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Biosand Filtration of High Turbidity Water: Modified Filter Design and Safe Filtrate Storage

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Biosand Filtration of High Turbidity Water: Modified Filter Design and Safe Filtrate Storage BIOSAND FILTRATION OF HIGH TURBIDITY WATER: MODIFIED FILTER DESIGN AND SAFE FILTRATE STORAGE by Clair Collin B.E. (Chemical) University of Sydney Submitted to the Department of Civil and Environmental Engineering in partial fulfilment of the requirements for the degree of Master of Engineering in Civil and Environmental Engineering at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 2009 © 2009 Clair Collin. 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 in any medium now known or hereafter created. Signature of Author:_____________________________________________________________ Clair Collin Department of Civil and Environmental Engineering May 15, 2009 Certified by:___________________________________________________________________ Susan Murcott Senior Lecturer of Civil and Environmental Engineering Thesis Supervisor Accepted by:___________________________________________________________________ Daniele Veneziano Chairman, Departmental Committee for Graduate Students BIOSAND FILTRATION OF HIGH TURBIDITY WATER: MODIFIED FILTER DESIGN AND SAFE FILTRATE STORAGE by Clair Collin Submitted to the Department of Civil and Environmental Engineering on May 15, 2009 in Partial Fulfilment of the Requirements for the Degree of Master of Engineering in Civil and Environmental Engineering Abstract Unsafe drinking water is a major cause of water-related diseases that predominantly affect people living in developing countries. The most prevalent water-related disease is diarrhoea, estimated to kill 1.8 million children every year and the second largest cause of childhood death. Today there are many technologies available to treat unsafe water; however, most of these are suited for use with low turbidity source water. The treatment of high turbidity water (>50 NTU) is a challenge that was investigated in this research. Biosand filters, based on an intermittent slow sand filtration process, are an established household scale water treatment technology widely used in developing countries to treat low turbidity drinking water. This research investigates modifications to the biosand filter design to promote effective pathogen and turbidity reduction in high turbidity water. During field tests conducted in Ghana, a modified biosand filter with dual sand layers for added filtration achieved the greatest pathogen and turbidity removals. This design was then optimised through laboratory studies at MIT. The dual sand layer biosand filter supports straining and sedimentation of particulate matter from the feed water in a 3-7 cm deep raised upper sand layer prior to biological treatment and further filtration of the water in a 15-16 cm deep lower sand layer. Field testing of the dual sand layer biosand filter showed this filter achieved 59% turbidity reduction, 38% higher than an unmodified control filter; and at least 85% E. coli and 95% total coliform reductions, comparable in performance to unmodified control filters. Laboratory testing demonstrated minimum average reductions of 93% turbidity, 97% E. coli and 71% total coliform after filter maturation, comparable to unmodified control filter results. Dissolved oxygen concentration profiling in the laboratory indicated sufficient oxygen diffused through the upper sand layer to the lower sand layer to support biological activity in the lower sand layer. Recommendations for future studies and design optimisation have been made. Recontamination of treated water is also a major concern and it is recommended that the biosand filter be used only as required and filtrate collected in a dedicated container with tight fitting lid and tap dispenser. Thesis Supervisor: Susan Murcott Title: Senior Lecturer of Civil and Environmental Engineering Acknowledgements I would like to convey my thanks to those who have assisted me to undertake and complete this master’s thesis: To my supervisor, Susan Murcott, for all of her help and support throughout the year. Thank you for providing me with the opportunity to write this thesis and the opportunity to work on this thesis in Ghana. To Pure Home Water in Tamale, Ghana, for constructing the biosand filters at the PHW house, helping out with water collection and for supporting the field work conducted as part of this thesis. To the MIT Ghana team: Sara, Dave and Derek for good times in Ghana and throughout the project. To all of the MIT CEE 2009 class, Eric, Pete and Susan for making my time at MIT so much fun and run smoothly. I’d like to give special thanks to everyone who helped out with the filters in the MIT laboratory, your help and support is very much appreciated. Lastly, but certainly not least, thank you to my parents and family for all of their support over the year. Table of Contents Abbreviations ............................................................................................................................................11 1. Introduction ......................................................................................................................................13 1.1 Project methodology..................................................................................................................13 2 Safe water supply .............................................................................................................................15 2.1 Water supply in developing countries .......................................................................................15 2.2 Household water treatment and safe storage .............................................................................16 2.3 Water supply in Tamale, Ghana ................................................................................................17 3. Biosand filtration process ................................................................................................................20 3.1 Slow sand filtration process.......................................................................................................20 3.2 Biosand filtration system...........................................................................................................21 3.2.1 Biosand filtration process......................................................................................................22 3.2.2 Biosand filter design .............................................................................................................24 3.2.3 Biosand filter performance....................................................................................................27 3.3 Use of the biosand filtration system ..........................................................................................29 3.3.1 Global biosand filter use .......................................................................................................29 3.3.2 Biosand filter use in Tamale, Ghana .....................................................................................30 4. Household water storage .................................................................................................................32 4.1 Safe water storage......................................................................................................................32 4.2 Current household water storage practices................................................................................32 4.2.1 Household water storage in developing countries.................................................................32 4.2.2 Household water storage in northern Ghana .........................................................................33 5. Biosand filter design modification options.....................................................................................34 5.1 Modified filter design ................................................................................................................34 5.1.1 Filtration process...................................................................................................................36 5.1.2 Filter filling cycle..................................................................................................................38 5.2 Modified BSF set up and operation...........................................................................................39 5.2.1 Filter set up............................................................................................................................39 5.2.2 Filter design modifications....................................................................................................40 5.3 Field biosand filter tests and results ..........................................................................................43 5.3.1 Test procedures .....................................................................................................................43 5.3.2 Source (dugout) water quality...............................................................................................44 5.3.3 Control filter operation efficiency.........................................................................................47 5.3.4 Modified filter operation efficiency ......................................................................................54 5.4 Recommendations .....................................................................................................................62 6. Dual sand layer biosand filter design optimisation .......................................................................63
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