Pilot-scale Study Of UniFed SBR+ Heterotrophic-autotrophic Combined Denitrification Process Integrated Equipment For Domestic Sewage Treatment

In recent years,our country has continued to promote the construction of beautiful and livable countryside,the construction of small towns has been accelerated,the discharge of domestic sewage has been increasing,and the concentration of nitrogenous substances in sewage has gradually increased,domestic sewage shows a trend of low carbon to nitrogen ratio,and if it is not collected and treated,it will harm the ecological environment.At present,the mainstream nitrogen removal process of sewage treatment plants in my country is still not suitable for the treatment of sewage in small towns.So,it is extremely urgent to research and develop a new biological denitrification treatment process suitable for the characteristics of domestic sewage in small towns.Considering that the heterotrophic-autotrophic combined nitrogen removal process can reduce the respective limitations of traditional autotrophic and heterotrophic biological nitrogen removal technologies,this study developed a set of integrated sewage treatment equipment based on this combined nitrogen removal process.In order to provide stable water quality for the combined nitrogen removal process,and to achieve the removal of most of the organic matter in the raw sewage and the partial conversion of ammonia nitrogen,the Uni Fed SBR process is used as the front-pretreatment（unit A）.Heterotrophic-autotrophic combined nitrogen removal process as a process,namely post-treatment（unit B）,aims at the occurrence of heterotrophic denitrification,autotrophic denitrification and anaerobic ammonium oxidation in a micro-aerobic environment for further achieve nitrogen removal.In this study,the domestic sewage of campus residents was used to simulate the domestic sewage of small towns,and the treatment effect of the pilot-scale integrated equipment reactor in the treatment of domestic sewage was explored.After preliminary preparations,the integrated sewage treatment equipment has been operated for 183 days for a long time.The main research contents are:the start-up operation of the pilot-scale integrated equipment,the optimization of the working conditions of the two units A and B respectively,and the comparison of the parameters in the process of parameter optimization,the removal capacity of pollutants and the changes of sludge indicators,the structure and succession of sludge microbial community in units A and B,etc.The main conclusions of the study are as follows:（1）Changing the aeration volume in unit A will affect the removal effect of the entire system on various pollutants.Appropriately reducing the aeration volume of unit A will promote the removal effect of the pilot-scale integrated equipment.Among the aeration rate parameters selected in this study,when the aeration rate was 1 L/min,the removal effect of COD,TN,and TP was the best,and the average removal rates were 70.52%,38.93%,and 53.61%,respectively.The initial setting of aeration mode in unit B is intermittent aeration（30 min aeration/30 min no aeration cycle）.Changing the aeration mode（90 min aeration/90 min no aeration）will improve the removal effect of COD and TN in the system,however,it will inhibit the removal effect of TP.The average removal rates of COD and TN increased by 5.34%and 4.34%,respectively,and the average removal rate of TP decreased by 13.93%.After optimizing the parameters,the average concentrations of COD,TN,and TP in the effluent of the whole system were 71.25 mg/L,38.32 mg/L,and 2.39 mg/L,respectively,which could not reach the first-class standard of effluent.（2）During the operation process,the changes of sludge concentration in units A and B both increased first and then decreased.The decrease of aeration rate had little effect on the EPS content of sludge in unit A,but the micro-oxygen environment caused the EPS content of unit B to increase significantly,the ratio of PN to PS in the sludge EPS of units A and B is both 3 during operation.（3）The community succession during operation was explored through the diversity analysis of sludge microbial community in different periods.Proteobacteria and Bacteroidetes in the sludge microbial community in unit A were enriched with the decrease of aeration rate,while the relative abundance of Actinobacteria and Chloroflexi decreased.Proteobacteria in unit B It was also enriched under micro-aerobic conditions and became an absolutely dominant phylum;the decrease in aeration rate significantly increased the abundance of OLB8,Mythyloparacoccus and norank＿f＿Bacteroidetes＿vadin HA17 in the sludge microorganisms in unit A.The denitrification process takes place inside the A unit,which increases the COD removal rate in the A unit;the sludge in unit B that is in the micro-oxygen state for a long time,some bacteria genera that are prone to sludge bulking are gradually reduced,such as:Candidatus＿Microthrix,Zoogloea,Pseudomonas and other bacteria genera,they have higher requirements for dissolved oxygen concentration and are not suitable for growth under micro-oxygen conditions.While the relative abundance of bacterial genera such as Dechloromonas and unclassified＿f＿Rhodocyclaceae increases,and the former can undergo autotrophic denitrification under facultative anaerobic conditions,which improved nitrogen removal in unit B.No anammox function-related bacterial accumulation was detected in unit B,indicating that anammox reaction did not occur inside unit B,but autotrophic denitrification and heterotrophic denitrification and denitrification took place.（4）The functional prediction of PICRUSt shows that:Appropriate reduction of aeration in unit A can increase the gene abundance of AMO and HAO,that is,the process of converting nitrogen to NH₂OH and NH₂OH to NO₂^—-N,and can promote the process of denitrification;Although the micro-oxygen environment and continuous aeration/continuous non-aeration method in unit B can also promote the denitrification process,they may inhibit the reduction process of N₂O,resulting in the accumulation of N₂O.