Study On The Influence Of Pollutant Metabolism And Biofilm Self-renewal Process In MBBR System With Different Sludge/Biofilm Ratios

Biocarrier is the important part of MBBR technology,the quality of biocarrier directly affects the treatment effect of MBBR system.Recent studies find that the special physical characteristics of Aerobic flexible suspension biocarrier Porous Bio-Gel（PBG）biocarrier are very consistent with the basic requirements of MBBR technology.However,the current research on PBG biocarrier mainly focuses on the optimization of treatment technology,lacks the in-depth analysis on the performance of a single biocarrier,which cannot provide effective reference for the promotion and application of PBG filler.In view of the above analysis,this paper will adopt the MBBR technology to conduct experimental study.Analyzing the physical characteristics,chemical composition,and microbial population distribution characteristics of the biofilm by studying the metabolic process of suspended sludge concentration and carrier biofilm,the change law of biofilm self-renewal process under different conditions.In addition,studying the self-renewal and shedding of biofilm to explore the dynamic change law of biofilm by selecting a test system with a high PBG biocarrier load,but a small number of microorganisms in the reactor,sparse bacterial micelles and a low removal rate.The main research contents and conclusions of this thesis are as follows:（1）Under the test conditions of DO of 2.0-4.0 mg/L,temperature of 15±2°C,and p H of 7-8,the effect of different initial sludge concentration on PBG carrier biofilm is studied by continuously feeding the simulated wastewater into the reactor.The test results show that the COD removal rate of 400 mg/L（R1 systems）,1000 mg/L（R2 systems）and 1800 mg/L（R3systems）with initial sludge concentration all reach more than 80%.Among them,the NH₄⁺-N removal rate of R1 system is 79.65%,the load of PBG biocarrier reaches 4899.38 mg/L,and there are many filamentous bacteria on the biocarrier surface and scattered;The NH₄⁺-N removal rate of R2 system is 97.78%,the load of PBG biocarrier reaches 7177.50 mg/L,and the microbial species on the biocarrier are richer,including bacilli and cocci,as well as protozoa and metazoan;The NH₄⁺-N removal rate of R3 system is 96.01%,the load of PBG biocarrier reaches 6773.13 mg/L,and there are obvious and sparse bacterial micelles in the carrier biofilm.（2）In the stable operation of the MBBR technology,the effect of suspended sludge concentration on membrane biomass and pollutant metabolism is studied by feeding the suspended sludge of different concentrations into 3 reactors.The test results show that when the suspended sludge concentration is 200 mg/L（R1-200 system）,the average removal rate of COD is 87.55%,the removal rate of NH₄⁺-N is higher than 70%,the load of PBG biocarrier decreases from 10251.25 mg/L to 7481.88 mg/L,and the metazoans in the carrier biofilm are constantly reproducing and activated sludge is fragmentation;When the suspended sludge concentration is 800 mg/L（R2-800 system）,the average removal rate of COD is 88.81%,the removal rate of NH₄⁺-N is more than 95.79%,the load of PBG biocarrier increases from10861.25 mg/L to 11575.63 mg/L,and the carrier biofilms enrich a large number of cold-resistant microorganisms,form a bacteria-protozoa-metazoan biological chain,which enhanced the nitrification performance;When the suspended sludge concentration is 1400mg/L（R3-1400 system）,the average removal rate of COD is 88.81%,the removal rate of NH₄⁺-N is 66.29%,the load of PBG biocarrier decreases from 13,418.75 mg/L to 11,398.75mg/L,and there are a relatively small number of microorganisms and sparse bacterial micelles in the carrier biofilm.（3）In the successful and stable operation of the MBBR technology,the influence of different sludge/membrane ratios on pollutant metabolism efficiency is quantitatively analyzed by controlling the sludge concentration in the system.The removal rate of COD in the system with more sludge and less membrane（R1-A system）can reach 93.50%,the removal rate of NH₄⁺-N is 60%,the removal rate of TN is 35%,but there is less intercellular material on the cell surface of the PBG carrier biofilm;The removal rate of COD in the system with less sludge and more membrane（R2-B system）can reach 92.54%,the removal rate of NH₄⁺-N is80%,the removal rate of TN is 60%,and the PBG biocarrier biofilm contains more intercellular substances.（4）A test system（R3-1400 system）with high PBG biocarrier load,a small number of microorganisms in the reactor,sparse bacterial micelles,and low removal rate is adopted to study the promotion mechanism of the competition between sludge and membrane to the self-renewal process of biofilm.The test results show that the PBG carrier biofilm in the MBBR technology takes about 28 days to complete a self-renewal process under the conditions that the volumetric load is 1.4 kg COD/（m³·d）and the load of PBG biocarrier is more than 10,000mg/L,and the shedding rate is 50%.In addition,the p H of R3-1400 system fluctuates significantly while is weakly acidic,the average removal rate of COD is 91.42%,and the removal rate of NH₄⁺-N fluctuates greatly,but finally stabilizes at more than 85%.Figure 26,table 12,reference 69.