Effects Of Microbial Carriers On MBBR Process Performance And Microbial Community Structure

The traditional microbial carrier materials used in MBBR are spherical polypropylene or tubular polyethylene.Although this kind of microbial carrier has relatively durable advantages,it also has the disadvantages of microbial adhesion and poor fluidization.In this study,the MBBR process was used to treat simulated wastewater.Three groups of MBBR reactors were operated synchronously with three kinds of microbial carriers : Polyurethane(PU),Polypropylene(PP)and Polyurethane(PPC).Under the influent conditions of ?(COD)=400 mg/L;?(NH4+-N)=20 mg/L;?(TP)=4 mg/L,the start-up performance of different microbial carriers on the MBBR process,COD removal effect,total nitrogen and total phosphorus removal effect was investigated;16S r DNA gene sequencing based on high-throughput sequencing technology was used to analyze the changes in the microbial community structure on the biofilm of the three carriers,and the metagenomic sequencing technology was used to analyze the functional genes.Study the nitrogen metabolism genes,and analyze the metabolic pathways of nitrogen elements.According to the effluent quality of three groups of MBBR,MBBR process has a good effect on COD removal,and the effluent COD concentration of each device meets the requirements of Class IV water in " ?Environmental Quality Standards for Surface Water?." In terms of nitrogen removal,the ammonia nitrogen removal rates of PPCMBBR,PU-MBBR and PP-MBBR were 69.32 %,71.24 % and 62.55 %,respectively.Although PU-MBBR had the best ammonia nitrogen removal effect,its denitrification effect was not ideal,so the total nitrogen removal effect was not good.Considering the ammonia nitrogen and nitrate nitrogen,PPC-MBBR had the best nitrogen removal effect in the three groups.In this experiment,three groups of MBBR device for TP removal effect is poor,effluent TP average concentration did not reach the ?Discharge standard of pollutants for urban sewage treatment plants? level A standard.The reason is that a large amount of free nitrate nitrogen inhibits polyphosphate accumulating bacteria.The 16 S rDNA sequencing of biofilm samples of three microbial carriers showed that PU carrier had the highest microbial richness.At the genus level,the difference of microbial community structure is obvious.There are high abundance of Denitratisoma and Nitrospira in PPC-MBBR,which may be the reason why PPC-MBBR has the most stable denitrification ability in the three groups.High abundance of Sphaerotilus was found in PU-MBBR,which may be related to high oxygen mass transfer efficiency of PU carrier and high Fe2 + concentration in raw water.In addition,high abundance of Haliscomenobacter was detected in PU-MBBR,indicating that filamentous bacteria swelled in PU-MBBR at low ambient temperature.The high abundance of bacteria in PP-MBBR did not have obvious nitrification / denitrification ability,and the relative abundance of Denitratisoma in PPC-MBBR was low(0.18 %),resulting in poor denitrification effect in PP-MBBR..In addition,the Thauera bacteria capable of aerobic denitrification only detected low relative abundance in the three sets of devices in this experiment,which led to the total nitrogen removal in the three sets of devices in this experiment not reaching a better level.According to the results of macro gene sequencing and KEGG functional gene annotation,687509,815894 and 802857 functional genes were obtained from PPC,PU and PP vectors,and 666 functional genes related to nitrogen metabolism were annotated,accounting for 0.097 %,0.082 % and 0.083 % of the total functional genes of PPC-MBBR,PU-MBBR and PP-MBBR,respectively.According to the nitrogen metabolism pathway diagram and the relative abundance of functional genes related to the reaction process,it was found that the relative abundance of denitrification-related functional genes measured in this experiment was the highest,followed by nitrification-related functional genes.These phenomena showed that nitrification and denitrification played a dominant role in the denitrification process of the three experimental devices in this experiment.The functional genes of this process were analyzed,and it was found that the Amo CAB and Hao genes in the reaction process of transforming ammonia nitrogen into hydroxylamine and nitrite nitrogen were less,which also led to the transformation of ammonia nitrogen into the rate-limiting step of the whole denitrification process,and it was also the reason why this experiment did not achieve higher total nitrogen removal rate.