Analysis Of N₂O Emission In Sequencing Batch Reactor Systems (SBR)

Nitrous oxide(N2O) emission from wasterwater treatment is the potential source of N2O produciton via nitification and denitrification, and depends on many operational parameters and microbial community structure. Two different sludge systems by sequencing batch reactor (SBR) playing simultaneous nitification and denitrification (SND) were compared on relations of N2O production and microbial community structure, and nitrogen conversion in different systems were also studied. The effections of operational parameters on N2O emission were investigated in one of SBR systems, eg:dissolved oxygen, concentrations of ammonia nitrogen, loads of chemical oxygen demand. The results showed:1) The characteristics of N2O emission frome different activated sludge in SBR systems are different significantly under the same control parameters and the efficiency of nitrogen removed. Not only the total N2O emissions bue also the main source of N2O production in SBR system is different depend on activated sludge. In one operation cycle , A systen emitted 2.887 mg·L-1 N2O-N accounting for removed nitrogen 7.11%, and is more than twice in B system. But for different stages, the aeration of A system is main source of N2O emission, the ratio of emitted N2O-N to the removed total nitrogen is 9.85% which is more than four times during anoxic phase; conversely, anoxic process is main source in B system, the ratio of emitted N2O-N to the removed total nitrogen during oxic process is 1.40% which is less than one fifth during anoxic phase..2) Microbial community structure is different if sludge has a different characteristics of N2O emission, although microbial community diversity index is the same, the similarity between A and B is only 0.49.There is no obvious distinguish about microbial community structure between oxic and anoxic in the same system.,the similarity of A and B system is 0.94 and 0.95 respectively.3) There is no relation between N2O emission and aerarion within a certain range (2.0~3.0 L·min-1) in SBR system, more aeration or less may result in increase of N2O emission. High load of ammonia nitrogen induces higher production of N2O. Increased the load of COD that not only enhances the effiicency of SND,but also decreases N2O emissions.The differences of microbial community structure lead to different characteristics of N2O emission in high and stable efficiency of nitrogen removal. So, it's very important to screen strains which have high efficient nitrogen removal and low N2O production in wastewater treatment. At the same time, N2O emission can be reduced when system is operated via optimal control parameters.