Study On Operational Optimization And Bacterial Population Structure Of A New Deep-bed Denitrification Filter

With the "Thirteenth Five-Year Plan" and the end of the battle against water pollution,environmental issues are still the key to the "Fourteenth Five-Year Plan".Deep-bed denitrification filter(DBDF),as one of the effective ways to solve the current conventional process of urban wastewater treatment plant effluent total nitrogen exceeds the standard,both nitrogen removal and phosphorus removal and sand filtration function.In this experiment,DBDF adopts a new air-water distribution system,which can directly support the filter media,reduce the infrastructure cost of the filter,uniform air-water distribution,and reduce operating energy consumption.In this paper,the efficacy of the self-developed DBDF for municipal wastewater treatment was investigated by using the effluent of the high efficiency sedimentation tank of the wastewater plant as the pilot influent,exploring the primary and secondary relationships of the influencing factors of the filter,optimizing the nitrogen release procedure,and investigating the species diversity and microbial flora structure of DBDF using high-throughput sequencing technology.In this experiment,DBDF tank treated municipal wastewater with good results.,it can ensure that the effluent TN is less than 5.00 mg/L and has considerable removal effect on TP and SS,which can replace the work of traditional sand filtration tank,can stably reach the standard A of " Discharge Standard of Water Pollutant for municipal wastewater(DB11 890-2012)".The influencing factors of DBDF tank were analyzed by single-factor test.Nitratenitrogen removal rate decreases with increasing filtration rate,and 6.25 m/h is the critical point in this experiment,and the consumption of sodium acetate for the removal of unit nitrate nitrogen will increase significantly when the filtration speed is greater than 6.25m/h;the removal rate of nitrate-nitrogen increases with increasing C/N,and a significant accumulation of nitrite-nitrogen occurs at lower C/N;the effect of temperature on denitrification was significant,with a 34.86 % decrease in nitrate-nitrogen removal at low temperatures in winter compared to high temperatures in summer;the backwashing process is not conducive to the denitrification process of the filter tank,and the recovery period is longer.The orthogonal test verifies the conclusion that the filtration rate,C/N and water temperature affect the depth denitrification of the DBDF.The influent water temperature is the most important factor affecting the denitrification effect of the DBDF.C/N And filtration rate are the secondary factors in turn.The traditional trigger conditions and procedures for nitrogen release have certain drawbacks,so they are optimized and improved,and the nitrate nitrogen removal load is included as a parameter,and the pressure loss and time interval are used as guarantee conditions.Instead of a fixed time,the trigger condition was changed to one in which the time and nitrate-nitrogen accumulation were the trigger conditions in the middle of the pre-backwash period,and the pressure became the main condition in the middle and late stages,which was more adapted to the different stages of the filter operation process.The nitrogen release program has been improved.After triggering the program,the backwash pump and wastewater valve are turned on directly,and the water flow releases the nitrogen accumulated in the filter tank while part of the suspended matter and sludge can be discharged through the wastewater valve and waste water pipe.Compared with the original program,the new program takes 65.69% less time for a single nitrogen release,and the water production rate of the new program has increased by 3.77 percentage points in four backwash cycles.The species diversity analysis shows that compared to biochemical pool sludge,DBDF sludge differs greatly in species diversity,with lower species richness,and microbial functional specialization.At the phylum,class,and genus levels,the microbial community structures on top of suspended sludge and filter media biofilm before and after backwashing in DBDF were similar in species composition,but there were some differences in the proportion of each type of species,and there were large differences in the relative abundance of species compared with biochemical pool sludge.Among them,bacteria related to denitrification accounted for the highest proportion of 49.5% in the DBDF,while only 8.9% of the biochemical pool.It indicates that the dominant microbial species of DBDF are more concentrated and have higher abundance of denitrifying functional flora than biochemical pool sludge,and have stronger denitrification capacity.The backwashing process has little effect on the relative abundance of bacteria in the DBDF,and the air-washing process in the backwash increases a part of aerobic denitrifying bacteria with low relative abundance,and the scouring effect leads to the reduction of biomass in the filter,which is the root cause of the poor denitrification effect within a short time after the backwash.