PERFORMANCE APPRAISAL OF RURAL WATER

PERFORMANCE APPRAISAL OF RURAL WATER SUPPLY SYSTEMS IN THAILAND

by

Krieattisak Sriaram

A thesis submitted in partial fulfillment of the requirement for the degree of Master of Science

Examination Committee

Dr. C. Visvanathan (Chairperson) Mrs. Samorn Muttamara Prof. N.C. Thanh

Nationality Previous Degree

Thai Bachelor of Science (Public Health) Khon Kaen University Khon Kaen, Thailand

Scholarship Donor

Partial Scholarship and Coffey MPW Pty, Ltd. (Australia)

Asian Institute of Technology School of Environment, Resources and Development Bangkok, Thailand August 1999

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Acknowledgment

I would like to express my gratitude to my advisor, Dr. C. Visvanathan, who initiated the research and provided invaluable guidance in the conduct of this study. The work could not have been completed without his motivation and encouragement. Appreciation is sincerely given to Mrs. Samorn Muttamara and Prof. N.C. Thanh for serving as the members of the examination committee. I have benefited extensively from their guidance and suggestions throughout this period study. Sincere gratitude is given to Mr. Wichien Junrungruang,the Director of Rural Water Supply Division, for research granted and his kind cooperation throughout the period of this study. Mrs. Raweewan Soyraya, Mrs. Devarugsa Krueklai and RWSD’s engineers for their cooperation throughout the field investigation. I also want to give special thanks to the staff of Environmental Quality Analysis Division and Water Supply Procurement Division of Region Office of Environmental Health Centers, who helped me during field investigations. Sincere gratitude is also given to Mr. Shozo Yamazaki, the Chief Advisor of Nation Waterworks Technology Training Institution, for research granted and his kind cooperation throughout the period of this study. I am grateful to Mr. Naomasa Oda, JICA expert, Mrs. Siwilai Kitpitak as well. The refreshing discussion and their insightful ideas made the work more practical. I would like to express my sincerest gratitude to Mr. Robert P. Simpson, Chief Executive Officer of Coffey MPW Pty, Ltd. (Australia) and Mr. Ian Binch for the Coffey scholarship granted, their encouragement to take up further education at the AIT Sincere gratitude is also given to all laboratory staff and secretariats of Environmental Engineering Program. Without their unselfish helps at every stage of the study, the work could not have been conducted so smoothly. Finally the author dedicated the whole work to my beloved family for their unconditional love and moral support during I is stay at AIT.

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Abstract

Between January and May 1999, the Asian Institute of Technology, the Department of Health(DOH) and the National Waterworks Technology Training Institute conducted a joint field study to evaluate the performance of selected slow and rapid sand filter treatment plants in small water supply systems in rural Thailand. Twenty filtration plants representing a geographic and technical cross section were evaluated in terms of their physical, operation, performance characteristics and examination of water quality. The study considered the consistent turbidity of 5.0 NTU from each plant as an optimum level of filter performance for surface water treatment. Seven of the 16 surface water treatment plants were rated acceptable for performance at this study period. All four rapid sand filters of the groundwater treatment had acceptable performance of iron in 0.3 mg/L and 0.1 mg/L of manganese. The number of operators did not significantly limit performance of the plants; instead, the primary problems were operational. Decreasing flows and increasing operating times were judged to be a practical alternative for intermittent operation. Disinfection is essential to improve the reliability of treatment. The approach of filter plant performance evaluation could lead to successful improvement and decreased risk from waterborne disease by identifying weaknesses and optimizing treatment. To achieve the maximum benefit, the filter plant performance evaluation should be integrated with the existing DOH’ safe drinking water program. This study conducted the randomly collected samples in each the selected rapid sand filter. Forty-eight samples were evaluated the hygienic quality in distribution system. Three samples of turbidity, forty samples of free Cl2 and thirty-one samples of bacteria were not in compliance with the WHO drinking water standards. Therefore boiled water is recommended for drinking purpose.

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Table of Contents

Chapter

1

Title

Page

Title Page Acknowledgment Abstract Table of Contents List of Tables List of Figures List of Abbreviations

i ii iii iv vi vii viii

Introduction 1.1 1.2 1.3 1.4

2

General Background Objectives Scope

1 1 2 2

Literature Review 2.1 2.2

2.3

2.4

2.5 2.6 2.7

Introduction Slow Sand Filtration 2.2.1 Introduction 2.2.2 Physical Characteristics 2.2.3 Biological and Physical Mechanisms 2.2.4 Organic Carbon Removal 2.2.5 Removal of Giardia and Crytosporidia 2.2.6 Schmutzedecke Scraping Operations Rapid Sand Filtration 2.3.1 Introduction 2.3.2 Filtration Process 2.3.3 Filter Media 2.3.4 The Underdrain System 2.3.5 Filter Backwashing 2.3.6 Filter Controls Rural Water Supply in Thailand 2.4.1 Design Criteria and Water Quality 2.4.2 Water Treatment Process Options 2.4.3 Installation of Rural Water Supply 2.4.4 Situation of Rural Water Supply Water Treatment Plant Performance Studies Filtration Plant Performance Evaluation Evaluation of Slow Sand Filter Performance -iv-

4 4 4 6 6 7 7 8 8 8 9 11 11 12 12 13 13 13 16

2.7.1 2.4.2 3

3.5

Introduction Data Collection Sample Collection Filter Plant Performance Evaluation 3.4.1 Evaluation of Major Unit Processes 3.4.2 Plant Operations Evaluation Evaluation of the Performance Limiting Factor

18 20 22 23 24 26

Results and Discussions 4.1

4.2

4.3 5

17 17

Methodology 3.1 3.2 3.3 3.4

4

Worldwide Thailand

Slow Sand Filter 4.1.1 Plant Descriptions 4.1.2 Physical Characteristics 4.1.3 Performance Characteristics 4.1.4 Operation Characteristics 4.1.5 Conclusions and Recommendations Rapid Sand Filter 4.2.1 Plant Description 4.2.2 Evaluation of Major Unit Processes 4.2.3 Plant Performance Assessment 4.2.4 Performance Limiting Factor 4.2.5 Proposed Improve Performance Activities Supplied Water Quality

28 30 31 34 35 36 46 48 50 52 52

Conclusions and Recommendations 5.1 5.2 5.3

Conclusions Recommendations Future Studies

54 54 55

References Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F Appendix G Appendix H

List of Selected Filtration Plant Schematic Flow Diagram of Selected Filtration Plant Questionnaires and Recorded Forms Water Quality Plant Characteristics Operation Characteristics Rating and Identified of Performance Limiting Factors Photograph of the Typical Observed Operation of the Selected Filtration Plant

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List of Tables

Table No. 2.1 2.2 2.3 2.4 2.5 3.1 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9

Title

Page

Process design criteria for existing rapid sand filtration Typical treatment performance of conventional of Slow Sand Filters Turbidity removal typical achieved by conventional slow sand filter Total coliform removal typical achieved by conventional slow sand filter Feacal coliform removal typical achieved by conventional slow sand filter Water quality parameter Characteristics of treatment plants Reduction of turbidity and bacteria Typical observed operation of the slow sand filter Summary of selected rapid sand filter plants Filter sand characteristics at operating rapid sand filter Typical observed operation of the selected rapid sand filter Summary of major unit process evaluation Reduction of iron and manganese at operating rapid sand filter Overall rating of top ten factors identified

14

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18 20 20 20 25 29 31 35 37 42 45 47 50 51

List of Figures

Figure No. 2.1 2.2 2.3 2.4 3.1 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15

Title

Page

Typical cross section of a slow sand filter Schematic section of a rapid sand filter Number of village serviced by water supply categorized by various operation agencies Number of village serviced by water supply categorized by DOH’s Regional, Year 1996 Schematic activities of the filtration plant performance evaluation Turbidity record for Jedeethong plant Total coliform record for Jedeethong plant Feacal coliform record for Jedeethong plant Filtration rate at operating slow sand filter Alum dosage comparison of operated, designed and Jar Tests Flocculation time at operating rapid sand filter Mixing energy at operating rapid sand filter Sedimentation time at operating rapid sand filter Filtration rate at operating rapid sand filter Backwash rate at operating rapid sand filter Chlorine at operating rapid sand filter Typical performance potential graph for 10 m3/h capacity Filtered turbidity data at operating rapid sand filter Settled turbidity data at operating rapid sand filter Sample of filter effluent turbidity profile after backwash –Plant 5

5 10 15

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15 22 32 33 33 34 39 39 40 41 42 43 44 47 48 49 49

List of Abbreviations

AIT ARD AWWA DOH DOC DMR FC GAC JTU MDD MPA MPN MOH NTU NWTTI NOM O&M PWA PWD TC THMFP TOC ROEHC RSF RWSD SSF STD UC USEPA UV WHO

Asian Institute of Technology Accelerated Rural Development American Water Works Association Department of Health Dissolved organic carbon Department of Mineral Resources Fecal Coliform Granular activated carbon Jackson candle turbidity unit Maximum daily demand Microscopic particulate analysis Most Probable Number Ministry of Health, Thailand Nephelometric turbidity unit National Waterworks Technology Training Institute Natural organic matter Operation and Maintenance Provincial Waterworks Authority Public Works Department Total Coliform Trihalomethane formation potential Total organic carbon Region Office of Environmental Health Center Rapid Sand Filtration Rural Water Supply Division Slow Sand Filtration Standards Uniform coefficient U.S. Environmental Protection Agency Ultraviolet World Health Organization

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Chapter 1 Introduction

1.1

General

In Thailand, four principal implementing agencies belonging to three ministries are currently responsible for small drinking water supply schemes. These are; 1. 2. 3. 4.

Department of Health (DOH), Ministry of Public Health Public Works Department (PWD), Ministry of Interior Department of Mineral Resources (DMR), Ministry of Industry Office of Accelerated Rural Development(ARD), Ministry of Interior

These departments have been responsible for small-scale water supply development activities since the late 1960s. Throughout these years, their areas of responsibility and capabilities with respect to rural water supply have expanded, diversified, and in some cases overlap with one another. The DOH has two divisions, which are directly involved in rural water supply. The Rural Water Supply Division is assigned to provide clean water to villages, particularly those with less than 3,000 inhabitants. It operates through the 12 Water Supply Procurement Divisions of Region Office of Environmental Health Center (ROEHC) throughout the country. The work covers facilities for drinking water supply such as deep wells, shallow wells, and village piped water supply systems. The Sanitation Division is in charge of rainwater collection and storage containers, such as tanks and jars. The DOH is second only to the DMR with respect to deep well construction. Its shallow well construction program is not very sizeable compared to the other major implementing agencies. Aside from construction, DOH is involved in rehabilitation of wells and improvement of water quality through water treatment, such as iron removal and disinfection. Training of volunteer technicians and community leaders in order to develop their water utilization and management skills is also conducted by the ROEHC. Since 1982, the DOH has successfully constructed village water supply systems involving community participation resulting in good water quality. The goal of the Prime Minister’s Office Regulation in Administration and Operation of Rural Water Supply B.E. 2535 (1992) is to form consumer groups and set up consumer committees to administer and operate rural water supply. Each system is managed in such ways that water charges are collected from users and the money is used to operate and maintain the system. 1.2

Background

Both Slow Sand Filtration and Rapid Sand Filtration have been considered for rural water supply. Slow Sand Filter (SSF) is an appropriate water treatment method for community water supply in developing countries because of its simplicity, reliability, and economy. SSF in -1-

Thailand is found primarily in rural area due to the low cost compared with alternative water treatment technologies. SSF is a water purification process in which water is percolated slowly through a porous bed of filter media. During passage of the water, its physical and biological quality improves considerably through a combination of biological, biochemical, and physical processes. Rapid Sand Filtration (RSF) is the flow of water through a bed of granular media, followed by settling basins in conventional water treatment trains. The purpose of this filtration is to remove any particulate matter left over after flocculation and settling. Early investigation revealed that, although the popularity of SSF was high, many SSF plants have been closed down and many are presently not operated. Others have been converted to RSF. A significant amount of land is necessary for SSF construction and, as a general policy since 1980, the DOH has constructed only RSFs in all its rural water supply systems. Although converting to RSF might look like an attractive option for most existing SSFs, it may not be suitable for small and low income group community rural water supplies. SSF is still a better option for such works. Although RSF has been promoted extensively by the DOH for the past 10 years, no known detailed technical review has been carried out to review the effectiveness of this system. Thus, there is a strong need to identify design, operation, and administration factors limiting performance and to determine possible improvements in plant performance of the rural water supply system in Thailand. 1.3

Objectives

The objectives of this study are: •

• •

• 1.4

To assess the existing performance levels of rural water supply systems in Thailand in regard to: - their ability to produce good quality water and control pathogens - their effect of design, operation and administration on treatment performance - effectiveness of monitoring and technical survey To address performance limiting factors, To identify feasible short and long-term water treatment solutions of the existing rural water supply systems in Thailand - Short-term, low capital improvements that could be made to improve performance - Long-term improvements to improve water quality and plant operation To monitor and evaluate the supplied water quality of rural water supply systems,

Scope

This study proposes to investigate the practicalities, focusing on critical stages of treatment, and identify key factors that contribute to the treatment performance of RSF and SSF located in rural communities. The data collected through the questionnaires at the plant mainly deal with operational procedure with respect to design criteria. A considered amount of laboratory analysis work is necessary to assess the treatment performance and limiting factors.

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RSFs had been proposed for the following provinces, which are under the direct responsibility Region Office of Environmental Health Center of the DOH, namely: Region I Region II Region III Region IV

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Nonthaburi Saraburi Chonburi Ratchaburi

In each of these provinces, One RSF for groundwater treatment, and 3 RSFs surface water treatment were assessed. Four SSF were selected from the existing plants in operation. A total of 20 field visits were made.

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Chapter 2 Literature Review

2.1

Introduction

In Thailand, most of the sources for water supply are surface water from river and streams. Water treatment technology has essentially been toward treating this source of water. Surface water is generally highly turbid and this problem is aggravated during the moonsoon hence the need for filtration. Filtration is a physical, chemical, and in some instances biological process for separating suspended impurities from water by passage through porous media (Schulz and Okun, 1984) or other porous material to remove as much fine suspended solids as possible (Reynolds and Richard, 1996). Two general types of filters commonly used in water treatment for rural water supply are slow sand filter and rapid sand filter. Each has its merits depending on different factors. The selection needs study about potential and suitability, and research work has to be undertaken to collect detailed data required for making a decision, for a given condition. 2.2

Slow Sand Filtration

2.2.1

Introduction

Slow sand filtration is one of the oldest treatment technologies still is use for public drinking water supplies. Its use spans two centuries in settings as varied as London and the highlands of Peru (Weber-Shirk and Dick, 1997). The history of slow sand filtration in small water supply has been one of reluctant acceptance. Many small communities choose slow sand filtration as a water treatment method because of its simplicity, reliability, and economy (Slezak and Sims, 1984; Visscher, 1990; Leland and III, 1990; Tanner and Ongerth, 1990; Collins et al., 1991; Hendricks, 1991 and Riesenberg, 1995). Slow sand filtration is an appropriate means of water treatment for community water supply in developing countries and for small water systems in many areas of the world (Visscher, 1990; Hendricks, 1991). Slow sand filters in the United States, for example are found primarily in smaller communities with fewer than 10,000 people. This is primarily due to the associated low cost of slow sand treatment facilities compared with alternative technologies (Slezak and Sims, 1984; Collins et al., 1991). 2.2.2

Physical Characteristics

Slow sand filtration is a water purification process in which water is passed through a porous bed of filter medium. A slow sand filter is typically characterized by certain design components: the supernatant is water above the filter sand that provides hydraulic head for the process, filter sand varying in depth, the underdrain medium usually consists of graded gravel and a set of control devices (Slezak and Sims, 1984; Visscher, 1990; and Hendricks, 1991). In a mature sand bed, a thin upper sand layer called “Schmutzedecke” forms. The Schmutzedecke consists of biologically active microorganisms that break down organic matter while suspended inorganic matter is removed by straining (Hendricks, 1991; Weber-Shirk and Dick, 1997). Slow sand filters are distinguished from rapid sand filters by the biologically -4-

active sand medium, including the Schmutzedecke, and slow detention times. Rapid sand filters utilize primarily a physical removal process, and are periodically backwashed for cleaning, and operate with long detention times. Slow sand filters are cleaned by periodically scraping the existing Schmutzedecke (Seelaus et al., 1984; Hendricks, 1991; and Riesenberg, 1995). Figure 2.1 is a schematic of a common cross section of a slow sand filter.

Source: Adapted from Hendricks (1991) Figure 2.1 Typical cross section of a slow sand filter. The supernatant serves two distinct purposes. First, it provides a head of water sufficient to pass the raw water through the filter bed. Second, the supernatant creates a detention time of several hours for the treatment of the raw water. The supernatant should not be considered as a reservoir for sedimentation. If the raw water has a high content of suspended mater, then pretreatment should be considered to prevent rapid clogging of the filter bed. The supernatant depth is typically a meter (Visscher, 1990; Hendricks, 1991). The physical characteristics of a sand bed are important in maintaining efficiency. The effective size is an opening that will pass ten percent by weight of the filter material (Hendricks, 1991). Effective sizes in the range of 0.15 mm to 0.35 mm are used (Seelaus et al., 1984;Visscher, 1990; Hendricks, 1991 and Riesenberg, 1995). The uniformity coefficient is the ratio of the size openings that pass sixty percent of filter material to the size openings that pass ten percent of filter material, e.g. the effective size (Hendricks, 1991). Uniformity coefficients range between two and five; most facilities maintain uniformity coefficients less than three (Visscher, 1990; Hendricks, 1991 and Riesenberg, 1995). The filter medium itself should consist of inert and durable grains; sand should be washed so that it is free of clays, loams, and organic matter. Depth of a filter bed ranges between 1.0 and 1.4 meters (Tanner and Ongerth, 1990). The underdrain system serves two purposes. It provides unobstructed passage for the collection of treated water and it supports the bed of filter medium. It is important that the underdrain system provide a uniform

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velocity over the entire filter area (Visscher, 1990; Hendricks, 1991). The underdrain gravel is placed so that the finest gravel is directly underneath the sand and the coarsest gravel is surrounding the underdrain pipes or covering the underdrain block (Hendricks, 1991). This prevents the filter sand grains from being carried into the treated water system. 2.2.3

Biological and Physical Mechanisms

Biological activity in the sand bed is not well understood. Scientists have a vague idea of the processes involved, but specific interactions are still unknown. Suggested biological removal mechanisms are predation, scavenging, natural death and inactivation, and metabolic breakdown (Hendricks, 1991). In the Schmutzedecke, algae, plankton, diatoms, and bacteria break down organic matter through biological activity. It has been hypothesized that as the raw water passes through the bed, it constantly changes direction. Thus, the sand grains developed a uniform sticky layer of organic material that absorbs to the particles by various attachment mechanisms. The sticky layer around the sand grains is biologically active as bacteria, protozoa, bacteriophages and the organic impurities are biologically converted to water, carbon dioxide and harmless salts. According to a study by Collins et al.(1992) the bacterial concentrations in the Schmutzedecke were a function of the elapsed time and potential for cell growth rather than the filtration of free-living bacteria from the source water. The biologically active section of the entire filter bed extends 0.4-0.5 m downward from the surface of the Schmutzedecke (McNair et al., 1987). Physical processes are also inherent to slow sand filter mechanisms. As the biological activity of the filter bed decreases, the physical processes of adsorption and chemical oxidation are the primary mechanisms (Hendricks, 1991; Weber-Shirk and Dick, 1997). Adsorption accounts for removals that were traditionally thought to be purely biological. For example, the removal of chlorinated organic and the distribution of viruses are thought to follow adsorption isotherms (Hendricks, 1991). Furthermore, suspended inorganic matter may be removed by the physical process of straining (Hendricks, 1991; Weber-Shirk and Dick, 1997). 2.2.4 Organic Carbon Removal The removal of natural organic matter (NOM) in slow sand filtration is related to biological maturity of the sand bed, and is attributable to a combination of biodegradation and sorption into the biological and biogenic material in the Schemutzdecke and deeper in the bed. Research conducted by Collins et al. (1992) showed that pilot slow sand filters operated satisfactorily in terms of turbidity removal could achieve 5-25 percent reductions in organic precursor materials, measured in terms of trihalomethane formation potential (THMFP), nonpurgeable dissolved organic carbon (DOC), and UV. In an investigation of full-scale municipal facilities, Collins et al. (1992) reported average DOC removals of 12-28 percent for conventionally scraped filters. Fox et al. (1984) used a sand with similar size characteristics an a similar loading rate to that used in the work reported here, achieved average total organic carbon (TOC) and THMFP removals of 15 percent. Several alternatives to enhance the removal of NOM in slow sand filters have been investigated, including the use of preozonation to increase the bioavailability of organic carbon, and filter media amendments, such as granular activated carbon (GAC) and anionic exchange resins. (Collins et al., 1992)

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2.2.5

Removal of Giardia and Cryptosporidia

In the past decade, the protozoan parasite Cryptosporidium parvum has been recognized as a significant threat to public water supplies. The resistant stage of Cryptosporidia is called an oocyst; this stage is relatively untouched by a chlorination disinfection process. Slow sand filtration has been looked at in numerous studies to determine the viability of this treatment process for the removal of Cyrptosporidia. Timms et al. (1994) found reductions of oocysts greater than 99.97%; the oocysts were found in the filter media above 2.5 cm and Fogel et al. (1993) found the removal efficiencies of 48 percent. They noted that they were operating well out of the range of the recommended design limits for the uniformity coefficient at 3.5. Furthermore, temperature can adversely affect the performance of a slow sand filter operating at extremely low temperatures of less than 1C.. A additionally, Seelaus et al., 1986; McNair et al., 1987; Tanner and Ongerth, 1990; Schuler et al., 1991 and Riesenberg et al., 1995 reported that slow sand filtration is a viable alternative for Cryptosporidia removal and has proven highly efficient in removing Giardia lamblia, a frequently identified pathogenic intestinal protozoa. Furthermore, Fogel et al. (1993) found that despite the uniformity coefficient parameter and the low temperatures, Giardia removals were complete. Feacal and total coliform counts were below the detection limit, and the removal rates were similar to Giardia removals. 2.2.6

Schmutzedecke Scraping Operations

Scraping typically involves the Schmutzedecke removal and the operation is site specific. Scraping frequency depends on the available head, the media grain-size distribution, the influent water quality, and the water temperature (Hendricks, 1991). Higher scraping frequencies are associated with increased water temperature, high solids concentrations in the influent, low head, and small media pore size. A typical operation involves draining the supernatant is usually by continuing filtration with no influent to 20 cm below the sand surface, skimming off one inch of the Schmutzedecke and associated sand, and then filling the filter from the bottom of the bed using filtered water to prevent air entrapment (Slezak and Sims, 1984; Bellamy et al., 1985; Seelaus et al., 1986; McNair et al., 1987; Visscher, 1990; Hendricks, 1991). The bed should be refilled until depth is sufficient to continue normal operations (Hendricks, 1991). Collins et al.(1992) suggestted a unique way to scrape the Schmutzedecke that minimizes the amount of biomass removal. The supernatant is drained to a height roughly 30 cm above the bed. A rubber-tired tractor equipped with a comb-tooth harrow is place on top of the filter to rake the sand; simultaneously the filter drains are opened, causing a steady discharge of overlying water. As the Schmutzedecke is loosened, the colloidal debris is caught by the moving water and discharged at the filter surface drain. The process is repeated as necessary by backflushing until the entire filter surface has been harrowed (Collins et al., 1992).

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2.3

Rapid Sand Filtration

2.3.1

Introduction

Rapid sand filtration is the flow of water through a bed of granular media, normally following settling basins in conventional water treatment trains. The purpose of this filtration is remove any particulate matter left over after flocculation and settling. The filter process operates based on two principles, mechanical straining and physical adsorption. Sand filtration is a physicalchemical process for separating suspended and colloidal impurities from water by passage through a bed of granular material. Water fills the pores of the filter medium, and the impurities are adsorbed on the surface of the grains or trapped in the openings (Reynolds and Richard, 1996). The key process is the relative grain size of the filter medium. Rapid sand filtration is contrasted slow sand filter to increased flow rate, method of cleaning the filter bed. A rapid sand filter can operate up to 40 times faster than a slow sand filter –typically 5 to 10 m/h or more. Rapid sand filters are cleaned often, usually backwash daily, by reversing the flow of water through the entire filter bed, referred to Slow sand filters are cleaned less frequently by removal of the top layer of media. In order to assure satisfactory performance of rapid filter, the proper application of coagulants to destabilize colloidal suspensions is critical. Additionally, as with slow filters, the initial period of filtration following cleaning normally produces water of inferior quality, which may have to be wasted. The duration of the ripening period in rapid filters with properly pretreated water is much shorter than in slow filters, raging from 5 to 10 min (McGhee, 1991).Figure 2.2 shows a cross section of single rapid sand filter employing a rate of flow controller. As discussed below, rapid sand filters may employ a variety of flow-regulation techniques, media other than sand, and many different underdrain and backwash system. 2.3.2

Filtration Process

Chemical coagulation, flocculation, and sedimentation always precede the rapid sand filter. The first filters, which operated at about 5 m3/m2-h, consisted of a quartz sand bed overlaying a gravel layer. The turbidity removals ranged from 90 to 98 % if the feed water turbidity was between 5 to 10 JTU. Although the standard rate of filtration is generally considered to be 5 m3/m2-h, most rapid sand filters are operated at 7 to 12 m3/m2-h and have coarse sand beds. As the water moves downward through the pore spaces, some of the fine suspended floc collides with the sand surfaces an adheres to the sand particles. As the water passes through pore constrictions, some of the fine floc is brought together, flocculation occurs, and the enlarged floc settles on top of the sand particles immediately below the constrictions. Also, the buildup of floc that that has been removed in the filter creates a straining action, and some of the incoming floc is removed by straining. During a filter run, the accumulated floc causes the pore spaces to become smaller, the velocities to increase, and some of the removed floc to be carried deeper within the filter bed. Straining may also occur at the surface of the filter if in filtering smaller particles (Reynolds and Richard, 1996). 2.3.3

Filter Media

The ideal filter medium should be of such a size that it will provide a satisfactory effluent, retain a maximum quantity of solids with minimum head loss, and be readily cleaned with a -8-

minimum quantity of water. The effective size and the uniformity coefficient characterize filter sands. The effective size is equal to the sieve size in millimeters that will pass 10 % (by weight) of the sand. The uniformity coefficient is equal to the sieve size passing 60 % of the sand divided by the size passing 10 %. Most rapid sand filters have sands with an effective size of 0.35 to 0.50 mm; however, some have sand with an effective size as high as 0.70 mm. The uniformity coefficient, which is a measure of gradation, is generally not less than 1.3 or more than 1.7. The gravel serves to support the sand bed and is usually placed in several layers. The total depth may be from 150 to 610 mm.; however, 460 mm. is typical. The size the top layer of gravel depends upon the sand size, whereas the sizes of the bottom gravel depends upon the type of underdrain system. Usually five layers are used, and the gravel grades from less than 1.6 mm. at the top to 25 to 50 mm at the bottom (Reynolds and Richard, 1996). 2.3.4 The Underdrain System The underdrain system consists of a method to collect and remove filter water, distribute backwash water and control flow rate through the filter. Collection and distribution is accomplished with an under drain, commonly called a filter floor as it may also support the filter bed. There are three main designs commonly used: • Perforated lateral • Suspended nozzle • Combination lateral and nozzle The underdrain must be maintenance and corrosion free. Uniform collection and distribution is important to the integrity of the filter bed. Short circuiting or stagnation caused by the under drain can greatly reduce the effectiveness of the filter. If the filter design is decreasing flow, then no flow control is used. As the filter bed fills with particulate matter the flow is reduced as more energy is expended in head losses. When head loss reaches a set maximum, cleaning by backwashing is required. Steady flow type filters are the most common. In this design head losses, and consequently flow rate, are held constant. At the start of operation (clean filter) head losses are maintained at the designated level through external mechanical means. As the filter media fills with particulate matter, increasing the internal head loss, the external losses are reduced to maintain a constant. When external losses reach their minimum value, cleaning is required(Reynolds and Richard, 1996). 2.3.5

Filter Backwashing

During the filtration process, particles suspended in the filtered water are removed largely through entrapment within the filter media. As more and more fluid is passed through the filter, the suspended particles accumulate within the media, reaching levels that lead to one of two detrimental events. It can either cause the head loss within the filter to reach excessively high levels (2 to 3 meter of hydraulic head), or it can become pushed through the filter, resulting in product water turbidities that reach unacceptable levels (greater than 1 NTU).

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Source: Adapted from Mcghee (1991) Figure 2.2 Schematic section of a rapid sand filter. Therefore, in order to maximize the use of a given filter, it becomes necessary to remove these entrapped particles from the media itself. Filter backwashing is the process by which this is accomplished. From an operational standpoint, backwashing is initiated when either one of the two aforementioned conditions occur, or more commonly, after a preset run-time interval has been reached (Reynolds and Richard, 1996). 2.3.5.1 Backwash Basics The backwashing process begins by pumping product water from the clearwell to the filter bottom through an underdrain system designed to distribute this "washwater" evenly across the bottom of the filter. Approximately 1-5% of the product water a filter produces during a run is ultimately used for backwash. Even distribution of washwater flow is necessary to prevent short-circuiting and channeling that might otherwise hinder the effectiveness of the -10-

backwash process and disrupt the filter structure. Wheeler Bottoms and Leopold Blocks are two examples of such underdrain systems specifically designed to distribute backwash flow. The backwash fluid velocity starts slow and is gradually increased to avoid disrupting the bed structure. Typical backwash flow velocities are between 0.61 and 0.81 m/min. As the washwater flows upward through the filter, it lifts the media, causing the bed to expand and assume a fluidized state. Usually the degree of bed expansion is in the range of 20 to 50% of the static bed depth. Bed expansion and fluidization permits entrapped particles to become released and flushed upward and out of the media. The dirty washwater that has passed through the filter is then collected in washwater troughs located about 0.90 m above the static filter surface, and is typically sent back to the head of the treatment plant, or to drying ponds. In some locations, the washwater is sent to wastewater treatment facilities (Reynolds and Richard, 1996). 2.3.5.2 Supplemental Techniques In many cases, bed expansion and fluidization is not sufficient to completely clean the bed. In these cases, surface wash and/or air scour techniques are employed in addition to backwash to increase the efficacy of the cleansing process. A surface wash system uses jets of water set at 1 to 5.08 cm above the surface of the static bed. These jets are turned on 1 to 2 minutes prior to backwash and continue to run until approximately 2 to 3 minutes before the backwash flow is shut down. The function of the jet wash is to increase the scouring effect necessary to dislodge stubborn particles from the media. Although such systems can be very effective for the upper regions of the filter bed, they tend to have little effect on particles in the lower reaches of the filter. Air scour systems, on the otherhand, function by pumping air through the bottom of the filter prior to backwash until just before the washwater begins to overflow into the washwater troughs. Because the air bubbles are less dense than the washwater, they travel at a greater velocity relative to the fluid, increasing the turbulence, and hence the shearing forces, within the media. Although air scour can be effective, it can be potentially damaging to the filter, as it increases the likelihood of the filter media itself being swept into the washwater trough. If too much media is lost, the filter would lose its functionality and expensive replacement would be required prematurely. Therefore, it is important to guard against this loss of media if air scour is to be used. This can be accomplished by either decreasing the backwash velocity while scouring is occurring or by shutting down the scour before the washwater overflows into the collection troughs (Reynolds and Richard, 1996). 2.3.6

Filter Controls

The original rapid-filter designs incorporated rate-of-flow controllers to maintain constant filtration rates despite variations in head loss within the filter during a run. Such controllers, while still available, are no the most desirable method of regulating filter flow rates. It is generally accepted that declining-rate filters produce better quality and larger volumes of water between backwash cycles, although some investigators have not found these differences to occur and not all state regulatory agencies have accepted the advantages of such designs (McGhee, 1991). The standard rate of filtration has been considered to be 5 m3/m2-h, of filter bed area since this is a common rate at which the first rapid sand filters were operated. Present coagulation and sedimentation practice allows the use of higher filtration rates. Frequently, plants are rated at 5 m3/m2-h, but previsions are made for operated at rates up to -11-

12 m3/m2-h. Although most filters are operated at a constant filtration rate, a declining rate of filtration is sometimes employed. In this type of operation, the rate of filtration is decreased as the filter run progresses and the degree of clogging increases. Frequently, this results in longer filtration runs and better effluent quality. It is limited to medium to large plants, because the filters must be staggered in the degree of clogging to permit a constant rate in the total water production from the plant (Reynolds and Richard, 1996). 2.4

Rural Water Supply in Thailand

2.4.1

Design Criteria and Water Quality

Currently, the Department of Health, in Thailand adopts the following criteria for rural water supply systems. Design served population = 2,000 person or more Water consumption = 50 Lpcd. Growth rate = 2% Designed period = 10 years Water loss = 25% Maximum hourly demand (MHD) = 4 x Average hourly demand Maximum daily demand (MDD) = 1.5 x Average daily demand Average pumping hour = 14 hour Total storage (clear water well) = 70% of MDD Elevated tank = 20% of MDD Min. pressure at the end of distributed pipe = 5 m. Min. pressure at tap water = 3 m. Main pressure pipe which pass household = < 20 m. These guidelines are set in order to help the practical engineer overcome the various problems encountered in the design and construction of the rural water supply system. However, one should keep in mind that certain elements of design are matters for local decision, depending on geographical constraints, local economy, customs, and other factors. Table 2.1 shows the process design criteria of existing rapid sand filtration. Various standards for drinking water have been developed as an aid to the improvement of water quality and treatment. In 1958, WHO first published International standards for drinking water that had been adopted in whole or in part by a number of countries as basis for formulation of national standards. The drinking water standard of DOH has been established based on WHO drinking water standards. 2.4.2 Water Treatment Process Options The type of treatment plant obviously depends on the water source natures. Both water quality and quantity conditions are influenced the variations in the technical design. There are three main types of treatment options: 1. Plants consisting of coagulation, flocculation, sedimentation, rapid sand filter and chlorination unit processes primarily for turbidity removal and disinfection. -12-

2. Plants consisting of aeration, rapid sand filter and chlorination unit processes primarily for inorganic removal (iron and manganese) and disinfection. 3. Plants consisting of chlorination only. 2.4.3

Installation of Rural Water Supply

The Operation Promotion and Maintenance Works of the Rural Water Supply Division of the DOH reported the installation of village water supply by various offices up to 1996, as follows: total 20,612 plants covering 21,864 villages (Department of Local Administration, January 1997) calculated 33 % of total village. Figure 2.3 shows a number of villages serviced by water supply categorized by various operation agencies and Figure 2.4 shows a number of villages serviced by water supply categorized by DOH’ s Regional, Year 1996. 2.4.4

Situation of Rural Water Supply

A recent investigation (Ritjitpian et al., 1997) was conducted at the 28 existing village piped water supply systems in Amphoe Khoka of Lampang Province in Thailand. This study surveyed water quality and user satisfaction. The study found that water quality was not compliance with existing standard by means of bacteriological, fluoride and iron. Some system was not got rid out or increasing concentration level after treated by the existing treatment process. Most of consumers were satisfied administer, plant operator, and supplies water quality. 2.5

Water Treatment Plant Performance Studies

Performance of water treatment plants can be evaluated by several methods, including turbidity, particle counts, heterotrophic plate counts, and microscopic particulate analysis (MPA). Particle counting and turbidity measurements are two of the most valuable water quality parameters used in assessing treatment plant performance. A comparison of source water and filtered water using these procedures has been proposed as a reliable method for determining treatment plant performance (Bellamy et al., 1993). Turbidity appears to be an adequate predictor of the removal of cyst-sized particles when source water turbidities are greater than 5 NTU; in less turbidity raw water sources, however, particle counting appears to be more reliable indicator. Burlingame et al. (1998) reported the measurement of turbidity has and will continue to be a valuable tool for guiding and monitoring the performance of water treatment processes and water distribution systems. Turbidity measurements remain the best means by which to assesses the particulate matter (living or nonliving) in treated drinking water. Turbidity is being used as a relative measure of reliable treatment process performance and as a regulatory parameter that requires monthly reporting and that can lead to public notification. USEPA selected turbidity as the treatment technique parameter to determine adherence to the minimum treatment removal requirements, replacing the turbidity MCL (Burlingame et al., 1998).

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Table 2.1

Process design criteria for existing rapid sand filtration

Parameters Process capacity- m3/h Raw water meter Range- m3/h Flash Mixing type Flocculation type

Number of stage Size of baffle(W x L x D)- m Number of Baffle- unit Mixing energy(G)- s-1 Detention time - min G x t - seconds Sedimentation type Size of tank(W x L x D)- m L : W ratio Inlet velocity(port) – m/s Detention time - h Surface loading- m3/ m2 -h Mean velocity – m/min Weir loading- m3/ m -h Sludge removal Filtration

Filter bed size – m Bed area - m2 Filtration rate – m/h Control system Filter Sand Effective size – mm U.C Depth Backwash rate – m/min Under drain Backwash flow meter Sampling tap Disinfection Type Dosage – mg/L Contact time – min Residual free Cl2 – mg/L

Surface water treatment 20 None None Hydraulic Jump Baffled channel with a horizontal “ around the end” 1 1.8 x 0.24 x 0.35 49 20(average) 22 2.64 x 104 Rectangular basin with horizontal flow 2.4 x 6.75 x 3.20 2.8 0.24 2.60 1.24 0.043 9.52 Manual Side Drain Rapid sand filter with declining-rate mode of operation 2.4 x 1.7 4 5 Effluent level control (gooseneck piping) Mono Media 0.45-0.55 1.5-1.8 0.6 0.8 Pipe lateral None None Calcium Hypochlorite 1.50 30 (minimum) 0.20

Surface water treatment 10 None None Hydraulic Jump Baffled channel with a horizontal “ around the end” 1 1.8 x 0.21 x 0.20 49 20(average) 22 2.64 x 104 Rectangular basin with horizontal flow 1.65 x 4.80 x 3.10 2.90 0.15 2.46 1.26 0.033 6.90 Manual Side Drain Rapid sand filter with declining-rate mode of operation 1.2 x 1.65 2 5 Effluent level control (gooseneck piping) Mono Media 0.45-0.55 1.5-1.8 0.6 0.8 Pipe lateral None None Calcium Hypochlorite 1.50 30 (minimum) 0.20

Source: Rural water supply division of DOH, Thailand

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Ground water treatment 10 None None None None

None

Rapid sand filter with declining-rate mode of operation ∅ 1.90 2 5 Effluent level control (gooseneck piping) Mono Media 0.45-0.55 1.5-1.8 0.6 0.8 Pipe lateral None None Calcium Hypochlorite 1.50 30 (minimum) 0.20

DOH

DMR

PWD

ARD

Others

2%

12%

28%

38% 20%

Source:

Rural Water Supply Division, Department of Health

Figure 2.3

Number of villages serviced by water supply categorized by various operation agencies

Serviced Village Number (Villages)

1,200 1,000 800 600 400 200 0 I

II

III

IV

V

VI

VII

VIII

IX

X

XI

XII

Region Office of Environmental Health Center

Source:

Rural Water Supply Division, Department of Health

Figure 2.4

Number of village serviced by water supply categorized by DOH’ s Regional, Year 1996 -15-

Nieminski, (1995) concluded that particle counts and turbidity measurement can be effective tool to determine expected removals of Giardia and Cryptosporidium but she did not demonstrate a correlation between the reduction of these organisms and heterotrophic bacteria. Hancock et al., (1996) reported that MPA can provide information on the effective of water treatment processes for removing particulate matter. The study found a significant correlation between reduction values generated by organism counts, centrifugate pellet measurements, and particulate counts 2.6

Filtration Plant Performance Evaluation

In 1988-1990, US Environmental Protection Agency (USEPA) evaluated the composite correction program (CCP)’s effective small treatment plant using surface water supplies in Montana (USEPA, 1990). The CCP approach consists of two phases, comprehensive performance evaluation (CPE) and comprehensive technical assistance (CTA). A CPE is a review and analysis of a surface water treatment such as design capability, associated administrative, operation and maintenance practices. A major objective of a CPE to identify factors that may prevent a plant from achieving optimal performance. A CTA is the performance-improvement phase implement if the CPE indicates improved performance can be achieved. The CTA systematically considers the specific factor or factors that limit the plant in achieving the desired finished water quality. Nine CPEs and three CTAs were completed (USEPA, 1990). Renner et al., (1993) implemented 36 small and medium-sized utilities across the U.S.A. The study found only 2 were operating optimally and several were considered treats to public health. The primary problems were operational. Four plants were selected to conduct implement the CTA. This study found finished-water turbidity requirements was achieved at a capital cost of less than U$ 10,000 per plant. In 1988, Pennsylvania’s Department of Environmental Protection (DEP) initiated a statewide filter plant performance evaluation (FPPE) program for safe drinking water and completed 506 FPPEs at 290 surface water treatment plants (Consonery et al., 1997). Only 39 percent of plants were rated “acceptable”, but by 1996 the percentage had increased to 91 percent demonstrating that assistance could lead to successful improvements and decreased risks from water borne protozoa. The study found that physical condition of the facilities, operation, design and administration all influenced a plant’s ability to work properly. Some of the primary operational problems involved improper chemical dose adjustments, insufficient process monitoring, and improper filter operation and backwash techniques. Overall, the variations in raw water quality, type of facilities, and the different personalities and skills of operators and administrative staff provided a complicated challenge to understanding problems at water treatment plants. (Consonery et al., 1992) The percentage of positive Cryptosporidium (presumptive) samples of finished water dropped from 35 percent in 1990 to