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BIOSAND HOUSEHOLD WATER FILTER PROJECT IN NEPAL
By Tse-Luen Lee B. A. Sc. Civil Engineering University of Toronto, 2000 SUBMITTED TO THE DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING IN CIVIL AND ENVIRONMENTAL ENGINEERING AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY JUNE 2001 © 2001 Tse-Luen Lee. All Rights Reserved The author hereby grants to MIT permission to reproduce and to distribute publicly paper and electronic copies of this thesis document in whole or in part.

Signature of Author: Department of Civil and Environmental Engineering May 11, 2001 Certified by: Susan E. Murcott Lecturer of Civil and Environmental Engineering Thesis Supervisor Accepted by: Oral Buyukozturk Chairman, Committee for Graduate Students

1

BioSand Household Water Filter in Nepal

Abstract

BIOSAND HOUSEHOLD WATER FILTER PROJECT IN NEPAL by Tse-Luen Lee Submitted to the Department of Civil and Environmental Engineering on May 11, 2001 in partial fulfillment of the requirements for the degree of Master of Engineering in Civil and Environmental Engineering Abstract This purpose of this study was to investigate the effectiveness and the performance of the BioSand filter in Nepal. To achieve this, the author undertook a field trip to Nepal in January, 2001. The trip was made possible with generous support provided by the Department of Civil and Environmental Engineering of MIT. The author spent 3 weeks in Nepal - 4 days in the vicinity of Tansen in the central Palpa region and 9 days in the Nawalparasi district in the Terai collecting water samples. Turbidity measurements were taken and presence/absence tests for total coliform, E.coli and H2S producing bacteria were carried out. At MIT, membrane filtration tests were also carried out. This study found that while filtered water from the BSFs in Nepal has low turbidity and flows at a sufficiently high rate, only 9 out of 12 properly functioning BSFs removed total coliform and 10 out of 12 properly functioning BSFs removed E. coli. Membrane filtration tests carried out in MIT indicate that the BSF technology is effective at removal of total coliform with an average removal of 99.5% of total coliform in the source water. Based on the effectiveness of the BSF in removing microbial contamination, the author recommends the BSF technology to be adopted on a large scale in Nepal, but only if it is coupled with a monitoring plan to ensure correct construction, operation and maintenance procedures are followed. A monitoring plan is necessary to reduce the fraction of BioSand filters that were not working properly.

Supervised by: Susan E. Murcott Title: Lecturer of Civil and Environmental Engineering 2

ACKNOWLEDGMENTS

Thanks to all the people who have helped me through my graduate career, including the following: Thesis supervisor, Susan Murcott, who offered invaluable advice and guidance all the way from the start of the project till the day this thesis was handed in, and who took time to meticulously read through numerous drafts; Faculty advisor, Dr. Eric Adams, who gave me the flexibility to choose the subjects that stimulate my learning in this institute; The Nepal group a.k.a. Naiad Engineering for making my stay in Nepal unforgettable: Nat, Meghan, Tim, and Jessie; Friends who kept me sane and made living in Cambridge enjoyable: Kirill, Fiona, Shan, Thor, Thomas Moore, Takashi, Shao-Hwei, Anthony, Wesley, Woody, Romeo, Win, William, Nadine, Tee and many more; Friends we met in Nepal: Kaanchu, Tili and others at the luxurious Hotel White Lake in Tansen; Friends back home in Singapore whom I have temporarily ignored while working on this thesis, for their kind understanding; Xin-Yun, for her support during the stressful times; Most importantly, to my parents and family, who have always been behind me.

3

This thesis is dedicated to the many kind people Nat and I met in Nepal, including the young boy who sat in our jeep as we went around Tansen in search for the next BioSand filter. I sincerely hope that this thesis will, in some way, contribute to the betterment of their lives.

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BioSand Household Water Filter Project in Nepal

Table of Contents

TABLE OF CONTENTS

1

INTRODUCTION........................................................................................................11 1.1 Purpose of Study ............................................................................................... 12 1.2 A Brief History of Slow Sand Filters................................................................ 13 1.3 History of The BioSand Filter........................................................................... 17

2

THEORY.......................................................................................................................22 2.1 Contrast Between Slow Sand Filter and Rapid Sand Filter .............................. 22 2.2 Contrast Between BioSand Filter and Slow Sand Filter................................... 24 2.3 The Schmutzdecke ............................................................................................ 25 2.4 Biological Removal Mechanisms ..................................................................... 25 2.4.1 2.4.2 Metabolic breakdown........................................................................ 26 Bacterivory........................................................................................ 26

2.5 Physical Removal Mechanisms ........................................................................ 27 2.5.1 2.5.2 Surface straining ............................................................................... 27 Inter-particle Attraction .................................................................... 28

2.6 Filter Ripening .................................................................................................. 29 2.7 Previous BioSand Filter Results ....................................................................... 29 3 ELEMENTS OF A BIOSAND FILTER...................................................................31 3.1 Concrete Body/Shell ......................................................................................... 32 3.1.1 3.1.2 3.1.3 3.1.4 3.1.5 Riser pipe assembly .......................................................................... 34 Preparation of mold........................................................................... 34 Mixing concrete ................................................................................ 36 Concrete Pour.................................................................................... 38 De-molding ....................................................................................... 39

3.2 Diffuser Plate .................................................................................................... 41 3.2.1 3.2.2 Materials ........................................................................................... 41 Design ............................................................................................... 43

3.3 Sand and Gravel................................................................................................ 46 3.3.1 Requirements .................................................................................... 46 5

BioSand Household Water Filter Project in Nepal

Table of Contents

3.3.2

Preparation ........................................................................................ 47

3.4 Lid ..................................................................................................................... 49 4 EVALUATION METHODOLOGY OF BIOSAND FILTER...............................50 4.1 Microbial Tests ................................................................................................. 50 4.2 Turbidity ........................................................................................................... 55 4.3 Flow Rate .......................................................................................................... 56 4.4 Physical Observations....................................................................................... 58 4.4.1 4.4.2 4.4.3 4.4.4 5 Spouts Attachment ............................................................................ 58 Diffuser Plate .................................................................................... 59 Sand Layer ........................................................................................ 59 Cracks in the Concrete Body ............................................................ 59

RESULTS AND DISCUSSION..................................................................................60 5.1 Microbial Tests Results..................................................................................... 60 5.2 Turbidity Results............................................................................................... 62 5.3 Flow Rate Results ............................................................................................. 64 5.4 Physical Observation Results............................................................................ 65 5.4.1 5.4.2 5.4.3 5.4.4 Spouts Attachment ............................................................................ 65 Diffuser Plate .................................................................................... 67 Sand Layer ........................................................................................ 68 Cracks in Concrete Body .................................................................. 70

5.5 Correlations....................................................................................................... 71 5.6 Drawbacks......................................................................................................... 71 6 EXPERIMENTS CARRIED OUT AT MIT ............................................................73 6.1 Membrane Filtration ......................................................................................... 73 6.2 pH...................................................................................................................... 75 7 SUMMARY AND CONCLUSIONS .........................................................................76

REFERENCES......................................................................................................................78 APPENDIX A: LIST OF EQUIPMENT USED DURING FIELD TRIP IN NEPAL.82 APPENDIX B: TURBIDITY MEASUREMENT STATISTICS ...................................83

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BioSand Household Water Filter Project in Nepal

Table of Contents

APPENDIX C: FIELD TEST RESULTS..........................................................................89

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BioSand Household Water Filter Project in Nepal

List of Figures

LIST OF FIGURES Number Page FIGURE 1: ARJUN G.C. OF HOPE FOR THE NATION (LEFT), BIOSAND FILTER (MIDDLE) AND A
TECHNICIAN (RIGHT) IN NEPAL.

12

FIGURE 2: A SCHEMATIC OF THE UNICEF FILTER, AN UPFLOW HOUSEHOLD SLOW SAND
FILTER (FROM [GUPTA AND CHAUDHURI, 1992])

21 31 33

FIGURE 3: CROSS-SECTION OF A CONCRETE BIOSAND FILTER FIGURE 4: PLASTIC BSF FROM DAVNOR WATER TREATMENT TECHNOLOGIES LTD. FIGURE 5: CONCRETE BSF MADE FROM SHOP DRAWINGS PROVIDED BY DAVNOR WATER TREATMENT TECHNOLOGIES LTD. FIGURE 6: CONCRETE BSF WITH SQUARE BASE. FIGURE 7: CONCRETE BSF WITH ROUND BASE. FIGURE 8: PVC PIPE DIMENSIONS (NOT TO SCALE)

33 33 33 34

FIGURE 9: UNASSEMBLED STEEL MOLD – INNER MOLD (LEFT) AND OUTER MOLD (RIGHT). 36 FIGURE 10: STEEL MOLD FOR CONCRETE BSF SHELL (ASSEMBLED) FIGURE 11: CONCRETE MIXING I FIGURE 12: CONCRETE MIXING II FIGURE 13: TAMPING THE CONCRETE MIXTURE WITH A WOODEN ROD FIGURE 14: A TYPICAL METAL DIFFUSER PLATE WITH HANDLE IN NEPAL FIGURE 15: LOW DENSITY POLYETHYLENE PLASTIC (LDPE) DIFFUSER PLATE IN NEPAL FIGURE 16: METAL DIFFUSER BASIN I FIGURE 17: METAL DIFFUSER BASIN II FIGURE 18: A METAL POT USED AS A DIFFUSER BASIN IN A ROUND BSF FIGURE 19: A SCREW TO AID LIFTING THE DIFFUSER PLATE OUT OF THE BSF FIGURE 20: SIEVES FOR SAND AND GRAVEL FIGURE 21: P/A BROTH IN GLASS AMPULE. FIGURE 22: PATHOSCREEN™ MEDIUM PILLOWS. FIGURE 23: WATERCHECK™ TEST KIT FIGURE 24: HACH POCKET TURBIDIMETER FIGURE 25: MEASURING FLOW RATE FIGURE 26: BSF MICROBIAL RESULTS 36 37 38 39 42 43 44 45 45 46 49 52 52 53 56 57 61

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BioSand Household Water Filter Project in Nepal

List of Figures

FIGURE 27: DISTRIBUTION OF OBSERVED PROBLEMS WITH THE BSF FIGURE 28: TURBIDITY REMOVAL RESULTS. FIGURE 29: DISTRIBUTION OF PERCENTAGE TURBIDITY REMOVAL FOR FILTERS THAT WERE
WORKING PROPERLY.

61 63

64 65 66 66 67 68 69 69 70

FIGURE 30: DISTRIBUTION OF FLOW RATE FIGURE 31: INTERMEDIATE STORAGE CONTAINER FOR FILTERED WATER FIGURE 32: SPOUT IS NOT PLUGGED, ALLOWING CONTINUOUS FLOW. FIGURE 33: A FLOATING LDPE DIFFUSER PLATE. FIGURE 34: DISTURBED TOP LAYER OF FINE SAND. FIGURE 35: WATER LEVEL AT REST BELOW TOP LAYER OF FINE SAND. FIGURE 36: WATER LEVEL AT REST MORE THAN 5CM ABOVE THE TOPMOST SAND LEVEL. FIGURE 37: A CRACKED BSF THAT WAS MENDED BY A TECHNICIAN FIGURE 38: MF RESULTS - CHARLES RIVER WATER BEFORE FILTRATION (LEFT); AFTER
FILTRATION (RIGHT)

75

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BioSand Household Water Filter Project in Nepal

List of Tables

LIST OF TABLES

Number Page TABLE 1: TYPICAL TREATMENT PERFORMANCE OF CONVENTIONAL SLOW SAND FILTERS (COLLINS, 1998) TABLE 2: TYPICAL DIFFERENCES BETWEEN SLOW SAND FILTER AND RAPID SAND FILTER TABLE 3: DIFFERENCES BETWEEN BSF AND SLOW SAND FILTER TABLE 4: CONTAMINANT REMOVAL EFFICIENCY OF BIOSAND FILTER TABLE 5: BSF DESIGN PARAMETERS TABLE 6: NUMBER OF SAMPLES ANALYZED TABLE 7: SUMMARY OF CORRELATIONS TABLE 8: MEMBRANE FILTRATION RESULTS TABLE 9: PH VALUES OF WATER BEFORE AND AFTER FILTRATION 17 23 25 30 32 60 71 74 75

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BioSand Household Water Filter Project in Nepal

Introduction

1

INTRODUCTION

The BioSand Filter (BSF) is a household-scale slow sand filter developed by Dr. David Manz of the University of Calgary, Canada. This filter has been tested by several government, research and health institutions as well as NGO agencies in Canada, Vietnam, Brazil, Nicaragua, and Bangladesh. A Nepali NGO, Hope For The Nation, has been promoting the filter in the central foothill region of Palpa and the southern flatland region of Nawalparasi. The filter was formerly called the Canadian Water Filter (CWF). The new legal and registered name of is “The BioSand Filter Using the Award-Winning CWF Design” or its short form, “BioSand Filter” (Ritenour, 1998). The filter was also given other names describing its intermittent process such as “Intermittent Operated Slow Sand Filter” (IOSSF) and “Manz Intermittent Slow Sand Filter” (MISSF) (Palmeteer et al., 1997). The filter was also called the “BioSand Water Filter” (BWF) in Cambodia and “Guras Water Filter” in Nepal after the national flower (Chettri, 2001b). Other names based on its physical appearance include “Barrel Filter” and “Cement Filter” (IDRC Module 5, 1998). In this thesis, the term “BioSand Filter” or BSF will be used.

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BioSand Household Water Filter Project in Nepal

Introduction

Figure 1: Arjun G.C. of Hope For the Nation (left), BioSand Filter (middle) and a technician (right) in Nepal.

1.1

PURPOSE OF STUDY

This purpose of this study was to investigate the effectiveness and the performance of the BioSand Filter in Nepal. To achieve this, the author undertook a field trip to Nepal in January, 2001. The trip was made possible with generous support provided by the Department of Civil and Environmental Engineering of MIT. The author spent 3 weeks in Nepal, 4 days in the vicinity of Tansen in the central Palpa region and 9 days in the Nawalparasi district in the Terai investigating the BSF pilot project in Nepal. The remainder of the time was spent in Kathmandu. The Palpa region is in the foothills of the Himalayas and is a highly mountainous terrain. The pilot project was started in these 2 locations in Nepal about 2 years ago by a local NGO; Hope for the Nations (HFTN), Nepal.

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BioSand Household Water Filter Project in Nepal

Introduction

Currently, there are a total of 15 such filters in Tansen (Chettri, 2001a) and more than 100 in Nawalparasi (Magar, 2001) and the numbers are increasing. 1.2 A BRIEF HISTORY OF SLOW SAND FILTERS

Slow sand filters have filtration rates of 0.1m/h as opposed to rapid sand filters that have filtration rates of 10m/h (Haarhoff and Cleasby, 1991). Slow sand filters have been used to deliver potable water to the public since the early nineteenth century. The first recognized use of slow sand filtration for water supply was in Paisley, Scotland in 1804 when John Gibbs set up an experimental slow sand filter to supply his bleachery and sold excess treated water to the townspeople (Baker, 1981). By 1852 the health advantages of filtered water were so evident that the Metropolis Water Act required all Thames River water to be filtered before use by Londoners. The 1854 Broad Street cholera outbreak further reinforced the need to filter public supply. Since then slow sand filters have been adopted by many major European cities including London, Amsterdam and Zurich for potable water treatment and are still in use today as a secondary filtration step (Baker, 1981). The development of slow sand filtration in the United States, in contrast with the European experience, was slow (Logsdon and Fox, 1988). The year 1832 saw the first slow sand filtration plant in the United States built in Richmond, Va. In 1833, the plant had 295 water subscribers. The next US plant to open was in Elizabeth, N.J., in 1855. Slow sand filters were introduced in Massachusetts in the mid-1870s. Sand filters and other treatments were primarily designed to improve the aesthetic quality of water. It took major developments in bacteriology during the 1870s and 1880s to demonstrate that microorganisms that exist in water supplies can cause human and animal diseases. This led to the realization that water treatment could help prevent disease. Robert Koch, the German physician and microbiologist who postulated the germ

13

BioSand Household Water Filter Project in Nepal

Introduction

theory of disease, and the Scottish surgeon Joseph Lister were major players in this work. By the 1890s filtration was gaining recognition for not only straining out undesirable particles, but also removing deadly germs. Towns and cities along the Hudson River in New York State that used filtration for water purification had fewer outbreaks and incidences of typhoid than communities that did not filter the Hudson River water. Installation of both slow rate and rapid rate filtration plants took place in the 1890’s and 1900’s, but shortly thereafter, rapid filters gained popularity. By 1940, the United States had about 100 slow sand filtration plants, whereas nearly 2300 rapid rate plants had been constructed (Baker, 1981). A number of factors may have been involved in this shift in interest. River water that was muddied by runoff from clay soils could be treated successfully with properly designed and operated rapid rate filtration plants. Such waters, on the other hand, clogged slow sand filters. Additional advantages for medium-sized and large water utilities were the reduced land requirements in populated areas and the lower labor requirements in operations and maintenance for rapid filters compared to slow filters (Logsdon, 1991). In the late 1970’s and early 1980’s, the potential for application of slow sand filtration in the United States was reconsidered. Increase in outbreaks of waterborne giardiasis in the USA throughout the 1970’s played an important role in the renewed interest in slow filters. Most giardiasis outbreaks had occurred in places where the raw water was of low turbidity and therefore appeared suitable for treatment by slow sand filtration. Although there was plenty of evidence that slow sand filters remove bacterial and viral contaminants, there was no data to verify that slow filters remove Giardia cysts. As a result, the U.S. EPA sponsored several

14

BioSand Household Water Filter Project in Nepal

Introduction

research projects in the early 1980’s to determine the capabilities of slow sand filtration, which includes controlling Giardia cysts in surface waters (Graham, 1988). The success of these projects led to a program of research in slow sand filtration at institutions such as Iowa State University, Ames; Colorado State University, Fort Collins; Syracuse University, Syracuse; Utah State University, Logan; University of Washington,

Seattle; and University of New Hampshire, Durham (Weber-Shirk and Dick, 1997). There was also evaluation of slow filters in the state of New York, and the province of British Columbia in Canada. Limitations for use by large water utilities were recognized, but the process was considered for use by small systems, where requirements for land and labor would not be a serious drawback. In 1980, the United Nations declared the beginning of the International Drinking Water Supply and Sanitation Decade. Provided that water demands were not too high and that sufficient land was available, the only water treatment considered reliable and recommended for developing nations was slow sand filtration (Graham, 1988). In 1985, the Surface Water Treatment Rule (SWTR) was passed in the United States; this regulation requires filtration and disinfection as minimum treatment for surface water. Although only about 50 slow sand filtration plants were in operation in the United States in 1991 (Schuler et al., 1991), more plants may be built as small communities (as well as places like campgrounds, adult and youth camps, and rural conference centers) comply with the SWTR. Slow sand filters in the United States are found primarily in smaller communities with fewer than 10,000 people, 45% of which serve fewer than 1,000 people (Sims and Slezak, 1991).

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BioSand Household Water Filter Project in Nepal

Introduction

Slow sand filtration has also been found to be a highly efficient means of removing the protozoan parasite, Cryptosporidium parvum, from water (Timms et al., 1994). In recent years, this parasite has been recognized as a significant threat to potable supplies. The resistant stage – an oocyst – is relatively untouched by chlorine disinfection. In experiments performed by Thames Water Utilities, United Kingdom, slow sand filters reduced concentrations of Cryptosporidium oocysts by 99.997% from 4000/L to 0/8L (Timms et al., 1994). Another study in British Columbia by Fogel contradicts the aforementioned study (Fogel et al., 1993). Fogel found removal efficiencies of 48%; this figure is significantly different from the 100% removals from previous literature. However, a point to note concerning the British Columbia filters is that they were operating well out of the range of the recommended design limits for the uniformity coefficient1 at 3.5 (Fogel et al., 1993). Furthermore, temperature can adversely affect the performance of a slow sand filter; the British Columbia filters were operating at extremely low temperatures of less than 1°C (Fogel et al., 1993). Overall, the literature supports data that strongly suggests slow sand filtration is a viable option for Cryptosporidia removals. Although slow sand filtration often has been replaced by faster and more advanced high-rate filtration methods, its low cost, ease of operation, minimal maintenance requirements, and success in removing pathogenic microorganisms make slow sand filtration an attractive option for rural communities and developing nations (Collins et al., 1992). The following table shows the typical treatment performance of conventional slow sand filters.

1

For a discussion of uniformity coefficient, see section 3.3.1.

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BioSand Household Water Filter Project in Nepal

Introduction

Table 1: Typical treatment performance of conventional slow sand filters (Collins, 1998) Parameters Turbidity Coliforms Enteric Viruses Giardia Cysts Cryptosporidium Oocysts Dissolved Organic Carbon Biodegradable Dissolved Organic Carbon Trihalomethane Precursors Zn, Cu, Cd, Pb Fe, Mn As Values 4 log units 2µm) pathogenic protozoa such as Giardia lamblia and Cryptosporidium oocysts (Weber-Shirk and Dick, 1998). 2.5 PHYSICAL REMOVAL MECHANISMS

Two proposed physical removal mechanisms in a slow sand filter are surface straining and interparticle attraction (or attachment). An experimental-based research to study the physicalchemical mechanisms responsible for particle removal in slow sand filters was recently conducted in Cornell University (Weber-Shirk and Dick, 1997b). Results of the study suggest that straining is the “dominant mechanism of particle removal in slow sand filter cakes where the pore sizes are the smallest”, while “inter-particle attraction is primarily responsible for particle removal within the slow sand filter beds”. 2.5.1 Surface straining

Surface straining is the “most obvious capture mechanism for particles too large to pass through the interstices between the grains” (Haarhoff and Cleasby, 1991). A tightly packed bed of spherical grains could capture particles about 15% of the grain diameter (Huisman and

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BioSand Household Water Filter Project in Nepal

Theory

Wood, 1974). A clean sand of 200µm effective size is expected to capture particles of about 30µm in size by surface straining. This is substantially larger than many particles to be removed from surface water such as cysts (1-20µm), bacteria (0.1 to 10µm), viruses (0.01 to 0.1µm), and colloidal particles (0.001 to 1µm) (Haarhoff and Cleasby, 1991). However, larger particles (such as algae and vegetative debris) can be captured by surface straining. As these particles are captured at the surface, the surface pore openings become smaller and surface straining is enhanced, allowing capture of much smaller particles as the filter cake develops. The filter cake, composed of living organisms and other debris from the water, ultimately becomes an effective filtering medium (Cleasby et al., 1984). The filter cake has been described as an extension of the filter bed containing the smallest interstices to achieve the most effective straining (Weber-Shirk and Dick, 1997b). Surface straining was also described as a “sieve effect which is amplified by deposit on the filters’ surface of a layer made up of clay, organic matter, algae, and macro- and microorganisms” (Barbier, 1992). 2.5.2 Inter-particle Attraction

Particle attachment to previously removed particles resulting from interparticle attraction can occur in both the filter cake and in the underlying filter bed. Prior to attachment, the particles are transported along flow streamlines unless they are captured by interception or transported across the streamlines causing them to reach a grain surface. If the conditions at the grain surface provide favorable particle-to-grain interaction, attachment will occur. The efficiency of particle attachment is related to the net attractive force between the medium (consisting of sand and previously removed particles) and suspended particles. Viscous forces hinder attachment or cause detachment by shearing particles from the medium. Shearing forces are expected to be the highest in the filter cake, because shearing forces increase as the

28

BioSand Household Water Filter Project in Nepal

Theory

pore size of the medium decreases. Thus, net attachment of particles to previously removed particles because of interparticle attraction may be less efficient in the filter cake than in the underlying filter bed (Weber-Shirk and Dick, 1997). 2.6 FILTER RIPENING

Slow sand filters require a long ripening period at the beginning of each filter run. This is to allow the biology in the sand layer to mature. Filter ripening is a complex process that involves both biological and physical mechanisms. As filtration progresses, biological growth consisting of algae, bacteria, and zooplankton occurs within the sand bed and gravel layer (Bellamy et al., 1985; Graham 1988). During the ripening period, the filter does not effectively remove bacteria. Bellamy et al. (1985) concluded that a new sand bed will remove 85% of the coliform bacteria in the influent. As the sand bed matures biologically, the percent removal improves to more than 99% for coliform bacteria. The ripening period for the BSF is usually one to two weeks. However, for slow sand filters, the ripening process can be accelerated by using synthetic polymers (Jellison et al., 2000) to agglomerate particles in the raw water and hasten their removal at the filter surface so as to quickly develop the filter cake. However, the addition of chemicals to the BSF would complicate the originally simple filtration process. 2.7 PREVIOUS BIOSAND FILTER RESULTS

According to the Davnor website, the BSF is effective in removing iron, manganese, sulfur, low concentrations of gases, bacteria, viruses, waterborne parasites, algae, silt and clay (Davnor Water Treatment Technologies Ltd.). The BSF has successfully treated water ranging in temperature from 1o to 45oC. Table 4 summarizes the contaminant removal performance of the BioSand Filter in other countries.

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BioSand Household Water Filter Project in Nepal

Theory

Table 4: Contaminant Removal Efficiency of BioSand Filter Country Nicaragua Canada Canada Organization Instituto Nicaraguense de Acueductos y Alcantarillados University of Calgary Date 7/1993 11/1995 Contaminant Coliform Bacteria Fecal Coliform Turbidity Heterotrophic Bacteria Giardia Cysts Organic and Inorganic Toxicants Total Suspended Solids Total Organic Carbon Chemical Oxygen Demand Reported Removal (%) 99.1-99.6 99.1-99.7 94.1-96.1 65 – 90+ (1) 99.99 50-99.99 100 14-18 100 95.8 (2) 99.7 (3) 99.8 (4) 99.8 (4) 60-100 (4) 74.3-100 (4) 91.5 85.7

National Water Research 11/1996 Institute

Vietnam Brazil Bangladesh

Samaritan’s Purse Samaritan’s Purse Proshika Manobik Unnayan Kendra

11/1998 11/1998 8/1999

Canada

Montana Native Reserve

E.coli Bacteria Fecal Coliform Total Coliforms (river water) Fecal Coliforms (river water) Total Coliform (three households) Fecal Coliforms (three households) Date not Iron available Turbidity

(1) Damage of 10 to 15 % of schmutzdecke discovered at the end of test period (2) Average of 32 households (3) Average of 21 households (4) Raw and treated water not tested on the same days. All samples show zero levels of fecal coliform and minimal levels of total coliform on day of final test (Source: Davnor Water Treatment Technologies Ltd.)

30

BioSand Household Water Filter Project in Nepal

Elements of a BioSand Filter

3

ELEMENTS OF A BIOSAND FILTER

Cross-section of a concrete BioSand Filter is shown in Figure 3. A BSF has several main components:- body/shell, diffuser plate, sand/gravel, and lid. Each of these components will be described in detail in this section. Figure 3: Cross-section of a concrete BioSand Filter

31

BioSand Household Water Filter Project in Nepal

Elements of a BioSand Filter

Table 5: BSF Design Parameters Design Parameter Fine Sand Size Coarse Sand Size Underdrain Gravel Size Surface Area of Sand Initial Flow Rate BSF Size Value

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