INTERMITTENT SLOW SAND FILTERS: IMPROVING THEIR DESIGN FOR DEVELOPING WORLD APPLICATIONS by Magdalena Pachocka A thesis submitted to the Faculty of the University of Delaware in partial fulfillment of the requirements for the degree of Master of Civil Engineering Summer 2010 Copyright 2010 Magdalena Pachocka All Rights Reserved INTERMITTENT SLOW SAND FILTERS: IMPROVING THEIR DESIGN FOR DEVELOPING WORLD APPLICATIONS by Magdalena Pachocka Approved: __________________________________________________________ Steven K. Dentel, Ph.D., P.E., D.E.E. Professor in charge of thesis on behalf of the Advisory Committee Approved: __________________________________________________________ Harry W. (Tripp) Shenton III, Ph.D. Chair of the Department of Civil and Environmental Engineering Approved: __________________________________________________________ Michael Chajes, Ph.D. Dean of the College of Engineering Approved: __________________________________________________________ Debra Hess Norris, M.S. Vice Provost for Graduate and Professional Education For my Dad iii ACKNOWLEDGMENTS The completion of this thesis was only possible thanks to a great deal of support that I have received from other people. First and foremost, I would like to thank my advisor, Dr. Steven Dentel. Thanks to Dr. Dentel’s great intellect and knowledge I have learnt so much over the course of this project. Dr. Dentel always put an emphasis on the student’s strengths, even when providing a critique. I am deeply grateful for his moral support. Secondly, I would like to express my deep gratitude to Dr. Diane Herson who allowed me to work in her microbiology laboratory. I would not be able to conduct my research if not for her kindness. I know that analyzing my samples often required a lot of bench space, and I realize that it could have been difficult to accommodate one more student in the laboratory. I also would like to thank Diane for all the academic and moral support that she was always ready to provide. I also would like to express my gratitude to Dr. Pei Chiu who has been also very supportive and interested in my research over the whole course of this study. We had many interesting talks which benefited my engineering knowledge substantially. Furthermore, Dr. Chiu provided many comments and suggestions on experiments with zero-valent iron, and his input is greatly appreciated. I also would like to thank Dr. Paul Imhoff and Dr. Jeff Furhmann who were always willing to provide help and advice whenever asked. Dr. Furhmann should be also acknowledged for providing his laboratory equipment for taking microscope pictures of the schmutzdecke and also for taking some of the pictures himself. iv My special thanks go to Rovshan Mahmudov who was the one who helped me gather all the needed equipment and setup my experiments at the beginning of my research. My thanks extend to Michael Davidson and Douglas Baker. Doug built all my filtration columns while Michael provided prompt assistance with laboratory equipment. They both were also very helpful with carrying heavy creek water jugs into the laboratory. I also would like to thank all the other staff members in CEE department and my lab, class and office mates. It is not possible to mention you all but I say thank you for all your help and friendship. I would like to acknowledge the Center for International Studies for funding this work; Wilmington Wastewater Treatment Plant and Newark Treatment Plant for allowing me to collect samples at their facilities; Unimin Corporation and Ricci Sand for providing free of charge sand and gravel for my experiment. I would like to thank my dear friends here in the United States: the Sawicki and Wirth families. Their friendship and assistance throughout these years have been very important to me. Especially, I would like to thank Lee Wirth and Deborah Barr. Finally, I want to express my gratitude to friends in Poland. Especially, I would like to thank Dr. Andrzej Czaja and my bother in law Dr. Pawel Daszkiewicz. Last but not least, I would like to thank my family: my mom, my sisters Asia and Marta, and my brother Wojtek for their continuous love and support. I love you all. Dad, I hope that you would be proud of me. v TABLE OF CONTENTS LIST OF TABLES ........................................................................................................ ix LIST OF FIGURES ........................................................................................................ x INTRODUCTION .......................................................................................................... 1 1.1 STATEMENT OF THE PROBLEM ......................................................... 1 1.2 OBJECTIVES AND OVERVIEW OF THE STUDY .............................. 2 BACKGROUND ............................................................................................................ 3 2.1 CONTINUOUSLY OPERATED SLOW SAND FILTER ....................... 3 2.1.1 History ........................................................................................... 3 2.1.2 Design and operation ..................................................................... 5 2.1.3 Water purification efficiency ......................................................... 7 2.2 INTERMITTENTLY OPERATED SLOW SAND FILTER .................. 10 2.2.1 Design .......................................................................................... 10 2.2.2 Operation ..................................................................................... 11 2.2.4 Water treatment for developing countries ................................... 13 2.2.3 Water purification efficiency ....................................................... 13 2.3 MECHANISMS OF REMOVAL IN SLOW SAND FILTRATION ...... 14 2.3.1 Biological removal mechanisms ................................................. 14 2.3.2 Physical removal mechanisms ..................................................... 16 2.3.3 Attachment mechanisms .............................................................. 19 MECHANISMS OF PATHOGEN REMOVAL IN INTERMITTENT SLOW SAND FILTRATION ....................................................................................... 21 3.1 INTRODUCTION ................................................................................... 21 3.2 MATERIALS AND METHODS ............................................................ 26 3.2.1 Sand and gravel ........................................................................... 26 3.2.3 Water quality ............................................................................... 27 3.2.3 Experimental challenge microorganisms and their enumeration ................................................................................. 28 3.2.4 Experimental setup ...................................................................... 31 3.2.4.1 Contribution of biological versus physical processes in pathogen removal ..................................... 32 3.2.4.2 Effect of residence time on E.coli and MS-2 removal ......................................................................... 35 3.2.4.3 Components and properties of the schmutzdecke material ......................................................................... 36 vi 3.2.4.3.1 Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analysis ..................... 37 3.2.4.3.2 Zeta potential analysis ................................ 37 3.2.4.3.3 Assessing flocculating properties of the schmutzdecke material ......................... 38 3.2.4.4 Importance of increased rate of collisions in the schmutzdecke ............................................................... 42 3.3 RESULTS AND DISSCUSION............................................................. 43 3.3.1 Contribution of biological versus physical processes to pathogen removal ........................................................................ 43 3.3.1.1 Results .......................................................................... 44 3.3.1.2 Discussion ..................................................................... 46 3.3.2 Effect of residence time on E.coli and MS-2 removal ................ 47 3.3.1.1 Results .......................................................................... 48 3.3.2.2 Discussion ..................................................................... 52 3.3.3 Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analysis ........................... 55 3.3.3.1 Results .......................................................................... 56 3.3.3.2 Discussion ..................................................................... 59 3.3.4 Zeta potential analysis ................................................................. 60 3.3.4.1 Results .......................................................................... 61 3.3.4.2 Discussion ..................................................................... 63 3.3.5 Assessing flocculating properties of the schmutzdecke material ........................................................................................ 64 3.3.5.1 Results .......................................................................... 65 3.3.5.2 Discussion ..................................................................... 67 3.3.6 Importance of increased rate of collisions in the schmutzdecke .............................................................................. 68 3.3.6.1 Results .......................................................................... 69