Performance And Mechanism Of Ammonia Removal And Electricity Generation In Ammonia-oxidizing Microbial Fuel Cell

Microbial fuel cell (MFC) is a novel technology which uses microbes to generate electricity, converting chemical energy (stored in organic/inorganic matters of wastewaters) to electrical energy. In 2013, the amount of ammonia discharged from industrial/agricultural wastewater and domestic sewage reached 2.46 million tons, thus exerting a severe pollution pressure on the water environment. The development of ammonia-oxidizing microbial fuel cell can remove ammonia and generate electricity simultaneously from wastewaters, which not only conforms to the environmental protection policy of "saving energy and reducing emissions" in our country, but also meets the development direction of nitrogen removal technologies.In this study, the aerobic ammonia-oxidizing microbial fuel cell (AAO-MFC) and the anaerobic ammonia-oxidizing microbial fuel cell (ANAMMOX-MFC) were constructed, and their performances and working mechanisms were investigated. The main results are as follows:1. The AAO-MFC was designed and constructed. Chemicals involved in nitrification were added to AAO-MFC to investigate their effects on the performance of electricity generation and to elucidate the pathway of electricity generation.It was proved that the AAO-MFC could be successfully started up with ammonia-oxidizing bacterial enrichment culture as inoculum, which showed a good performance of ammonia removal and electricity generation. The results of this study indicated that apart from the primary nitrification substrate (ammonium), the intermediates (hydroxylamine and nitrite) could also serve as fuels to generate electricity. Hydroxylamine and nitrite exhibited either stimulatory effect or inhibitory effect depending on their dosage, and the end product nitrate always showed an inhibitory effect on the electricity generation. Based on the research, a pathway of electricity generation was proposed for AAO-MFC:ammonium was oxidized first to nitrite by ammonia-oxidizing bacteria, then the nitrite in anolyte and the potassium permanganate in catholyte constituted a chemical cell to generate current. In other words, the electricity generation in AAO-MFC was not contributed by microbial reaction merely as we expected, but contributed by both microbial and electrochemical reactions.2. The ANAMMOX-MFC was designed and constructed. The effects of anode potential on its performance and microbial community were investigated.It was proved that the ANAMMOX-MFC could be successfully started up with anaerobic ammonia-oxidizing bacterial enrichment culture as inoculum. The ANAMMOX-MFC showed a good performance of nitrogen removal and electricity generation, with a nitrogen removal rate of 0.913±0.027kgN m-3d-1 and a maximum power density of 2.54 mW/m2. Anode potential showed weak impacts on the nitrogen removal performance of ANAMMOX-MFC. However, it showed significant impacts on the electricity generation performance of ANAMMOX-MFC. Either up-regulation or down-regulation of anode potential weakened its performance of electricity generation. Besides, up-regulation of anode potential exacerbated the death of microbes on the anode surface, which increased the internal resistance of MFC. Anode potential also showed significant impacts on the anodic microbial community. The dominant anammox bacteria in the system were changed from Candidatus Kuenenia and Candidatus Brocadia to Candidatus Kuenenia after up-regulation or down-regulation of the anode potential.