RELATIONSHIP BETWEEN WASTEWATER SLUDGE QUALITY AND ENERGY PRODUCTION POTENTIAL YEE PONG, CHUA SUPERVISORS: PROF. ANAS GHADOUANI, DR ELKE REICHWALDT, PROF. RAJ KURUP SCHOOL OF ENVIRONMENTAL SYSTEMS ENGINEERING FACULTY OF ENGINEERING, COMPUTING AND MATHEMATICS THE UNIVERSITY OF WESTERN AUSTRALIA JUNE 2013 Cover photo: Subiaco wastewater treatment plant (UWA, 2013) This thesis is presented in partial fulfilment of the requirements of the Bachelor of Engineering (Environmental) at The University of Western Australia. ABSTRACT Wastewater Treatment Plant (WWTP) plays an irreplaceable role in the overall wellbeing and development of societies. Wastewater treatment is an ongoing process that requires high- energy consumption, and this demand contributes negatively to climate change. Nonetheless, there are options available for energy production and recovery in WWTPs during its treatment process, which can also reduce the negative environmental impacts. This study aims to investigate the potential of energy production and recovery at one WWTP, and the reduction of environmental impacts achieved. The study site is a WWTP situated at Subiaco of Western Australia, operated by Water Corporation. Currently, the WWTP uses an activated sludge treatment system and aerobic sludge stabilisation system. This process does not allow for energy production and recovery. On the other hand, an anaerobic sludge treatment system can produce energy during its treatment process in the form of biogas that can be captured and converted into energy for treatment use. The research evaluated sludge samples from the Subiaco WWTP at the UWA SESE laboratory for the characteristics of the sludge. Laboratory batch scale anaerobic digestion studies were also carried out to evaluate the efficiency of the system. The results of this study were then compared with data from the neighbouring WWTPs that use anaerobic treatment for sludge stabilisation. Further analyses were carried out to determine the economical values of the generated energy potential and the reduced environmental impacts. The experimental results showed that sludge samples from the Subiaco WWTP had a biogas production capacity of 0.015 m3/L sludge or 0.6 m3/VS, with a potential energy production of 40.4 megawatt-hour (MWh) per day. The biogas conversion to electricity used a combined heat and power (CHP) unit with an assumed energy efficiency factor of 70 %, and results indicated that Subiaco WWTP has the potential to recover 78 % of its overall electricity consumption through anaerobic treatment, with a generated value of A$1,012,291 per year. The payback period of purchasing a CHP unit using this generated value alone is between 2.2 to 9.6 years in the Best Case scenario, and 4.2 to 12.5 years in the Worst Case scenario. The amount of avoided carbon dioxide (CO2) emission from the substitution of treatment system is 7,475 metric tons annually. This study had successfully demonstrated the sustainability and i economical advantage of an anaerobic treatment process, and concluded that energy production and recovery is a feasible option for Subiaco WWTP. ii ACKNOWLEDGEMENT The completion of this undergraduate dissertation was possible with the support of several people. I would like to express my sincere gratitude to all of them. First of all, I am grateful to my research supervisors, Prof. Anas Ghadouani, Dr. Elke Reichwaldt and Prof. Raj Kurup for their help and academic support rendered to me throughout the research work. I thank Prof. Raj Kurup for his valuable guidance, scholarly inputs and consistent encouragement throughout the journey. I am much thankful and appreciative of the lessons they taught me along the way. Besides my research supervisors, I would like to also give thanks to John Langan for his invaluable assistance and guidance with all the laboratory work associated with the research. This research would also not be possible without the help I had received from Water Corporation, in particular the plant operators at Subiaco, Beenyup and Woodman Point wastewater treatment plant, for their patience and assistance in sampling and data collection. The completion of this research was made less obstacle ridden because of the presence of a few special individuals. Firstly, I sincerely offer my gratitude to my parents for providing me with unwavering support and consistent encouragement at every stage of both my personal and academic life. Secondly, I thank Skyler Han, for playing a strong supportive role throughout the course of this research. She supported me in every possible way to the completion of this work and I thank her for volunteering her time to painlessly proofread and correct any grammatical mistakes in the writing. Lastly, I thank all who had offered their good wishes to me throughout the period of this research. iii Table of Contents ABSTRACT ............................................................................................................................... i ACKNOWLEDGEMENT ..................................................................................................... iii LIST OF FIGURES ............................................................................................................ viiii LIST OF TABLES ................................................................................................................. ix ABBREVIATIONS ................................................................................................................. x 1. INTRODUCTION............................................................................................................. 1 1.1. Background .................................................................................................................. 1 1.2. Popularity and Consequences of Fossil Fuels ............................................................. 1 1.3. Climate Considerations ................................................................................................ 1 1.4. Anthropogenic Contributions to Climate Change ....................................................... 2 1.5. Emissions from Waste Treatment Facilities ................................................................ 2 1.6. Energy Consumption, Generation and Recovery ........................................................ 3 1.7. Purpose of Study .......................................................................................................... 3 2. LITERATURE REVIEW ................................................................................................ 4 2.1. Wastewater Treatment Plants ........................................................................................ 4 2.2. Wastewater Treatment Objectives ................................................................................. 4 2.3. Constituents of Wastewater ........................................................................................... 5 2.4. Wastewater Treatment Processes ................................................................................... 5 2.5. Sludge Management....................................................................................................... 6 2.5.1. Types and Characteristics of Sludge ............................................................................ 7 2.6. Anaerobic Treatment and Processes .............................................................................. 8 2.6.1. Inhibition and Limiting Factors ................................................................................... 9 2.6.2. Principles of Methane Generation ............................................................................. 12 2.6.3. Enhancement of Anaerobic Digestibility ................................................................... 14 iv 2.6.3.1. Optimisation of Process Conditions ....................................................................... 14 2.6.3.2. Pre-Treatment of Feed Sludge ................................................................................ 14 2.6.3.3. Staging Process and Higher Operating Temperature .............................................. 14 2.6.3.4. Digester-Mixing Regime ........................................................................................ 16 2.7. Energy in Wastewater Treatment................................................................................. 16 2.8. Energy Recovery in Sludge ......................................................................................... 18 2.9. Energy Generation Technologies ................................................................................. 19 2.9.1. Fuel Cells ................................................................................................................... 19 2.9.2. Microturbines ............................................................................................................. 20 2.9.3. Biogas Powered Reciprocating Engines .................................................................... 20 2.9.4. Biogas Upgrade .......................................................................................................... 22 2.9.5. Defective Components in Biogas............................................................................... 23 2.10. Climate Change Benefits ............................................................................................ 23 2.10.1. Mitigation efforts in Australia ................................................................................. 23 2.11. WWTP Energy Recovery in Western