| The combination of SNAD process and MBR reactor can not only provide a good growth environment for microorganisms,maintain high sludge concentration and activity,but also ensure high quality effluent quality,reduce the output of excess sludge,operating costs and energy consumption,hence it has extensive application prospects.Nevertheless,for this SNAD process in micro-oxygen upflow membrane bioreactor,there were few studies on the mechanism of information exchange and energy metabolism in this high sludge concentration system.Therefore,on the basis of maintaining the stable operation of the system performance,this study conducted the following research and drew conclusions from the perspectives of quorum sensing and sludge reduction:(1)Under the condition of C/N = 1(COD/ammonia nitrogen =200mg/L:200 mg/L),the stable operation of the system was maintained by regulating DO.The removal rate of ammonia nitrogen was about 90-100%,the concentration of nitrite nitrogen in effluent was about 3 mg/L,the concentration of nitrate nitrogen in effluent was about 5 mg/L,the removal rate of total nitrogen was above 85% and the overall removal of COD had been maintained above 90%.The activity of sludge was high,and its concentration was basically stable at about 23 g/L.The degree of sludge granulation in the system was high,and the particle size gradually increased with the operation.At the same time,a large number of full red particles could be seen flooding the reactor.(2)Repeated attempts were made to extract AHLs in the early stage,but they were unsuccessful.By analyzing the reasons for the failure of extracting AHLs from different angles,and combining with two metagenomic data,it could be found that the abundance of AHLs synthesis precursor genes was high,but the abundance of AHLs synthetic and sensing genes was much lower than that of AHLs quenching genes,and AHLs might be more quenched,so it was impossible to extract AHLs successfully.Combined with species analysis,AHLs synthetic genes were mainly distributed in Planctomycetes and Proteobacteria,AHLs sensing genes were mainly distributed in Proteobacteria,and AHLs quenching genes were mainly distributed in Chloroflexi and Proteobacteria.From the point of view of metabolic pathway,among QS metabolic pathways,unclassified＿c＿＿Anaerolineae,Rubrivivax and unclassified＿p＿＿Chloroflexi had higher contribution rates.(3)The mechanism of sludge reduction in the system was analyzed from a macro perspective,and it was found that the protease activity in the system was high(about 7 U/g),which laid a foundation for the system to exert hydrolysis and realize sludge reduction.Dehydrogenase activity,electron transfer rate activity and ATP content were relatively high,which were about100 U/g-VSS,220 U/g-VSS and 0.9 μmol/m L,respectively.The system realized sludge reduction by inducing more energy for cell metabolism instead of cell synthesis in low oxygen environment.(4)Through the analysis of metagenome data and KEGG,GO,COG and CAZy databases,it was found that the hydrolase in the system was relatively abundant and stably distributed,and the phylum-level bacteria containing more lysozyme were Proteobacteria and Chloroflexi,and a large number of hydrolases and hydrolytic bacteria promoted sludge reduction to some extent;the abundance and proportion of hydrolase activity,transferase activity,oxidoreductase activity,GT and GH were relatively high,indicating that the hydrolysis activity and energy metabolism of the system were high,thus achieving sludge reduction.(5)Combining the denitrifying genes and microbial phase analysis,it was found that a large number of denitrifying genes were distributed in Proteobacteria,Planctomycetes,Chloroflexi,unclassified＿d＿＿Bacteria,while nitrifying genes and anaerobic ammonium oxidation genes were less abundant but more active,which was also consistent with the microbial data.Under the joint regulation of the three processes,the system realized stable operation. |
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