compatibility and attenuative properties of blast furnace slag treated

THE JOURNAL OF SOLID WASTE TECHNOLOGY AND MANAGEMENT

Formerly The Journal of Resource Management and Technology (Volumes 12-22) Formerly NCRR Bulletin (Volumes 1-11) February 2009

Volume 35

Number 1

THE JOURNAL OF SOLID WASTE TECHNOLOGY AND MANAGEMENT ISSN: 1088-1697 Indexed/Abstracted by: Chemical Abstracts; Engineering Abstracts; Environmental Abstracts; Environmental Periodicals Bibliography; Pollution Abstracts, AllRussian Institute of Scientific and Technical Information (VINITI, REFERATIVNYI ZHURNAL )

EDITOR AND FOUNDER: Iraj Zandi University of Pennsylvania U.S.A.

EDITOR: Ronald L. Mersky Widener University U.S.A.

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EDITORIAL BOARD


Noah I. Galil Department Civil Engineering Technion—Israel Institute of Technology Haifa 32000, Israel Email: [email protected]

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A.J. Griffins Cardiff University U.K. Patrick Hettiaratchi University of Calgary Canada Mervat El-Hoz University of Balamand Lebanon Gennaro J. Maffia Widener University U.S.A. Franco Medici University of Rome “La Sapienza” Italy Yusuf Mehta Rowan University U.S.A. Ilan Nissim Israel Ministry of the Environment Israel Ram Ramanujam, P.E. California EPA/DTSC U.S.A. N.C. Vasuki Delaware Solid Waste Authority U.S.A. Ming-Yen Wey National Chung Hsing University Republic of China Keith P Williams Cardiff University U.K. Anita Závodská Barry University U.S.A.

The Journal of Solid Waste Technology and Management, is published by Widener University School of Engineering. The responsibility for contents rests upon the authors and not upon the University. This journal is available by subscription and may be purchased at the rate of US$130 per volume (4 issues) for individuals and US$305 for libraries, businesses and organizations. Editorial and subscription address is: Department of Civil Engineering, Widener University, One University Place, Chester, PA 19013-5792, U.S.A.; Telephone (610) 499-4042; Fax (610) 499-4461. Email: [email protected]. Web site: www.widener.edu/solid.waste. Copyright © 2009 by Widener University. Printed in U.S.A.

THE JOURNAL OF SOLID WASTE TECHNOLOGY AND MANAGEMENT

Formerly The Journal of Resource Management and Technology (Volumes 12-22) Formerly NCRR Bulletin (Volumes 1-11) February 2009

1

Volume 35

Number 1

COMPATIBILITY OF CEREAL STRAW WITH HYDRATION OF CEMENT

P. Soroushian, O. Simsek, M. Elzafraney, T. Ghebrab 7

COMPATIBILITY AND ATTENUATIVE PROPERTIES OF BLAST FURNACE SLAG TREATED LATERITE

Kolawole J. Osinubi, Adrian O. Eberemu 17

APPLICATION OF IONIZING RADIATION FOR SLUDGE DISINFECTION AND ITS USE FOR IRRIGATION AND FERTILIZATION

G. Shani, S. Segman-Magidivich 26

SORPTION POTENTIAL OF THE BIOMASSES OF PEANUT HULL AND FLY ASH FOR DECOLOURIZATION OF METHYLENE BLUE AQUEOUS SOLUTION

G.M. Taha 35

AN IMPROVED NUMERICAL DESIGN METHOD FOR THE REMEDIATION OF CONTAMINATED SITES BASED ON SENSITIVE TRACER TESTS

Kazuei Ishii, Toru Furuichi 51

DRIVING COMMERCIAL AND INDUSTRIAL WASTE REDUCTION IN QUEENSLAND, AUSTRALIA—THE POTENTIAL APPLICATION OF A UK WASTE MINIMISATION CLUB MODEL

Georgina Davis, Paul Phillips, Thomas Coskeran

COMPATIBILITY OF CEREAL STRAW WITH HYDRATION OF CEMENT P. Soroushian*, O. Simseka, M. Elzafraneyb, T. Ghebrabc *

Department Civil and Environmental Engineering, Michigan State University Room 3546, Engineering Building, East Lansing, MI 48824-1226, USA Email: [email protected]; Tel: (517) 355 2216; Fax: (517) 432 1827 a

Department of Construction, Faculty of Technical Education Gazi University, 06500, Ankara, Turkey Email: [email protected] b

Technova Corporation, 1926 Tunrner St. Lansing, MI 48906, USA Email: [email protected]

c

Department Civil and Environmental Engineering, Michigan State University Room 3546, Engineering Building, East Lansing, MI 48824-1226, USA Email: [email protected]

ABSTRACT

Cereal straw is an abundantly available agricultural by-product with attractive mechanical performance and cost position for reinforcement of cement-based products. The composition of straw, however, is distinguished from that of wood by the presence of relatively large quantity extractives with potentially strong inhibitory effects on strength development of cement. Thinsheet fiber cement products offer attractive technical, economic and aesthetic qualities for use in diverse building construction applications, including siding and tile backerboard. Commercially successful thin-sheet fiber cement products generally utilize chemically processed wood pulp or mechanically milled wood as reinforcement for achieving enhanced levels of flexural strength, toughness and workability. Cereal straw offers a slender geometry which favors their mechanical processing as replacement for milled wood in thin-sheet cement products. As a renewable resource and as a generally low-valued agricultural residue, straw offers economic and environmental advantages for replacement of wood in thin-sheet cement products. The differences in composition of wood and straw should be considered in devising pre-treatment techniques for use of straw in conjunction with cement. Such pre-treatments should address the potential for inhibitory effects of some straw constituents on strength development of cement. Keywords: Straw; Treatment; Cement; Strength development; Reinforcement

INTRODUCTION Cereal (wheat, barley, rice, rye and oat) straw is a major COMPATIBILITY OF CEREAL STRAW WITH HYDRATION OF CEMENT

by-product of agricultural activities, with a generation rate of 300 million tons per year in U.S. and Canada. . Current applications as a supplementary animal feed, fuel and feedstock

1

for chemical industry still leave substantial quantities of surplus straw [1,2,3,4,5,6]. Straw is distinguished from wood by a relatively high concentration of (water-soluble) extractives; potential inhibitory effects of such extractives on hydration of cement and stability of straw in alkaline environments need to be addressed for successful use of straw in conjunction with cement [7,8]. Past efforts to use straw in cement-based products have resorted to CO2 curing to overcome the inhibitory effects of straw on hydration of cement, and to lower the alkalinity of the cement-based matrix for improved compatibility with straw [9]. Once the inhibitory and stability concerns are addressed, straw offers desirable reinforcement attributes for use in cement-based products. The value of straw as a reinforcement system for improvement of the tensile strength and toughness of cement-based matrices, and the potential of cement-bonded straw systems to provide desirable durability characteristics under repeated wet-dry and freeze-thaw cycles have been demonstrated in past research [9]. Efforts reported here to enhance the compatibility of straw with cement-based matrices add to the value of straw as an economical and environmentally friendly reinforcement in thin-sheet cement products [9,10,11,12].

MATERIALS AND TEST PROCEDURE Broad categories of cereal straw were subjected to different pre-treatment conditions prior to addition to Portland cement mortar mixtures. Compressive strength was used as a measure for assessment of the relative inhibitory effects of different pre-treatment conditions and straw types on cement.

Compression tests were performed per ASTM C39 on 100 mm diameter by 200 mm height specimens using a hydraulic compression test system. The specimens were consolidated on vibrating table, cured at 100% relative humidity and 22oC for 7 days, and then demolded, capped and tested. There was a time lag of 3 hours between demolding and testing, during which the specimens were stored at 50% relative humidity and 22oC. Experiments were conducted on mortar specimens comprising Type I Portland cement: siliceous sand (3.35 mm maximum size): water at 1: 2: 0.5 weight ratios. Six replicated specimens were tested for each mix. Straw was introduced into the matrix at 2.5% by weight of cement. The straw used in mortar was shredded and sieved through a 4.75 mm sieve, yielding the following mean values (ranges) of dimensions: 13.4 (2.08-37.0) mm length; 3.63 (0.69-6.69) mm width; and 1.40 (0.63-3.15) mm thickness. The following types of straw were used in this investigation: wheat, oat, rye, rice, and barley. Straw was used either as-received (untreated) condition, or after the following pretreatments: immersion in 96oC water for 1, 2, 3 or 4 hours, immersion in 96oC lime-saturated water (5% lime content) for 1, 2, 3 or 4 hours, immersion in water at room temperature for 24 hours, or immersion in lime-saturated water at room temperature for 24 hours. A water/straw weight ratio of 10 was used for all these treatment conditions. Straw was washed thoroughly and dried in oven at 40oC over a period of 72 hours prior to use in Portland cement mortar. Table 1 summarizes the notation used in this investigation for different straw treatment and addition conditions.

TABLE 1 Notations for different straw treatment and addition conditions Treatment/addition condition

Mix notation

No Straw (Plain Mortar)

1

Untreated Straw

2

Straw immersed in water for 24 hours

3

Straw immersed in boiling water for 1 hour

3.1

Straw immersed in 96oC water for 2 hours

3.2


3.3


3.4

Straw immersed in lime-saturated water for 24 hours at room temperature

4

Straw immersed in 96oC lime-saturated water for 1 hour

4.1

Straw immersed in 96oC lime-saturated water for 2 hours

4.2


4.3


4.4

2

JOURNAL OF SOLID WASTE TECHNOLOGY AND MANAGEMENT

VOLUME 35, NO. 1

FEBRUARY 2009

RESULTS AND DISCUSSION Figure 1 shows a failed compression specimen incorporating straw. Figures 2 - 6 present, for different straw types, the mean values and ranges of compressive strength test results after different straw treatment conditions. When compared with plain mortar (Mix 1, with no straw addition), introduction of straw lowers the compressive strength of mortar. This can be attributed to the inhibitory effects of straw constituents on hydration of cement, and also to the fact that straw constitutes a low-modulus inclusion within mortar and contributes little to compressive load-carrying capacity. It should be noted that straw offers viable levels of tensile strength to enhance the tensile strength and toughness of cement-based materials [9]. The results suggest that proper treatment of straw (e.g., in hot lime-saturated water for sufficient period of time) can enhance the compatibility of straw

with the cement-based matrix, yielding higher levels of compressive strength. These treatments would remove lignin and extractives with inhibitory effects on strength development of cement; the high alkalinity of lime-saturated hot water makes it particularly effective in removal of inhibitory compounds from straw [3]. Different straw types exhibit different inhibitory effects on strength development of cement. Among untreated straws (i.e., treatment “2”), rye followed by oat straw have particularly strong inhibitory effects on strength development of cement. The effectiveness of various treatment conditions also depends on straw type. While wheat and oat straws benefited only slightly from pre-treatment, rice and rye straw exhibited improved compatibility with strength development of straw after pre-treatment. Among the straw types considered, rice straw (after proper pre-treatment) offers the best compatibility with the cement-based matrix.

FIGURE 1 Shredded straw and failed compression specimen incorporating straw

Strength (MPa)

14 12 10 8 6 4 2 0 1

2

3

3.1 3.2 3.3 3.4

4

4.1 4.2 4.3 4.4

Treatment FIGURE 2 Compressive strength test results with wheat straw COMPATIBILITY OF CEREAL STRAW WITH HYDRATION OF CEMENT

3

14

Strength (MPa)

12 10 8 6 4 2 0 1

2

3

3.1

3.2

3.3

3.4

4

4.1

4.2

4.3

4.4

Treatment FIGURE 3 Compressive strength test results with barley straw

14

Strength (MPa)

12 10 8 6 4 2 0 1

2

3.2

3.3

4.2

4.3

Treatment FIGURE 4 Compressive strength test results with rice straw

The use of straw as reinforcement in cement-based matrices yields improved flexural strength and toughness for applications such as building panels where compressive strength is not a factor [9]. Compressive strength is used in this research as a measure of cement-based matrix quality, noting that the reinforcing effects of straw do not contribute to compressive strength but the inhibitory effects of some straw extractives would adversely influence the compressive strength of matrix. The pre-treatment techniques developed in this research would reduce the inhibitory effects of straw extractives on cement-based matrices, and would thus yield better products for use as building panels.

CONCLUSIONS The effects of introduction of straw after different pretreatments on compressive strength of Portland cement mor-

4

tar mixtures were evaluated experimentally in order to assess the inhibitory effects of straw on hydration of cement and determine the effectiveness of various treatments on enhancement of this compatibility. The following conclusions were derived based on experimental results. • Untreated straw has strong inhibitory effects on strength development of cement; the extent of such inhibitory effects depends on straw type. • Immersion in lime-saturated water for 2-3 hours is particularly effective in removal of inhibitory compounds from straw, thereby improving the compatibility of straw with cement. • Different straw types respond differently to different treatment conditions; relative standings of different straw types based on their inhibitory effects would be different prior to and after immersion in hot, lime-saturated water. • Proper selection and treatment of straw can open the prospects for value-added use of an abundantly available


VOLUME 35, NO. 1

FEBRUARY 2009

14

Strength (MPa)

12 10 8 6 4 2 0 1

2

3.2

3.3

4.2

4.3

Treatment FIGURE 5 Compressive strength test results with rye straw

14

Strength (MPa)

12 10 8 6 4 2 0 1

2

3.2

3.3

4.2

4.3

Treatment

FIGURE 6 Compressive strength test results with oat straw

agricultural by-product as lightweight reinforcement (in lieu of wood particles) in thin-sheet cement panels (cement-bonded particleboards) and other cement-based products. The primary reason for use of straw in cementbased products is to improve their flexural strength and toughness as key measures of quality in applications such as building panels. Compressive strength is used here as a measure of the cement-based matrix quality, and the pre-treatment techniques developed in this project for reducing the inhibitory effects of some straw extractives on cement-based matrices would enhance the value of straw as a reinforcement system in cementbased products.

ACKNOWLEDGEMENTS The authors would like to thank National Science Foundation (NSF) and DPD, Inc. for funding this work.

REFERENCES 1.

2.

COMPATIBILITY OF CEREAL STRAW WITH HYDRATION OF CEMENT

Al-Akhras, M., A. Abu-Alfoul, “Effect of wheat straw ash on mechanical properties of autoclaved mortar,” Cement and Concrete Research, Volume 32, No. 6 (2002) pp. 859-863. Biricik, H., F. Akoz, I. Berktay, N. Tuglar, “Study of pozzolanic properties of wheat straw ash,” Cement and

5

3.

4. 5. 6. 7. 8.

6

Concrete Researches, Volume 29, No. 5 (1999) pp. 637643. Galletti, C., P. Bocchini, E. Guadalix, G. Almendros, T. Martinez, “Pyrolysis products as markers in the chemical characterization of paperboards from waste paper and wheat straw pulps,” Bioresource Tech, Volume 60, No. 1 (1997), pp. 51-58. Doyle, J., C. Mason, D. Bake, Biological Waste, Volume 23 (1988), pp. 39-56. Roffael, E., H. Sattler, “Adsorptios Science Technology,” Volume 45 (1991), pp. 4545-4554. Srivastava, C., R. Gupta, Biological Waste, Volume 33 (1990), pp. 63-65. Rai, N., D. Mudgal, Biological Waste, Volume 27 (1987), pp. 203-212. Schiesser, A., C. Filippi, G. Totani, A. Lepidi, “Fine structure and mechanical,” Biological Wastes, Volume 27 (1989) pp. 87-100.

9.

Soroushian, P., F. Aouadi, H. Chowdhury, A. Nossoni, G. Sarwar, “Cement-bonded straw board subjected to accelerated processing,” Cement and Concrete Composites, Volume 26, No. 7 (2004) pp. 797-802. 10. Cooper, A., T. Ung, C. Huang, X. Wang, Cement bonded boards using CCA-treated wood removed from service, 6th Int Inorganic-Bonded Wood & Fiber Composite Material Conference, USA, (1998) pp. 330-348. 11. Hermawan, D., T. Hata, S. Kawai, W. Nagadomi and Y. Kuroki, “Effect of carbon dioxide-air concentration in the rapid curing process on the properties of cementbonded particleboard,” Journal of Wood Science, Volume 48, No. 3 (2002), pp. 179-184. 12. Sulastiningsih, M., P. Sutigno and R. Priyadi, 1998. The Properties of Cement-Bonded Boards From Sengon Wood. 6th International Inorganic-Bonded Wood & Fiber Composite Material Conference, USA, pp. 308-328.


VOLUME 35, NO. 1

FEBRUARY 2009

COMPATIBILITY AND ATTENUATIVE PROPERTIES OF BLAST FURNACE SLAG TREATED LATERITE Kolawole J. Osinubi1*, M.ASCE., F.NSE., R.Engr. Adrian O. Eberemu,2 SM.ASCE., M.NSE., R.Engr. 1

Professor, Dept. of Civil Engineering, Ahmadu Bello University Zaria 810001 NIGERIA Tel: +2348037037241 Email: [email protected]

2

Lecturer, Dept. of Civil Engineering, UNIAGRIC Makurdi, Benue State, NIGERIA Email: [email protected]

ABSTRACT Major concerns exist regarding potential pollution problems related to contamination by toxic liquids emanating from waste landfills. Increasing environmental awareness is making it necessary to assess the effects of waste leachates in proposed clayey liners for waste landfills. Results of a study on the feasibility of using laterite treated with ground blast furnace slag (BFS) as a construction material for waste containment liners and impermeable covers are presented. Liners can be constructed using laterite treated with ground BFS to meet the regulatory permeability value of < 1x 10-9 m/s. The effects of permeation with municipal solid waste (MSW) leachate on compacted soil treated with up to 15% ground BFS at the energy of the British Standard heavy (BSH) compaction using different molding water contents for a period of one month are reported. Batch equilibrium studies were conducted for a duration of 48 hours using 0, 5, 10, 15 and 100% ground BFS treated soil, respectively. The MSW leachate had no detrimental effect on the liner permeability. Adsorption isotherms were obtained for the cations of calcium, iron and chromium that were selected to represent the dominant and critical contaminants in the leachate and these showed strong attenuative properties. 5% BFS treatment gave the optimum mix performance. Keywords: Adsorption Isotherm, Attenuation, Batch Equilibrium, Compatibility, Hydraulic Conductivity, Laterite, Municipal Waste Leachate

INTRODUCTION Large amounts of solid wastes generated every year are mostly placed in landfills. The materials in landfills mix with

moisture from rain and dew to form a leachate, which chemical composition varies widely depending on the waste material involved. Leachates are the main sources of ground water pollution; hence they must be contained properly in landfill within some liner system that serves as a hydraulic barrier to

_____________________________________ * Corresponding author.


7

flow of fluids thus minimizing the infiltration of leachate into ground water Poor waste management practices often lead to severe soil and ground water contamination at sites. Adverse health effects have been attributed to contamination of municipal and industrial waste (Benson, 1999). Inadequate containment of municipal and industrial waste is one of the primary causes of ground water contamination. Consequently, solid and liquid wastes were disposed by placing them in unlined holes referred to as dumps. Often liquid waste (particularly aqueous solution) was intentionally placed in surface impoundments with the intention of disposing the waste by “evaporation and infiltration.” In other cases existing fine-grained soil layers were assumed to be capable of isolating the wastes from the surrounding environment. The fallacy of reliance on natural fine-grained soil layers was revealed by the fiasco at Love canal. Engineers believed that clay underlying the chemical disposal pit in Love canal would retain liquid chemical wastes. However, extensive contamination ultimately occurred (Daniel, 1993). The creation of non-decaying waste materials, combined with a growing consumer population has resulted in a waste disposal crisis. Some of these wastes include plastics, glass, municipal waste combustion ash, scrap tires, carpet fibers waste, roofing shingle waste, coal combustion by-products (fly and bottom ashes), blast furnace and steel slags etc. One of the solutions to this problem is the beneficial recycling of hitherto waste products into useful products. Large quantities of slag are generated each year by the various steel plants and foundries in Nigeria. With continuous steel production, the yearly tonnage of slag as a waste product will become very significant and disposal problems will arise. Environmental benefits arising from the use of slag include (i) Energy conservation and preservation of natural resources. (ii) Release of land for storing waste slag. However, with the advent of increased environmental regulation, and increasing cost of waste disposal, the steel industry would be searching for more beneficial reuse of its waste slag. A large part of Nigeria is underlain by basement complex rock, the weathering of which has produced lateritic materials spread over most of the area. It is virtually impossible to execute any construction work in Nigeria without the use of lateritic soils. The possibility of using lateritic soils in waste containment systems have been reported by Osinubi and Nwaiwu (2002, 2005, 2006 and 2008). This paper presents the results of laboratory tests on the compatibility and attenuative properties of compacted laterite treated with up to 15% BFS as a suitable liner material (hydraulic barrier) for the containment of environmental pollutants emanating from municipal solid waste dump sites.

repositories for unwanted or unusable waste. Waste materials can generally be grouped into four: (i) Municipal or sanitary waste. (ii) Industrial waste (iii) Hazardous waste (iv) Lowlevel radioactive waste. Landfill liners are often called clay liners, because clay is largely responsible for the low hydraulic conductivity of earthen liners. Braja (1998) and Daniel (1993) suggested that the liner material must have a hydraulic conductivity value of 1 x 10-9 m/s with percentage fines of 20-30%. It should not contain particles or chunks larger than 25 - 50 mm. It was further suggested that the liner system should be able to minimize the movement of leachate and prolong the release of chemicals in leachate. Furthermore, the liner material must maintain its strength and low hydraulic conductivity after prolonged contact with leachate solution, and should have an absorptive, attenuative capacity for critical pollutants, such as heavy metals (i.e., it should be resistant to chemical attack). Daniel (1993) further suggested that materials compacted between 2 - 4% on the wet side of optimum moisture content would give the best hydraulic conductivity. Other waste materials such as paper mill sludge (Stoffel and Ham,1979); pozzolanic fly ash (Edil et al., 1992); foundry green sand (Abichou et al., 2000) etc. have been used as soil liners either solely or in combination with clay additives; Compatibility test refers to hydraulic conductivity test in which the permeant fluid is the actual waste leachate expected in the field during the performance period of the clay liner or synthetic leachate. The purpose of compatibility test is to determine if the chemicals in the leachate can attack the liner material and hence increase its hydraulic conductivity (Shackelford, 1994). This test helps to determine changes in the intrinsic permeability due to permeation with different chemical solutions. Two procedures namely (i) Batch equilibrium test and (ii) Column percolation test have been shown to be useful for demonstrating this reaction and in evaluating the effectiveness of the attenuation mechanism. The batch equilibrium or adsorption testing is performed to determine the relationship between the amounts of a given solute adsorbed to the surface of clay particles relative to the amount of the same solute remaining in the pore water of the soil under equilibrium condition (Shackelford, 1994). The relationship between the adsorbed and the pore water concentrations is shown by the adsorption isotherm since the test is typically performed at constant temperature. The test can be completed relatively quickly and it is ideally suited for determining attenuation characteristics on a number of samples at a time. Results from the column test generally describe the attenuation process more truly. However, column tests may require several months to generate useful data for materials with low hydraulic conductivity (Daniel, 1993).

LITERATURE REVIEW

MATERIALS AND METHODS

Sanitary landfills consist of a refuse disposal area in which the waste is disposed in cells with thicknesses up to about 5 m. Requirement for landfills vary with the type of waste and other factors such as hydrogeology of the site, climate, and type of waste to be buried. Landfills are the final

Slag

8

Bulk samples of blast furnace slag (BFS) were obtained from the foundry of Defense Industries Corporation of Nige-


VOLUME 35, NO. 1

FEBRUARY 2009

ria (DICON).in Kaduna State. The BFS was obtained in lumps but was ground to particle sizes passing through BS No.200 sieve. The ground BFS was mixed with laterite at 0, 5,10 and15% by weight of dry soil in order to obtain four soil-slag mixtures.

Soil The soil samples used were obtained from a borrow pit

in Zaria using the method of disturbed sampling. A study of the geological and soil maps of Nigeria after Akintola (1982) and Areola,(1982), respectively, shows that the samples taken belong to the group of ferruginous tropical soils derived from acid igneous and metamorphic rocks. The index properties of the natural soil as well as its oxide composition are summarized in Tables 1 and 2, respectively. The predominant clay mineral in the soil from the borrow pit was reported by Osinubi(1998) to be kaolinite with some quartz based on qualitative and quantitative assessments by ways of differential

TABLE 1 Properties of the natural soil Property

Quantity/description

Natural moisture content (%)

5.8

Liquid limit (%)

42

Plastic limit (%)

32

Plasticity index (%)

10

Linear shrinkage (%)

7.6

Percentage passing BS No. 200 sieve

73.5

AASHTO classification

A-7-6 (8 )

USCS classification

CL

Specific gravity

2.76

Maximum dry density (BSH)(Mg/m3)

1.85

Optimum moisture content (BSH)(%)

13.1

pH

6.67

Color

Reddish brown

TABLE 2 Oxide composition of lateritic soil Oxide

Concentration (% by weight)

CaO

0.28

SiO2

35.60

Al2O3

27.10

Fe2O3

24.0

MgO

0.22

Na2O + K2O

-

SO3

0.85

Mn2O3

2.0

P2O5

-

Loss on ignition

1.46


9

thermal analysis (DTA) and X-ray diffraction (XRD) analysis of material passing through a British Standard No. 200 sieve.

Leachate The leachate used in the study was obtained from an active open landfill located in Samaru, Zaria (Latitude 11o15'N and longitude 7o45'E) along the Zaria - Sokoto road. The chemical characteristics of the leachate are summarized in Table 3.

=

h1 h2 g o l x 0 3 0 0 1 3 x . 2 t x x 0 L 6 x x a A

k

Compaction

provided both the head of water and the means for measuring the quantity of permeant fluid flowing through the sample. The compacted soil sample in the mold was initially saturated by soaking in distilled water for a minimum period of 96 hours to allow for full saturation before being connected to a permeant liquid. Distilled water was used as the permeant liquid to avoid the possibility of ion exchange taking place. Hydraulic gradient used in the tests ranged from 5 to 15, while readings from the standpipe were taken every 24 hour time interval. The coefficient of permeability (k) was calculated using the expression: (1)

The compaction tests were conducted in accordance with BS 1377; 1990 parts 4; 3.5 using the British Standard heavy (BSH) compactive effort in a 1000 cm3 mold Soil passing through 4.76 mm aperture sieve weighing about 2.5 kg was placed in a tray and mixed with tap water. Thereafter, the soil was divided into five batches that were separately placed in the mould and compacted with a 4.5 kg rammer falling from a height of 450 mm with the application of 27 blows to each layer.

Where: aCross sectional area of standpipe (mm2) LLength of specimen (cm) ACross-sectional area of soil sample (mm2) t Time in minutes h1 & h2 - Initial and final heights of standpipe permeant levels (cm)

Hydraulic Conductivity

Column Test

The falling head permeability test procedure was adopted similar to the method reported by Daniel and Wu (1993). A relatively short sample was connected to a standpipe that

The column test was carried out on four soil samples treated with 0, 5, 10, and 15% BFS by weight of dry soil in order to assess the compatibility of the mixtures with MSW

TABLE 3 Chemical composition of leachate Parameter

Concentration

pH

8.9

Biological Oxygen Demand

45

Chemical Oxygen Demand

1050

Chloride

424.9

Sulphate

2500

Hardness

663.5

Potassium

188

Calcium

232.6

Sodium

236.8

Chromium

3.0

Iron

18.4

Magnesium

20.1

Copper

0.42

Manganese

0.068

Total Dissolved Solids

4100

Note: All data with the exception of pH values are in mg/l

10


VOLUME 35, NO. 1

FEBRUARY 2009

o

=

V x C M

C

Five soil samples treated with 0, 5, 10, 15 and 100% BFS were used in the tests. 100% BFS was used to check if the material would leach any dangerous chemical into the solution. A known mass of treated soil (30g) for each of the soilslag combination was placed in a 500 ml plastic container and 120 cm3 of MSW leachate with known initial concentration of solute constituent introduced into it. This soil-leachate mixture was placed in a reciprocating shaker and allowed to mix continuously for a period of 48 hours. At the end of the experiment, the solid and the solution phases were separated. An aliquot portion of the solution phase was taken and the equilibrium concentrations of some cations were determined. The mass of solute absorbed per mass of solid soil was calculated from the following expression:

−

s

Batch Equilibrium Test

C

leachate. Only samples with hydraulic conductivity values < 1 x 10-9 m/s were used. Samples of each laterite-slag mixture were compacted on the wet side of the optimum moisture content (OMC) and maximum dry density (MDD) using only ︵ the BSH compactive effort. Soil samples containing 0, 5, 10, and 15% slag by weight of dry soil were compacted at moisture contents that were greater than OMCs by 2.3, 4.6, 5 and 2.2%, respectively. The compacted samples were permeated with distilled water for a period of five days before the MSW leachate was introduced. Only short term tests were conducted on the four laterite-slag mixes for duration of one month each.

(2)

s

Where ︶ Cs Mass of solute adsorbed per mass of solid soil (μg/g) Co Initial concentration of leachate (mg/l) VVolume of leachate used (cm3) CEquilibrium concentration of solute (mg/l) Ms Mass of dry soil (g) The whole process was repeated twice with different initial concentrations. The equilibrium concentrations of some selected cations were determined from the solution phase using a ‘UNICAM 969’ Atomic Absorption Spectrometer. The pH meter model No. 7020 of Electronic Instrument Ltd with a Lutron pH electrode model PE-03 was also used in the study.

DISCUSSION OF RESULTS Column Test Most inactive soils (i.e., soils with low cation exchange capacities) whose clay minerals consist of illites, chlorites and kaolinite are relatively insensitive to leachate from MSW. The hydraulic conductivity will normally decrease, probably because of cation adsorption and double-layer expansion, and possibly because of bacterial clogging (Griffin et al., 1976). The result of the short-term column test is shown in Figure 1. Untreated soil, compacted at 2.3% on the wet side of

0% Slag Content(2.3% Moulding Water Content Relative to Optimum. )

1.00E-09

Hydraulic Conductivity(m/s).

5% Slag Content(4.6% Moulding Water Content Relative to Optimum). 10% Slag Content(5% Moulding Water Content Relative to Optimum). 15% Slag Content(2.2%Moulding Water Content relative to Optimum).

1.00E-10

1.00E-11 1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

Time(days).

FIGURE 1 Variation of hydraulic conductivity with time for different slag content using modified Proctor compactive effort with MSW leachate as the permeating fluid COMPATIBILITY AND ATTENUATIVE PROPERTIES OF BLAST FURNACE SLAG TREATED LATERITE

11

optimum had permeability that ranged from 7.31 x 10-11 to 8.48 x 10-11 m/s; for 5% slag treatment samples compacted at 4.6% wet of optimum had values that ranged from 3.26 x 1011 to 5.48 x 10-11 m/s. 10% slag treatment of samples compacted at 5% wet of optimum had values that ranged from 6.24 x 10-11 to 7.28 x 10-11 m/s. At 15% slag treatment, specimen compacted at 2.2% wet of optimum had permeability that ranged from 3.81 x 10-11 to 5.21x 10-11 m/s. From the above results, the MSW leachate caused a slight reduction in hydraulic conductivity of natural and 10% slag treated soils. Treatment with 5 and 15% slag produced hydraulic conductivity values that were relatively unstable initially suggesting rapid clogging of pores followed by stabilization. Generally, the MSW leachate did not affect the hydraulic conductivity results. The compacted samples were

able to minimize the flow of leachates through it, thus acting as a very good hydraulic barrier and hence preventing the flow of dangerous toxic chemicals through the medium. On completion of the permeation, the specimens were removed from the permeameter and examined. There was no significant difference in the strength and texture of the material from physical observation. Furthermore, it was observed that the material was able to maintain its strength and low hydraulic conductivity after prolong contact with the leachate hence satisfying the compatibility requirement.

Batch Equilibrium Test The test results were used to plot adsorption isotherms (see Figures 2 – 4) for three cations namely; chromium, cal-

Mass of Constituent Solute(ug/g)

950 900 850 800

0% Slag

750

5% Slag

700

10% Slag

650

15% Slag

600 550 500 0

10

20

30

40

50

Equilibrium Concentaration (mg/l)

FIGURE 2 Adsorption Isotherm for Calcium 83

Mass of Constituent Solute(ug/g)

78 73 68

0% Slag 5% Slag

63

10% Slag

58

15% Slag

53 48 43 -0.2

0

0.2

0.4

0.6

0.8

Equilibrium Concentration(mg/l)

FIGURE 3 Adsorption Isotherm for Iron

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13

Chromium was completely adsorbed from the solution for all slag treatments. Consequently, the plots overlap

Mass of Constituent Solute (µg/g)

12

11 0% Slag 5% Slag

10

10% Slag 15% Slag

9

8

7 -1

-0.5

0

0.5

1

1.5

2

Equilibrium Isotherm for Chromium (mg/l).

FIGURE 4 Adsorption Isotherm for Chromium

cium and iron which were selected to represent the dominant and critical contaminants present in the leachate. From Figures 3 and 4, the trends for Fe2+ and Cr2+ suggest that the mass of the contaminant removed from solution is proportional to the equilibrium concentration. This is in agreement with Rowe et al. (1995) who reported that linear isotherms are reasonable representations of the adsorption of contaminants found in leachate from municipal waste disposal sites where concentrations are relatively low. The average slope of the graph (kd) is given by the expression:

Kd =

Cs C

(3)

Where Cs = Mass of solute adsorbed per mass of solid soil (μg/g) C= Equilibrium concentration of solute (mg/l) The value obtained from eqn (3) is the distribution coefficient or partition coefficient which is a key parameter in the assessment of contaminant transport in barrier materials. The values for different slag treatments for the three contaminants observed are shown in Table 4. Furthermore, a dimensionaless product ρkd in accordance with Rowe et al. (1995) was used to measure the amount of adsorption which is likely to occur in the mixture where ρ is dry density of the laterite/laterite-slag mixture. These values are shown in Table 5 for the various slag treatments.

TABLE 4 Distribution coefficients for the selected cations at various slag contents Slag Content (%)

Partition Coefficient (kd) Calcium

Iron

Chromium

0

24.9

280.6

∞

5

68.2

263.6

∞

10

70.7

353.1

∞

15

87.9

368.5

∞


13

TABLE 5 ρkd for the selected cations at various slag contents Slag Content (%)

Partition Coefficient (kd) Calcium

Iron

Chromium

0

44.21

502.3

∞

5

123.4

477.1

∞

10

128.7

642.6

∞

15

161.7

1182.4

∞

rous hydroxide etc. At 100% BFS treatment there was an observed reduction in alkalinity between 15 and 100%. Probably there must have been some other intrinsic materials present in the slag that were responsible for this trend. The variations of percentage of cation removed from the MSW leachate solution as a function of slag content are shown in Figures 5 – 7. Approximately over 80% of calcium cation was removed from each of the three leachate solutions at 0% BFS treatment. This value was increased to over 93% removal at 5% BFS treatment. At 10% BFS treatment, there was a slight decrease to over 90% removal, while at 15% BFS treatment over 91% removal was achieved. On treatment with only BFS (i.e., 100%) over 66% of calcium ion was observed to have been removed from the leachate solution. This result shows that increment in BFS content generally aided the adsorption of calcium ion from the MSW leachate. At 100% BFS content, even though there was reduced adsorption, which could have been due to the initial high, concentra-

From Tables 4 and 5 it is seen that chromium cation with the greatest values of ρkd is most strongly sorbed from the leachate by the soil than iron and then calcium.

Effect of Slag Content Values summarized in Tables 4 and 5, show that adsorption of contaminants increased with higher slag content. The increment in BFS treatment up to 15% generally increased the alkalinity of the equilibrium solution. The pH increased from 8.1 to 8.8, from 8.2 to 8.8 and from 8.7 to 9.2 for leachate solutions 1, 2 and 3, respectively. The increases in pH were as a result of the increasing free lime present in the soil with higher BFS treatment. By raising the pH alkalinity, free lime reacted with the bi-carbonate alkalinity present and any carbon-dioxide, calcium, magnesium, and ferrous ions etc to form calcium carbonates, magnesium hydroxide, fer-

100 98 96

Percentage Removal

94 92

Calcium Iron

90

Chromium 88 86 84 82 80 0

10

20

30

40

50

60

70

80

90

100

Slag Content(%)

FIGURE 5 Variation of percentage removal of cations with slag content for leachate sample Solution 1

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100

Percentage Removal

95 90 85

Calcium

80

Iron Chromium

75 70 65 60 0

10

20

30

40

50

60

70

80

90

100

Slag Content(%)

FIGURE 6 Variation of removal of cations with slag content for leachate sample solution 2

100

Percentage Removal

95 90 85

Calcium

80

Iron Chromium

75 70 65 60 0

20

40

60

80

100

Slag Content(%)

FIGURE 7 Percentage Removal of Cations Versus Slag Content for Leachate Sample Solution 3

tion of calcium ions in the BFS, calcium ion was still removed. This removal of calcium from the solute as stated earlier is basically due to the formation of insoluble calcium carbonate in the solution. For the ferrous ions at 0% BFS treatment, approximately over 98% was removed from each of the three leachate solutions. These values were reduced slightly to over 97% at 5% BFS treatment. A further decline was recorded at 10% BFS treatment with over 90% adsorption being recorded. At 15% BFS treatment approximately over 98% adsorption was achieved, while at 100% BFS content over 96% removal was recorded. There was a slight decline in the percent removal with increment in BFS content up to 15% BFS treatment. It is

possible to attribute the occurrence to the high iron content originally present in laterite and BFS as well as the equilibrium change with the addition of higher dosage of BFS. Chromium was completely removed from the leachate by the different soil-BFS mixtures except for 100% BFS content, in the leachate of solution 1 where pH of 8.2 and over 98% removal was recorded. The average percent removal of calcium and iron cations for the three leachate solutions were (84 and 99.5), (94.3 and 98.2), (93.3 and 97.5), (94.2 and 98.1), respectively for 0, 5, 10 and 15% BFS treatment. In view of the above 5% BFS treatments gave the optimum mix performance.


15

CONCLUSION Batch equilibrium test results showed that for the three leachate sample solutions considered, a substantial reduction in the amount of multivalent cations contaminants present in the leachate was achieved. This removal was basically a function of the alkalinity of the sample and the ability of the free lime present in the BFS to raise the pH, which favored the precipitation of insoluble oxides and metal hydroxides. It was also noticed that with the use of 100% BFS dangerous contaminants were not leached into the solution. Furthermore, results of the column test indicated that the compacted laterite treated with up to 15% BFS was able to maintain the low hydraulic conductivity required for a good hydraulic barrier material after prolonged contact with the permeant fluid. In addition to the attenuation of some critical pollutants, the contamination of groundwater could be reduced. Compacted laterite treated with up to 15% blast furnace slag is suitable for lining as a hydraulic barrier for a MSW landfill to prevent the migration of leachate from contaminating groundwater.

REFERENCES Abichou, T., C.H Benson, and G.T. Edil, (2000). “Foundry green sand as hydraulic barriers 1aboratory studies.” Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Volume 126, No. 12, pp. 1174 –1183. Akintola, F. A. (1982). Geology and Geomorphology. Nigeria in Maps, R.M. Barbour, Editor, Hodder and Stoughton. London, U.K. Areola, O. (1982). Soils. Nigeria in Maps. R.M. Barbour, Editor Hodder and Stoughton, London, U.K Benson, C.H. (1999). Environmental Geotechnics in the New Millennium. Geotechnics for Developing Africa, Wardle, Blight & Fourier (Editor). Balkema, Rotterdam, pp. 9-22. Braja, D.M. (1998). Principles of Geotechnical Engineering 4th Edition. PWS {ITP). pp. 627-641. BS1377 (1990). ‘Methods of test for soils for civil engineering purposes’. British Standard Institute, London, United Kingdom. Daniel, D.E. (1993). Geotechnical Practice for Waste Disposal. London, Chapman and Hall. p. 683. Daniel, D.E. and Y.K. Wu, (1993). “Compacted clay liners

16

and covers for arid site.” J. Geotech. Engrg. ASCE. Volume 119, No. 2, pp. 223–237. Edil, B.T., L.K. Sandstorm, and P.M. Berthouex, (1992). “Interaction of inorganic leachate with compacted pozzolanic fly ash.” Journal of Geotechnical Engineering ASCE Volume 118, No. 9, pp. 1410-1430. Griffin, R.A., C. Keros, N.F. Shrimp, J.D. Steel, R.R. Ruch, W.A. White, G.M. Hughes, and R.H. Gilkeson, (1976). “Attenuation of pollutants in municipal landfill leachate by Clay Minerals: Part 1- Column Leaching and Field Verification, Environmental Geology Notes, Illinois State Geological Survey (78), November. Osinubi, K.J. (1998). “Permeability of lime treated lateritic soil.” Journal of Transportation Engineering Volume 124, No. 5. ASCE pp. 465-469. Osinubi, K.J. and C.M.O. Nwaiwu, (2002). “Compacted lateritic soils as hydraulic barrier in waste containment systems.” Proc. 4th Inter. Congress on Environmental Geotechnics (ICEG), Rio De Janeiro, Brazil, 11 – 15th August, pp. 225–230. Osinubi, K.J. and C.M.O. Nwaiwu, (2005). “Hydraulic conductivity of compacted lateritic soil.” J. Geotech. And Geoenviron. Engrg., ASCE, Volume 131, No. 8, pp. 1034–1041. Osinubi, K.J. and C.M.O. Nwaiwu, (2006). “Design of compacted lateritic soil liners and covers.” J. Geotech and Geoenviron. Engrg., ASCE, Volume 132, No. 2, pp. 203– 213. Osinubi, K.J. and C.M.O. Nwaiwu, (2008). “Desiccation – induced shrinkage in compacted lateritic soils.” Journal of Geotechnical and Geological Engineering, GEGE, Springer, Netherlands. ISSN 0960-3182 (Print), 15731529 (Online). Rowe, R.K., J.R., Booker, and R.M. Quigley, (1995). Clayey Barrier Systems for Waste Disposal Facilities. E&FN Spon (Chapman and Hall), London. Shackelford, C.D. (1994). “Hydrogeotechnics of clay liners for waste disposal.” Proceedings of the First International Conference on Tailings & Mine Wastes’94. Fort Collins, Colorado U. S.A. pp. 9-22. Stoffel, G., and R. Ham, (1979). Testing of High Ash Content Paper-mill Sludge for use in Sanitary Landfill Construction. Prepared for City Education Claire, Wis., Avers and Association Inc.


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APPLICATION OF IONIZING RADIATION FOR SLUDGE DISINFECTION AND ITS USE FOR IRRIGATION AND FERTILIZATION G. Shani Department of Biomedical Engineering, Ben Gurion University POB 653 Beer Sheva ISRAEL Email: [email protected]

S. Segman-Magidivich Department of Biothechnology, Ben Gurion University POB 653 Beer Sheva 84105 ISRAEL

ABSTRACT The sludge produced in the central, most populated area in Israel, is now dumped into the sea. Ionizing radiation was used to investigate the possibility of developing an industrial method for disinfection of the sludge, preparing it for use in farm land for irrigation and fertilization. A simple and inexpensive method for disinfection and preparing it for agricultural use is proposed. Sludge samples were irradiated with photons and electrons, it was found that relatively low radiation dose is enough to bring it to level A which is acceptable for the proposed use. Any dose of gamma radiation from a Co 60 source, from 0.2 Mrad and up, killed all coliforms in the sludge. Similar results were obtained for 3 MeV electrons. The irradiation stopped all biological activity in the sludge, therefore causing the solid part to separate from the water and sink. This stopped the gas (odor) emission from the sludge. The radiation did not have any effect on the heavy metals concentration in the sludge, but had some effect on the concentration of some of the light elements (some of it remained in the solid). The water, containing important minerals, was then tested for field irrigation. The product was tested for irrigation using droppers and found to be suitable. Keywords: Sludge, Irradiation, Coliform, Disinfection, Gases emission, Droppers

INTRODUCTION The non industrial sludge obtained from a populated area is the solid part of the municipal sewage, after separation of the solid and liquid (water) parts. It is mostly organic material in which some light elements such as nitrogen, phosphorus, potassium and others, and some heavy metals are present, in small quantities. The sludge also contains pathogens which must be removed if the sludge is to be used for fertilization and irrigation of farm land.

APPLICATION OF IONIZING RADIATION FOR SLUDGE DISINFECTION

The non industrial sewage of Tel Aviv (Israel) metropolitan area is treated in a plant operated by the SHAFDAN Co. After separation of the water from the solids, the solid sludge is mixed with pure water to a level of 1.5% solid. This liquid sludge, 15,000 m3 a day, is dumped into the Mediterranean. There are several stages of treatment in which different kinds of sludge are obtained.(1) The first (primary sludge) is obtained after simple separation of the liquid from the solid, it is done with minimal treatment of the solid. Higher level of treatment is biological treatment in which micro-organisms are used to disintegrate the organic material. Further treat17

ment includes chemical treatment in which the phosphorus is removed. Generally, the primary sludge is dumped into the sea or incinerated because it does not fit farming applications due to pathogens present. Incineration is very expensive, air polluting, and a wasteful treatment of this valuable resource. Dumping the sludge into the sea, besides being wasteful is illegal due to the Barcelona agreement of 1995, which prohibits such action, i.e. polluting the Mediterranean.(2) Another way of removing the sludge is burying it under ground. This must be done taking care not to pollute the neighboring areas and aquifers, with pathogens, heavy metals or other hazardous materials. It also releases methane and carbon dioxide to the air.(1) Other methods such as ozone treatment, u.v., composting, calcification and heat, are expensive and not always efficient. What seems to be the easiest, most effective and least expensive method of sludge treatment, preparing it for agricultural use, is disinfection by irradiation, namely shining an electron beam on a thin sludge layer. Some preliminary trials have been done in several countries, of irradiating sludge with an electron beam or gamma radiation. Sludge irradiation has been tried in several places. Generally it was an electron beam used, because, in order to disinfect large amount of sludge, the intensity of the gamma source (Co-60) required is prohibitive large. An electron beam is obtained from an accelerator. The penetration of the electrons into the sludge is a few mm up to a few cm, depending on the electron energy (accelerator’s voltage). The throughput depends also on the accelerator current (number of electrons emitted per second). The first sludge disinfection plant using gamma radiation from Co-60 was built in Germany in 1973, their throughput was 32,000 gal/day (3,4). In 1976 a plant was built in the US, using electrons to treat up to 105 gal/day (5). In Boston an electron accelerator was used to treat 18.5 m3/h (6). There were other small pilot plants but no full scale sludge disinfection plant is known to be in operation. This current research, although not on the scale of a sludge disinfection plant, seems to be the only thorough investigation of the effect of radiation on sludge. The method we have developed for sludge disinfection using radiation, is based on the fact that ionizing radiation is able to kill living cells by double strand breaking of the DNA. The radiation breaks the electron bond in more than one location along the DNA strands and therefore stops the cell division and multiplication. Both electrons and photons are capable of breaking the chemical bond between atoms in molecules. Bearing this in mind we applied the radiation to the sludge, intending to kill all coliform bacteria and all other microbes in the sludge. 100 cm3 samples of this liquid sludge were taken for treatment and analysis. For some purposes such as solid precipitation tests and other, 1 litter samples were taken. For testing irrigation with irradiated sludge, 240 liters sample was taken. Radiation dose is described by the energy absorbed in the material per unit mass. In the CGS system it is: 1 rad = 100 erg/ gram. A more modern unit in MKS system is: 1 Gy

18

(Gray) = 1 Joule per Kg. The ratio of the two units is therefore 1 Gy = 100 rad.

EXPERIMENTAL TECHNIQUE AND METHODS Samples weighing 100gr. in plastic test cups were irradiated with photons from a Co-60 source. Alternatively, the sludge was irradiated with electrons from a 3 MeV electron accelerator. In this case the samples were contained in flat trays, in which the sludge layer thickness was 12 mm due to the electrons range in the sludge. Radiation dose is measured in energy absorbed per unit mass. The units are: 1 rad = 100 erg/gram or 1Gy = 1 Joule/ Kg. 106 rads are 1 Megarad (Mrad), this is the unit we used in the present research. Gamma irradiation of the sludge samples was done at the Soreq Nuclear Center in Israel. This facility has a 7500 Ci of Co-60 gamma source. Its main use is medical equipment and food sterilization. The radiation dose to a sample going once through the gamma beam in the Co-60 irradiation facility, is 0.8 Mrad. (going once through means that the sample passed 6 times by the radiation source, each time another face of the box is facing the source). For 1.6 Mrad the sample went through the system twice. The sludge was contained in 100 cm3 plastic cups. Electron beam irradiation of the sludge was done using the Dynamitron accelerator at Golan Plastic Products (Shaar Hagolan, Israel). This is a 3MV 50mA accelerator used for electric cable and other plastic products irradiation. For the electron irradiation the samples were prepared in layers of thickness 1.2 cm since the range of the 3 MeV electrons in water is about 1.5 cm. Steel trays were used for the irradiation, the trays were open at the top so that the electron beam reached the sludge un-interrupted. The dose from the electron accelerator is very high so the sample went through the beam at a speed of 1 cm/sec. Tests done to the irradiated sludge are as follows. All tests were done at officially certified laboratories. 1. General counts of microbes: The general count of microbes was done using the pour plate method. This method is useful for small sample volumes (0.1-20 ml). Small colonies are formed, not overlapping each other. The tests were done immediately after irradiation. Samples are dissolved in hot water and then prepared for incubation. The last step is colonies counting. 2. Coliform counts: Coliforms are pathogens and are an indicator for the sludge contamination. The measurement was done by the Most Probable Number (MPN) method. The number of coliforms per 100 ml is counted. This is done following fermentation and gas emission observation. 3. Biochemical Oxygen Demand (BOD). This is an empirical method to test biological activity in the sludge. Disintegration of the organic materials, follow by oxidation of the inorganic elements. It gives an estimate of the amount of organic material in the sludge. The sample is incubated for 5 days and the dissolved oxygen is measured in the sample before and after the in-


VOLUME 35, NO. 1

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cubation. Chemical Oxygen Demand (COD). The sample is injected into boiling sulfuric acid, oxygen consumed is obtained by measuring the amount of acid left and the organic material oxidized. 5. Organic Materials Scanning. The organic materials content in the sludge was measured by gas chromatograph-mass spectrometer, comparing the results to Wiley 7 library (7) which has 350,000 spectra for volatile organic materials. 6. Heavy metals concentration in the sludge was measured by Induced Coupled Plasma (ICP). The sample is sprayed into a torch and turns into plasma at temperature of 6000-8000 deg. k. The atoms are ionized emitting typical spectrum. 7. PH was measured by measuring an electric potential. 8. Viruses were measured with polyethylene glycol (peg) treatment using the plaque forming assay method. Viruses were incubated on a single layer of cells. The viruses formed a plaque on the cells bedding and the number of plaque forming units (PFU) was counted. 9. Smell (odor) was measured using Gas Chromatograph- MS system analyzing samples of air taken from above the irradiated and un-irradiated sludge. 10. For droppers tests, 240 litters of sludge, irradiated to 0.8 Mrad were used to irrigate an experimental system with a number of different droppers. The number of droppers clogged as a function of time was counted.

low (0.2 Mrad) to very high (2.5 Mrad), killed all coliform bacteria. The number of coliforms in the un-irradiated sludge was in the range 106 -108 per cc. It was reduced by the radiation to below the laboratory detection limit i.e. 2 bacteria per cc. The measurements were done at Aminolab Laboratory in Nes-Tsiona, Israel. This is a demonstration of the ability of radiation as a tool for disinfection and sterilization. Similar results were obtained for general (other than coliform) bacteria removal from the sludge. The effect of gamma radiation on the general count of pathogens is shown in Table 2. At high dose level the number of bacteria was lower than the laboratory detection limit; 10 CFU/gr. At 0.8 Mrad, which we consider a standard dose level, the number was less than 1000 CFU/gr which is the permissible level as set by the environmental authority. Lower radiation levels, although they did not eliminate the bacteria, reduced its concentration by 4 orders of magnitude. Electron radiation yielded similar results as shown in Table 3. The electron radiation is less uniformly distributed in the sludge, therefore at low dose, not all coliforms were killed. As a result of the bacteria killing, the biological activity (oxygen demand) was reduced in the irradiated sludge. While chemical oxygen demand changed only a few percent, the biological oxygen demand was reduced considerably as shown in Table 4. In order for the sludge to be useful for agricultural purpose, it should be free of heavy metals. We investigated heavy metal content in the sludge before and after irradiation. The results are shown in Table 5. There is no effect of the radiation on metal content in the sludge, as expected, but it is important to note that the concentration of Cd and Hg, the two most hazardous metals in the sludge, is lower than the laboratory detection limit. Another important result of sludge irradiation is the separation of the solid and the liquid fractions of the sludge. We

4.

RESULTS Table 1 shows the effect of photons on coliform survival. It shows, that any level of radiation dose we used, from very

TABLE 1 Coliform concentration before and after gamma irradiation Coliform, control [MPN/gr]

Rad. dose [Mrad]

Coliform, irradiated [MPN/gr]

1.1x105 1.4x106 3.5x106

2.5