Experimental Study On Low Consumption Treatment Of Low C/N Wastewater With Biofilter Reactor

A single-stage biofilter reactor（BFR）coupling anaerobic digestion（AD）with Denitrifying Anaerobic Methane Oxidation（DAMO）and a two-stage BFR combing partial denitrification with anammox（PDA）were used to treat low C/N sewage in this study to explore a high-efficiency and energy-saving process for low C/N sewage treatment.Firstly,AD could be coupled with DAMO in a single-stage BFR through the operational mode of two step start-up and shortening hydraulic residence time（HRT）gradually;Then,the start-up of PDA was realized in two-stage BFR,and the effects of COD/NO₃^--N and temperature changes on the reaction rate of partial denitrification and the accumulation of NO₂^--N were explored in partial denitrification BFR（PD-BFR）;Finally,the stable PD-BFR and anammox BFR（A-BFR）were ran in series to explore the feasibility and nitrogen removal performance of the domestic sewage mixed nitrate wastewater treatment by two-stage PDA-BFR.The main results and conclusions of this study were as follows:（1）When the influent concentrations of NH₄⁺-N and COD at the bottom were 30±3mg/L and 200±10 mg/L respectively,and the influent concentration of NO₂^--N at the middle was 38±3 mg/L,the AD-DAMO was realized in a single-stage BFR by shortening HRT gradually.Under the conditions of HRT of 1.0 h and temperature of 30±1℃,the average concentrations of TN and COD in the effluent were 4.83 mg/L and 21.08 mg/L respectively,which led the average removal rates of TN and COD to 92.92%and 89.57%respectively in the stable period,implying that the high-efficiency of nitrogen and carbon removal could be achieved in a single-stage BFR coupled with AD and DAMO.（2）COD removal mainly occurred in the AD section of 0～60 cm,NH₄⁺-N and NO₂^--N removal and NO₃^--N production mainly occurred in the section of 60～135 cm in a single-stage BFR coupled with AD and DAMO.In addition,the 80～100 cm zone was the main nitrogen removal functional zone,and there were the highest extracellular polymeric substances（EPS）content and protein/polysaccharide（PN/PS）of the biofilm in the80～100 cm zone.The biofilm structure with high EPS and high PN/PS ensured the stability of microbial structure,and maintained high microbial activity under high load.At last,the results of high-throughput sequencing and qPCR showed that denitrifying bacteria,anaerobic ammoxidation bacteria,methanogens and methane-oxidizing bacteria were the main strains of biofilm in the 80～100 cm zone,while DAMO bacteria had low abundance but high activity.The high expression of functional genes that related to methanogenesis,methane oxidation,denitrification and anaerobic ammoxidation process was important to high efficiency removal of nitrogen and carbon.（3）When the ratio of COD to NO₃^--N was 2.3,the temperature was 30±1℃and HRT was 3 h,the average nitrate-to-nitrite transformation ratio（NTR）was 52.23%in PD-BFR.When the ratio of COD to NO₃^--N was increased to 3.0 and the temperature was decreased to 25±1℃,the average NTR was 43.68%,indicating that increasing COD/NO₃^--N and decreasing temperature had influence on NO₂^--N accumulation.The result of high-throughput sequencing analysis showed that increasing COD/NO₃^--N and decreasing temperature increased the species and abundance of denitrifying bacteria in PD-BFR system.In addition,the start-up of anammox was realized in A-BFR under the condition of influent NH₄⁺-N and NO₂^--N concentrations of 40±2 mg/L,temperature of 25±1℃and HRT of 6 h.The A-BFR maintained high efficient removal and stable operation when HRT was shortened to 3 h.The average effluent concentration and removal rate of TN were 11.12 mg/L and 86.15%respectively in the stable period.（4）The two-stage PDA-BFR running in series had high efficient removal to the low ratio of C/N domestic sewage mixed nitrate wastewater treatment.The effluent concentration of TN was lower than 15 mg/L and the average effluent concentration of COD was 15.03 mg/L in the stable period.The microbial analysis results of A-BFR showed that anammox bacteria and denitrification bacteria were existed in all zones.Especially in the 0～20 cm zone,Candidatus＿Brocadia was the dominant bacteria at the genus level,and there was a certain abundance of denitrification bacteria,such as Denitratisoma and Thauera.The anammox and denitrification process completed the advanced PD effluent treatment together.