Study On Microbial Structure And Function Of Wastewater Biological Treatment System Based On Metagenomic Sequencing

The distribution and function structure of microbial community in wastewater treatment plants(WWTPs)directly decides the wastewater treatment performance.In this study,activated sludge samples of oxidation ditch process from two WWTPs in Altay and Urumqi,and biofilm sample from MBBR process in a WWTP located in Urumqi were collected.Illumina metagenomic sequencing was used to explore the microbial community structure,functional category,nitrogen metabolism pathway and antibiotic resistance gene distribution of the biological treatment system that operates in a cold-region WWTPs.The main results of this study are as follows:(1)In activated sludge and biofilm,the relative abundance of bacteria was between96% and 99%,and that of archaea,eukaryote and virus was very low in all samples,indicating that the bacteria community played the most important role in wastewater treatment in WWTPs.The dominant phyla in all samples were Proteobacteria,Bacteroidetes,Chloroflexi,Actinobacteria and Verrucomicrobia.At the genus level,there were some differences among the dominant bacterial genera in different WWTPs in this study.The dominant genera in activated sludge of oxidation ditch were Dokdonella ? Dechloromonas ? Flavobacterium ? Haliscomenobacter and were Sulfuritalea?Acidovorax?Nitrospirae in biofilm of MBBR.(2)The results of functional annotation based on COG and KEGG database in activated sludge and MBBR biofilm were basically consistent.Among the activated sludge of oxidation ditch and biofilm of MBBR,the relative abundance of the functions related to metabolism was the highest,among which carbohydrate metabolism,amino acid metabolism and energy metabolism were the main functional categories.Compared with the activated sludge from oxidation ditch,the abundance of genes involved in the transport and metabolism of lipids,coenzymes,carbohydrates and nucleotides,as well as energy conversion were higher in the biofilm,indicating that the cell metabolism of microbial community in MBBR process was more diversified.(3)In this study,the pathways of nitrogen metabolism in the WWTPs were similar,which were mainly based on the nitrification and denitrification of traditional biological nitrogen removal,and unable to carry out a complete anammox reaction.In activated sludge of oxidation ditch and biofilm of MBBR,six functional genes related to nitrification were detected,including amo CAB,hao and nxr AB,and the relative abundance in biofilm of 12.38% was highest;ten functional genes related to denitrification were detected,including nar GHI,nap AB,nir K,nir S,nor BC and nor Z,the relative abundances of these functional genes of the WWTPs was 27.47% ? 28.57%.Hzs and Hdh genes related to anammox were not detected in the WWTPs in this study.(4)In activated sludge of oxidation ditch and biofilm of MBBR,the proportion of antibiotic resistant bacteria(ARB)is less than 1%,and the relative abundance of Acinetobacter was the highest,which was 0.05% ? 0.52%.The relative abundance of polypeptide antibiotics resistance genes(ARGs)was the highest,which was 14.01% ?14.48%,followed by fluoroquinolone ARGs.The relative abundance of tetracycline and sulfadiazine ARGs was low.Among all ARGs,the relative abundance of mac B belonged to Macrolide ARGs was the highest,which was 4.19% ? 4.33%;the relatively abundant ARGs,including evgs,mfd and sav1866,all had multiple resistances.The main resistance mechanism of ARGs in the WWTPs was the antibiotic efflux pump in this study.