Study On The Effect And Microflora Characteristics Of Oxidation Ditch And MBR In Treating Municipal Wastewater

The structure of microflora in wastewater treatment plants（WWTPs）determines the effect of wastewater treatment.In this study,samples of influent,effluent and activated sludge from oxidation ditch and membrane bioreactor of a WWTP in Urumqi were collected,and 16S r RNA gene sequencing technology was used to explore the flora structure and functional bacteria in the system.Metagenomic sequencing technology was used to explore functional genes,antibiotic resistance genes（ARGs）and mobile genetic elements（MGEs）carried by th e flora.The main research results of this paper are as follows:（1）The effluent water quality of oxidation ditch and MBR system can meet the design discharge standard stably,and both of these two processes have a high removal effect on pollutants.Among them,the average removal rates of COD,BOD₅,SS,NH₄⁺-N,TN and TP by oxidation ditch process are94.41%,97.12%,98.13%,98.47%,83.47%and 95.21%,respectively.The average removal rates of MBR process were 95.19%,98.69%,98.93%,97.28%,80.35%and 97.18%,respectively.（2）Bacteria w as absolutely dominant,with a relative abundance of 95.66to 99.23%.The dominant bacteria in influent were Firmicutes and Proteobacteria,Lactobacillu and Trichococcu;anaerobic selection tank did not inhibit most filamentous bacteria.Under the same influent condition,there was no significant difference in the species and relative abundance of bacterial community between oxidation ditch and MBR activated sludge（P>0.05）,which was not affected by process type.The bacterial communities in the effluent of oxidation ditch and MBR system were quite different at the genus level.Unclassified＿d＿Bacteria and Pseudomonas were dominant in the effluent of oxidation ditch,while Ardenticatena,Deinococcus,Microthrix and Mycobacterium were dominant in MBR effluent.（3）Nitrifying bacteria were the most abundant in the sludge of MBR membrane tank,which is caused by the long sludge retention time and membrane interception of MBR membrane tank;Nitrosomonas and Nitrospira were the dominant ammonia oxidizing bacteria（AOB）and nitrite oxidizing bacteria（NOB）in the sludge,respectively;Acidovorax was the dominant denitrifying bacteria,the relative abundance was 0.49～15.73%;Tetrasphaera was the dominant phosphate accumulating organisms（PAOs）,the relative abundance was0.22～2.70%.（4）Nitrification and denitrification pathways were intact in oxidation ditch and MBR system.Six nitrification genes were detected in all samples,including amo CAB,hao and nxr AB,and nxr AB was the most abundant,ranging from 8.73%to 10.93%.Ten denitrifying genes were detected in all samples,including nar GHI,nap AB,nir K,nir S,nor BC and nor Z.The relative abundance of nar GHI was the highest,ranging from 10.06%to 12.12%.A total of 17 functional phosphorous accumulation genes were identified,among which phn P,pat and E4.1.1.82 were abundant in the sludge samples.（5）Twenty ARGs were detected in all samples,and the relative abundance of all ARGs were 16.16～27.31%,12.97～14.40%and11.95～13.10%,respectively,with multiple resistance,polypeptide and fluoroquinolones.There was no significant difference in ARGs subtyp es between oxidation ditch sludge and MBR sludge,mainly including mac B,pat A,rpo C,lia R,ole C,mfd and ala S,and their relative abundances were 4.22～6.03%,1.51～3.83%,2.67～7.62%,0.47～3.73%,0.82～3.53%,2.97～3.64%and2.05～2.91%,respectively,which mig ht be caused by the absence of significant difference in bacterial flora.The removal rates of ARGs by oxidation ditch and MBR system were 77.17%and 12.16%,respectively,and the oxidation ditch system was more effective in removing ARGs.（6）A total of 10 MGEs types were detected in oxidation ditch aerobic sludge and MBR membrane tank sludge,of which transposon was absolutely dominant,with the highest relative abundance of 67.71%and 64.04%,and the abundance in MBR membrane tank sludge（25.66copies/cell）was higher than that in oxidation ditch aerobic sludge（20.60copies/cell）,which was mainly related to the higher suspended solid concentration of mixed liquid（MLSS）in MBR membrane tank.