table 3.2

Main Characteristics of Some Selected Industries Wastewater………...3-4

Table 3.3

Advantages and Disadvantages of Membrane Desalination Systems…3-9

Table 3.4

Advantages and Disadvantages of EDR Process………………………3-25

Table 3.5

Advantages and Disadvantages of Ion Exchange………………………3-27

Table 4.1

Summary of the Example 1 Basic Data………………………………….4-13

Table 4.2

Example 1 Desalination Plant Capital Costs Summary………………...4-15

Table 4.3

Example 1 Desalination Plant Annual Costs Summary………………...4-17

Table 4.4

Summary for the Required Information for Example 2..........................4-20

Table 4.5

Cost Summary for Example 2, Calculated by WTCOST© Software…..4-22

Table 4.6

Energy Requirement for the Common Desalination Systems…….......4-25

Table 4.7

Relevant Airborne Emissions Produced by Desalination Systems……4-27

Table 4.8

The Most Common Chemicals Used in Membrane Processes……..…4-30

Table 4.9

The Ranking System Specifications.....................................................4-32

Table 6.1

Raw Water Quality Data for the WTP from November 2005 to August 2006............................................................................................6-6

Table 6.2

Operation and Maintenance Staff for Membrane Processes…………..6-13

Table 6.3

Information Summary for the WTP……………………………………….6-15

Table 6.4

The WTP Desalination Plant Capital Costs Summary………………….6-16

Table 6.5

The WTP Desalination Plant Annual Costs Summary………………….6-16

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Table 6.6

The WTP Desalination Plant Cost Summary Calculated by WTCost© Software……………………………………………………………………...6-18

Table 6.7

Information Summary for Three CWW Trade Waste Facilities……......6-22

Table 6.8

Summary of the Support Information for Facility X, Y, and Z................6-26

Table 6.9

Facility X Cost Summary Calculated by WTCOST© Software…….......6-27

Table 6.10

Facility Y Cost Summary Calculated by WTCOST© Software…….......6-28

Table 6.11

Facility Z Cost Summary Calculated by WTCOST© Software…….......6-29

Table 6.12

Summary of the Support information for Common Desalination...........6-34

Table 6.13

Common Desalination plant Cost Summary Calculated by WTCOST© Software................................................................................................6-35

Table C.1

WTP Desalination Plant Cost Summary Calculated By WTCost© Software for Granulated Activated Carbon Pre-Treatment System.......C-1

Table C.2

WTP Desalination Plant Cost Summary Calculated By WTCost© Software for Gravity Filtration Pre-Treatment System............................C-2

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LIST OF FIGURES AND CHARTS

Figure 2.1

Energy Intensity of Water Sources in San Diego County………………..2-3

Figure 3.1

General View of a Desalination train……………………………………….3-6

Figure 3.2

Size Separation Capabilities of Different Membrane Systems……….…3-8

Figure 3.3

Typical Conventional Pre-Treatment……………………………………..3-10

Figure 3.4

Typical UF Membrane Pre-Treatment……………………………………3-11

Figure 3.5

Single Stage Flow…………………………………………………………..3-12

Figure 3.6

Two Stage Flow……………………………………………………………..3-12

Figure 3.7

Two Pass Flow……………………………………………………………...3-12

Figure 3.8

Hollow Fibre Module………………………………………………………..3-14

Figure 3.9

Spiral-Wound Module………………………………………………………3-14

Figure 3.10

Tube Module………………………………………………………………...3-14

Figure 3.11

Plate and Frame…………………………………………………………….3-15

Figure 3.12

Guide to Application for Tubular, Hollow Fibre, and Spiral-Wound Systems…………………………………………………………………...…3-15

Figure 3.13

Schematic of Multi-Stage Flash (MSF) Desalination Process…………3-19

Figure 3.14

Schematic of Multi-Effect Distillation (MED) Desalination Process...…3-20

Figure 3.15

Schematic of Single Stage MVC Desalination Process.........................3-21

Figure 3.16

An ED Unit in Operation……………………………………………………3-23

Figure 3.17

Ion Exchange Principals for Water Softening……………………………3-26

Figure 4.1

Sustainable Development Components..................................................4-1

Figure 4.2

Costs for a RO Desalination Plant Versus Feed Salinity………………...4-4

Figure 4.3

Costs of Low to Medium Saline Water Desalination……………………..4-5

.

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Figure 4.4

Cost Breakdowns for RO Desalination of Brackish Water……………....4-8

Figure 4.5

Cost Breakdowns for RO Seawater Desalination………………………...4-9

Figure 4.6

Cost Breakdowns for Typical Seawater MED Desalination Plant……....4-9

Figure 4.7

Comparison of Concentrate Disposal Methods for all Brackish Processing Facilities in the U.S.A…………………...………………..…..4-24

Figure 4.8

Energy Consumption Comparison RO-EDR Systems……………….....4-26

Figure 4.9

Feed Pressure versus Feedwater TDS for Different RO Systems…....4-29

Figure 4.10

Four-Level Hierarchy in Mohsen et al. Study........................................ 4-31

Figure 4.11

Relative Global Weight for the Commercial Desalination

...

Technologies.........................................................................................4-32 Figure 5.1

Developed DSF to Select the Best Desalination Technologies for Wastewater Reclamation…………………..………………………………..5-4

Figure 5.2

Thermal Desalination Technologies Route………………………………..5-8

Figure 5.3

Typical Blending Form of Permeate and Raw Wastewater.................. 5-10

Figure 5.4

Blending Option Route…………………………………………………….. 5-11

Figure 5.5

EDR Technology Application Route………………………………………5-13

Figure 5.6

Raw Chemicals Recovery/Reuse Route………………………………....5-16

Figure 5.7

Closeness to a Residential Area Route……………………………….… 5-17

Figure 5.8

A Typical Boiler House Operation………………………………………...5-18

Figure 5.9

Water Softening Route……………………………………………………..5-19

Figure 6.1

Western Treatment Plant Location......................................................... 6-2

Figure 6.2

Wastewater Treatment Train at the WTP………….................................6-4

Figure 6.3

The WTP Site Plan……….………………………………………………….6-8

Figure 6.4

Simple Plant Schematic for the WTP Desalination Plant......................6-12

Figure 6.5

Effects of Various Pre-Treatment Systems Costs for the WTP………. 6-19

Figure 6.6

Simple Schematic of Facilities X, Y and Z Wastewater Streams…….. 6-31

.....

...

.....

....

....

............

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Figure 6.7

Simple Plant Schematic for the Common Desalination Plant.............. 6-33

Figure 6.8

Cost Comparison of the Case Studies………………………...…...........6-36

Figure 6.9

Energy Comparisons Between Case Studies………............................ 6-37

Figure 6.10

Greenhouse Gas Emission (GHG) Comparisons Between Case

..

Studies.................................................................................................6-38 Chart B.1

Total Construction Cost – MSF Process..................................................B-1

Chart B.2

Total Construction Cost – MED Process.................................................B-1

Chart B.3

Total Construction Cost – MVC Process................................................B-2

Chart B.4

Total Construction Cost – SWRO, BWRO, and NF Processes..............B-2

Chart B.5

Total Construction Cost – EDR Process..................................................B-3

Chart B.6

Concentrate Disposal Pipeline Cost - Thermal Processes.....................B-3

Chart B.7

Concentrate Disposal Pipeline Cost - Membrane Processes.................B-4

Chart B.8

Site Development Cost - Thermal Processes.........................................B-4

Chart B.9

Site Development Cost - Membrane Processes.....................................B-5

Chart B.10

Product Storage Tank Cost - Thermal Processes...................................B-5

Chart B.11

Product Storage Tank Cost - Membrane Processes...............................B-6

Chart B.12

Land Requirements - Thermal Processes..............................................B-6

Chart B.13

Land Requirements - Membrane Processes..........................................B-7

Chart B.14

Labour Cost - Thermal Processes..........................................................B-7

Chart B.15

Labour Cost - Membrane Processes......................................................B-8

Chart B.16

Chemical Cost - MSF Process............................................................... B-8

Chart B.17

Chemical Cost - MED Process...............................................................B-9

Chart B.18

Chemical Cost - MVC Process...............................................................B-9

Chart B.19

Chemical Cost - Membrane Processes................................................B-10

Chart B.20

Electricity Cost - MSF Process.............................................................B-10

Chart B.21

Electricity Cost - MED Process.............................................................B-11

..

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Chart B.22

Electricity Cost - MVC Process...........................................................B-11

Chart B.23

Electricity Cost - Membrane Processes..............................................B-12

Chart B.24

Steam Cost - Thermal Processes.......................................................B-12

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LIST OF ABBREVIATIONS

ABS

-

Australian Bureau of Statistics

AF

-

Acre Foot (1 acre foot = 1,233.48 m3)

AGO

-

Australian Greenhouse Office

AHP

-

Analytical Hierarch Process

BOD

-

Biochemical Oxygen Demand

CA

-

Cellulose Acetate

CP

-

Cleaner Production

COD

-

Chemical Oxygen Demand

CO2-e

-

Carbon Dioxide Equivalents

CSIRO -

Commonwealth Scientific and Industrial Research Organisation

CWW

-

City West Water

DCC

-

Direct Capital Cost

DEEP

-

Desalination Economic Evaluation Program

DSE

-

Department of Sustainability and Environment

DSF

-

Decision Support Framework

ED

-

Electrodialysis

EDR

-

Electrodialysis Reverse

EPA

-

Environmental Protection Authority (NSW, Victoria etc.)

IAEA

-

International Atomic Energy Agency

IBID

-

Latin: At the Same Place (or ibid)

IX

-

Ion Exchange

MED

-

Multi Effect Distillation

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MF

-

Microfiltration

MSF

-

Multi Stage Flash

MWC

-

Melbourne Water Corporation

MVC

-

Mechanical Vapour Compression

NF

-

Nanofiltration

NTU

-

Nephelometric Turbidity Units

OH&S

-

Occupational Health and Safety

O&M

-

Operating and Maintenance

RO

-

Reverse Osmosis

SAR

-

Sodium Absorption Ratio

SDI

-

Silt Density Index

SS

-

Suspended Solids

TCC

-

Total Capital Cost

TF

-

Thin Film

TDS

-

Total Dissolved Solids

TSS

-

Total Suspended Solids

UF

-

Ultrafiltration

UNEP

-

United Nations Development Program

USA

-

United State of America

UV

-

Ultraviolet

VC

-

Vapour Compression

WTP

-

Western Treatment Plant

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CHAPTER 1: INTRODUCTION

CHAPTER 1 INTRODUCTION 1.1

BACKGROUND

Fresh water resources on Earth are limited. The human stress on these resources is increasing as the global population increases, and consequently demands for urban, irrigation and industrial usages are increased. In addition, improving living standards, the global warming and the extended drought in some parts of the world make this situation worse.

Several options have been practised around the world to reduce the pressure on fresh water resources. These include increasing the water usage efficiency, seawater desalination and stormwater reuse. Combination of these options or their solo application has been reported in the literature, especially in relation to arid and semi-arid areas (Thomas et al., 2003). In recent years, more efforts have been concentrated on wastewater reclamation by desalination as a new alternative water resource especially for agricultural applications (Harussi et al., 2001). It is also anticipated that the trend of using desalination as a means of reclaiming water from wastewater will be increased in the future (Cooley et al., 2006).

Although desalination technologies have been practised commercially for seawater and groundwater desalting for more than half a century (Buros, 2000), its application for wastewater reclamation is relatively new. Wastewater has different characteristics to seawater and groundwater in terms of uniformity of quality and quantity (Redondo, 2001), and complexity of removing salts. Thus, more care is required to select the appropriate desalting technique and the optimum desalination train (i.e. pre-treatment; main treatment; post treatment and waste disposal) for wastewater desalination.

Wastewater reclamation via desalination has significantly changed the view to wastewater from a “waste view” to a “commodity view” (Asano, 2001). It also can help to close the loop between water supply and wastewater disposal. At present, the secondary treated wastewater from some wastewater treatment plants which used to be

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discharged to the environment, are reclaimed via desalination and utilised as a water source for agricultural irrigation purposes. The Sulaibiya Reclamation Desalination Plant in Kuwait is the current largest wastewater reclamation plant in the world (Water Technology, 2005) that uses membrane technology for water reclamation. This plant treats 375,000 m3/d

wastewater to potable quality for non-potable uses in agriculture,

industry and aquifer recharge. This plant contributes 26% of Kuwait’s overall water demand (ibid).

The recent extended drought in Australia has pushed the Australian Government to investigate more seriously about alternative water resources including wastewater reclamation via desalination. The new Kwinana Water Reclamation Plant in Perth - the largest of its kind in Australia - is an example of the Australian view on this subject. This plant reduces the volume of potable water supplied to industry by replacing an expected 6 GL a year - about 2% of the Perth’s total unrestricted water demand - with high quality industrial grade water (Water Technology, 2007).

Wastewater also can be reclaimed within the industrial facilities and be utilised for industrial applications including cooling systems (Kinhill, 1999). There are many examples of reusing reclaimed wastewater for industrial applications in the literature (e.g. Jefferson et al., 2004). Currently, dairy, textile, beverage, tanning, and electronic industries are the leading sectors in terms of interest for on-site wastewater reclamation via desalination (ibid). There are further examples of desalination practices for wastewater reclamation in other industrial sectors (Brown, 2003).

1.2

WASTEWATER RECLEMATION IN MELBOURNE

Melbourne currently is faced with an extended severe drought (1997 - to date) and therefore, finding alternative water resources for such a growing city is a vital task for the Melbourne water industry decision makers. The Victorian State Government has requested Melbourne water retail companies to reduce water consumption per capita by 15% and recycle 20% effluent from Melbourne’s sewage treatment plants by 2010 (Corby, 2005). The current wastewater reclamation in Melbourne is not significant. In fact, just about 2% of Melbourne sewage effluent was treated and recycled in 2001-02 (Radcliff, 2004). However, in recent years more efforts have been undertaken to

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increase this usage. A report by the Australian Academy of Technological Science and Engineering has outlined the list of these efforts which include the details of ongoing commercial and demonstration projects in Melbourne (ibid).

Melbourne Water Corporation (MWC) manages the Melbourne water resource supplies and wastewater treatment. There are also three retail water companies which co-operate with MWC in this regard. City West Water (CWW) is one of these companies which delivers fresh water and conveys sewerage and trade waste (industrial effluent) into its treatment plant in Altona and also into MWC owned Western Treatment Plant (WTP) at Werribee. The CWW working area is mainly the central and western parts of Melbourne.

To meet the State Government recycling target by 2010, MWC and CWW pursue options to reclaim wastewater in Melbourne especially wastewater reclamation at the WTP. The biggest challenging issue to use the WTP secondary treated wastewater for agricultural usage is its high salt content (about 1000 mg/L). The required salinity for sustainable wastewater usage for agricultural applications is less than 600 mg/L (GHD, 2004). With regard to this point, the conventional wastewater treatment technologies are mainly designed to remove the suspended particles (Muttamara, 1996) from wastewater, and the current conventional wastewater treatment train at the WTP cannot reduce the salt level to the required level for agricultural applications. Therefore, a desalting device needs to be adopted for the WTP to remove the salt from the secondary treated wastewater before any reuse in agriculture.

A trial desalination plant at the WTP examined performance of various desalination technologies for wastewater reclamation during November 2005 to August 2006 (Poon et al., 2007). Having a 200 ML/d desalination plant at the WTP, will help MWC and CWW to enhance the Melbourne alternative supply sources and also will provide a “drought-proof” water resource for the 70 million dollar a year agricultural business for farmers around the WTP (MWC, 2005a).

Wastewater reclamation at the WTP is a typical example of “end-of-pipe” or “Centralised” solution to tackle water shortage in Melbourne. Another approach, which in particular CWW is interested to study, is wastewater reclamation at the wastewater generation source or “Decentralised Option”, such as at industrial and commercial

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facilities. CWW has more than 5000 trade waste facilities (URS, 2005). These facilities account for about 44% of the WTP salt content (ibid). The top 30 salt discharger companies account for more than 60 per cent of the CWW trade waste Facility salt discharge to the WTP (ibid).

In addition to the salts generated by the CWW trade waste facilities, salts also come to the WTP from other sources such as domestic detergents which contribute to about 35 per cent of the plant salinity (GHD, 2004). However, the investigation of other salt sources coming to the WTP is not within the scope of this research project and the project is focussed on salt discharged from the CWW trade waste facilities into the WTP.

1.3

AIMS OF THE PROJECT

The main aim of this research project is to develop an easy and practical tool for determining the best desalination technology for wastewater reclamation. This practical tool is a Decision Support Framework (DSF) which can systematically assess the commercial desalination technologies for wastewater reclamation based on their technical feasibility and sustainability criteria (cost, environmental, and social aspects). Therefore, the DSF is expected to aid water industry decision makers reclaiming wastewater at “lowest cost to community”.

A secondary aim of this research project is to address the most challenging issues which are associated with construction and operation of the DSF selected desalination technology plant. These challenging issues include the costs associated with the construction and operation of the desalination plant, the land and staff requirement for the operation of the desalination plant, the energy requirement for the desalination process, and the greenhouse gas emissions associated with the operation of the desalination process. The information related to these challenging issues is called DSF support information in this thesis.

1.4

METHODOLOGY

The above aims (Section 1.3) were achieved by conducting research into:

Page 1-4


Primary aim:

1. Assessing the suitability of the commercial desalination technologies for wastewater reclamation based on their technical and sustainability aspects (i.e. cost, environment and social). 2. Clarifying the dependency nature of the best desalination technology to the facility (i.e. whether it is site-specific or a desalination technology can be recommended for a group of industrial facilities). 3. Identifying key parameters or conditions which can be used to classify industrial facilities, if a desalination technology can be recommend for a group of industrial facilities. 4. Developing a Decision Support Framework (DSF) to select the best desalination technology for wastewater reclamation based on technical and sustainability aspects of desalination processes. 5. Demonstrating the DSF applicability through its applications to several case studies.

Secondary aim:

6. Identifying information sources which can be used to address the challenging issues related to DSF selected desalination process.

1.5

SIGNIFICANCE OF THE RESEARCH

The Victorian State Government has requested the Melbourne water companies to recycle 20% of Melbourne wastewater by 2010 (Corby, 2005). This research project is of direct relevance to this State Government target for Melbourne wastewater reclamation and reuse.

The Decision Support Framework (DSF) developed in this study is expected to be used as an easy and practical tool to facilitate the selection of the best desalination technology for wastewater reclamation for certain applications. The DSF uses information from the literature or best practised examples, nationally or internationally.

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It is anticipated that the results of this research project could save significant cost, time and energy for Melbourne water decision makers who consider wastewater reclamation via desalination as a possible solution to water shortage in Melbourne. For instance, CWW pursues feasibility studies of wastewater reclamation via desalination in its hundreds of trade waste facilities. The DSF will enable CWW to investigate the best desalination technology for each facility, based on the facility specific conditions (i.e. available energy source, wastewater quality, desired reclaimed water quality and quantity, etc.). The DSF support information including the cost estimating tools also will provide CWW and its trade waste facilities a full understanding of the capital and operating costs associated with desalination projects. The DSF support information will also provide the decision makers some tools to estimate the amount of energy required for desalination and the amount of greenhouse gas emissions, resulting from the operation of the desalination plant. In another words, the results of this research project will help the Melbourne water authorities to implement wastewater reclamation via desalination at “lowest community cost”.

1.6

OUTLINE OF THE THESIS

Chapter 1 provided an overview of the thesis and importance of wastewater reclamation as an alternative water resource. The aims of the research project and a brief methodology were also presented in Chapter 1.

Chapter 2 reviews the Melbourne current water issue, the Victorian State Government recycling target and the major opportunities for Melbourne water authorities to meet this target. Wastewater reclamation via desalination at the WTP is investigated in more detail in Chapter 2 due to its high potential to be considered as the best technology for wastewater reclamation in Melbourne. The salinity caused by the CWW trade waste facilities is also investigated in Chapter 2, and the CWW plans such as the CWW Cleaner Production Strategy is also reviewed.

Chapters 3 and 4 provide a comprehensive review of the literature in relation to wastewater

reclamation

via

desalination.

Technical

and

sustainability

(cost,

environmental and social) aspects of the commercial desalination technologies are discussed in detail in these chapters.

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In order to select the best desalination technology for wastewater reclamation, either for centralised option (i.e. the WTP) or for decentralised option (i.e. the CWW trade waste Facility sites), a Decision Support Framework (DSF) was developed in this research project. This DSF is discussed in Chapter 5.

Chapter 6 presents several case studies that were used to demonstrate applicability of the DSF. These case studies include the wastewater reclamation via desalination at the WTP, and at three CWW trade waste facilities. In the latter case, the DSF was applied to CWW trade waste facilities as single facilities and as a group sharing one desalination plant. The results of these applications are also presented in Chapter 6.

A summary of the work conducted and the conclusions arose from this work are detailed in Chapter 7. Recommendations for future work, based on the findings of this research project, are also presented in Chapter 7.

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CHAPTER 2: MELBOURNE CURRENT WATER ISSUE

CHAPTER 2 MELBOURNE CURRENT WATER ISSUE 2.1

INTRODUCTION

Melbourne is the second largest city in Australia, and is located at the south-eastern tip of the Australian mainland. Over the past century and a half, Melbourne has grown from a city of a few hundred thousand people to over 3.5 million people, and is expected to continue to grow during this century. Melbourne has a temperate climate and dry heat. Historically, Melbourne has depended on large, surface water storage for its water supplies (MWC, 2005a).

Approximately 90% of Melbourne’s water comes from

uninhabited and restricted access catchment areas located high in the Yarra Ranges (MWC, 2005b). The dependency on rainfall for water supply has exposed this city to some main concerns about its future sustainable growth. A recent study undertaken by CSIRO (MWC, 2005b) about the impacts of climate change on Melbourne water resources indicates that there are some vital areas of risk in this regard. This study projects reduced streamflows between 3% and 11% by 2020, and as much as 7% to 35% by 2050. In addition, this study estimated increase in the summer temperature of up to 2.5ºC in 2050. In another words, Melbourne will experience less rainfall, and an increase of dry and hot days in the future. In response to the projected increase in Melbourne’s population and to mitigate the impacts of climate change on the Melbourne water supplies, the Victorian Government has taken steps toward future action. The Our Water Our Future action plan (which is commonly known as the White Paper), which was released in 2004 and sets out 110 actions to secure Victoria’s water future over the next 50 years (DSE, 2004). It covers all aspects of water management-water allocation, smarter use of urban water and irrigation water, the protection of rivers and aquifers, pricing for sustainability and improvements to the water industry. The two major targets of the Victorian Government for water conservation listed in the White Paper are 20% water recycling and 15% water consumption reduction per capita. The Melbourne water businesses have started to meet these targets through different strategies and projects including the Salt Reduction

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Strategy. The activities that are related to water conservation in Melbourne are discussed in more detail in the remainder of this chapter. 2.2

DEVELOPING ALTERNATIVE WATER RESOURCES FOR MELBOURNE

There is no doubt that relying on conventional water resources such as rainfalls is too risky for Melbourne, as there is the possibility of severe drought. Soon, Melbourne water demands will exceed the available fresh water supplies (DSE, 2005a) and therefore, Melbourne water businesses need to find alternative water resources to overcome the water shortage. Currently, Melbourne water authorities are examining various options to solve this problem. In other Australian capital cities such as Sydney and Perth, the water planners have included seawater desalination in their water resource management, in addition to water conservation and recycling options including stormwater management and increasing water usage efficiency. The Melbourne water planners have also employed some of these options and continue to examine the possibility of constructing a seawater desalination plant in Melbourne.

Wastewater reclamation via desalination for non-

potable applications such as irrigation and industrial usage (e.g. cooling tower application) has been also considered by the Melbourne water decision makers. Construction of a trial wastewater reclamation (via desalination) plant at the Melbourne’s biggest wastewater treatment plant, the Western Treatment Plant (WTP) in Werribee is a typical example of this interest. In spite of the current strong support from communities for the construction of a desalination plant in Melbourne, there are some concerns about the energy consumption of the desalination process compared to other water resources. This might be a valid concern for seawater desalination which requires a significant amount of energy usage for water production, but it might not be a valid concern for wastewater desalination. The results of a survey conducted in San Diego in the U.S.A (Cooley et al., 2006) indicate that wastewater reclamation via desalination requires the minimum amount of energy among seven water supply options. Figure 2.1 summarises the results of this study. In this figure, reclaimed wastewater has an energy intensity of less than 500 kWh/AF.

Page 2-2


Figure 2.1 Energy Intensity of Water Sources in San Diego County (Cooley et al., 2006) The only major drawback of wastewater reclamation via desalination is consumer perception. People are usually reluctant to drink water that has been a waste at some stage. Thus, some recommend constructing a seawater desalination plant rather than a wastewater desalination plant, because of this public concern. However, this anxiety can also be addressed if the application of reclaimed wastewater is limited only to some crop irrigation or industrial applications. Wastewater desalination is able to produce water which is of suitable quality for agricultural and industrial usage. An appropriate desalination train can remove pathogens, viruses and all water born pollutants. On a global scale, about 70 per cent of water from available sources is used for agriculture purposes, primarily irrigation, with the remainder used for domestic and industrial purposes (Schmidt, 2004). This research project does not consider the usage of reclaimed wastewater for Melbourne domestic consumption such as being used as drinking water. However, it should be noted that the water quality produced from wastewater desalination may even be better than the current drinking water in terms of quality, depending on the

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desalination train used. Application of reclaimed wastewater for Melbourne industrial and agricultural purposes is the main objective of this research project. The Melbourne industry distribution and water demand is studied in the next section due to its association with the project. 2.3

MELBOURNE INDUSTRIAL WASTEWATER

Melbourne industries are more concentrated in the western side of the city. There are several reasons (MWC, 2005a) for this concentration including: •

Initially, industries in Melbourne chose locations near ports, railways, and waterways to enable transport of goods. Most of these infrastructures were in the west of the city.

•

After the Second World War, Melbourne industrial growth was mostly in the west.

•

The local government councils offered cheap leases for land located in the western parts of Melbourne, to speed up economic growth of the western suburbs.

Accumulation of the Melbourne’s heavy industries in its western parts has both benefits and drawbacks. Trade waste discharged by these industries which are usually are very concentrated and polluted can be diluted by other wastewater sources including domestic wastewater and stormwater at Western Treatment Plant (WTP). In addition, due to the economy of scale, heavy industries trade waste can be treated more cheaply when they all discharged to the same treatment plant (i.e. at WTP). However, the high level of salt discharged by industry has a negative impact on WTP water reclamation opportunities. Approximately, 65 % of the salts discharged into the WTP come form the industry (URS, 2005). As salts cannot be removed by the existing treatment facilities at the WTP, the secondary treated wastewater of the WTP is too salty and it cannot be directly reused for applications such as crop production. Industry and commerce use almost one-third of Melbourne drinking water supplies with the top 200 water users accounting for about 10 per cent of this figure (DSE, 2005b). They use water for various applications including as a raw material (i.e. the beverage industry), as a coolant (i.e. in cooling tower) and as wash down and for dust suppressions.

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The required water quantity and quality in Melbourne industrial facilities vary from sector to sector and even from plant to plant within the same sector. Some have supplementary water resources such as internal or external recycled water. However, in general, it can be said that water recycling has not been practised by Melbourne industries to a great extent. Based on a report published by Australian Bureau of Statistics (ABS, 2003), the Victorian water recycling in the industrial sector accounts for less than 5% of the total water reused in Victoria, excluding agriculture industry, in the financial year 2000-2001 year. In Japan, this figure is about 40% (Asano et al., 1998). The major issues for Melbourne industrial wastewater recycling appear to include water quality, potential health impacts, public and employee perceptions, lack of information, potential liability and relative cost of alternative water sources. Overcoming such issues and having an onsite water reclamation plant for each individual Melbourne industrial unit requires long term planning (Brown, 2003). Therefore, to address the current Melbourne water shortage, reclaiming wastewater at the WTP should be considered as a strong candidate for consideration. The details of wastewater reclamation opportunities at the WTP (which are sometimes referred to as “end-of-pipe” or centralised wastewater reclamation option in a general sense) are presented in the next section. 2.4 WESTERN TREATMENT PLANT (WTP) The Western Treatment Plant (WTP), one of the largest treatment plants in the world, is situated on the shores of Port Phillip Bay at Werribee, southwest of Melbourne. This plant is operated and managed by Melbourne Water Corporation. The WTP receives and treats most of the sewage produced in Melbourne’s western and northern suburbs, comprising approximately 500 ML/day of raw sewage (MWC, 2005a) including most industrial wastes. Generally, the purpose of sewage treatment is to remove suspended solids, organic matter, nutrients and disease-causing organisms until all that remains is a liquid effluent, suitable for discharge on land, inland waterway or the ocean. At the WTP this is achieved by three modern lagoon systems. A lagoon system is made up of 10 lagoons or ponds. Sewage flows slowly through these lagoons, allowing bacteria already in the water to break down the organic material. The water gets cleaner and cleaner as it flows

Page 2-5


through each of the lagoons (MWC, 2005a) until the effluent meets the EPA Victoria license requirements for discharge into Port Phillip Bay. 2.4.1

Loads of the Major Pollutants Discharged into WTP

Table 2.1 presents eight sources of the major pollutants discharged into WTP (DSE, 2005b). Table 2.1 Major Sources of Pollutants Discharged into the WTP (DSE, 2005b)

Western Sewage Treatment Plant Werribee (WTP)

Source

Flow (ML p.a.)

BOD (t.a)

SS (t.p.a)

Nitrogen (t.p.a)

TDS (t.p.a)

Domestic

93984

19079

25000

5357

35245

Commercial

29187

5925

764

1663

10946

Septage

11

117

251

10

9

Ind/Greasy

2456

498

653

140

921

Trade Waste

26890 (15%)

35321 (45%)

16651 (26%)

1744 (15%)

79201 (44%)

Inflow

576

0

8

0

690

Infiltration

8675

0

43

32

16706

Unaccounted

12750

18065

13882

2627

37310

Total WTP

174529

79006

64252

11575

181027

Based on this table, trade waste (industrial wastewater) accounts for about 15% of the flow to the WTP, about 45%, 26%, and 15% respectively for biological oxygen demand,

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suspended solids and nitrogen pollutant load into the WTP. The total dissolved solids (TDS) load contribution of trade waste is about 44%, which is the biggest salinity source at the WTP.

2.4.2

Wastewater Reclamation at WTP

Water reclamation and recycling at the WTP has two significant benefits for the Melbourne water authorities. They are as follows (MWC, 2005a): 

It helps them to work towards meeting the State Government water recycling target of 15% by 2010.



It assists them in their commitments to provide sustainable and safe water for the Werribee District development projects including the Werribee Irrigation District project.

The existing wastewater treatment processes at the WTP are able to meet the reclaimed water quality, specified by EPA Victoria, except the TDS limit (MWC, 2005b). Dissolved salts cannot be removed by the existing conventional treatment processes which are normally designed for the removal of suspended particles (Sonune et al., 2004). The typical salinity level of sewage effluent from the WTP is 1050 (mg/L) but investigations have shown that the most appropriate and sustainable uses of recycled water require a salinity level of 550 (mg/L) (GHD, 2004).

2.4.3

Tackling the WTP Salinity Problem

As outlined in Section 2.4.1, the biggest salinity source at the WTP is industry, which accounts for about 44% of the total salt contributed. Melbourne Water Corporation and City West Water both investigate ways to minimise the salt level discharged by the Melbourne western industries by pursuing various strategies including the Salt Reduction Strategy. The Salt Reduction Strategy aims to reduce the salts generated by the industry through a combination of at-source and end-of–pipe initiatives and therefore reduce the salts level in the recycled water from the WTP by 40% by 2009 (MWC, 2005a).

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Examples of at-source activities include encouraging industries to minimise their trade waste salinity level through the implementation of the cleaner production opportunities (e.g. replacing HCl to CO2 as a cleaning chemical in dairy industry). The examples of end-of-pipe activities include the construction of a wastewater reclamation plant at the WTP.

2.5

CLEANER PRODUCTION STRATEGY

Cleaner Production (CP) is defined by the United Nations Environment Program (UNEP) as:

“The continuous application of an integrated preventative, environmental strategy applied to processes, products and services to increase eco-efficiency and reduce risks to humans and the environment” (UNEP, 2000).

The Environment Protection Authority Victoria requires all water businesses including CWW to implement all practical options to avoid waste generation (EPA Vic, 2003). In response to this requirement, CWW Cleaner Production Strategy was finalised in July 2003 (CWW, 2003). The strategy directs CWW to work with industrial facilities to: 

Reduce parameters of concern such as TDS to sewer;



Reduce the use of potable water by industrial facilities; and



Identify options for using reclaimed water in the future.

Approximately 550 tonnes of TDS enter the WTP each day. It has been estimated that 30% of this, or 168 tonnes per day, emanates from CWW’s facility base trade waste discharge (Corby, 2005). Approximately 80% of this load is discharged by 30 of CWW’s trade waste customers (ibid). Successful implementation of the Cleaner Production opportunities in these facilities can create a significant reduction in the salt level discharged into the WTP.

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2.5.1

Cleaner Production Opportunities

Cleaner production opportunities are site specific. Those opportunities that might create a significant reduction on the salt level discharged by trade waste facility are facilityactivity dependent. However, there are some similarities in Cleaner Production opportunities over the majority of the industrial sites. For instance, most industrial processes in CWW area produce an acid waste stream, which must be neutralised with caustic (NaOH) before discharge. Caustic usage for this purpose leads to an increase in the facility’s TDS level. Substitution of caustic for another neutralisation chemical or changing the neutralisation process into more environmental friendly process is a Cleaner Production opportunity.

2.5.2

CWW Cleaner Production Research and Development Program

The CWW Cleaner Production Research and Development program is an important aspect of the CWW Cleaner Production Strategy. As a part of this program, CWW has developed a cooperative link between its research projects and local educational institutions. Projects under this program are designed to bridge the gap that exists between current and emerging technologies and their applications at CWW industrial sites.

Projects are developed to encourage moving from an end-of-pipe mentality of dealing with waste to that of at-source reduction. Several research projects for postgraduate students are currently underway and more will be introduced in the future. This research project belongs to the CWW Cleaner Production Research and Development program.

2.6

SUMMARY

The current Melbourne water issue was discussed in this chapter. As previously stated, Melbourne is currently experiencing a fresh water shortage due largely to an increase in population and the extended drought. The current water supply systems in Melbourne, such as the Melbourne water catchments, need to be boosted by alternative water sources such as seawater desalination and wastewater reclamation via desalination.

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In response to the Melbourne fresh water shortage, the Victorian State Government has identified a wastewater reclamation target of 20% by 2010 for the Melbourne water industries. To meet this target, the Melbourne water planners including Melbourne Water Corporation (MWC) and City West Water (CWW) pursue opportunities to reclaim wastewater in Melbourne. The wastewater reclamation at the Melbourne’s biggest wastewater treatment plant, Western Treatment Plant (WTP), and at the CWW major trade waste facilities seem to be more beneficial options in terms of the volume of the reclaimed wastewater and the costs required in implementation. The wastewater reclamation at the WTP also assists the Melbourne water planners to provide a reliable water source for the agricultural industry in the areas surrounding the WTP.

The major problem with wastewater reclamation at both the WTP or at the CWW trade waste Facility sites is salinity. The solids dissolved in a wastewater stream cannot be removed by the WTP existing wastewater treatment facilities as they are designed for removing the wastewater suspended solids. There are several options to handle the WTP salinity issue including reducing the salts discharged by the CWW trade waste facilities through the implementation of the Cleaner Production Strategies. However, as the Cleaner Production Strategies can be classified as long term solutions for the WTP salinity issue, a short term solution such as construction of a wastewater desalination plant at the WTP may initially be a better strategy to reduce the WTP secondary wastewater salinity for wastewater reuse applications.

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CHAPTER 3: TECHNICAL ASPECTS OF DESALINATION PROCESSES

CHAPTER 3 TECHNICAL ASPECTS OF DESALINATION PROCESSES 3.1

INTRODUCTION

Wastewater may be defined as a combination of liquid water-carried waste removed from different generation sources including households, institutions, and commercial and industrial sites. It generally has a high content of oxygen demanding wastes, pathogenic or disease causing agents, organic materials and nutrients (Sonune et al., 2004).

Domestic or commercial sourced wastewater is usually discharged to the sewer and then treated in a public owned treatment plant until its quality is such that it is safe to be released to the environment. In coastal areas, the final destination of treated wastewater is usually the ocean. Industrial wastewaters may also be subjected to the same process if they meet a set of defined qualities before being discharging to the sewer. Thus, in most cases, a preliminary on-site treatment is required. The final treated wastewater eventually undergoes to the natural cycle of evaporation and rainfall.

In arid and semi-arid areas such as Israel, where people suffer from fresh water shortages, instead of discharging secondary treated wastewater to a body of water, it might be reutilised for other purposes including agricultural usages. Indeed, the view on wastewater is not a “waste view” any more; it is a “commodity view”. However, long term application of secondary treated wastewater for agricultural purposes may not be a sustainable way to mitigate the water shortage due to soil deterioration.

Experiences in Israel indicate that soil gradually loses its quality due to the existing salts in wastewater (Harussi et al., 2001). As the conventional treatment techniques in the majority of the wastewater treatment plants are designed for removing suspending materials, the salts and other dissolved chemicals cannot be removed from wastewater by the conventional treatment techniques. Salt can be removed from wastewater only by desalination technologies.

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3.2

WATER AND WASTEWATER IN INDUSTRY

The success of wastewater reclamation processes in meeting the objectives of the water planner is highly dependent on the planner having a clear understanding of the feedwater quality and characteristics, and required quality of the treated wastewater. In order to select a suitable desalination technology for industrial wastewater reclamation, the feedwater characteristics must be carefully understood. A wastewater stream that has a high content of suspended solids is very susceptible to deposit formation on the desalting device surface (Al-Ahmad et al., 2000), and hence, an appropriate pretreatment must be used to ensure the smooth operation of the desalting device. Conducting a trial study is a common strategy employed to understand the feedwater characteristics in the planning stage of a wastewater desalination project.

In addition to characterising the feedwater of a wastewater reclamation plant, it is necessary to identify the required quality of reclaimed water. These days, up to 99 per cent of salts and other wastewater pollutants can be removed by some desalting devices including Reverse Osmosis (RO) and produce nearly pure water. However, water of such high quality, which also has a considerable production cost, may have a limited applications in industry.

In this section, general information about water quality is presented. This information will be useful in selecting the best desalination technology for wastewater reclamation via desalination.

3.2.1

Desired Water Quality

Specifications for industrial water purity vary widely and depend entirely on the intended use. Having water with a very low Total Dissolved Solids (TDS) often requires employment of an expensive and complex treatment.

No formal quality standards exist for an entire industry, or even for specific products, although estimates of quality tolerances by industries are available in various reports. One such set of limits is given in Table 3.1. This table presents the minimum required water quality in some exemplary industries. However, within a specific industrial sector

Page 3-2


water quality can vary significantly. Appendix A presents a brief description of the water and wastewater quality parameters that are used in membrane desalination technologies, and also includes some parameters listed in Table 3.1.

Table 3.1 Typical Quality Limits for Selected Industries (mg/L) (RosTek, 2003).

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According to the information presented in Table 3.1, the majority of the outlined industries require reclaimed water with TDS range between 100-300 mg/L. However, more saltier water is still accepted for applications such as carbonated beverages (around 850 mg/L).

3.2.2

Generated Wastewater Quality

The typical characteristics of the wastewater generated in some industrial sectors are presented in Table 3.2. As shown in this table, the wastewater characteristics of the generated wastewater could be different from one industrial sector to another. For example, while in the plastic and resin facilities pH and volatile organic compounds are the main characteristics of the produced wastewater, whereas for the textiles facilities biological oxygen demand (BOD), total suspended solids (TSS) and alkalinity are the main wastewater characteristics.

Table 3.2 Main Characteristics of Some Selected Industrial Wastewater (www.pge.com) Industry

Associated Wastewater pollutants

Textiles

BOD, TSS, alkalinity

Tanning

BOD, TSS, Chromium

Food Brewed beverages Meat & Poultry Soft drink Pharmaceuticals

BOD BOD BOD, TSS, alkalinity BOD

Pulp & Paper

pH, TSS, inorganic compounds

Metal-plating

Acidity, heavy metals

Plastics & Resin

pH, Volatile organic compounds

It is also important to note that the properties of the generated wastewater can differ considerably within a specific industrial sector. For instance, Yusuff et al. (2004) conducted a study to characterise the effluents from five major textile industries in Nigeria. The results of their study indicated that despite the fact that these facilities all

Page 3-4


belong to the textile industry, the major wastewater compounds such as BOD, TSS, and alkalinity are significantly different from one textile mill to another.

3.3

INDUSTRIAL WASTEWATER DESALINATION CONCEPT

Desalination techniques were initially invented to augment the fresh water sources by desalting seawater and groundwater (Arora et al., 2004). Some of commercial desalination technologies such as Electrodialysis (ED) have been employed for water desalting purposes for more than fifty years (IONICS, 2004). Over this time, many studies have been conducted by researchers from industry, technology suppliers and academic institutions in order to understand different aspects of the desalination processes including technical, financial, environmental and social impacts (Wilbert et al., 1998).

The results of the conducted studies about seawater and groundwater desalination aspects are well documented in the literature (RosTek, 2003) and could be used for any future seawater or groundwater desalination projects. However, the application of these results to wastewater desalination is not recommended by many researchers (RosTek, 2003, and Wilbert et al., 1998). Industrial wastewater desalination is more complex than other water desalination as it demands the consideration of more factors and parameters. To produce reclaimed water from industrial wastewater, the desalination process train should include pre-treatment, main treatment, post treatment and waste disposal, and must be selected and designed carefully. Indeed, the energy intensity of the desalination process is a challenging issue. This can be mitigated by using the energy recovery devices in seawater or groundwater desalination. However, in industrial wastewater desalination, the energy intensity of the process must be handled through other approaches such as reducing wastewater salinity by implementation of the cleaner production opportunities including pinch technology or wastewater segregation (Gianadda et al., 2002, and Dunn et al., 2001).

Another example is the required pre-treatment in a desalination train. In seawater or groundwater desalination, usually pre-treatment is simple and easy to perform. Due to the high level of organic and inorganic pollutants in most industrial wastewater streams,

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pre-treatment must be very effective and more tolerant against the high levels of the feedwater quality and quantity variations for industrial wastewater desalination.

3.3.1

Desalination Train

The idea of separating salts from water is ancient, dating to the time when salt, not water, was a precious commodity. Later, as demand for fresh water increased, the desalination process was used to produce fresh water. The techniques for removing salts from saline water have changed significantly, especially in the recent decades. The new generation of desalination techniques are very sophisticated and are able to produce high quality water for various applications including potable water.

The desalination process usually goes through a set of sub-processes or a desalination train. A desalination train typically comprises three stages: pre-treatment; main treatment, and post-treatment. Waste disposal also might be included in some desalination trains. Figure 3.1 shows a general view of a desalination train.

Saline water

Product (Permeate) Pre-treatment

Waste stream

Main treatment

Post-treatment

Waste stream

Figure 3.1 General View of a Desalination Train

Each component of the desalination train has a specific function. Generally, pretreatment removes suspended solids, colloidal material, and some dissolved minerals (from feedwater) and protects the main treatment from scaling and the deposition of chemical or biological materials on the desalting device. Therefore, pre-treatment helps maintain the smooth running of the plant with less trouble shooting. Pre-treatment can be very simple (e.g. a filter) or it can be very complex (a membrane separation device), and depends on the proposed desalting device, feedwater quality and the invested capital.

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The main-treatment section of a desalination train removes salts from water. This separation allows salts to go to the waste or reject (or brine or concentrate) stream and leaves the relatively pure water (or permeate) into the product storage space. The commercial desalination technologies used in this part of the train are broadly divided into two major categories: Membrane technologies and Thermal technologies. However, there are other desalination techniques such as Ion Exchange (IX) technology which have also been practised in some desalination projects (Miller, 2003). The last part of the desalination train is the post-treatment. In order to adjust the permeate to the desired water quality, it is undergoes processes to remove the corrosive gases and/or to add some desirable chemicals (RosTek, 2003).

3.4

PRESSURE-DRIVEN DESALINATION TECHNOLOGIES

These desalination technologies have been designed based on the phenomenon of filters which can selectively permit or prohibit the passage of certain ions through semipreamble membrane. Membrane processes are mostly pressure driven technologies, except Electrodialysis (ED) technology, which is voltage-driven. In the membrane pressure-driven systems, a high pressure pump forces water to pass through the semipermeable membrane so that salts and other particles are rejected.

There are four membrane systems; Microfiltration (MF), Ultrafiltration (UF), Nanofiltration (NF), and Reverse Osmosis (RO). These systems are usually categorised according to pore size (i.e. sieving properties of the membrane) as demonstrated below.

Microfiltration (MF) Decreasing membrane pore size

Ultrafiltration (UF) Nanofiltration (NF) Reverse Osmosis (RO)

In reality the boundaries between MF, UF, NF and RO membranes are not uniform as the performance specifications vary from supplier to supplier. For example, one supplier’s “loose” Nanofiltration membrane may be equivalent to another’s “tight”

Page 3-7


Ultrafiltration membrane (Wilbert et al., 1998). Figure 3.2 shows the relative sizes of typical membrane separation processes (Envirowise, 1997).

Figure 3.2 Size Separation Capabilities of Different Membrane Systems (Envirowise, 1997)

Based on this figure, only NF and RO are able to remove aqueous salts and metal ions from water. MF and UF are more suitable for the separation of particles which have an approximate size above 0.01 micron. Therefore, for the rest of this thesis, the pressuredriven membrane devices referred to only NF and RO processes. However, MF and UF are still relevant in areas of this study due to their excellent abilities to be used as a pretreatment device for NF and RO (Wolf et al., 2005).

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Despite the many advantages of membrane desalination systems over other desalination technologies, these systems have some potential drawbacks. Table 3.3 summarises the advantages and disadvantages of membrane desalination systems.

Table 3.3 Advantages and Disadvantages of Membrane Desalination Systems (URS, 2002 and Wilbert et al., 1998) Advantages        

Physical process with few moving parts. Simple connections and utility requirement (e.g. electricity) Can operate continuously or on demand as a batch process. Often no additive is required. Equipment is modular and compact. System can be scaled up or down easily and integrated with other treatment processes. Membrane properties can be varied. Can be used for single- or multi-stage desalination.

Disadvantages    

3.4.1

Do not destroy biological substances. Therefore, they must be removed in either pre-treatment or post-treatment, if the water is to be used for potable water or process water. Those membranes that are of the polyamide type cannot be used if there is chlorine in the water. The chlorine must be chemically removed. The performance of membrane plants tends to decline progressively with time due to fouling of the membrane. Membrane plants need to be cleaned regularly.

Technical Review

From a technical point of view, a smooth performance of a membrane desalination plant is highly dependent on the type and extent of the pre-treatment used, and to a lesser degree it is dependent on the membrane material type, membrane system configuration and operation parameters such as temperature.

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I.

Pre- Treatment

The main function of pre-treatment in a membrane desalination train is to protect the membrane surface against fouling caused by the chemical or tiny biological material present in feedwater. Fouling has an adverse effect on the system costs and productivity. By definition, fouling is “a process resulting in loss of performance of a membrane due to the deposition of suspended or dissolved substances on its external surface, at its pore openings or within its pores” (Madaeni et al., 2001). Several types of fouling can occur in the membrane systems, e.g. inorganic fouling or scaling, particulate and colloidal fouling, organic fouling, and finally biological fouling or biofouling (ibid).

Membrane desalination plant pre-treatment is broadly classified into two major categories: conventional pre-treatment and non-conventional (integrated or membrane based) pre-treatment. The conventional pre-treatment (mostly using chemical addition and sand filtration, followed by a fine filter system) has been widely applied in the past for seawater RO plants to lower the Silt Density Index (SDI). SDI is a feedwater quality index that indicates the susceptibility of feedwater to form biofilm or scale on the surface of the desalting device surface (Mohammadi et al., 2002). Figure 3.3 shows a typical conventional pre-treatment (Wolf et al., 2005).

Figure 3.3 Typical Conventional Pre-treatment (Wolf et al., 2005)

In non-conventional pre-treatment, Ultrafiltration (UF) or Microfiltration (MF) replaces all the conventional treatment units. A typical UF membrane pre-treatment is shown in Figure 3.4. (ZeeWeed® is a UF brand name).

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Figure 3.4 Typical UF Membrane Pre-treatment (Wolf et al., 2005)

A membrane pre-treatment method requires more capital investment than the conventional pre-treatment method (RosTek, 2003). However, the membrane pretreatment method has many other benefits that overcome the drawback of its higher initial investment (Wolf et al., 2005). Some of these benefits are listed below:

1

High surface area offered by the membranes in a compact arrangement means that UF plants are significantly smaller than their conventional counterparts, easing space constraints during expansions or retrofits and providing potential saving in land acquisition.

2

Significantly reduces RO membrane fouling and frequency of membrane cleaning.

3

Extends the life of RO membrane.

4

Lower consumption of operational and cleaning chemicals.

5

Lower requirement of operation staff due to complete automation.

6

Higher RO membrane operating flux (therefore fewer RO membrane pressure vessels, manifolds and space), resulting in lower total water treatment cost even considering the higher RO energy input required.

7

Module design enables simple and efficient sand filter retrofits.

II. Membrane System Configuration

The membrane desalination plants are available in various configurations including single stage, two stages and two-pass systems (RosTek, 2003). Selection among these

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configurations depends on desired quality of the water produced. In this regard, the twopass system gives the highest purity product; therefore, it is suitable for preparation of make-up boiler water. The single stage system gives the simplest schematic of all configurations and applications. The two-stage system is quite common for brackish water use, where it is necessary to increase the overall recovery ratio. Figures 3.5 to 3.7 show the basic design of these configurations (Al-Enezi et al., 2002).

Figure 3.5 Single Stage Flow (Al-Enezi et al., 2002)

Figure 3.6 Two Stage (Al-Enezi et al., 2002)

Figure 3.7 Two-Pass Flow (Al-Enezi et al., 2002)

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In these figures, a high pressure pump forces feedwater into the main desalting device. Water is passed through a membrane, and salts and other particles are rejected and sent into the waste (or concentrate) stream. The product may leave the process as in Figures 3.5 and 3.6 or it can pass through another membrane, as shown in Figure 3.7, in order to reduce its salinity to the desired value. This would require use of intermediate pressure pumps to increase the permeate pressure from near atmospheric pressure to a higher pressure ranging from 20 bar up to 40 bar. For the most part, this pressure gain can be made through pressure exchanges with brine streams leaving the first and the second pass. This would considerably reduce the energy required to increase the permeate pressure (Al-Enezi et al., 2002).

III. Membrane Structure

Commercial membrane modules

typically

come in four

structural

forms (or

configurations), hollow-fibre, spiral-wound, tubular, and plate-and-frame module (Envirowise, 1997). The hollow-fibre systems have a high membrane surface area per module, but must operate at low hydrostatic pressure (Wilbert et al., 1998). Hollow fibres are typically less than 0.5 mm in diameter and for this reason the systems are more prone to blockage unless pre-filtration systems are used (ibid). The spiral-wound membrane provides a greater surface area per module than the plate-and-frame or tubular configurations, but are much more difficult to clean (ibid). The tubular membrane modules have a lower membrane surface area per module than hallow-fibre units, but they can operate at higher pressure (Envirowise, 1997). Tubular membranes tend to be around 10 mm in diameter and therefore need more space, but they are more robust (ibid). Tubular membranes also have superior solids handling capabilities compared to spiral-wound, plate-and-frame or hollow-fibre modules. Spiral-wound and hollow-fibre modules require a higher standard of pre-filtration when solids are likely to be present (ibid). In plate-and-frame membrane, the membrane plated form and also the membrane material allows higher flux rates (Wilbert et al., 1998). In addition, because the membrane is supported on both sides, back-flushing (reverse filtration with permeate) can be used to help extend membrane life (ibid). Figures 3.8-3.11 show these configurations (Envirowise, 1997).

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Figure 3.8 Hollow-Fibre Module (Envirowise, 1997)

Figure 3.9 Spiral-Wound Module (Envirowise, 1997)

Figure 3.10 Tube Module (Envirowise, 1997)

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Figure 3.11 Plate and Frame (Envirowise, 1997)

The suitability of tubular membrane system for specific applications is compared with other systems, hollow-fibre and spiral-wound, in Figure 3.12 (Envirowise, 1997).

Figure 3.12 Guide to Applications for Tubular, Hollow Fibre, and Spiral-Wound Systems (Envirowise, 1997)

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IV. Membrane Material Type

There are basically two types of commercial membrane used in desalination applications today: cellulose acetate (CA) and thin film (TF) (RosTek, 2003). The former is considered an integral membrane, and the latter is a composite membrane. CA initially achieved environmentally acceptable results with brackish water, but never with seawater because of the compressibility of the membrane itself under the required pressures (ibid). Today, CA has lost its overall popularity due to pH, temperature and performance limitations which are associated with this membrane type (Madwar, 2002). However, CA’s superior chlorine and fouling resistance still make it the membrane of choice for many brackish water desalination applications (ibid).

The Thin Film (TF) membrane was invented in the 1980s and is suitable for seawater desalination. In general, the TF membranes have good temperature and pH resistance, but typically are not tolerant of oxidizing environments, especially chlorine (Envirowise, 1997).

V. Operational Parameters

Pressure, water temperature, level of water recovery, and oxidation potential of the feedwater are the most important operational parameters that determine the membrane plant performance (RosTek, 2003). The first three of these factors are related to the feedwater composition. The last is related to the material used in the membrane. Engineers usually change the operational parameters in order to maximise the product quality or reduce the production cost. In the membrane desalination plants, the common strategies used to achieve a better water quality include increasing pressure, reducing temperature and running the plant at lower water recover rate (Wilbert et al., 1998).

Membrane plants are also designed and built using many parameters, but the overriding criterion is the permeate flow rate per unit of membrane area (or flux) through the membrane under operating conditions. Flux is typically expressed as volume or mass per unit membrane area per unit time, for example litres/m2/hour. Temperature can affect the flux significantly. Operating at high flux levels means that less membrane area is

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required and economies can be defined in terms of capital, operating and membrane replacement costs.

3.4.2

Practical Concerns

Scaling and fouling are two major technical concerns associated with membrane system performance which effectively impact the system costs and productivity. These issues are investigated in detail in this section.

I.

Fouling

As stated in Section 3.4.1, the membrane fouling is defined as:

“a process resulting in loss of performance of a membrane due to the deposition of suspended or dissolved substances on its external surface, at its pore opening or within its pores” (Madaeni et al., 2001).

Biofilm is one of the most common types of biofouling which is usually described as the accumulation of micro-organisms such as bacteria, algae and fungi on the membrane surface. Biofouling can have many adverse effects on the membrane system such as a decline in the membrane flux, an increasing in the membrane pressure drop, and an increase in the passage of salt to the membrane product side (RosTek, 2003).

Prevention and/or controlling of membrane fouling are typically site specific (RosTek, 2003). Strategies including good process design, good operator training, and selection of effective disinfectants can minimise this issue (ibid).

II. Scaling

Membrane scaling is usually defined as the deposition of the sparingly soluble mineral such as Ca+2 and Mg+2 on the membrane surface (Rahardinato et al., 2006). Scaling usually occurs in high water product recovery (ibid). As product recovery is increased, the brine (or waste) stream is concentrated, particularly near and at the membrane’s surface. As the concentration of ions in solution exceeds the saturation levels of various

Page 3-17


sparingly soluble mineral salts (e.g. calcium carbonate), these mineral salts may crystallise in bulk on the membrane surface, leading to mineral scale formation and thus permeate flux decline, and eventually shortening of membrane’s life.

There are several strategies to minimise the risk of scale formation including using antiscale chemicals and adjustment of feedwater pH (RosTek, 2003).

3.5

THERMAL (OR DISTILLATION) DESALINATION TECHNOLOGIES

Distillation is the oldest and most commonly used method of desalination (Buros, 2000). The world's first land-based desalination plant, a multiple-effect distillation (MED) process plant that had a capacity of 60 m3/d, was installed in the island of Curacao, in the Netherlands Antilles, in 1928. Further commercial development of land-based seawater distillation units took place in the late 1950s, and initially relied on the technology developed for industrial evaporators (such as sugar concentrators) and for the shipboard distillation plants which were built during World War II.

Thermal (or distillation) desalination processes mimic the natural water cycle in that saline water is heated, producing water vapour, which is in turn condensed to form fresh water. Thermal processes are mainly used for seawater desalination in the following major forms: 

Multi-Stage Flash (MSF)



Multi-Effect Distillation (MED)



Vapour Compression (VC)

3.5.1

I.

Technical Review

Multi-Stage Flash (MSF)

The multi-stage flash (MSF) units are widely used in the Middle East and they account for over 40% of the world’s desalination capacity (Buros, 2000). As previously outlined, MSF is a distillation (or thermal) process that involves evaporation and condensation of water. The evaporation and condensation steps are coupled in MSF so that the latent

Page 3-18


heat of evaporation is recovered for reuse by preheating incoming water. Figure 3.13 shows a simple schematic of this process (Miller, 2003).

Figure 3.13 Schematic of Multi-Stage Flash (MSF) Desalination Process (Miller, 2003)

As shown in this figure, the saline feed is pressurised and heated to the plant’s maximum allowable temperature (Miller, 2003). When the heated liquid is discharged into a chamber (or stage) maintained slightly below the saturation vapour pressure of water, a fraction of its water content “flashes” into steam. The flashed steam is stripped of suspended brine droplets as is passes through a mist eliminator and condenses on the exterior surface of the heat transfer tubing (ibid). The condensed liquid drips into trays as hot product (or fresh) water.

The recirculating steam, flowing through the interior of the tubes that condense the vapour in each stage, serves to remove the latent heat of condensation (Miller, 2003). In doing so, the circulating brine is preheated to almost the maximum operating temperature of the process, simultaneously recovering the energy of the condensing vapour. This portion of the MSF plant is called the “heat recovery” section, which is shown in the top of Figure 3-13. The preheated brine is finally brought up to maximum operating temperature in a brine heater supplied with steam from an external source (ibid).

To maximise water recovery, each stage of an MSF unit operates at a successively lower pressure. A key design feature of MSF system is bulk liquid boiling (Buros, 2000). This alleviates problems with scale formation on heat transfer tubes. In the Persian Gulf

Page 3-19


region, large MSF units are often coupled with steam or gas turbine power plants for better utilisation of the fuel energy (ibid). Steam produced at high temperature and pressure by the fuel is expanded through the turbine to produce electricity. The low to moderate temperature and pressure steam exiting the turbine is used to drive the desalination process (RosTek, 2003).

II. Multi-Effect Distillation (MED)

The multi-effect distillation (MED) process has been used for industrial distillation for a long time. Traditional uses for this process are the evaporation of juice from sugar cane in the production of sugar and production of salt with the evaporation process. Some of the early water distillation plants used the MED process, but MSF units, due to the better resistance against scaling, displaced the MED process (RosTek, 2003). Figure 3.13 presents a simple schema of this process (Miller, 2003).

Figure 3.14 Schematic of Multi-Effect Distillation (MED) Desalination Process (Miller, 2003)

As demonstrated by this figure, vapour from each stage is condensed in the next successive stage thereby giving up its heat to cause more evaporation. To increase the performance, each stage is run at a successively lower pressure (Miller, 2003). The MED process can have several different configurations according to the type of heat transfer surface (i.e. vertical climbing film tube, rising film vertical tube, or horizontal tube falling film) and the direction of the brine flow relative to the vapour flow (forward, backward, or parallel feed). The MED plants are typically built in units of 2,000 to 20,000

Page 3-20


m3/d (Buros, 2000). Some of the more recent plants have been built to operate with a top temperature (in the first effect of each multi-effect distillation) of about 70º C, which reduces the potential for scaling of the plant (ibid).

III. Vapour Compression (VC)

The vapour compression (VC) distillation process is generally used in combination with other processes (like MED) for large scale desalting applications or by itself for small and medium scale desalting applications. The heat for evaporating the water comes from the compression of vapour rather than the direct exchange of heat from steam produced in a boiler.

VC units are often used for resorts, industries and drilling sites where fresh water is not readily available. Their simplicity and the reliability of their operation make them an attractive unit for small installations. Figure 3.15 shows a simple schematic of a VC plant.

Figure 3.15 Schematic of Single Stage MVC Desalination Process (Miller, 2003)

As illustrated in this figure, VC is similar in process operation to MED. The main difference is that the vapour produced by evaporation of the brine is not condensed in separation condenser. Instead a compressor returns vapour to the steam side of the same evaporator, in which it originated, where it condenses on the heat transfer

Page 3-21


surfaces, giving up its latent heat to evaporate an additional portion of the brine (URS, 2002).

3.5.2

I.

Practical Concerns

Scaling

Scale forms when solid materials are deposited on solid surface. There are three main deposit materials in distillation plants: calcium sulfate, CaSO4, magnesium hydroxide, Mg (OH) 2; and calcium carbonate, CaCO3. Scale is particularly undesirable when it forms on a surface through which heat must be transferred, like a metal tube in a distillation unit. As scale has a much lower thermal conductance than the metal of the heat transfer tubes, scaling can greatly reduce the overall heat transfer (RosTek, 2003). Formation of some of these scales cannot be limited by pre-treatment. Therefore, they must be controlled by limiting the operating temperature or by limiting the concentration of calcium and/or sulphate ions in the concentrate.

II. Corrosion

Distillation plants are subject to corrosion. Factors that influence seawater and concentrate corrosively includes pH, temperature, high chloride concentration, and dissolved oxygen. Product waters are also very aggressive to metal and concrete. Corrosion can be minimised by the use of corrosion-resistance materials (e.g. highperformance steel) in feed and concentrate streams, and with proper pre-treatment through the flash chamber, along with the proper choice of materials (Sommariva, 2001).

3.6

OTHER DESALINATION TECHNOLOGIES

A number of other processes have been used to desalt saline waters. These processes have not achieved the level of commercial success that thermal and membrane have had, but they may prove valuable under special circumstances or with future development. In this section, Electrodialysis (ED) and Ion Exchange (IX) technologies will be discussed in more detail. However, in addition to these two technologies, there are other desalination processes including Freezing, Membrane Distillation and Solar

Page 3-22


Humidification which will not be considered (in this research) due to their very limited commercial applications.

3.6.1

Electrodialysis (ED) and Electrodialysis Reverse (EDR)

Although the ED process is a membrane type desalination technique, it was not described in Section 3.4, since all membrane desalting devices presented in Section 3.4 are “pressure-driven” membrane technologies, while ED is a “voltage-driven” membrane device (URS, 2002).

Most salts dissolved in water are ionic, being positively (cationic) or negatively (anionic) charged. These ions are attracted to electrodes with an opposite electric charge. In ED, membranes that allow either cations or anions (but not both) to pass are placed between a pair of electrodes. These membranes are arranged alternately. A spacer sheet that permits feedwater to flow along the face of the membrane is placed between each pair of membranes. Figure 3.16 shows an ED assembly with feed spacer and ion exchange membrane placed between oppositely charged electrodes. Positively charged ions (Na+ etc) migrate to cathode and negatively charged ions (Cl- etc) migrate to anode.

Figure 3.16 An ED Unit in Operation (Arthur et al., 2005)

During migration, similarly charged ion exchange membranes reject the charged ions. As a result, water within the alternate compartment is concentrated leaving desalted water within the next compartment of the ED unit. The concentrate and desalted water are continuously removed from the unit. The basic electrodialysis unit consists of several

Page 3-23


hundred cell pairs bound together with electrodes on the outside and is referred to as a membrane stack.

If the product and the brine channels are identical in construction, the ED process is called Electrodialysis Reversal (EDR) unit. In EDR, the polarity of the electrodes is reversed at intervals of several times an hour, and the flows are simultaneously switched so that the brine channel becomes the product water channel, and the product water channel becomes the brine channel (Avlonities, 2003).

The result is that the ions are attracted in the opposite direction across the membrane stack. Immediately following the reversal of polarity and flow, enough of product water is dumped to ensure the stack and lines are flushed out and the desired water quality is restored. The reversal process is useful in breaking up and flushing out scales, slimes and other deposits in the cells before they can build up and create a problem (Arthur et al., 2005).

I.

Advantages and Disadvantages

In the past two decades, ED and in particular EDR have earned reputations as membrane desalination processes that work economically and reliably on wastewater streams. The reason EDR is successful in wastewater desalination applications is due to a combination of equipment design and membrane properties (IONICS, 1991). Equipment design permits routine operation at higher levels of turbidity and Silt Density Index (SDI) than other membrane desalination technologies. The design also allows disassembly and manual cleaning if particular fouling should occur (ibid). The membranes have substantial resistance to oxidising disinfectants, are not affected by exposure to pH values of 0-10, and have extreme resistance to irreversible fouling by organics. This combination allows EDR to operate on wastewater desalination with economical pre-treatment and to survive when pre-treatment systems d not operate as intended (ibid).

The Electrodialysis process also has some drawbacks. For instance, the energy required for separating salts from water is highly dependent on the feedwater salinity (RosTek, 2003). This energy increases sharply for feedwater salinity greater than 3,500 mg/L

Page 3-24


(ibid) and therefore, reduces EDR cost-effectiveness against other desalination technologies. For example, the energy cost of an EDR desalination plant with capacity 3,785 m3/d and feed salinity of 2,500 mg/L is about 14% of the production energy cost (ibid), while for the same desalination plant capacity but feedwater salinity of 5,000 mg/L is about 23% of the production cost (ibid). The typical energy cost for a RO desalination plant of 3,785 m3/d capacity and 5,000 mg/L salinity is about 11% of the production cost (Miller, 2003). Table 3.4 summarises the advantages and disadvantages of the EDR process.

Table 3.4 Advantages and Disadvantages of a EDR Process (URS, 2002, Wilbert et al., 1998 and Envirowise, 1996). Advantages      

Can treat feedwater with a higher level of suspended solids. Pre-treatment has a low chemical usage and does not need to be very precise. The energy usage is proportionate to the salts removed, instead of the volume of water being treated. The membranes for EDR have a life expectancy of 7-10 years, which is longer than for RO. EDR is conducted at much lower pressure drop across the process compared to RO, usually less than 25 psi for EDR and 400-1400 psi for RO. Plate and frame configuration of the EDR system enables easier maintenance and cleaning.

Disadvantages  

The EDR process is usually only suitable for a feedwater salinity of up to 12,000 mg/L. Above this limit, the process rapidly becomes more costly since power consumption sharply increases with salinity. Bacteria, non ionic substances and residual turbidity are not affected by the system and can therefore remain in the product water and require future treatment before certain water quality standards are met.

II. Practical Concerns

Scale formation will foul the membrane surface and block the passage in the stack. The result of scale formation is that the water passes slowly and then becomes highly desalted due to the lengthened period of exposure to the electromotive force. This highly desalted water has a lower conductivity and offers a high resistance to current flow, thus decreasing the efficiency of the process. Some scale formations can be removed by

Page 3-25


introducing chemicals into the stacks in attempt to dissolve or loosen scaling so that it can be washed out (Mohammadi et al., 2002), however in more severe cases the stack will need to be disassembled. Leaks are also another technical concern of the ED process. Operating and/or maintenance problems can result from leaks in two parts of the electrodialysis stack, either between the stacked membranes and spacers, or through the membranes themselves (URS, 2002).

3.6.2

Ion Exchange (IX)

Ion Exchange is a method of separation that depends on the interaction of ions between a solution and the surface of the ion exchange material or resin (Envirowise, 1996).

There are several types of ion exchange resin, including (ibid): 

Natural minerals such as zeolites (minerals with a unique interconnecting lattice structure);



Organic polymers (large organic molecule formed by combining many smaller molecules in a regular pattern)

Water softening is one example of an ion exchange process where high purity is required (e.g. high pressure boilers).

As shown in Figure 3.17, the ion exchange

process in this figure replaces sodium ions with hard components (calcium and magnesium ions). Therefore, the produced water becomes suitable for water cooling applications (i.e. for cooling towers application) or for the boiler make-up water.

Figure 3.17 Ion Exchange Principles for Water Softening (www.zeoliet.nl)

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The calcium-loaded resin is regenerated using a sodium chloride solution (or the regeneration solution) to bring it back to the sodium from, ready for another cycle of operation.

I.

Advantages and Disadvantages

Ion exchange processes can remove effectively divalent ions such as Ca+2 and Mg+2 and reduce the water “hardness” (Miller, 2003). In order to have an effective IX performance, the regeneration chemicals are required to be replaced with fresh chemicals after their effectiveness is diminished. The waste (or old) regeneration chemicals are usually discharged to sewer (Envirowise, 2005). This wastewater stream contains a high level of dissolved solids such as NaCl. Discharging such a highly salty stream into a public owned treatment plant increases the treatment plant’s salt level and reduces its potential for any possible reuse such as agricultural irrigation applications. In addition to this drawback, the IX process has other advantages and disadvantages which are summarised in Table 3.5.

Table 3.5 Advantages and Disadvantages of Ion Exchange (URS, 2002 and Wilbert et al., 1998) Advantages  Effective decontamination - very low final TDS (in product) is possible.  Possible recovery of valuable species.  No sludge produced - metal ions removed directly, not by precipitation. Disadvantages  Efficiency depends on the feed stream.  Stability of ion exchangers - these deteriorate with time, both mechanically and chemically.  Cost may be higher than for other technologies.  Regeneration is usually not very efficient and therefore extra chemical is required. II. Practical Concerns

A high level of suspended solids can cause excessive pressure drops in the resin bed, and the resin can also be fouled by the irreversible adsorption of large organic molecules. Ageing of the resins also can affect the process performance as a result of either chemical degradation or physical change. Loss of performance may also occur

Page 3-27


because of the precipitation of insoluble compounds such as calcium sulphate (URS, 2002).

3.7

SUITABILITY OF TECHNOLOGIES FOR WASTEWATER RECLAMATION

As stated in Chapter 1, the main objective of this research project is to develop a Decision Support Framework (DSF) for wastewater reclamation, based on several key criteria including the technical aspects of desalination technologies. Several technical issues related to commercial desalination technologies (i.e. the practical concerns associated with the desalination technologies) were investigated in this chapter. The review of the technical details of desalination processes, presented in this chapter, could lead to some outcomes which are useful in developing the DSF. For example, as stated in Section 3.5, the best conditions for employing thermal desalination technologies are desalting a feedwater which has a volumetric flow rate more than 5,000 m3/d and TDS more than 35,000 mg/L. However, these conditions do not exist in majority of wastewater reclamation via desalination projects. Similarly, wastewater reclamation projects are typically characterised with low to moderate salinity and water demand less than 2,000 m3/d. For example, in top 20 most significant salt discharges of City West Water, the average TDS concentration is about 3,593 mg/L (URS, 2005) and more than 80% of them require less than 2,000 m3/d reclaimed water. Therefore, based on the information presented in this chapter, membrane desalination processes are superior over thermal processes for wastewater reclamation. The DSF will be able to use the level of information to select the appropriate desalination technology to suit the conditions.

Another important outcome of the review of the technical aspects of desalination technologies in this chapter is identifying the technical limitations which are associated with the application of various membrane desalination technologies for wastewater reclamation. For example, based on the information presented in Section 3.6.1, despite of many advantages of the EDR process for wastewater reclamation (i.e. less susceptible to fouling and scaling than RO and NF), this technology is not suitable for wastewater reclamation at food and beverage industries, as bacteria and viruses are not removed from the product water which could cause serious health problems for humans.

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This point needs to be considered in the developing the DSF, when EDR technology is applicable for wastewater reclamation.

3.8

SUMMARY

This chapter investigated the technical aspects of the commonly used desalination technologies. These technologies included membrane desalination processes (Reverse Osmosis, Nanofiltration, and Electrodialysis), thermal processes (Multi-Effect Distillation, Multi-Stage Flash, and Vapour Compression), and Ion Exchange Processes. After the description of the desalination technologies in terms of their operation and practical concerns in particular those technical issues which interfere with the smooth operation of the processes (i.e. biofilm formation on the membrane surface in membrane processes or corrosion phenomena in thermal desalination processes) the advantages and disadvantages of each desalination technology were outlined.

The technical details presented in this chapter are directly relevant to the main objective of this research project, which is to develop a Decision Support Framework (DSF) to select the best desalination technology for wastewater reclamation. This chapter identified those technical parameters which must be considered in assessing various desalination technologies.

Page 3-29

CHAPTER 4: SUSTAINABILITY ASPECTS OF DESALINATION PROCESSES

CHAPTER 4 SUSTAINABILITY ASPECTS OF DESALINATION PROCESSES

4.1

INTRODUCTION

Sustainably assessment of wastewater desalination is an important task that should be conducted in the planning stage of any wastewater reclamation via desalination project. The aim of the sustainability assessment is to include the social, environmental and economical aspects of the desalination project in the process of decision making.

Wastewater desalination projects can be developed in accordance with sustainable development, drawing together resource (wastewater), society, environment and economic needs (Mahi, 2001). Figure 4.1 illustrates the connections between these items. SOCIETY

ECONOMICS

PROJECT DEVELOPMENT

RESOURCE

ENVIRONMENT

Figure 4.1 Sustainable Development Components (Mahi, 2001)

Sustainability is a broad concept, and therefore, investigating all sustainability indicators in a detailed manner is not possible in this research project due to the project time limitations. In this thesis, the cost aspects of the desalination technologies were investigated comprehensively but for environmental and social aspects of the

Page 4-1


desalination technologies, the main attention was focused on some selected sustainability indicators including waste disposal, intensified use of energy, and greenhouse gas emissions resulted from operation of desalination plant as environmental issues, noise pollution, and occupational health and safety as social issues. These aspects are covered in this chapter.

4.2

COST ASPECTS

Cost is one of the most important factors in determining the ultimate success and the extent of desalination. In cost analysis, the decision makers are usually interested in the following issues: 

Comparability and reliability of desalination costs or the built or under construction plants, which are reflected in the literature.



Hidden costs of desalination.



Cost breakdown of a typical desalination plant.



Future cost of desalination in terms of cost trends.

Traditionally, desalination has been considered by the planners as a costly method to supply water. In seawater or groundwater desalination projects, where desalination is the only feasible option to produce good quality water, the relatively high cost of desalination is not a concern, since no other alternative water supply is available, and in this case less attention is paid to the project cost. Most often, these projects are commissioned by the government agencies and receive various direct or indirect subsidies such as low capital interest rate or free land (Younos, 2005).

The conditions in wastewater desalination projects are different. In wastewater reclamation via desalination, especially in trade waste facilities, desalination is just one option among of other options to mitigate the water shortage, and therefore desalination has to be economically affordable. Generally, those projects that have a long term investment payback period are not supported by industry, because of their costs.

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The following sections provide an overview of factors that determine wastewater desalination cost, presents desalination cost estimating methods, and demonstrate the application of these cost estimating methods.

4.2.1

Cost Factors of Desalination

Desalination costs are usually site-specific, and depend on several variables including feedwater quality, plant capacity and site characteristics (Younos, 2005). There is no general rule to rank these variables based on their effectiveness. In fact, their effectiveness is related to the type of selected desalting process.

I.

Quality of Feedwater

The quality of feedwater, especially its total dissolved solids (TDS), is a critical design factor. Feedwater TDS is such an important design parameter that in some desalination textbooks (e.g. RosTek, 2003 and Wilbert et al., 1998), it has been selected as a classification parameter. For example, feedwater less than 5000 mg/L salt is usually considered as brackish water, above that up to 12000 mg/L as groundwater (or highly brackish water) and around 35,000 mg/L as seawater (ibid).The typical wastewater TDS is less than 5,000 mg/L (ibid) and therefore can be considered as brackish water. The average wastewater TDS of the majority of the industrial facilities in the western part of Melbourne is about 3,500 mg/L (URS, 2005).

The feedwater salinity impacts differently the desalination cost in the membrane processes and thermal desalination processes. In thermal desalination techniques, the total desalination cost is not significantly sensitive to the feedwater TDS value (RosTek, 2003, and Wilbert et al, 1998) since feedwater must be evaporated and the energy requirements for evaporation of low saline feedwater is not significantly higher than the energy requirements for evaporation of medium saline feedwater (RosTek, 2003). However, in the membrane desalination processes, the feedwater TDS value is a main cost factor, since feedwater must be forced by an external pump to pass through the membrane (ibid). As the pump energy requirement increases with increase in the feedwater salinity (ibid), the feedwater salinity significantly affects the desalination process energy requirements and hence affects the desalination process energy cost.

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Both capital costs and operating costs of a membrane desalination plant are affected by TDS. Figure 4.2, shows the typical variation of the capital costs and operating costs of a Reverse Osmosis (RO) desalination plant with respect to feedwater TDS. The costs in this figure and subsequent relevant figures are shown in US$.

As shown in Figure 4.2, both capital costs and operating costs are increasing gradually with TDS increasing up to about 1,100 mg/L, sharply increase from 1,100 mg/L to 1,300 mg/L and then increase gradually again. The requirement for using stronger materials for construction an RO system to resist high pressure pumps performance above 1,100 mg/L (Wilbert et al., 1998) is the main reason for the capital cost increasing. For the operating costs sharply increasing above 1,100 mg/L, the reasons are deferent. Desalting less salty feedwater require less energy and less chemical for pre-treatment and cleaning (Younos, 2005). In addition, the maintenance cost, such as membrane replacement cost, is also less for less saline feedwater.

Thousands of 1995$

4000

3000 Operating Cost

2000

Capital Cost

1000

0 800

1200

1600

2000

2400

Total Dissolved Solids (mg/l)

Figure 4.2 Costs for a RO Desalination Plant versus Feed Salinity (Wilbert et al., 1998)

II.

Plant Capacity

Plant capacity is an important design factor. It affects the size of treatment units, pumping, water storage tank and water distribution system (Younos, 2005). There are no

Page 4-4


limitations in relation to the plant size of most desalination technologies including membrane

systems.

However,

for

thermal

desalination

plants,

there

some

recommended plant sizes, and the plants would not work economically below these recommended sizes (RosTek, 2003).

As a general rule, due to economy of scale, the unit production cost (or cost of reclaimed water) for large capacity plants is lower than the low capacity plants. However, large capacity plants require high initial capital investment compared to the low capacity plants (Younos, 2005). The unit production cost of the commercial membrane desalination technologies for low (2,500 mg/L) to medium (5,000 mg/L) saline water is plotted against the plant capacity in Figures 4.3 (RosTek, 2003).

ED= Electrodialysis EDR= Electrodialysis Reverse

Figure 4.3 Cost of Low to Medium Saline Water Desalting (RosTek, 2003)

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III.

Site Characteristics

In order to save the delivery cost of feedwater into a desalination plant, the wastewater reclamation via desalination plants are usually constructed inside or very close to a trade waste facility, or inside or nearby a wastewater treatment plant.

Site characteristics can affect the water production cost. For example, availability of land and land condition can determine the cost. The plant location will affect the production cost in terms of waste disposal cost. A plant located close to a water body such as the ocean, will have substantially reduced costs for waste disposal.

IV.

Costs Associated with Regulatory Requirements

These costs are to meet local/state permits and their regulatory requirements. Meeting more stringer environmental requirements especially in terms of waste disposal methods or noise pollution (e.g. caused by high pressure pumps in membrane processes) can increase the total water production cost.

4.2.2

Cost Components of Desalination

In a broad sense, the desalination plant costs can be categorised as construction costs (or capital costs) and annual costs. The capital costs are usually referred to as those costs that are needed to construct the plant, and the annual costs are referred to as the costs after commissioning the plant (RosTek, 2003).

I.

Construction Costs

Construction costs consist of direct and indirect capital costs. The indirect capital cost is usually estimated as percentages of the total direct capital cost (Younos, 2005) and may include freight and insurance, construction overhead, owner’s costs, and contingency costs. As this research project is focused on wastewater desalination, those costs such as feedwater intake costs which usually are associated with seawater or groundwater desalination, are not discussed in the following section.

Page 4-6


A. Direct Costs 

Land. This cost is site-specific. It may vary considerably from zero to a sum that depends on site characteristics and plant ownership (i.e. public versus private).



Process equipment. The process equipment includes water treatment units (e.g. membranes), instrumentation and controls, pre- and post-treatment units and cleaning systems. Process equipment costs depend on plant capacity and feedwater quality (Younos, 2005).



Auxiliary equipment. Costs to purchase equipment such as generators, transformers, pumps, pipes, valves, storage tanks, electrical wiring, etc.



Building. Building costs include the construction of structures such as control room, laboratory, workshop, and offices.



Concentrate disposal. The cost of concentrate disposal system depends on the type of desalination technology, plant capacity, discharge location, and environmental regulations.

B. Indirect Costs 

Freight and insurance. Freight and insurance cost is typically estimated as 5% of total direct costs (Younos, 2005).



Owner’s cost. This cost varies considerably, depending on owner’s method of accounting (RosTek, 2003), and includes engineering design, contract administration, administrative expenses, commissioning and/or start up costs, and legal fees. The normal value is 10 per cent of the direct capital costs (ibid).



Contingency. This cost is included for possible additional services, which is Contingency allocation is generally 10 per cent of the total direct costs (ibid).

II. Annual Costs

The annual costs consist of fixed costs and variable costs. Fixed costs include insurance and amortization costs. Usually, the insurance cost is estimated as 0.5 per cent of the total capital cost (Younos, 2005). Amortization compensates for annual interest payment for direct and indirect costs, and depends on the interest rate and the service life of the plant. Typically, an amortization rate in the range of 5-10 per cent is used (ibid).

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Major variable costs include the cost of energy, chemicals, labour and maintenance. Energy cost depends on the type of energy source and its availability. Chemical cost depends on mainly on feedwater quality and degree of pre-/post-treatment and cleaning process. Labour costs can be site-specific and also depend on the plant ownership. The major maintenance cost in membrane desalination is the frequency of membrane replacement, which is affected by feedwater quality. The membrane replacement rate can be varied from 5 to 20 per year (Younos, 2005). The cost for maintenance and spare parts is typically less than 2% of the total capital cost on an annual basis (ibid).

4.2.3

Cost Breakdown of Desalination

The individual contribution of cost items on the overall cost of a desalination plant depends substantially on feedwater type. For example, while electric power accounts for about 11% of the cost a typical RO brackish water desalination plant, it is accounted about 44% of a typical RO seawater plant (Miller, 2003). Other cost breakdowns are presented in Figures 4.4 and 4.5.

The cost breakdown of desalination also depends on the type of desalination technology even for an identical feedwater type. For example, while energy cost for RO seawater desalination is about 44% of the overall desalination cost, for typical Multi Effect Distillation (MED) plant it is about 28% (representing fuel cost of steam and electrical power) (Miller, 2003). More detailed cost breakdown of a seawater MED desalination plant is presented in figure 4.6.

Figure 4.4 Cost Breakdowns for RO Desalination of Brackish Water (Miller, 2003)

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Figure 4.5 Cost Breakdowns for RO Seawater Desalination (Miller, 2003)

Figure 4.6 Cost Breakdowns for Typical Seawater MED Desalination Plant (Miller, 2003)

4.2.4

Hidden Costs of Desalination

In addition to direct costs (such as equipments costs) or indirect costs (such as freight cost) for commissioning of a desalination plant, there are other (hidden) costs which are not included in desalinated water production cost but in most cases, the community pay these costs. Subsidies are the most significant type of the desalination plant hidden cost. Low interest capital, free land or low energy fee are the typical examples of the subsidies. Land cost can be a major cost item especially for those countries which suffer from land shortage such as Japan (Dore, 2005).

4.2.5

Future Costs of Desalination

There are different opinions about the future costs of desalination in the literature. Some believe that the cost will continue its downward trend (Cooley, 2006) and a 50% cost reduction by 2020 (ibid) is achievable. Technology improvements especially in

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membrane desalination systems, such as development of the long-lasting membrane, and also innovative plant configurations such as co-location/co-generation plants have the highest cost reduction impacts on desalination cost.

In contrast, some experts believe that there are substantial barriers for further cost reductions in the short term (Cooley, 2006) due to increasing energy prices and environmental restrictions.

4.2.6

Cost Estimating Methods

There are several desalination cost estimation models (or methods) in the literature. Some of them assess the economics of desalination with respect to a certain aspect. For example, the International Atomic Energy Agency (IAEA) has developed a software program which called the Desalination Economic Evaluation Program (DEEP) to assess economic aspects of nuclear desalination plants (www.iaea.org) where energy is sourced from nuclear power. Attention of these models to these aspects limits their applicability.

Based on the literature review conducted throughout this research project, two models have been selected for wastewater desalination cost estimation purposes. The methods are referred to as Cost-Chart method and Computer-Based method in this thesis. These methods were selected because they are more reliable (both methods developed for the US Bureau of Reclamation, which has a long history of developing such methods and engineering solution), easier to use and more comprehensive. Details of these cost estimating methods are presented in the next section.

The main objective of presenting these cost estimating methods in this thesis is for comparison of the associated costs of various desalination technologies. These methods should not be employed for designing an actual desalination plant, since they were developed based on the USA cost values (such as chemicals, electricity, and labour prices) which might be different in Australia, and also other associated issues such as inflation and the variable rate of exchange between the Australian currency and the American currency.

The actual cost information should be obtained from the local

contractors.

Page 4-10


I.

Cost - Chart Method

The United States Bureau of Reclamation in collaboration with some consulting firms has developed a manual (a handbook), Desalination Handbook for Planners, as part of the United States of America Desalination and Water Purification Research and Development Program (RosTek, 2003). The Cost-Chart method is based on the information provided in RosTek (2003). This handbook provides cost estimates for commercial desalting processes (membrane and thermal technologies). The information presented in this handbook was derived from actual bids, vendor quotations, experience, and personal cost data files, with the implied level of accuracy around ± 30 per cent. The cost information is provided in the handbook graphically. For example, the annual cost of chemicals for brackish water membrane desalination (in U.S $) has been plotted against the plant capacity (in m3/d). Appendix B presents all charts (for brackish feedwater) which are required for estimating the capital and operating costs associated with the commercial desalination technologies.

II. Computer-Based Method

I.Moch & Associates and Boulder Research Enterprises with the assistance of the United States Bureau of Reclamation have developed a computer program, WTCost©, to evaluate the capital and operating costs for membrane desalination processes and ion exchange process. Thermal desalination technologies are not included in the computer program at the current time (RosTek, 2003).

The information sources which have been used for development of WTCost© are basically similar to the information sources which have been used for development of Cost-Chart method (ibid). The cost indices used in the method can be found in the Engineering News Record (http://enr.construction.com/Default.asp).

This computer program contains cost algorithms for RO/NF, UF/MF, ED and IE. All inputs required for the calculations such as water analysis, energy and chemical usages and prices, labour staffing and rates, and amortization have default values, but can be replaced when better information is available. The main advantage of Computer-Based cost estimating method over Cost-Chart method is the availability of options which can

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be used for the desalination train components. For example, the software presents three different pre-treatment systems. This allows the user to select that pre-treatment system which is more suitable for the facility wastewater reclamation project.

4.2.7

Examples of Using Cost Estimating Methods

Two examples are presented in this section to show the application of the cost estimating methods outlined in Section 4.2.5. One of these examples shows how to use the Cost-Chart method and the other shows how to use Computer-Based method for estimating the capital and operating costs associated with a wastewater reclamation desalination plant. The examples selected in this section are similar to the case studies which are presented in Chapter 6 of this thesis. In fact, the cost details presented in this section provide an information background for the cost estimation of those case studies. Chapter 6 also presents the application of both methods to estimate the costs associated with a wastewater desalination plant at Western Treatment Plant (WTP), in an attempt to compare the two different methods.

I.

Cost-Chart Method — Example 1

This example estimates the costs associated with wastewater reclamation via desalination at a small wastewater treatment plant at Melbourne. The plant treats about 18,000 m3/d of wastewater, mainly discharged by the nearby industries. The plant wastewater salinity is relatively high (around 9,000 mg/L), because of discharging industrial wastewater from the nearby trade waste facilities into this treatment plant. In this example, it is assumed that RO is selected as the desalination technology for wastewater reclamation.

The reclaimed wastewater at this plant is expected to be used for various applications including industrial applications at nearby industries. The plant wastewater treatment train comprises a grit chamber, two primary sedimentation tanks, four trickling filters, two secondary sedimentation tanks, and one Extended Aeration plant.

Page 4-12


The plant secondary treated wastewater has relatively good quality, except the high level of TDS. For example, the plant effluent has biological oxygen demand (BOD5) less than 5 mg/L and suspended solids (SS) less than 10 mg/L. Therefore, it can be assumed that a conventional pre-treatment type such a multi media filter would be sufficient to remove the tiny materials which cause biofilm and scale formation on the RO membrane surface. Table 4.1 summarises the plant basic information which is required for estimating the desalination project costs.

Table 4.1 Summary of the Example 1 Basic Data (from a confidential report provided by City West Water)

PROJECT DESCRIPTION: Wastewater reclamation at a Wastewater Treatment Plant Location: Melbourne

PRODUCT WATER CHARACTERISTICS Annual Requirement (Production): 4,681 ML Required Quality: Less than 200 mg/L TDS Distance Point of Delivery from Desalination Plant: Between 2-3 kilometres

WASTEWATER CHARACTERISTICS Wastewater Quality: Secondary Treated Wastewater with TDS around 9000 mg/L, BOD5 less than 5 mg/L, and SS: 10 mg/L

DESALINATION PLANT CHARACTERISTICES Desalting Device: RO Plant Capacity: 13.5 ML/d Pre-treatment Type: Conventional Plant Recovery: 75% Waste Disposal Method: Outfall to Port Phillip Bay Plant Life: 20 Years Interest Rate: 7% Plant Reliability: 95%

Page 4-13


As was presented in Section 4.2.2, Direct Capital Costs (DCC) for a RO wastewater desalination plant includes the costs for (RosTek, 2003): 

Total construction cost of desalting plant train which includes pre-treatment, desalting and post-treatment,



Concentrate disposal,



Site development, and



Auxiliary equipment.

The corresponded value for each of these DCC items can be estimated via the cost charts presented in Charts B.4, B.7, B.9, and B.11 in Appendix B (for a brackish RO desalination plant) as below: 

Desalting plant train cost: Chart B.4, presents the desalting plant train cost for membrane desalination technologies. Based on this chart, for a brackish water RO desalination process (BWRO) with the plant capacity of 13,500 m3/d, the desalting plant train cost is approximately US$10,000,000.



Concentrate disposal: the liquid waste produced by desalination plant (brine or concentrate) is assumed to be discharged into the bay. The construction costs for concentrate disposal for membrane processes are mainly due to the construction of pipeline and are presented in Chart B.7. It is assumed that the pipeline length is about 450 meter (1,500 feet). The pipeline construction cost for this example is approximately US$ 45,000.



Site development: the cost associated with development of a site for a membrane desalination plant is presented in Chart B.9. The site development cost for this example is approximately US$ 50,000.



Auxiliary equipment: the main auxiliary item required for this example is a storage tank which allows storage of one day desalination plant product. This cost item is presented in Chart B.11. The Auxiliary equipment cost for this example is approximately US$ 1,500,000.

The Total Capital Cost (TCC) of the desalination plant is the combination of DCC and other costs including land cost, freight & insurance (5% of DCC), contingency (10% of

Page 4-14


DCC), and owner’s direct expenses (approximately 10 % of DCC) . Table 4.2 summarises the capital costs estimated for Example 1.

Table 4.2 Example 1 Desalination Plant Capital Costs Summary

ITEM

COST (US$ (2000))

Desalting Plant (Chart B.4)

10,000,000

Concentrate Disposal (Chart B.7)

45,000

Site Development (Chart B.9)

50,000

Auxiliary Equipment, Daily product Storage Tank (Chart B.11)

1,500,000

Subtotal DCC

11,595,000

Land (assumed free, as part of the plant will be used )

N/A

Freight and Insurance (5% of DCC)

579,750

Contingency (10 % of DCC)

1,159,500

Owner’s Direct Expense (10% of DCC)

1,159,500

Total Capital Cost (TCC)

≈14,500,000

As stated in Section 4.2.3, the annual cost items associated with a desalination plant include operating and maintenance (O&M) costs (i.e. insurance (0.5 % of TCC), repairs and spares (1% of DCC), labour, chemicals, and electricity) and other costs (i.e. contingency (10% of O&M), membrane replacement, and capital depreciation).

Membrane replacement cost can be estimated (RosTek, 2003) via Equation (4.1). membrane replacement cost = membrane cost x annual production

(4.1)

where: membrane cost ($/m3) = the annual costs that should be paid to replace membrane, for brackish RO, NF, and MF it is about 0.021 $/m3 (RosTek, 2003), and annual production = plant capacity (m3/d) x Annual Plant Factor x 365

(4.2) (ibid)

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The annual plant factor in Equation (4.2) is defined as the amount of time (per cent) that the plant will operate during the year. This allows sufficient time for preventive maintenance and unforeseen shutdown. For this example, the plant capacity of 13,500 m3/d and the annual plant factor is assumed as 95%. Therefore the annual production is 4,681,125 m3 desalinated water (permeate).

The capital depreciation can be estimated based on the following equation (RosTek, 2003): Capital Depreciation= (TCC— Membrane Cost X Membrane Life) X CRF (4.3)

In Equation (4.3), the membrane life for RO and NF is assumed about 7 years and for EDR about 10 years (RosTek, 2003), and CRF is the Capital Recovery Factor or interest amortization, (which is the annual payment to repay principal and interest as the present sum of money). Equation (4.4) can be used to estimate the Capital Recovery Factor (ibid): CRF= i x (1+ i )y /(1+i) (y-1)

(4.4)

where i is interest rate (%) and y is repayment period (year).

In this example, it is assumed that the interest rate is 7% and the plant life (or repayment period) is 20 years. Based on these values, CRF is estimated as 0.075.

As stated earlier the operating and maintenance (O&M) costs of a membrane desalination plant include costs for labour, chemical, and electricity. These costs need to be estimated from the Cost Charts. Charts B.15, B.19, and B.23 of Appendix B present labour cost, chemicals cost, and electricity cost respectively.

Based on the cost Equations (4.1) to (4.3) and Cost Charts (Charts B.15, B.19, and B.23), the annual costs for Example 1 were estimated and is presented in Table 4.3. The cost values for labour, chemicals, and electric power are respectively US$ 230,000, US$ 200,000, and US$ 300,000 respectively.

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Table 4.3 Example 1 Desalination Plant Annual Costs Summary

ITEM

COST (US$ (2000))

Labour (Chart B.15)

230,000

Chemicals (Chart B.19)

200,000

Electric Power (Chart B.23)

300,000

Insurance (0.5 % of TCC)

72,500

Repairs and Spares (1 % of DCC)

115,500

Total O&M Costs

918,000

Contingency (10 % of O&M Costs)

91,800

Membrane Replacement (Equations 4.1 and 4.2)

98,303

Capital Depreciation (Equations 4.3 and 4.4)

1,035,890

Total Annual Costs

2,143,993

Tables 4.2 indicates the capital costs and Table 4.3 indicates the annual costs of the desalination plant for Example 1. These tables do not indicate the cost of water production per unit of volume (US$/m3). The commonly used term (RosTek, 2003) for expressing water production cost (or cost of water) is Unit Production Cost (US$/m3). The unit production cost can be estimated by the following equation (RosTek, 2003): Cost of Water (US$/m3) = (Total Annual Costs/Yearly Production)

(4.5)

in this example: Cost of water (US$/m3) = (2,143,993)/ (4,681,125) = 0.46 US$/m3

Note that all costs in this example are given in 2000 US dollars.

Page 4-17


II. Computer-Based Method — Example 2

This example considers a trade waste facility, located in one of the capital cities in Australia, which produces Suspension Poly Vinyl Chloride (PVC). In 2004, this trade waste facility conducted a study to find the opportunities to reduce its water consumption and effluent generation. The study identified on-site wastewater reclamation via desalination as a viable opportunity for minimising the facility water needs and minimising the facility wastewater discharged into sewer. In this section, the costs associated with construction and operation of a RO desalination plant at this facility is estimated by WTCost© Software.

The facility requires good water quality for its sensitive operations, and therefore the desired reclaimed water TDS needs to be less than 100 mg/L. The current Facility wastewater characteristics include daily effluent of 1,200 m3/d, TDS of 356 mg/L, BOD5 of 23 mg/L and SS of 22 mg/L. The facility is willing to build a desalination plant with capacity approximately twice of its water need (current needs around 2,000 m3 fresh water per day) to allow for its future production expansion. Therefore, the plant capacity of 4,000 m3/d is considered with an annual plant factor (plant availability) of 95%. Based on Equation (4.2), the desalination plant annual production would be 1,387,000 m3.

There is no existing on-site appropriate wastewater pre-treatment at the facility, therefore, another membrane separation system such as Microfiltration (MF) or Ultrafiltration (UF) must be employed to protect the RO membrane surface against biofilm or scaling formation. Table 4.4 presents a summary of the information required for the application of WTCost©. Table 4.5 presents a cost summary, resulted from the application of WTCost© Software for the example. Table 4.5 comprises of two separated windows. The upper window, which has two separated sections, shows the software’s basic inputs (in the top section of the upper window) and the details of the desalination train (in the second section of the upper window). As shown in this table, the basic inputs of the software include the plant capacity, process recovery, plant factor, and plant operation time. The desalination train details include the pre-treatment disinfection type (Ultraviolet-UV), desalting device (RO), product water disinfection (UV), pre-treatment type (MF or UF), and miscellaneous equipment (pumps).

Page 4-18


The lower window in Table 4.5 presents the project construction costs (or capital costs) and operating costs (or annual costs) summary for each desalination train process. These costs are described below: 

Pre-treatment Disinfection: The cost is related to feedwater disinfection to protect MF/UF pre-treatment membrane from biofilm formation. (UV) light is considered as the disinfectant for feedwater disinfection.



Chemical Feed System: This cost is related to using chemical systems to control scaling of sparingly chemicals on the membrane surface. Chemical Feed System is normally used for seawater and brackish water over 10,000 mg/L feedwater TDS (I.Moch, 2004). Therefore, in Example 2 no Chemical Feed Systems cost is listed in Table 4.5.



Media Filtration: This cost is related to use Micro/Ultra filtration as pretreatment.



De-Chlorination: This cost is related to use De-Chlorination process to protect the membrane surface from oxidation by chlorine (ibid). The most common chemicals which are used in De-Chlorination systems include sodium bi-sulfite sodium sulfite and sulfure dioxide (ibid). These chemicals are selected in this case study.



Desalting: The cost associated with using main desalting device. RO is the main desalting device in this case study.



Product Water Treatment: This cost is related to the disinfection of produced water. UV is considered as disinfectant for this case study.



Miscellaneous Equipment: The cost associated with considering extra pumps as “stand-by” pumps in case of any problem for the RO system pumps.



Indirect Capital Cost: Indirect costs are for other than equipment and labour during construction (ibid).



Capital Recovery: This cost compensates for annual interest payment for direct and indirect costs.

Based on Table 4.5, approximately 3.5 million US dollars investment is required for the construction of a RO desalination plant at this Suspension PVC producer. The unit production cost (US$/m3) of desalinated wastewater in this facility is also about 1.3 US$/m3.

Page 4-19


Table 4.4 Summary of the Required Information for Example 2 (Extracted from a Confidential Report) PROJECT DESCRIPTION: Wastewater Reclamation at a Suspension PVC Producer

PRODUCT WATER CHARACTERISTICS Annual Requirement (Production): 1,387,000 m3 Required Quality: Less than 100 mg/L TDS Distance Point of Delivery from Desalination Plant: On-Site

WASTEWATER CHARACTERISTICS Annual Capacity: 520,000 m3 Wastewater Quality: TDS around 356 mg/L, BOD5 around 23 mg/L, and SS: 22 mg/L

DESALINATION PLANT CHARACTERISTICS

Process Being Considered: Reverse Osmosis (RO) with no Blending of Feedwater and Product Plant Capacity: 4,000 m3/d Pre-treatment Type: Microfiltration (MF) or Ultrafiltration (UF) Plant Recovery: 75 % Waste Disposal Method: Discharge to Sewer Plant Reliability: 95% Feedwater Disinfection Type: UV Product Water Disinfection Type: UV Miscellaneous Equipment: Extra Pumps for Stand-by Plant Operation Hours: 3 Shifts, 24 Hours Plant Life: 20 Years Interest Rate: 7 %

Page 4-20


Table 4.5 Cost Summary for Example 2, Calculated by WTCost© Software

Page 4-21


4.2.8

Cost Comparison of Desalination Technologies

This section compares the cost of wastewater reclamation via the commercial desalination technologies, based on analysis of cost charts presented in Appendix B. It is assumed in this comparison that the desalination technology type is the only variable and the other parameters including the plant capacity are the same for all the desalination technologies. This cost comparison is required for the development of the DSF, presented in Chapter 5 of this thesis.

1. As stated in Chapter 3, the most suitable desalination technologies for highly saline wastewater reclamation (TDS more than 55,000 mg/L) are Seawater Reverse Osmosis (SWRO), Multi-Effect distillation (MED), and Mechanical Vapour Compression (MVC). Based on Charts B.2 to B.4 in Appendix B, the relative total construction costs for these technologies (for a identical desalination plant capacity) can be presented as below:

SWRO< MED≈ MVC

The above cost relation is also valid for the annual cost components (labour, chemical, and electricity) of these technologies, based on Charts in Appendix B, B.14-B.15 for labour cost, Charts B.17-B.19 for chemical cost, and Charts B.21B.23 for electricity cost. Therefore, the relative production cost ($/m3) of the reclaimed wastewater for SWRO, MED, and MVC technologies are as below:

SWRO< MED≈ MVC

2.

As stated in Chapter 3, the most suitable desalination technologies for

medium to

low saline wastewater (with TDS less than 44,000 mg/L) are

Brackish Water

Reverse Osmosis (BWRO), NF, and Electrodialysis

Reverse (EDR). Based on reclamation,

Charts B.4 in Appendix B, for brackish wastewater

the relative total desalting capital costs for these technologies are

as below:

NF200 mg/L acceptable?

Is non-food processing application?

N

N N

N

N

Return to DSF

Y

Return to DSF

Return to DSF

Return to DSF

Y

ED/EDR

Figure 5.5 EDR Application Route

Page 5-13

CHAPTER 5: DECISION SUPPORT FRAMEWORK

The first parameter (box) in this figure is about the feedwater salinity. As an electricity driven membrane process, the more salty the wastewater, the more power is required to reclaim that wastewater by an EDR system (Pilat, 2003). The higher energy consumption is also associated with a higher production cost, and more greenhouse gases generation. The maximum TDS considered for EDR application for wastewater reclamation is about 3,500 mg/L (RosTek, 2003) and this has been considered in the DSF. It means over this limit, it is more beneficial, in terms of cost and energy, to employ RO or NF for wastewater desalination.

The second parameter in Figure 5.5 is on the level of on-site existing pre-treatment facilities. As stated in Section 3.6.1, SDI and Turbidity limits for using EDR systems are much higher than the corresponded values for RO and NF systems. This means that EDR systems are less susceptible for fouling and scaling, and therefore, EDR is the superior desalination technology for wastewater reclamation for those facilities which have low to moderate pre-treatment. This could significantly reduce the reclaimed wastewater production cost, and reduce the desalination footprint (or space). The third parameter in Figure 5.5 is about the desalination plant capacity. For practical hydraulic reasons, EDR capacity has a finite limit (RosTek, 2003). Depending on the desalting load required, the biggest single unit commercially available is about 5,680 m3/d (ibid). A typical EDR plant usually consists of less than 10 units (ibid) therefore the maximum EDR capacity would be less than 57,000 m3/d. The DSF does not recommend selecting EDR for a wastewater reclamation project which requires a production capacity more than 57,000 m3/d.

The fourth parameter in Figure 5.5 is the desired product TDS. The DSF does not recommend the EDR application to produce high quality water (i.e. TDS around 20 mg/L), as a number of passes must be designed for EDR to achieve such water quality. Increasing the number of passes requires high investment, which diminishes the EDR cost-effectiveness for wastewater reclamation (Wilbert et al., 1998). In addition, the energy consumption for desalting feedwater increases sharply as the feedwater solution becomes more pure (ibid). This also increases the operating costs of EDR significantly (RosTek, 2003). Product TDS around 200 mg/L is very typical for most existing EDR plants (ibid).

Page 5-14


Another EDR constraint is its application for food processing industry, which is indicated as the last box in Figure 4.5. The EDR process does not properly remove organic or micro-organisms (RosTek, 2003), as this process is designed to remove wastewater pollutants based on their electrical charges (Blackburn, 1999). Pollutants including cyst or virus will not be removed completely by EDR, and these pollutants are big concerns for food processing industry where water is required to meet Safe Water Drinking Act (RosTek, 2003). Thus, the DSF does not recommend the EDR application for food processing industry.

5.3.4

Raw Chemical Recovery and Reuse Route

Raw chemicals recovery and reuse can be defined as an activity in which non-product output from one process is used productively and safely as an input for the same or a different process (Berkel, 2006). Some industrial sectors including textile (Woerner, 2001), pulp & paper (USEPA, 1997), dairy products (Gesan-Guiziou et al., 2002), and breweries (Ockert, 2004) are characterised by using a large quantity of raw chemicals and huge quantities of water. The needs for the chemicals are varied, depending on the chemical type and the industry sector characteristics. Generally, a large portion of them become part of the product, however, many of them just perform necessary functions (e.g. detergents applications to remove dirt, grit, oils and waxes). Those parts of the raw chemicals which do not belong to final product normally appear as by-products and most often are treated as waste.

Review of literature indicated that some practice have been reported (Gesan-Guiziou et al., 2002 and Durham et al., 2001) on the recovery and reuse of chemicals available in wastewater discharged from some specific industrial sectors including dairy, tanning, and beverage facilities by means of membrane desalination processes, in particular NF process. A reason for higher use of NF compared to RO and EDR for raw chemicals recovery and reuse might be related to the selective separation phenomenon of the NF process. As stated in Section 5.3.2, NF nearly rejects all multivalent ions but allows monovalent ions to pass through the membrane. This selective separation phenomenon is used as a basis to recover and reuse chemicals. For example, caustic (NaOH solution) recovery and reuse opportunities via NF have been investigated by many studies (Gesan-Guiziou et al., 2002, and Novalic et al., 1998). Caustic is broadly used in

Page 5-15


dairy or beverage industrial facilities for cleaning and hygienic purposes. This cleaning solution is periodically drained when it is considered too polluted. The amount of the required caustic solution could be very significant. For example, the total amount of caustic drained by a factory processing 106 litres of milk per day represents approximately 120 metric ton per year (ibid). By using NF in this facility, the monovalent ions (i.e. Na+ and OH—) available in the wastewater can be recovered and used again. This will be financially and environmentally (in terms of caustic disposal after drainage) beneficial.

As can be seen from Figure 5.1, a part of the DSF has been allocated to raw chemicals recovery and reuse. This part of the DSF is presented in Figure 5.6. Y

Raw chemicals recycling/reuse viable?

N

Return to DSF

Is feedwater combined of mono and multivalent ions?

Y

NF

N

Return to DSF

Figure 5.6 Raw Chemicals Recovery and Reuse Route

The first parameter in Figure 5.6 is to check the viability of raw chemical recovery and reuse. Recovery and reuse of raw chemicals by membrane desalination processes is feasible if these chemicals can be presented in feedwater in form of dissolved solids (or ion form), since non-dissolved chemicals (i.e. polymer compounds) cannot pass through the membrane (Wilbert et al., 1998), and therefore cannot be separated from the other wastewater components.

The second parameter in Figure 5.6 is on the characteristic of the ions presented in a facility wastewater stream. If the wastewater contains ions with the same valent number (e.g. monovalent ions), NF allows the ions to pass through the membrane (if they are monovalent ions) or NF rejects them (if they are multivalent ions), since NF selective separation phenomenon is based on the electrical charge of ions and the type of ions (Wilbert et al. 1998). Therefore, as stated in the second box in Figure 5.6, feedwater must consist of a combination of mono and multivalent ions in order to recover and

Page 5-16


recycle the raw chemicals available in feedwater, by the NF membrane. The wastewater generated from the typical chromic tannery facilities is an ideal feedwater for raw chemical recovery and reuse (Nacheva et al., 2004). This wastewater is consisted of a combination of monovalent ions (Na+ and Cl—) and multivalent ions (Cr+4 and Cr+6). By passing wastewater generated in the chromic tannery facility through the NF membrane, Na+ and Cl— solution can pass through the membrane and is collected as permeate but the solution that contains Cr+4 and Cr+6 cannot pass through the NF membrane and is collected as waste. The solution that contains Na+ and Cl— can be used again in the tanning process as raw chemicals.

5.3.5

Residential Area Closeness Route

NF and RO are pressure-driven membrane technologies. Depending on the feedwater salt content, these devices need external pressure to pass water through the membrane and leave the salt behind (Burse, 2000). The external pressure is provided by highpressure pumps. The pump operation is usually associated with considerable noise (Einav et al., 2002). To address this issue, the DSF recommends the application of NF which requires much lower pressure than the RO process for wastewater desalination. While, the typical RO operating pressure is about 15-60 bar (Envirowise, 1997), for the NF systems the operating pressure is between 20-40 bar (ibid). This means, if both NF and RO permeate quality can meet the desired reclaimed water quality, selecting NF would minimise the required operating pressure and consequently, reduce the noise associated with the operation of the desalination plant pumps.

Figure 5.7 presents that part of the DSF which addresses the best membrane desalination technique selection for those industrial facilities which are located close to a residential area.

Y

Close to a residential area?

N

NF

Return to DSF

Figure 5.7 Residential Area Closeness Route

Page 5-17


5.3.6

Water Softening Route

Water with high levels of calcium and magnesium is termed “hard water” (RosTek, 2003). The minerals in hard water reduce the effectiveness of commercial detergents, scaling up the water distribution systems, and cause faster rate in the facility equipments corrosion (ibid). To solve the problems caused by hard water, water softener devices are often used. Ion Exchange (IX) is one of the most common water softener processes (which is also classified as a desalination process) which has been employed in many industrial facilities especially for those places that need a high quality water for cooling water make-up and boiler house operation (Miller, 2003). Kinhill (1999) reported that a large power facility in the USA requires up to 6.5 million litres per minute water for cooling. Figure 5.8 shows how a typical boiler house operation comprises an IX system (Envirowise, 2005). In this figure, mains water can be replaced with wastewater.

Figure 5.8 A typical Boiler House Operation (Envirowise, 2005)

Page 5-18


Ion Exchange performance is usually associated with producing a waste stream containing regeneration chemicals (normally NaOH solution), which is an input to IX. The most common practice for handling of this waste stream is discharging it into sewer, as illustrated in Figure 5.8. This regeneration stream typically has a high TDS value and discharging it into the sewer increases the wastewater salinity of the public owned treatment plant. In other words, the IX regeneration process could be considered as a salt discharging source into a public wastewater treatment plant, since regeneration chemicals add more salt into wastewater. Because of this IX characteristic, the DSF developed in this research project does not recommend IX as a desalination technology by itself.

The strategy presented by the DSF to reclaim wastewater for those facilities that require water free from minerals for their operation and have an existing IX system is to keep the IX process but followed it with a NF process. That part of the DSF which addresses this point is presented in Figure 5.9.

Existing water softening process?

Y

Is IX used for water softening?

Y

Keep IX?

Y

IX+NF

N N

N

Return to DSF Return to DSF

Return to DSF

Figure 5.9 Water Softening Route

Regenerated wastewater discharged from IX, which has considerable amounts of ions (i.e. Ca+2, Mg+2, Na+, and Cl- (or OH-)) will pass through the NF membrane. Divalent ions will be rejected and monovalent ions will be passed through to permeate. Then, the permeate could be returned again to the system and be used as a fresh regeneration chemicals. In other words, in the IX + NF system, the IX process is the main desalting device for wastewater reclamation and the NF system is the supporting device for raw chemical recovery and reuse. This combination of two different systems has been practised in diary industry (Durham et al., 2001).

Page 5-19


5.4

FURTHER DEVELOPMENT OF DSF

There are number of areas for future further development of the DSF developed in this research project. They include extending the DSF to include emerging desalination technologies and extending the DSF to cater for other wastewater reclamation applications (or routes), which are not covered in this chapter.

At present, the DSF only deals with those desalination technologies (RO, NF, EDR, MED and VC) which are currently commercially available. It means that the emerging desalination technologies (those technologies which are in the research and development stage) are not included in the DSF. However, the DSF has the ability to include the emerging technologies when they become commercially available in the future. For example, currently the environmental impacts associated with construction and operation of some emerging desalination technologies (i.e. freeze desalination process) are significantly less than desalination technologies included in the DSF (Miller, 2003) but due to a number of practical considerations including inexperience with designing and sizing the components that are utilised for desalination on a large scale (ibid), these technologies have not been included in the DSF. These practical considerations may be solved in the future, and therefore, the new technologies can be included in the DSF.

The future extending of the DSF routes will assist the water industry decision makers to select the best desalination technology for wastewater reclamation for those industrial facilities which currently cannot be covered by any DSF route. The DSF is not applicable to these facilities because the conditions in these facilities (i.e. wastewater TDS, plant capacity, wastewater reclamation propose, etc.) are specific. However, the DSF has the ability to cover these facilities if more industrial facilities with the same conditions become identified. These facilities together must create a group of industrial facilities which have in common some key parameters or conditions, to be considered as a new DSF route. For example, in the future, a group of industrial facilities may be interested to utilise a desalination technology to address their water demand needs and also to remove a specific water pollutants (i.e. a specific heavy metal ion) from their wastewater stream, before discharging into sewer. This application can be considered as a new DSF route, leading to a desalination technology.

Page 5-20


5.5

SUMMARY

Although, selecting the best desalination technology for wastewater reclamation in a facility is “site-specific”, the technology should be selected based on the facility basic conditions (i.e. water demand quality and quantity, wastewater characteristics, available energy source etc). However, it is feasible to recommend a specified desalination technology for a group of industrial facilities which have in common some key parameters and conditions. This idea was used in this chapter as the basis for development of a Decision Support Framework (DSF).

The DSF developed in this study is an easy and practical tool for determining the best desalination technology for wastewater reclamation. For wastewater reclamation applications, the DSF considers the available commercial desalination technologies based on their technical performance, costs, environmental and social aspects. The DSF has a “tree-shape” format, which makes it easy to follow. The DSF consists of six branches (or routes); each branch belonging to a group of industrial facilities which have in common some key parameters or conditions. These routes are: 

Thermal desalination technologies route



Blending viability route



EDR application route



Raw chemicals recovery and reuse route



Residential area closeness route



Water softening route

These routes are expected to cover the most wastewater reclamation projects (or scenarios) regardless of the facility size and activity. The DSF has also the ability to be expanded and to cover more scenarios if they are later identified.

Page 5-21

CHAPTER 6: CASE STUDIES

CHAPTER 6 CASE STUDIES 6.1

INTRODUCTION

Chapter 5 described the Decision Support Framework (DSF), as a systematic approach to select the best desalination technology for wastewater reclamation. This chapter aims to demonstrate the applicability of the DSF through several case studies.

The first case study is related to the Western Treatment Plant (WTP) at Werribee. Based on the Victorian Government wastewater recycling target, the Melbourne water retail companies are required to reuse 20 per cent of the effluent from the Melbourne wastewater treatment plants by 2010 (Corby, 2005). Wastewater reclamation at the WTP is one of the most significant wastewater reclamation projects in Melbourne which is currently being pursued by Melbourne Water Corporation (MWC) and City West Water (CWW). The WTP case study represents the application of the DSF as a centralised wastewater reclamation project.

In the second case study, the DSF is applied to three CWW trade waste customer sites: a leather processing factory (i.e. a tanning factory), a poultry company, and a food processing factory. These three trade waste facilities are located close to each other. The DSF was applied individually to each of these facilities, considering each as a decentralised wastewater reclamation project. These sites are named in this thesis as Facility X, Facility Y and Facility Z for confidentiality reasons.

The third case study is the application of the DSF into a wastewater reclamation plant which is shared between Facilities X, Y and Z. This case study is considered as a semicentralised (or cluster) wastewater reclamation project.

6.2

WESTERN TREATMENT PLANT CASE STUDY

The Western Treatment Plant (WTP) is the largest sewage treatment facility in Australia (MWC, 2003). The plant is bounded by Port Phillip Bay to the south, Princes Freeway to

Page 6-1


the north, the Werribee River to the east and Western Road to the West. Figure 6.1 shows the location of the WTP.

Figure 6.1 Western Treatment Plant Location (MWC, 2006)

The WTP occupies 10,823 hectares on the western side of Port Phillip Bay, of which 6,950 hectares is utilised for sewage treatment. The WTP treats on average 500 megalitres of sewage per day (MWC, 2006) and serves the central, northern and western suburbs of Melbourne. Currently, a portion of the plant effluent undergoes

Page 6-2


tertiary treatment (pathogen reduction via Ultraviolet process) and is recycled as Class A for crop production (MWC, 2005a) and the rest is discharged to the Bay.

6.2.1

Wastewater Treatment Train

The method of sewage treatment in the WTP is dependent of season and the inflow of sewage (Coppen, 2004). Basically, the treatment at the WTP comprises two main processes which are outlined in Figure 6.2 (MWC, 2005a) and described as follows: 

Lagoon Systems — Sewage travels slowly under gravity through a series of connected ponds (or lagoons), which contain high concentrations of naturally occurring bacteria. The bacteria convert the organic and inorganic nutrients in the sewage into bacteria cells and inorganic products like carbon dioxide, water, ammonia and phosphate. These inorganic products are then consumed by algae. The initial pond in the lagoon system at the WTP is partly covered to collect gases from bacterial breakdown of solids settled from the sewage. These gases contain methane and odorous compounds, and are combusted on-site to produce electricity and non-odorous gaseous by-products (ibid).



Activated Sludge Treatment — The process of removing nitrogen from the WTP sewage is boosted by an Activated Sludge Treatment Plant, which has been added into the WTP wastewater treatment train since 2001 (ibid).

As shown in Figure 6.2, in both summer and winter, wastewater is initially treated in the lagoons and then a part of the secondary treated effluent passes into the Activated Sludge Treatment plant for further nitrogen removal and another part is directly discharged into the Bay.

Page 6-3


Figure 6.2 Wastewater Treatment Train at the WTP (MWC, 2005a)

6.2.2

Salt Reduction Demonstration Project

A trial study was conducted at the WTP from November 2005 to August 2006 to investigate the applicability of the commercial desalination technologies for secondary treated wastewater (Poon et al., 2007). The main objectives of this demonstration trial study include (ibid): 

Demonstrate the operation of the salinity reduction technology using wastewater from the WTP.



Provide an opportunity to develop or optimise desalination technology or applications specifically for the WTP.



Assess the operation and performance of the commercial desalination technologies and to identify any design or operational issues that may affect project costs (operating and capital).



Develop more reliable estimates of the costs for the future business case.



Assess the longer term performance and reliability of the desalination technologies and identify a longer term operating regime.

Page 6-4


Reverse Osmosis (RO) was one of the commercial desalination technologies which was utilised in this trial study. Two RO systems developed by Veolia Water Systems and United Utilities Australia were used in the trial. The major difference between the two systems was the type of the membrane technology that was used for pre-treatment. Veolia Water Systems employed Microfiltration (MF) as the RO pre-treatment, while United Utilities Australia used Ultrafiltration (UF) as the RO pre-treatment. Electrodialysis Reversal (EDR) has also been studied for the trial, however at the time of writing this thesis; no information was available on the EDR trial.

6.2.3

Feedwater Quality

Depending on the treatment processes which are utilised in a wastewater treatment plant, the treated wastewater can be classified into classes A to D (Coppen, 2004). Class A treated wastewater has the highest quality and can be used for even nonpotable urban applications with uncontrolled public access (EPA Victoria, 2003), and Class D treated wastewater has the lowest quality and usually is used for non-food crop irrigation applications (ibid). Up-grading from one effluent quality to another requires further treatment. For example, utilising a disinfection process such as Chlorination or Ultraviolet can up-grade effluent quality from Class C to Class A, as it is currently undertaken in the WTP (MWC, 2005a). However, removing dissolved solids from wastewater is only feasible via desalination.

The quality of the WTP treated wastewater which is currently discharged into Port Phillip Bay is classified as Class C (MWC, 2005a). This wastewater was used as raw water for the salt reduction demonstration trial study (Poon et al., 2007). A comprehensive water quality sampling and analysis program was undertaken during the course of the trial. The raw water (Class C) quality from the WTP, based on nine months of sampling data, is summarised in Table 6.1.

Page 6-5


Table 6.1 Raw Water Quality Data for the WTP from November 2005 to August 2006 (Poon et al., 2007)

As shown in this table, the Total Dissolved Solids (TDS) is close to 1000 mg/L, which included 376 mg/L of chloride ions and 244 mg/L of sodium ions. Other important quality parameters for wastewater reclamation via desalination include SAR, and turbidity, with average values of 7.9 and 2.1 NTU respectively, as seen in Table 6.1.

6.2.4

Desired Reclaimed Water Quality

The desired reclaimed water quality is mainly dictated by the type of its application (Cleantechindia, 2004). The reclaimed wastewater from the WTP is expected to be used for several water recycling schemes (MWC, 2005a) including:

Page 6-6




Werribee Tourist Precinct



Werribee Irrigation District



Werribee Technology Precinct



Residential developments

Other projects that could also use recycled water in the future include major industrial and commercial operations in Altona and Laverton.

For these water recycling applications, the WTP secondary treated wastewater is required to be up-graded from Class C effluent to Class A with Electro Conductivity (EC) less than 1,000 µS/cm (i.e. TDS less than 600 mg/L) (GHD, 2004). Achieving such reclaimed water quality (with TDS less than 600 mg/L) is particularly of importance for the Werribee Irrigation District water recycling scheme for sustainable pasture and crop production in the region (ibid).

6.2.5

Site Infrastructure

In this study, the site infrastructure refers to the basic site facilities including utilities, wastewater and land. The type and amount of these facilities affect the process of selecting the best desalination technology for wastewater reclamation. For example, if sufficient waste heat for desalination is available at the site, then thermal desalination technologies are very competitive against membrane desalination techniques.

I.

Land

Figure 6.3 presents the WTP site plan and the type of the plant treatment processes (GHD, 2004).

Page 6-7


Figure 6.3 The WTP Site Plan (GHD, 2004).

As can be seen from the figure, there is a sufficient land in this plant for constructing a wastewater desalination facility. The secondary treated wastewater from the WTP is discharged into the Port Phillip Bay via four outlets. The effluent quality and quantity which are discharged via these outlets are not the same. The best effluent quality belongs to 15 East (15 E) Main Drain Outlet, as it comes from 25 West (25 W) and 55 East (55 E) Lagoons. These lagoons are the most advanced at the WTP (MWC, 2006). Therefore, the best land location to construct a wastewater desalination plant at the WTP would be a location after lagoons 25W and 55E and before 15E Main Drain Outlet.

Page 6-8


II.

Energy

All desalination technologies require some form of energy to separate the product water from the saline feedwater. Membrane desalination techniques use electrical energy to force water through the membrane. Thermal processes use a combination of thermal and electrical energy (RosTek, 2003). Thermal processes become more attractive when there is a cheap source of power or where waste heat streams can be utilised.

The energy source available at the WTP is in the form of electricity. The plant energy usage is supplied through electricity imported from the grid and the electricity which is generated on-site via the generators which convert the plant lagoon biogas into electricity (MWC, 2005a). Currently, around 70% of the energy required for conventional wastewater is supplied via 3000 m3/h biogas captured by the covered lagoon sections (ibid). Based on a biogas energy value of 24 Mj/m3 (GHD, 2004), this equates to 72,000 Mj/h or 20 MW of power (ibid). Approximately, thermal desalination processes require 1.5-14 kWh electricity and 6-21 kWh thermal energy per each m3 of product (ibid). Therefore, the available waste heat (from biogas) at the WTP is just sufficient for a desalination plant with a capacity less than 30,000 m3 per day (ibid). As the desired desalination plant capacity at the WTP is expected to be around 85,000 m3 per day beyond Year 2010 (ibid), the available waste heat at the WTP is not enough for wastewater desalination purpose. It should be noted that the desalination plant capacities (30,000 m3/d and 85,000 m3/d) are less than the required reclaimed wastewater demands from the WTP (see Section III below), since the desalination plant product (permeate) will be blended with a side stream of feedwater.

III.

Wastewater

As stated earlier, the WTP treats approximately 500 megalitres (or 500,000 m3/d) sewerage per day (MWC, 2007). The reclaimed wastewater demand from the WTP is about 70,000 m3 per day to 2010 and 200,000 m3 per day beyond 2010 (GHD, 2004). This means, there is a sufficient raw wastewater for a wastewater desalination plant at the WTP, and therefore, there is no need for supplying feedwater from the external sources such as nearby facilities to meet the required demand. In addition, the availability of the plenty of raw wastewater at the WTP makes blending viable. Blending

Page 6-9


can make a significant reduction in the desalted water production cost and also minimises the desalination plant environmental impacts.

6.2.6

Application of DSF

Similar to any decision making system, the DSF developed in this research project requires some basic information (or data) as input. The most important information is listed below: 

Waste heat availability: as stated earlier, sufficient waste heat is not available; therefore thermal desalination processes are not applicable.



Cost: cost trend between the commercial desalination technologies (i.e. RO, NF, EDR) is presented on the top of the DSF (Figure 5.1). Based on this cost trend, NF is the most cost-effective desalination process for wastewater reclamation at the WTP and RO is the second.



Blending option viability: the amount of the WTP secondary treated wastewater which is required to be used as the desalination plant feedwater (40,000 m3/d) is less than 10 per cent of the WTP total secondary treated wastewater (500 megalitres per day). Therefore, there is a sufficient wastewater for blending to be viable. The figure of 40,000 m3/d is explained in section 6.2.7.



Feedwater total dissolved solids (TDS) value: the WTP secondary treated wastewater TDS value is approximately 1,050 mg/L (GHD, 2004).



Desired reclaimed wastewater TDS value: the desired reclaimed wastewater TDS value is ranged between 500-600 mg/L (MWC, 2006, and GHD, 2004). Salinity more than 600 mg/L is not suitable for sustainable crop irrigation.



Desired reclaimed water application: the WTP reclaimed wastewater is desired to be used for the several water recycling schemes. The water consumption for crop irrigation is more than the water consumption in other water recycling schemes (MWC, 2006).



Desalination plant capacity: the WTP desalination plant capacity is 30,000 m3/d to 2010 (GHD, 2004), which is expected to be expanded to 85,000 m3/d beyond 2010 (ibid). This is considering blending of secondary treated wastewater with the permeate from desalination, which is explained in Section 6.2.7.

Page 6-10




Raw chemicals recycling objective: water recycling is the only objective of the WTP wastewater reclamation project. Separations of the chemicals which exist in the WTP secondary treated wastewater is not a current objective of this wastewater reclamation project.



Location with respect to residential areas: the WTP is located far enough from the residential areas (MWC, 2003), and therefore, operation of membrane desalination process (which consists of high pressure pumps) would not cause any noise pollution problems for the surrounding residential areas.



Existing water softening facilities: currently, there is no water softening facility at the WTP.

Based on the above information, in particular blending viability and the applications of the WTP reclaimed wastewater (i.e. for crop irrigation), the most suitable DSF route for the WTP case study is the Blending Viability Route (Section 5.3.2 and Figure 5.4). The data for this route is presented below:

o

The target TDS is more than 400 mg/L.

o

The reclaimed wastewater application is expected to be used mainly for pasture and crop production.

o

The feedwater sodium absorption ratio (SAR) is above 6 (as stated in Table 6.1, SAR has an average of 7.9).

Based on this data, the DSF recommends RO as the best desalination process for wastewater reclamation at the WTP.

6.2.7

DSF Support Information

Support information refers to some additional information related to the selected desalination technology by the DSF. They describe the desalination plant more clearly in terms of a plant schematic, land and staff requirements, the capital and operating costs associated with the desalination plant, the energy requirement for desalination process, and greenhouse gas emissions associated with the desalination process.

Page 6-11


I.

Plant Schematic

Drawing a wastewater reclamation plant schematic, similar to what is presented in Figure 6.4 for the WTP, assists the planner to have a better understanding about the total dissolved solids (TDS) mass flow, blending stream and the type of processes involved with wastewater reclamation plant (i.e. desalination train, disinfection, waste disposal, etc.).

25 W

Final Flow: 70,000 m3/d TDS required< 600 mg/L

55E

Disinfection

Lagoon effluent: TDS= 1050 mg/L

Side Stream Flow= 80,000 m3/d Bypass flow Flow= 40,000 m3/d

Flow= 30,000 m3/d TDS< 20 mg/L Pretreatment Plant RO Effluent from other WTP treatment systems

Flow = 10,000 m3/d TDS ≈ 4,000 mg/L

15 Main Drain Outlet

Figure 6.4 Simple Plant Schematic for the WTP Desalination Plant

As shown in Figure 6.4, the wastewater reclamation plant at the WTP comprises a RO membrane desalination train, which consists of pre-treatment and main RO membrane systems, and a disinfection plant. A side stream with flow capacity around 80,000 m3/d secondary treated wastewater Class C is taken from the effluent from lagoons 25 West (25W) and 55 East (55E). A portion of this side stream (about 50%) goes into pretreatment plant, which can be a membrane pre-treatment system such as Ultrafiltration (UF) or Microfiltration (MF) or a conventional pre-treatment system such as combination

Page 6-12


of multimedia filters and sludge treatment. After pre-treatment, wastewater goes into a RO membrane system for salt reduction. Assuming 75% recovery for the RO systems, which is typical for RO brackish systems (RosTek, 2003), around 10,000 m3/d product is discharged from the RO systems as the waste stream (brine). The waste stream finally mixes with the effluent from other WTP treatment systems, diluted, and finally discharged into the Bay. The RO permeate (or the product), which is around 30,000 m3/d, is blended with 40,000 m3/d bypass flow (secondary treated wastewater) and the final flow around 70,000 m3/d with a TDS value less than 600 mg/L goes into the distribution system to be used for the various recycling applications including agricultural irrigation purposes.

II.

Land Requirements

Chart B.13 of Appendix B presents the amount of the land requirement for different membrane desalination plants (RosTek, 2003). Based on this chart, for a RO plant with capacity of 30,000 m3/d, approximately half a hectare (5,000 m2) land is required. This includes land area for roads, product storage, buildings and the desalination process units.

III. Staff Requirements The following table presents staff requirements for operation and maintenance of a membrane desalination plant with various plant capacities (RosTek, 2003).

Table 6.2 Operations and Maintenance Staff for Membrane Processes Capacity (m3/d)

3,785

18,925

37,850

94,625

189,250

6

12

15

18

20

6

10

12

15

17

Technology SWRO

BWRO, EDR, NF

SWRO = Seawater Reverse Osmosis

BWRO = Brackish water Reverse Osmosis

EDR = Electrodialysis Reverse

NF = Nanoflitration

Page 6-13


Based on this table, for the WTP case study (with a RO plant capacity around 30,000 m3/d) the number of staff required for operation and maintenance is about 10-12 persons.

IV.

Costs

Two desalination plant cost estimation methods were presented in Section 4.2.5. They were: cost estimation based on cost charts and cost estimation based on a compute software (i.e. WTCost© software). These cost estimating methods are used in this section to estimate the costs associated with construction and operation of the RO desalination plant at the WTP. It should be noted that the costs estimated for the case studies of this research project are suitable only for comparison of desalination technologies. The real cost of a desalination plant should only be obtained from the local technology suppliers.

Cost-Chart Method: Example 1 in Section 4.2.5 has many similarities with the WTP case study. Therefore, the methodology which was used to estimate the cost associated with construction and operation of the RO desalination plant of Example 1, can be repeated for the WTP case study. Table 6.3 summaries the information required for the application of the Cost-Chart method for the WTP.

As it was shown in Figure 6.3, the desalination plant product (or permeate) with TDS less than 20 mg/L will be blended with 40,000 m3 feedwater with TDS around 1,050 mg/L to produce the final reclaimed wastewater with TDS around 600 mg/L. Therefore, two unit production costs ($/m3) will be presented later: one referred to the desalination plant product and the other referred to the final reclaimed wastewater (blending of permeate and secondary treated wastewater). These costs excluded the costs for delivery of the reclaimed wastewater to the end users. The approximate distances between the points of consuming reclaimed wastewater and the WTP desalination plant are around of 5-6 kilometres (MWC, 2006), which is relatively a long distance, and therefore the costs for delivery of the reclaimed wastewater would be significant. Table 6.4 presents the capital cost associated with construction of a RO plant (capacity of 30,000 m3/d) at the WTP, and Figure 6.5 presents the annual costs of this plant.

Page 6-14


Table 6.3 Information Summary for the WTP

PROJECT DESCRIPTION: Wastewater Reclamation at Western Treatment Plant (WTP)

LOCATION: Werribee, Melbourne

PRODUCT WATER CHARACTERISTICS Annual Requirement (Production): 10, 402,500 m3 Required Quality: Less than 20 mg/L TDS Distance Point of Delivery from Desalination Plant: Between 5-6 kilometres (MWC, 2006)

REQUIRED RELIABILITY: 95% OF Design Capacity

WASTEWATER CHARACTERISTICS Wastewater Quality: Secondary Treated Wastewater with TDS around 1050 mg/L, BOD5 less than 4 mg/L, and TSS: 6 mg/L

DESALINATION PLANT CHARACTERISTICS Process Being Considered: Reverse Osmosis (RO) with Blending of Feedwater and Product Plant Capacity: 30,000 m3/d Annual Production: 10,402,500 m3/d Pre-treatment Type: Conventional Plant Recovery: 75% Waste Disposal Method: Outfall to Port Phillip Bay Interest Rate: 7% Plant Life: 20 years

Page 6-15


Table 6.4 WTP Desalination plant Capital Costs Summary Calculated by CostChart Method

ITEM

COST (US$ (2000))

Desalting Plant (Chart B.4)

22,000,000

Concentrate Disposal (Chart B.7)

150,000

Site Development (Chart B.9)

100,000

Auxiliary Equipment, Daily product Storage Tank (Chart B.11)

2,200,000

Subtotal DCC

24,450,000

Land (assumed free, as part of the plant will be used )

N/A

Freight and Insurance (5% of DCC)

1,222,500

Contingency (10 % of DCC)

2,445,000

Owner’s Direct Expense (10% of DCC)

2,445,000

Total Capital Cost (TCC)

30,562,500

Table 6.5 WTP Desalination Plant Annual Costs Summary Calculated by Cost-Chart Method ITEM

COST (US$ (2000))

Labour (Chart B.15)

280,000

Chemicals (Chart B.19)

450,000

Electric Power (Chart B.23)

700,000

Insurance (0.5 % of TCC)

152,812

Repairs and Spares (1 % of DCC)

244,500

Sub total O&M Costs

1,827,312

Contingency (10 % of O&M Costs)

182,731

Membrane Replacement (Equations 4.1 and 4.2)

208,050

Capital Depreciation (Equations 4.3 and 4.4)

2,182,961

Total Annual Costs

4,401,054

Page 6-16


Based on the total annual cost of water production, estimated in Table 6.4, and Equation 4.5, the unit production cost of desalinated water in the WTP is: Cost of RO water (US$/m3) = (4,401,054)/ (10, 402,500) = 0.43 US$/m3 Blending produces 70,000 m3/d (or 24,272,500 cubic meter per year) of reclaimed wastewater. The final reclaimed wastewater unit production cost then is: Cost of final reclaimed wastewater= (4,401,054)/ (24,272,500) = 0.20 US$/m3

Computer-Based Method: The costs associated with construction and operation of a RO membrane desalination plant at the WTP can also be estimated by WTCost© Software. The information which is required to use WTCost© Software for the WTP was already presented in Table 6.3. A summary of the costs and the main facilities which are considered in the WTP desalination plant train are presented in Table 6.6.

Based on Table 6.6, the unit production cost of product water estimated by the WTCost© Software at the WTP is US$ 0.57 per cubic meter. The production cost estimated by the Cost-Chart method was around US$ 0.43 per cubic meter. The reasons for this difference could be the differences between information sources in the two cost estimating methods and the difference between the types of pre-treatment used in the two methods. The pre-treatment used in the Cost-Chart method was conventional pretreatment (which was included in Chart B-4 in Appendix B, while the type of pretreatment which was considered in Table 6.6 was membrane (MF or UF) pre-treatment, which is named “Media Filtration” in Table 6.6. As stated in Section 3.4.1, a membrane type pre-treatment requires more capital than a conventional type pre-treatment (RosTek, 2003). In order to estimate the extent of the impact of pre-treatment type on the desalination production cost in the WTCost©, two other pre-treatment systems (Granulated Activated Carbon and Gravity Filtration) available in the software were used for the WTP case study. The cost results are presented in Appendix C at Tables C.1 and C.2. As shown in Tables C.1 and C.2, the pre-treatment type affects the desalination plant production cost. The unit production costs considering these three pre-treatment systems are compared in Figure 6.5.

Page 6-17


Table 6.6 WTP Desalination Plant Cost Summary Calculated by WTCost© Software

Page 6-18

Unit Production Cost (US$/m3)


0.8 0.67 0.57

0.6

0.48 0.4 0.2 0 Granulated Activated Micro/Ultra Filtration Carbon

Gravity Filtration

Pre-treatment Type

Figure 6.5 Effects of the Various Pre-treatment Systems Costs for the WTP

Based on the results of a survey conducted by Cooley et al. (2006), the unit production cost of reclaimed wastewater is in a range of 0. 45 US$/m3 (Singapore) to 0.92 US$/m3 (Perth, Australia). Therefore, the unit production costs estimated by both cost estimating methods are within this range. However, this cost should be considered only for planning purposes. For budgeting, the real cost of desalination should be estimated by obtaining information from local technology suppliers.

V.

Energy Requirement

Section 4.3.3 presented information related to estimation of energy requirement for operation of the membrane desalination processes. For the RO plant at the WTP, this energy can be estimated by Equation (4.7): Energy Consumption (MW) = [Energy Consumption (kWh/m3) x Plant Capacity (m3/d)]/1000

For this case study: Energy Consumption = ≈ 0.88 kWh/m3 (from Figure 4.8 for Standard Pressure RO and TDS=1050 mg/L); 3

Plant Capacity= 30,000 m /d

Therefore, the WTP desalination plant energy requirement is: (0.88 x 30,000)/1000= 26.4 MW

Page 6-19


VI.

Greenhouse Gas Emissions

The greenhouse gas emissions associated with the operation of the RO plant at the WTP can be estimated from Equation (4.6), which was initially presented in Section 4.3.3: GHG emission (t CO2-e) = [Activity (Q) x Emission Factor (EF)]/1000

For the WTP case study: Q= 0.88 (from Figure 4.8 for Standard Pressure RO and TDS=1050 mg/L)

Therefore, the WTP desalination plant greenhouse gas emissions based on Equation (4.6) is: GHG (t-CO2-e) = (0.88 x 1.444)/1000 = 1.27 x 10-3 (t-CO2-e) per m3 reclaimed wastewater = 1.27 kg CO2-e/m3 The GHG estimated in the WTP case study is less than the GHG emission value reported by Raluy et al. (2005) for the RO systems, which was listed in Table 4.7. The main reason for this difference could be that the above reported value (1.78 kg CO2/m3) was estimated based on a conducted Life Cycle (construction, operation, and discarding of the desalination plant) Assessment study, but the GHG emission estimated in this research project was restricted to the operation of the desalination plant.

6.3

TRADE WASTE FACILITY CASE STUDIES

City West Water (CWW) has more than 5000 trade waste customers (URS, 2005). Some of these facilities use a considerable amount of potable water for their operations. They are also accounted as the main salt dischargers to WTP. More than 64% of the salts discharged into the WTP in 2003-2004 had come from the CWW trade waste facilities (ibid), mainly from a small number of key facilities. The 10 most significant trade waste dischargers contribute approximately 54% of the total trade waste TDS load (GHD, 2004); approximately 69% of the load is contributed by the 20 most significant dischargers (URS, 2005).

Page 6-20


Three of the top 30 CWW trade waste facilities, in terms of water usage and salt dischargers, were selected for the case studies in this research project, in addition to the WTP case study (Section 6.2). In these case studies, the DSF was used to demonstrate its applicability for decentralised desalination projects. A brief description for each of these facilities is presented in Table 6.7. The facilities ranking in this table indicates the facility position among all CWW trade waste facilities. These facilities are located in the area of Laverton in the western part of Melbourne.

According to Table 6.7, Facility X is the third CWW trade waste customer in terms of TDS discharge. However, the facility water demand rank is not as high as the facility TDS rank. The facility average TDS is more than 11,000 mg/L due to use of intensive salts for the facility production process (i.e. tanning). The average facility wastewater discharge is 512 m3/d, more than the facility water use of 401 m3/d. The excess water (512-401=111 m3/d) discharged by the facility could come from the raw materials (e.g. hides and skins of animal), and chemicals used in the tanning process such as sodium chloride solution (Based on communication with Nigel Corby from CWW).

Facility Y (a fat and oil processing company) is the sixth TDS discharger in the CWW TDS ranking and sixteenth water user. The facility average TDS is 1,708 mg/L and the average facility water demand and wastewater discharge are 768 m3/d and 925 m3/d respectively.

Facility Z (a poultry company) is the twentieth TDS discharger and eighth water user among of the CWW trade waste customers. This facility wastewater salinity is relatively low (TDS less than 300 mg/L) with the average water demand and wastewater discharge of 1,286 m3/d and 939 m3/d respectively. Despite Facilities X and Y, the water demand in Facility Z is higher than wastewater discharge as a main part of water coming to the facility evaporated by the cooling towers and boilers exist in the facility (Based on the communication with Nigel Corby from CWW).

It should be noted that the TDS values presented in Table 6.7 are inorganic TDS (i.e. inorganic salts such as sodium salts). It is assumed that the facilities’ organic TDS (i.e. organic salts such as carboxylic salts) is reflected in the facilities’ Biological Oxygen

Page 6-21


Demand (BOD), which does not affect the design and construction of the desalination plant. Table 6.7 Information Summary for Three CWW Trade Waste Facilities (provided by Nigel Corby of CWW, 2007 in a meeting)

Facility Name

Industry Sector

TDS Rank

H2O Rank

Average TDS (mg/L)

Target TDS

X

Tanning

3

30

11,569

wastewater reclamation desalination technologies: a

wastewater reclamation desalination technologies: a

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