Key Influencing Factors And Microbial Community Characteristics Of Advanced Nitrogen Removal By Denitrifying MBBR For Reverse Osmosis Concentrate

Dalton Filtration Reverse Osmosis(DFRO)unit are often used to reclaim high-quality water from Wastewater Treatment Plant(WWTP)effluent,which produces reverse osmosis concentrate(ROC)with high NOx--N(NO3--N+NO2--N)ratio and low C/N ratio at the same time.In this research,denitrifying MBBRs are constructed to remove nitrogen from ROC,and the effects of carriers,substrate concentration and temperature on the denitrification capability and microbial community structure are studied.The main results are as follows:(1)The denitrification efficiency of MBBRs filled with polyethylene(PE),commercial modified PE and modified PE by liquid phase oxidation-water bath grafted acrylic acid modification method are extensively compared.NO3--N and TIN removal efficiency of the modified PE MBBR,which has the optimal nitrogen removal capability,are 90.45%±4.74%and 85.7%±5.99%.The copy numbers of nitrogen removal genes and microbial community richness in the modified PE MBBR are the highest.Proteobacteria,Gammaproteobacteria and Methyloversatilis were the dominant denitrifying bacteria in all MBBRs.PICRUSt predicts that the relative total proportions of genes involved in denitrification of MBBRs with different carriers are corresponding to the nitrogen removal capability.(2)High ROC denitrification rate are achieved by applying Arundo donax as solid carbon source and bio-carrier for denitrifying MBBR,and NO3--N and TIN removal efficiency are 73.19%±19.53%and 69.8%±16.99%,respectively.The genes copy numbers,relative abundance of dominant microorganisms and relative total proportions of genes involved in denitrification of Arundo donax MBBR are similar with other MBBRs.(3)When the influent NO3--N and TN increase within the range of 24.23±8.69 and 44.10±7.37 mg/L in the modified PE MBBR,their removal ratio remains stable with increasing removal rate,and the NO2--N removal ratio and rate decrease.When the influent NO2--N increases within the range of 20.94±5.78 mg/L,both of the removal ratio and rate of NO3--N and TN decrease,while the NO2--N removal ratio and rate increase.The copy numbers of nitrogen removal genes,relative abundance of dominant microorganisms and relative total proportions of denitrifying genes are corresponding to the variation of nitrogen removal efficiency.(4)The NO3--N and TN removal ratio and rate are similar when the water temperature of MBBR are at 25℃ and 15℃.The copy numbers of nitrogen removal genes and relative total proportions of denitrifying genes are also similar while the relative abundance of Proteobacteria,Alphaproteobacteria and Thauera at 25℃ are higher than those at 15℃.The relative abundance of Bacteroidetes、Flavobacterium and Methylotenera at 25℃ are lower than those at 15℃.