Effect of Microbubble on the Performance of the Partial Nitrification and Anammox Process

Effect of Microbubble on the Performance of the Partial Nitrification and Anammox process XIA ZHU Degree of Doctor of Philosophy Under the supervision of Professor William Zimmerman & Dr. Stephen Wilkinson Department of Chemical and Biological Engineering University of Sheffield November 2012 I Summary Summary Nitrogen pollution is an increasingly important global concern because it has multiple impacts on terrestrial, aquatic and atmospheric environments. Nitrogen is usually present in wastewater as ammonium. Ammonium can be removed from wastewater by a variety of physicochemical and biological processes, but biological processes are preferred because they are usually more efficient and environmentally friendly. Conventional biological nitrogen removal is carried out by autotrophic nitrification and heterotrophic denitrification via nitrate, which use biodegradable organic matter as electron donor. However there are some kinds of wastewater with low concentrations of biodegradable organic matter such as landfill leachate and anaerobic digester supernatant. In these cases an external organic carbon source is necessary in order to obtain a complete denitrification, which implies higher economic cost. Partial nitrification- Anammox process as a promising and novel biological technology of removing nitrogen from high-strength ammonium wastewater with a low C/N ratio has attracted increasing attention due to its higher efficiency and cost-effectiveness compared with the conventional nitrification–denitrification nitrogen removal process. However, many challenges were faced during the development of stable and high- efficiency partial nitrification-Anammox performance, such as NOB activity, the effort to save energy, strict conditions and influent with favourable composition for Anammox. In order to improve the efficiency of Partial nitrification- Anammox process as much as possible whereas using the least energy, the microbubble generation system was firstly applied into the partial nitrification-Anammox process. The steady microbubble cloud produced by fluidic oscillator was verified size ranging from 60 μm to 600 μm which provides higher mass transfer rates and gas hold-up in gas-liquid phase bioreactor due to the fact that the microbubble was characterized by higher surface area to volume ratio and slower rising velocity. The simulation of the inner motion of the airlift loop reactor with COMSOL offered a visual difference between microbubble aeration and fine bubble aeration. In the partial nitrification process dissolved oxygen is a key factor for the growth of ammonia oxidizing bacteria (AOB). Two contrasting experiments in sequencing batch airlift loop reactors (SBAB) with and without fluidic oscillator were conducted over 200 I Summary days to investigate the effect of microbubble aeration system on the long term partial nitrification process. The results showed the microbubble aeration system can significantly enhance the activity of AOB to speed up the biological treatment with fewer oxygen requirements and effectively prevent the production of nitrate. The performance of the partial nitrification in an airlift loop bioreactor with fluidic oscillator was greatly improved in terms of treatment capacity and stability compared to the one without fluidic oscillator. Thereafter different operational parameters such as temperature and pH were examined to optimize the operational strategies for the partial nitrification process. The microbial communities that catalyse partial nitrification were analysed by molecular biotechnology. The morphology of bacteria at different growth stages was observed by SEM and TEM. Real-time PCR was used to quantify populations of ammonia-oxidizing bacteria and nitrite oxidizing bacteria. For the Anammox process, a strict anaerobic condition is required to operate successfully. As we all know, the stack gas is usually consists of depleted oxygen but mostly nitrogen (typically more than two-thirds) derived from the combustion, carbon dioxide (CO2), and water vapour, among which CO2 is considered as a greenhouse gas contributing to global warming. Bubbling the synthetic power station stack gas into the Anammox reactor by means of the microbubble generation system not only obtain this circumstance but also provide the heat required by good activity of anammox bacteria. In addition to maintaining desirable conditions, the dissolved CO2 can provide a carbon source for the growth of anammox bacteria and adjust the value of pH in the reactor which is able to save substantial operational cost caused by pH control. Two contrasting experiments in round sequencing batch gas lift loop bioreactors (SBGB) with and without fluidic oscillator were carried out nearly 100 days. The performance of Anammox process in the SBGB with fluidic oscillator was noticeably improved comparing to the one without fluidic oscillator. The size distribution of granular Anammox sludge was analysed by ImageJ to investigate the effect of microbubble on the granulation. The batch assays were conducted to measure the maximum specific Anammox activity in different gas lift loop bioreactors. The morphology of Anammox bacteria at different growth stages was observed by SEM and TEM. Real-time PCR was used to quantify populations of Anammox bacteria in different stage and different bioreactors. The kinetic model for laboratory-scale partial nitrification and Anammox (anaerobic ammonium oxidation) process with sequencing batch gas lift loop bioreactors (SBGB) II Summary with and without fluidic oscillator were investigated. According to Monod model and Stover–Kincannon model the kinetic parameters of the model including maximum specific rates and half-maximum rate concentrations for partial nitrification and Anammox were estimated respectively from the results obtained from a laboratory-scale SBGB fed with synthetic wastewater. III Acknowledgements Acknowledgements First of all, I would like to express my sincere gratitude to my supervisor Professor William Zimmerman for introducing me to the challenges of wastewater treatment with microbubble application, for all his support and for the great enthusiasm he has always shown for my work. I cannot imagine having any other supervisor than Will. Thanks for his encourage I could always find inspirations in my study. Furthermore, his careful reading of this thesis has improved its quality considerably. I also want to thank my second supervisor Dr. Stephen Wilkinson who gave me great support in my experimental work and the research in the first two years of my PhD. I am so impressed by his carefulness and sense of responsibility. I greatly appreciated Thomas Holmes for proofreading the thesis and providing me with huge amounts of detailed comments and suggesting important improvements with regard to the content of the thesis. In addition to this, Thomas has helped me solve various practical problems in my experiments and English Learning. At the same time, I would like to thank all the technicians at the Department of Chemical and Biological Engineering, who gave me a lot of assistance, especially Andy and Adrian. Without their help I could not finish my experiment successfully. I have had the great honour of being part of a large, interdisciplinary research Group— Microfluidics Group, working within the field of wastewater treatment, during the last 4 years. A large amount of important research has been carried out and a lot of valuable results were obtained. Nowadays Microfluidics group is internationally recognized for its work. I would like to take this opportunity to thank all my friends and colleagues. It is my sincere wish that our group would approach more great achievements and have a promising future. I would also like to thank Dr Hemaka Bandulasena (Lecturer in Chemical Engineering at Loughborough University) Dr Dmitriy Kuvshinov and Dr Jaime Lozano-Parada who have inspired me and provided me with valuable comments over the years. I am much indebted to them for help me order a lot of experiment devices (over and over again). Working with them has been a great experience. I want to show my great appreciation to Dr Dayi Zhang from Department Civil & Structure Engineering who gave me significant technical support in the aspect of microbiology. Two MSc students Sisi Ge and Meng Lian also did good job as IV Acknowledgements experiment assistants under my supervision. Thanks to them I was allowed to have more time to do further research on my project. I am also grateful to every member of our group who have contributed to my work. I would especially like to thank Kezhen Ying, Yuzhen Shi and James O Hanotu for providing the creative and friendly atmosphere which makes work a pleasure. They not only gave me great help in my experiment but also close personal friends. Finally, I thank my parents and the other members of my immediate family for the love, support and trust that they have always shown towards me. The work has been supported financially by China Scholarship Council and Department for Innovation, Universities and Skills and the University of Sheffield. Their support is gratefully acknowledged. V Contents Contents Chapter 1. Introduction ..................................................................................................... 1 1.1 Background ............................................................................................................. 1 1.2 Project Overview ....................................................................................................

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