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Anaerobic Treatment of Nightsoil and Toilet Sludge from On-Site Sanitation Systems in Ghana

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Anaerobic Treatment of Nightsoil and Toilet Sludge from On-Site Sanitation Systems in Ghana Anaerobic treatment of nightsoil and toilet sludge from on-site sanitation systems in Ghana By Isaac Adjei Doku Submitted in accordance with the requirements for the degree of Doctor of Philosophy The University of Leeds School of Civil Engineering January 2002 The candidate confirms that the work submitted is his own and that appropriate credit has been given where reference has been made to the work of others. 1 Acknowledgements Firstly, I wish to take this opportunity to express my appreciation and gratitude to my supervisors, Professor Duncan D. Mara and Dr. Nigel J. Horan, both of the School of Civil Engineering, University of Leeds, for their leadership, useful suggestions and financial support in carrying out this work. My special thanks goes to the Association of Commonwealth Universities and the Ghana Scholarship Secretariat for their joint collaborative effort in providing the scholarship and funding to enable me undertake this work. My special thanks also goes to my employers the TREND Group, Kumasi, Ghana, for granting me the study leave to pursue this research work. Furthermore, I wish to extend my gratitude to Professor K. A. Andam, Head, Department of Civil Engineering, University of Science and Technology, Kumasi, Ghana, for granting me access to the laboratories to enable me carry out all my laboratory analysis in Kumasi. I will also like to thank Martin Strauss and his colleagues at SANDEC and Peter Hawkins, Project Co-ordinator, Urban Environmental Sanitation Project, Accra, Ghana for their keen interest in this work and very useful suggestions and review of portions of the work. My sincere thanks also goes to the laboratory technicians at both laboratories used in Leeds and Kumasi for their assistance during the laboratory analysis. Also I wish to thank all the staff in the CERI Office for their administrative support during this research. I will also like to thank my family for their moral support and understanding which gave me the peaceful atmosphere to concentrate on my work. Finally, I want to thank God for granting me the wisdom, knowledge, sound and good health, and all the strength that I needed to carry out this work, for “He is before all things and by Him all things consists.” Abstract The feasibility of faecal sludge treatment by an upflow anaerobic sludge blanket (UASB) reactor was studied using first, untreated primary sludge from a sewage treatment works treating only domestic sewage, and then actual faecal sludge. The primary sludge was diluted in the ratio 1:20 - 1:10 while the faecal sludge was diluted in to the ratio 1:6. The UASB reactor treating the primary sludge had a volume of 15 litres and was operated at a mean hydraulic retention time (HRT) of 9.8 h, at a temperature of 37 °C, and at an organic loading rate (OLR) in the range of 5.6 - 15.0 kg COD/m\d. The UASB reactor treating the faecal sludges had a volume of 50 litres and was operated at a mean HRT of 12.1 h, at ambient temperatures in the range of 23.0 - 31.2 °C, and at OLR in the range of 12.5-21.5 kg COD/nr\d. The first experiment involving the untreated primary sludge was run for 114 days while the second was run for 119 days. The results from both experiments indicate that it is feasible to treat faecal sludges using the UASB reactor. The average removal efficiencies obtained for the first experiment were: 78% for COD, 62% for total solids (TS), 75% for total volatile solids (TVS) and 91% for total suspended solids (TSS). The pH was in the range of 6.9 - 7.4. With regards to faecal sludges, the average removal efficiencies were: 71% for COD, 61% for TS, 74% for TVS and 73% for TSS. The removal efficiencies are comparable to those obtained for a UASB reactor treating for domestic sewage. High removal efficiencies were obtained in a much shorter time compared to UASB reactors treating domestic sewage. The COD concentration in the effluents is too high for direct discharge and hence a form of post-treatment would be necessary. The calculated volume of methane in the biogas collected ranged from 4 - 8 1/kg COD, not accounting for practical losses. Ill Table of Contents A cknowledgem ents.............................................................................................................. i A b stra ct................................................................................................................................. ii Table of C ontents................................................................................................................iii List of T ables....................................................................................................................... ix List of F ig u res..................................................................................................................... xi List of P lates...................................................................................................................... xiv A bbreviations.................................................................................................................... xvi C hapter O n e.........................................................................................................................1 1 Introduction................................................................................................................1 1.1 Background..........................................................................................................1 1.2 Problem Statement.............................................................................................. 8 1.3 Objective of Study.............................................................................................10 1.3.1 Overall Objective...................................................................................... 10 1.3.2 Specific Objectives....................................................................................10 1.4 Choice of the UASB Reactor.......................................................................... 11 1.5 Organisation of the report................................................................................ 11 C hapter Two...................................................................................................................... 13 2 L iterature Review....................................................................................................13 2.1 Introduction........................................................................................................13 2.2 Definitions: nightsoil, toilet sludge, septage and faecal sludge............... 13 2.2.1 Introduction................................................................................................ 13 2.2.2 Nightsoil...................................................................................................... 13 2.2.3 Toilet Sludge.............................................................................................. 14 2.2.4 Septage........................................................................................................ 15 2.2.5 Faecal Sludge............................................................................................. 15 2.3 Quantities, Characteristics and Classification of Faecal Sludges............. 16 2.3.1 Per Capita Quantities of Faecal Sludges................................................ 16 2.3.2 Characteristics of Faecal Sludges............................................................17 2.3.2.1 Septage................................................................................................ 17 iv 2.7)22 Nightsoil and Toilet Sludge.............................................................19 2.3.3 Classification of Faecal Sludges.............................................................23 2.4 Collection and Treatment of Nightsoil and Faecal sludge......................... 24 2.4.1 Collection................................................................................................... 24 2.4.1.1 Nightsoil..............................................................................................24 2.4.1.2 Toilet Sludge and Septage................................................................25 2.4.2 Treatm ent................................................................................................... 25 2.5 Anaerobic Digestion Process..........................................................................42 2.5.1 Introduction................................................................................................42 2.5.2 Basic Concepts.......................................................................................... 43 2.5.3 Conversion Processes in Anaerobic Digestion.....................................45 2.5.3.1 Hydrolysis.......................................................................................... 46 2.5.3.2 Acidogenesis...................................................................................... 46 2.5.3.3 Acetogenesis...................................................................................... 48 2.5.3.4 Methanogenesis..................................................................................48 2.5.4 Organic nitrogen transformations...........................................................49 2.5.5 Stability of the Conversion Processes....................................................49 2.5.5.1 Temperature....................................................................................... 50 2.5.5.2 pH.........................................................................................................52
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