| This study is based on two sewage treatment processes: Oxidation Ditch and Membrane Bioreactor.The flat-sheet membrane modules are placed in a laboratory-scale oxidation ditch,and an aeration device is provided under the membrane module.Four underwater pushers were placed in four different areas to perform cyclic thrusting,and a new type of Oxidation Ditch Membrane Bioreactor(Oxidation Ditch Membrane Bioreactor,OD-MBR)was assembled.Compared with the traditional MBR,this reactor not only has the advantages of simultaneous nitrification and denitrification in the oxidation ditch,but also has the characteristics of high efficiency interception and high sludge load operation of the membrane bioreactor,and can effectively reduce membrane pollution and energy consumption.This article mainly analyzes the various operating performances of the OD-MBR system,especially the study of the distribution,fraction and transformation of phosphorus(P)during the operation of the reactor,the P release and uptake process,and the variation of the microbial community.It’s hoped that the obtained results may provide a useful reference for optimizing the design and operation of an enhanced MBR to achieve higher and more stable P-removal.In this experiment,the speed and structure of the underwater pushers in the OD-MBR are modified to make it have a more suitable and stable flow.The sludge was poured into OD-MBR after cultivation for simulated wastewater treatment experiments.The reactor was operated stably in continuous flow mode for 80 days,during which the various water quality indicators of the reactor and the properties of the sludge mixture were tested,and the results showed that: OD-MBR had a high and stable removal of COD and TN,which the average removal efficiency could reach about 95% and 85%,respectively.TP removal was not ideal and showed large fluctuations,and the phosphorus concentration in the effluent achieved the highest value on the 40 th day.After discharging parts of sludge was discharged for three times from day 40 to 42(total 110.56 g dry sludge altogether)from the reactor,the removal efficiency of phosphorus significantly improved.The morphology,distribution and migration of phosphorus in the reactor at different time stages were studied.31 P nuclear magnetic resonance technology(31P NMR)was used to identify and analyze the specific types and relative content of phosphorus compounds in the sludge.Anaerobic Phosphorus Release Rate(PRR)and Aerobic Phosphorus Uptake Rate(PUR)of the sludge during the period were measured,and the above-obtained data was curve-fitted by Data processing software such as Origin to establish OD-MBR anaerobic phosphorus release and aerobic release Phosphorus absorption theoretical model,analysis of model parameters and fitting effects.High-throughput sequencing technology was used to observe the composition characteristics and changes of the microbial community during the operation of the OD-MBR system,and to explore the succession of populations related to phosphorus-accumulating microorganisms.The results showed that in the OD-MBR system,phosphorus mainly occurred in microbial cells,followed by extracellular phase and the least in aqueous phase.in terms of the fraction of phosphorus,inorganic phosphorus(IP)is the reactor The main form of medium phosphorus,and non-apatite inorganic phosphorus(NAIP)is the main form of inorganic phosphorus.31 P NMR results showed that orthophosphate(Ortho-P)and phosphate monoester(Monoester-P)were the main types of inorganic phosphorus and organic phosphorus in sludge cells,respectively.After running for a period of time without sludge,the content of polyphosphate(Poly-P)was obviously decreased,indicating that the activity of PAOs has been weakened.The results of HTS exhibited the various microbial community structure of the bioreactor in different periods,and the stability of the microbial community continued to increase with the long-term operation of the reactor.The relatively high abundance of bacteria at the phylum level included Proteobacteria,Chloroflexi,Actinobacteriota and Bacteroidota.It was found that in sample A40(reactor running for 40 days),the content of Proteobacteria(a large number of PAOs belonged to)got evident decline.It is speculated that the decrease of this type of bacteria may be the biological factor of the decrease in the efficiency of nitrogen and phosphorus removal during the corresponding period.In summary,this experiment proves that the oxidation ditch membrane bioreactor can efficiently and stably remove COD and TN under high load conditions.What’s more,in terms of maintaining a stable P-removal efficiency,an OD-MBR should discharge excess sludge at a suitable time point by comprehensively considering the distribution,fraction and transformation of phosphorus. |
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