Treatment Performance,Nitrous Oxide Production And Microbial Community Under Low-ammonium Wastewater In A CANON Process

As a new wastewater treatment process,completely autotrophic nitrogen removal over nitrite?CANON?has highlighted its many advantages during the decades.Compared to traditional nitrification and denitrification process,the CANON process has numerous advantages of reduced aeration without additional organic carbon,less sludge production,reduced operational and construction costs,and enhanced sustainability and economic benefits.However,due to the extremely harsh operating conditions required in the CANON process,it was still restricted to use.Currently,CANON technology has been successfully applied in various industrial wastewater treatments,such as sludge digestion,landfill leachate and other high-ammonium nitrogen,low-carbon wastewaters.Nevertheless,studies on the use of CANON technology to treat low-ammonium wastewater are still in the exploration stage and rarely reported.Therefore,it is necessary to study the application of CANON process to treat different types of low-ammonium wastewater.Additionally,Nitrous oxide?N₂O?as a powerful greenhouse gas in the atmosphere is capable of seriously damaging the ozone layer,in addition to producing acid rain.Nevertheless,wasterwater treatment process is an important source of N₂O production.Therefore,it is imperative to study the N₂O production in the CANON process with respect to the treatment of low-ammonium wastewater.To investigate the treatment characteristics,N₂O production during operation and the dominant microbial communities of anaerobic ammonia oxidation for treating low-ammonium wastewater,a continuous-flow CANON biofilm reactor which has been operated stably for a long time with high ammonia-nitrogen wastewater was studied.Two operational experiments were performed:the first one fixed the hydraulic retention time?HRT?at 10 h and gradually reduced the influent ammonium concentrations from 210,136,100,70 to 50 mg L^-1;the second one fixed the influent ammonium concentration at 30 mg L^-11 and gradually decreased the HRT from 10,7,5 to 3 h.At the same time,a temperature was held at 32±2°C,pH value varied between 7.5 and 8.2,and the dissolved oxygen?DO?was held at no more than 1.2 mg L^-1 through adjustments to the aeration rate.The major conclusions were summarized as follows:?1?Based on the CANON process,the total nitrogen removal efficiency exceeded80%,with a corresponding total nitrogen removal rate of 0.26±0.01 kg N m^-3 d^-1 at the final low ammonium concentration of 30 mg L^-1.?2?N₂O production was monitored by a N₂O microsensor in this work.The results showed that small amounts of N₂O up to 0.015±0.004 kg N m^-33 d^-11 at the ammonium concentration of 210 mg L^-1 were produced in the CANON process and decreased with the decrease in the influent ammonium loads.?3?The optimal DO concentrations for the CANON process in the treatment of different loads wastewater decreased with decreasing influent ammonium loads and ranged from 0.8 to 0.25 mg L^-1,corresponding to TNRR values of 0.47 to 0.09 kg N m^-3d^-1,respectively.?4?High-throughput 16S rRNA gene sequencing technology was used to identify the microbial communities at influent ammonium concentrations of 210 and 30 mg L^-1 in this work.The results showed that dominant functional bacteria Candidatus Kuenenia under high influent ammonium conditions was gradually succeeded by Armatimonadetes_gp5 under low influent ammonium conditions.