Determination of the Potential Energy Contribution and Green House Gas Mitigation of Small and Medium Anaerobic Digester Systems in Bangladesh Khondokar Mizanur Rahman A thesis submitted in partial fulfilment of the requirements of the University of Brighton for the degree of Doctor of Philosophy The University of Brighton 2011 Determination of the Potential Energy Contribution and Green House Gas Mitigation of Small and Medium Anaerobic Digester Systems in Bangladesh Abstract This research is to determine the anaerobic digestion (AD) potential and green house gas mitigation of small and medium anaerobic digester systems in Bangladesh which could provide energy for the country‘s need. This was determined for two common feedstocks: cattle dung and poultry litter. A third potential feedstock is also investigated as a novel and significant new source: waste rice straw used in cattle markets. These three feedstocks were chosen because between them, they cover a large fraction of scenarios in the country where AD could be used. All of the data needed to determine the energy parameters of these three representative AD facility types were collected (i.e. biogas yield, biogas composition, life cycle data). Highest biogas yield of 0.099 m3/kg feedstock and methane percentage 74.4% were found from cattle market rice straw feedstock. The relative potential contributions to energy were then calculated. Where no reliable secondary data was available, primary data was obtained, through site visits and surveys. In order to determine the potential distribution of these representative AD facility types across the country, a survey of 125 smallholdings/farms in one district was carried out. This showed that 70% of the potential energy from AD would come from the cattle feedstock (87% of energy for the cattle feedstock would come from domestic plants). The poultry feedstock contributes 16% of the potential energy (63% of energy from poultry feedstock would come from medium sized plant) and the rice straw from the cattle markets is 14% (53% large and 47% very large). The energy capacity is presented in terms of the potential development of small, medium and large AD facilities. The total potential for biogas energy from cattle farms, poultry farms and cattle market rice straw in Bangladesh is 240 x106 MJ (240 TJ). This energy is equivalent to 66.7 x 106 kWh which can meet the cooking energy requirements of 30 million people in Bangladesh. This study also contains a Life Cycle Assessment (LCA) and the result showed that the lifetime Global Warming Potential (GWP) of a 3.2 m3 cow dung fed AD plant is 130 tonnes of CO2 equivalent. Biogas as cooking fuel can reduce the GWP by 109 tonnes of CO2 equivalent. It means the reduction of GWP of a domestic AD plant is of 84% to 21 tonnes CO2 equivalent. I Content Title Page Chapter 1 Introduction 1 1.0 Overview leading to Aim and Objectives.................................................... 1 1.1 Aim and objectives...................................................................................... 8 1.2 Layout of the thesis..................................................................................... 10 1.3 Overview of the research Framework......................................................... 12 Meeting with experts and field work.......................................................... 13 Identify the representative AD facility types.............................................. 13 Determine the biogas energy parameters..................................................... 13 Smallholdings/Farm/cattle market Survey.................................................. 14 Life Cycle Assessment................................................................................ 14 ---------------------------------------------------------------------------------------------------------------- Chapter 2 Introduction to Bangladesh, AD and LCA 15 2.1 Contextual Information on Bangladesh................................................... 15 2.1.1 Country background.................................................................................... 15 2.1.2 Bangladesh and agriculture.......................................................................... 18 2.1.3 Energy status Bangladesh............................................................................ 20 Traditional energy........................................................................................ 21 Commercial energy..................................................................................... 23 Renewable energy....................................................................................... 24 2.1.4 The Evolution Biogas technology in Bangladesh....................................... 25 2.1.5 Large sized AD facility in developed world............................................... 30 2.1.6 Organizations involved in this research...................................................... 31 2.2 Anaerobic digestion……………………………………………………........... 31 2.2.1 Context of Anaerobic digestion…………………………………………........... 32 2.2.1.1 Concept of anaerobic digestion.................................................................. 32 2.2.1.2 Factors affecting anaerobic digestion......................................................... 35 Temperature................................................................................................ 35 Loading Rate of raw materials................................................................... 36 Retention Time........................................................................................... 36 Volatile Solids............................................................................................ 36 pH value..................................................................................................... 37 2.2.1.3 Common Digester types in Bangladesh..................................................... 37 Floating dome digester…………………………………………………... 37 Fixed dome digester……………………………………………………... 38 Fibreglass digester...................................................................................... 39 2.3 Life Cycle Assessment.............................................................................. 40 2.3.0 Introduction............................................................................................... 40 2.3.1 LCA; an assessment tools.......................................................................... 41 2.3.1.1 Concept of LCA........................................................................................ 41 2.3.1.1.1 Goal and Scope………………………………………………………….. 41 Functional Unit.......................................................................................... 42 System boundary....................................................................................... 42 2.3.1.1.2 Inventory………………………………………………………………… 42 2.3.1.1.3 Impact assessment……………………………………………………….. 42 II 2.3.1.1.4 Interpretation…………………………………………………………….. 43 2.3.1.2 Publicity Available Specification (PAS)/PAS 2050................................... 44 2.3.1.3 LCA Software SimaPro 7........................................................................... 45 Summary of chapter.................................................................................... 46 ---------------------------------------------------------------------------------------------------------------- Chapter 3 - Review of Literature 47 3.0 Introduction................................................................................................ 47 3.1 The Energy scenario in Bangladesh........................................................... 47 3.2 Contextual AD and energy capacity of AD.............................................. 51 3.2.1 AD plant construction materials................................................................. 52 3.2.2 AD potential feedstock.............................................................................. 54 3.2.3 Factor affecting biogas and methane yield................................................ 60 3.2.3.1 Feedstock.............................................................................................….. 61 3.2.3.2 % Total Solid (TS)...................................................................................... 62 3.2.3.3 Temperature................................................................................................ 63 3.2.3.4 Hydrolic Retention Time (HRT)................................................................ 64 3.2.3.5 Organic Loading Rate (OLR)/Volatile Solid (VS).................................... 65 3.2.3.6 pH............................................................................................................... 66 3.2.3.7 Other factors............................................................................................... 67 3.3 Impact of AD.............................................................................................. 67 3.3.1 Social impact.............................................................................................. 68 3.3.2 Economic impact........................................................................................ 70 3.3.3 Environmental impact................................................................................ 73 3.3.4 GHG mitigation and CDM........................................................................ 77 2.4 Conclusion from Literature Review........................................................... 81 ----------------------------------------------------------------------------------------------------------------