Optimization Of Operating Conditions Of Biofilm Process And Anaerobic Denitrification Characteristics In Aquaculture System

Microorganisms and their extracellular polymers are spatially distributed in biofilms,and their denitrification functions are directly related to abiotic factors and attached microbial community structures in membrane bioreactors（MBR）.In recent years,the exploration of MBR operating conditions is mostly for the study of single or two factors,and there are few reports on the interaction of multiple factors.At the same time of biofilm formation,the surface of biofilm is dominated by aerobic layer,and aerobic bacteria is the dominant genus.With the construction of biofilm,facultative anaerobic layer with facultative anaerobic and anaerobic bacteria is formed.Anaerobic layer,and anaerobic denitrification is an indispensable part of biological nitrogen removal.In the previous studies,most of them explored the metabolic characteristics of biofilm-attached microbial carbon sources under aerobic conditions,and little research has been reported on the metabolic characteristics of carbon sources under anaerobic conditions of biofilm-attached microorganisms.So how do you explore the best conditions for biofilm reactions?How to analyze the carbon source metabolism characteristics and community structure characteristics of attached microorganisms under anaerobic conditions?How to improve the efficiency of biofilm denitrification?In this experiment,a self-made aerated cylindrical membrane bioreactor was combined with orthogonal test to explore the optimal reaction conditions of MBR.At the same time,an ecological base was added as a carrier of biofilm in aquaculture system,and Biolog microplate technology was used to study the anoxia during biofilm formation.Metabolic characteristics of microbial community carbon sources under oxygen conditions,using Miseq sequencing technology to study the attachment of microbial community structure from biofilm to maturity,in order to explore the differences in carbon source metabolism under the anaerobic conditions of attached microorganisms during biofilm formation.The changes of microbial community structure in the process of biofilm formation,so as to clarify the carbon source metabolism characteristics under microbial anaerobic conditions,understand the biofilm anaerobic denitrification process,and provide a theoretical reference for improving the biofilm denitrification efficiency.The main findings are as follows:1)Most of the experimental groups in the orthogonal experiment completed the membrane on the 18th day of the experiment.In the experimental group of the 9groups,the removal rate of NH₄⁺-N was about 85%,and the removal rate of NO₃^--N was up to 8 About 90%,the removal rate of NO₂^--N is stable between 60%and 80%,and the removal rate of PO₄³⁺-P is stable at above 40%.The experimental results show that the influence of each element on the removal rate of NH₄⁺-N is:HRT>pH>DO>C\N,and HRT has the greatest influence on the removal rate of NH₄⁺-N.The optimal operating parameters for MBR operation are HRT of 4 h,DO of 6±0.5 mg\L,C\N of 3/1,pH of 7.The optimized NH₄⁺-N removal rate of MBR is as high as89.44%.2)With the formation of biofilm,the AWCD value of the attached microorganisms increased significantly under the anaerobic conditions（P<0.05）,that is,the carbon source utilization capacity gradually increased.The utilization of the six major carbon sources under anaerobic conditions during the biofilm formation process is significantly different from that under aerobic conditions.Under anaerobic conditions,the attached microorganisms have the highest utilization rate of amines,while in the case of aerobic conditions,The demand for polymers and amino acids is high;the utilization of single carbon sources under anaerobic conditions of biofilm-attached microorganisms is not the same as that under aerobic conditions.The types of microorganisms attached to single carbon sources under anaerobic conditions The demand is significantly less than the demand for a single carbon source under aerobic conditions.3)The results of Miseq sequencing indicate that the biofilm-attached microbial dominant bacteria include Proteobacteria,Bacteroidetes,Cyanobacteria and Firmicutes.In this experiment,the bacteria with higher degree of microbial enrichment during biofilm formation include Rhodobacter ofα-proteobacteria,Janthinobacterium,Burkholderiales andγ-proteobacteria ofβ-proteobacteria.Two species of bacteria,Xanthomonadaceae,Thermomonas,Rhodobacter and Janthinobacterium,play an important role in the denitrification of biofilms.