Startup And Denitrification Mechanism Of A Novel Microaerobic Process Treating Manure-free Piggery Wastewater

Manure-free piggery wastewater is a kind of high ammonium and low chemical oxygen demand to total nitrogen ratio（C/N ratio）wastewater.The conventional nitrification-denitrification process treating manure-free piggery wastewater are poor in nitrogen removal and high in engineering investment and management cost.The upflow microaerobic sludge reactor（UMSR）and upflow microaerobic biofilm reactor（UMBR）had been devleloped in previous research,achieved favorable nitrogen removal efficiency.Due to method of aerating the effluent and returning it back to maintain the microaerobic condition,both UMSR and UMBR require higher reflux ratio and aeration intensity.In order to solve this problem,this work developed an internal aeration microaerobic reactor（IAMR）,which does not need reflux and supply oxygen to the microaerobic system directly.To confirm the feasibility of treating manure-free piggery wastewater,the IAMR was started up with the method of gradually increasing the influent ammonia nitrogen concentration.The carbon and nitrogen removal efficiency and the denitrification mechanism of IAMR were investigated.The activated sludge from a secondary sedimentation tank of a municipal sewage treatment plant was used as the seed sludge of IAMR.IAMR was operated under conditions of HRT of 8 h,32 °C,and a dissolved oxygen（DO）of 0.4 mg·L-1.The IAMR reached stable operation after 124 days of operation.During the stable operation of treating raw water,the influent chemical oxygen demand（COD）,NH4+-N,and total nitrogen（TN）concentrations were in the range of 214.7-324.4,193.3-234.8 and 310.6-388.8 mg·L-1,respectively.The average effluent concentration of them is 57.3,13.1,and 59.1 mg·L-1,and the average removal rates reached 77.60%,94.67%,and 82.98%,respectively.The results of high-throughput sequence analysis of activated sludge indicated that after IAMR was successfully started up,the denitrifying genuses Brachymonas,Aquimonas,and Ottowi were dominant genuses with a relative abundance of 19.6%,the ANAMMOX genus Candidatus Kuenenia were also rich in IAMR with the relative abundance of 0.63%.This shows that there may be many biological denitrification pathways in the IAMR system.By analyzing the ratio of the variation of COD,TN,total Kjeldahl nitrogen（TKN）and NO3--N between influent and effluent（ΔCOD/?TN,?TN/?TKN and ?NO3--N/?TKN）,the main denitrification pathway of IAMR system transitions from the completed nitrification and denitrification way to shortcut nitrification and denitrification way gradually,and ultimately to ANAMMOX way.Investigate the activity and kinetic parameters of the ANAMMOX and denitrifying bacterial flora by static experiments.The results shows the NH4+-N oxidation of the IAMR system only proceeds to the NO₂^--N stage,while the oxidation from NO₂^--N to NO3--N is negligible.And limited by the shortage of carbon sources,the shortcut denitrification pathway has a maximum TN removal rate of 20.2%,that is to say,the TN removed by the ANAMMOX pathway is up to 79.8%.