Influence Of The Sodium Acetate On Anammox Biofilm System

With the rapid economic development and the improvement of people’s living standard,water pollution in China has changed from organic pollution to eutrophication caused by nitrogen and phosphorus.Anaerobic Ammonium Oxidation（ANAMMOX）has become a promising biological nitrogen removal process because of its high nitrogen removal efficiency and low cost;it has been studied and applied to wastewater treatment.However,the ANAMMOX bacteria are sensitive to the environment with low growth rate,which limits its applications.For example,high concentration of the influent substrates（NH₄⁺-N and NO₂^--N）can inhibit ANAMMOX bacteria.Besides,organic matter is another important factor affecting the stability of ANAMMOX system when treating the real wastewater.Biodegradable organic matter can participate in the denitrification process,which will inhibit ANAMMOX under its high concentration.However,the low concentration of organics can also promote the nitrogen removal.The biodegradable organics can change the nitrogen removal efficiency,with altering the microbial structure and the interaction among the microorganisms in the system.Therefore,in this study,the ANAMMOX biofilm system was coupled with sequencing batch reactor（SBR）.The activity of ANAMMOX bacteria was further improved by gradually increasing the concentration of the influent substrates.The biofilm under high and low nitrogen-load conditions were analyzed by high throughput sequencing to understand the variations of microbial structure and distribution of functional microorganisms in the biofilm.After the ANAMMOX biofilm system was stable,sodium acetate was selected as the biodegradable organic matter to investigate its influence on nitrogen removal of the ANAMMOX biofilm system.The variations and diversity of microbial community were analyzed from the micro-aspect,to understand the effect of organic matter on synergetic-competition among nitrogen removal functional microorganisms.Furthermore,the mechanism of nitrogen removal in the system was also studied.An immobilized polyurethane and polypropylene packing were applied in SBR reactor to enrich ANAMMOX bacteria.The ANAMMOX biofilm system was successfully started after 35 days,and the total nitrogen removal efficiency（NRE）reached more than 85%.Subsequently,the concentration of influent substrates was increased gradually,and the total NRE was maintained at 90%when the nitrogen loading rate（NLR）was increased to 0.6kg/（m³·d）.The high NLR promoted the biofilm formation;under the protection of biofilm,the activity of ANAMMOX bacteria was improved and the resistance of system to loading fluctuation was also enhanced.In addition,the microbial community structures under different nitrogen loadings were analyzed by high throughput sequencing.The results showed that as nitrogen load increased,the relative abundance of the phylum Planctomycetes increased from 6.16%to 9.98%.The genera Candidatus＿Kuenenia,Candidatus＿Brocadia and unclassified＿f＿＿Brocadiaceae were detected in the biofilm,and Candidatus＿Kuenenia had the highest abundance among these three ANAMMOX bacteria genera.With the influent nitrogen load increased,the abundance of Candidatus＿Kuenenia increased from 5.78%to 8.06%,which guaranteed the stable nitrogen removal in the ANAMMOX biofilm system.After the ANAMMOX biofilm system was stable,sodium acetate was added as a biodegradable organic matter to investigate its impact on the nitrogen removal in this system.The results showed that denitrifying bacteria and ANAMMOX bacteria displayed synergetic effect under the condition of low and medium sodium acetate concentrations（120±10mg/L and 240±10mg/L,respectively）;the total NRR reached 96%when the sodium acetate concentration was 240±10mg/L.Under the condition of high sodium acetate concentration（350±20mg/L）,the competition between denitrifying bacteria and ANAMMOX bacteria was stronger,leading to significant inhibition on ANAMMOX;NRR decreased below 85%,with NH₄⁺-N and TN removal efficiency of 70%and 83%,respectively.High throughput sequencing results of biofilm samples at different sodium acetate concentrations found that the relative abundance of the phylum Chloroflex decreased,while the phyla Proteobactria and Planctomycetes became the dominant phyla with the sodium acetate concentration increased.Meanwhile,the relative abundance of the family Brocadiaceae,which included all ANAMMOX bacteria genera,increased to 12.79%,which suggested that the sodium acetate promoted the enrichment of ANAMMOX bacteria in the biofilm and provided a basics for nitrogen removal in the system.The genera Candidatus＿Kuenenia,Candidatus＿Brocadia and unclassified＿f＿＿Brocadiaceae were also detected in the biofilm;the relative abundance of Candidatus Brocadia was very low among all biofilm samples.The unclassified＿f＿＿Brocadiaceae and Candidatus Kuenenia were the dominant genera,but they were both affected by the concentration of sodium acetate.