Study On Characteristics Of Sludge And N₂O Production During Anoxic-oxic Biological Wastewater Treatment Process

Nitrous Oxide?N₂O?is a strong greenhouse gas,which plays an important role in the global climate change.During wastewater treatment biological nitrogen removal process,large amounts of N₂O are generated from it.So,it is considered as an important source of anthropogenic greenhouse gas emission.Therefore,it is of great practical significance to study the mechanism that affects the production of N₂O in the process of biological nitrogen removal.In this paper,using anoxic-oxic operation mode of the SBR reactor to treat synthetic wastewater,selection of operating parameters that have a critical impact on the characteristics of sludge?sludge concentration?MLSS?,carbon source and shear stress?.Study on the characteristics of activated sludge and the characteristics of N₂O production in the treatment system under different conditions,combined with the change of pollutant concentration,the microbial community structure and succession rules.Analysis of the relationship between the characteristics of sludge and the production of N₂O.Revealing the influence mechanism of operation conditions on the production of N₂O in biological nitrogen removal process and providing theoretical support for the development of high efficiency nitrogen removal and greenhouse gas N₂O emission reduction technology.The contents of the study and the results of the experiment are as follows:To explore the effect of biological density on sludge characteristics and N₂O production in sewage treatment process,three groups of parallel experiments of anoxic aerobic process were established,and MLSS was 2000±100 mg/L,3000±100 mg/L and 4000±100 mg/L respectively.The results show that with the increase of MLSS,PHA and EPS content in the sludge and sludge particle size increased,COD,TN and TP removal rate increased,the conversion rate of N₂O-N increased from 2.6% to 4.1%,the activated sludge microbial abundance and microbial diversity were enhanced with the increase of MLSS,the relative abundance of Haliscomenobacter,Ignavibacterium and Sporosarcina dominant fungi increased with the increase of MLSS,the relative abundance of Blastocatella and Ferruginibacter were decreased.The effect of carbon source on the sludge characteristics and N₂O production were investigatedwith acetic acid,propionic acid and mixed acid as carbon sources respectively.With mixed acid as carbon source,sludge particle size larger particle size,and the contents of PHA and EPS in activated sludge,the removal rate of TN is minimum,however,the release rate of N₂O,the amount and conversion rate of N₂O is maximum;when using acetic acid as carbon source,the removal rate of TN,and the release rate,the yield and conversion rate of N₂O is minimum;carbon source has an important influence on the microbial population structure system,with propionic acid as carbon source,the relatively abundance and diversity of microorganisms is higher in the system.In order to investigate the effect of shear stress on sludge characteristics and N₂O production in water treatment process,three groups of parallel experiments were establishment by SBR reactors.The internal shear stress was 15.3×10-3 N/m2,35.5×10-3 N/m2 and 60.7×10-3 N/m2 respectively.With the increase of the internal shear stress,the removal rate of NH4+-N,COD and TN gradually increased,while the removal rate of TP decreased.The size of the activated sludge and the content of EPS were positively correlated with the shear stress,but the PHA content of the sludge was negatively correlated with the shear stress.The greater the shear stress in the system,the greater the microbial species in the activated sludge,the higher the diversity.The relative content of heat stroke Thauera,Ferruginibacter and Terrimonas increased with the increase of shear stress.