| At present, the prevalent problems in urban sewage treatment plants of nitrogenand phosphorus removal unstable caused by lack of carbon source have influenced onthe ecological environment increasingly serious. In this case, it is necessary to developand optimize the effective utilization of the carbon source and integrate nitrogen andphosphorus removal wastewater treatment technology. The advantages of the systemcombining step-feed process with aerobic biofilm are saving internal reflux facilities, noexternal carbon source, improving system resistance to impact load and increasingsystem biomass, etc. By the means of theoretical analysis, pilot tests combined withsmall scale tests, a systematic study on the performance of the combined process iscarried out to hope to provide guidance of promoting the application in the field oflow-carbon source area and upgrading sewage plants of similar processes.In order to ensure the combined-process reactor in the state of the plug-flow aswhole, the structure of the reactor has been transformed through flow patternexperiments, providing a suitable reactor flow pattern for subsequent biochemical tests.Through the research of HRT, temperature, influent flow distribution ratio, sludgerecycle ratio and anoxic zone volume ratio impacting on the combined process efficacy,the study researchs on the features and advantages of the combined processsystematically, optimizes reasonable range of parameter values. It is found that theefficiency against external shock of the combined process system was more obviouscompared with purely activated sludge system. In the case of low HRT, the measures ofincreasing aeration and reducing sludge can improve denitrification effect of the system,and TP can be removed by chemical approach; temperature changes can be mainlyachieved by adjusting the sludge concentration and DO concentration in order to ensurebetter treatment effect. Through analyzing test urban sewage water conditions, it is foundthat the segmented water distribution pattern is progressively decreasing. The sludgereturn ratio made little influence on denitrification of the combined process, and thereturn ratio of50%to100%is more appropriate in view of not affecting thedenitrification performance and reducing energy consumption. Under the premise ofbest water diversion ratio, maximizing the anoxic zone ’s volume can improve system TN removal.Obvious simultaneous nitrification and denitrification phenomenon appeared in theaerobic zone of th combined proces, it can be found that simultaneous nitrification anddenitrification performance of all levels of aerobic zone differs significantly, the firstlevel best, the second stage, followed by the third level worst. Dosing filler enhance theability of simultaneous nitrification and denitrification. In the case of the treatmenteffect of the overall consideration of various water quality indicators, pilot reactortaking the cascade aeration dissolved oxygen with0.5mg/L,1.0mg/L,and1.5mg/Lrunning condition, simultaneous nitrification reactor denitrification capacity has beenfully played, and the study analyzed denitrification mechanism from the angle of thewater way combined with biofilm.Using microscope microscopic examination technology, through observingmicrobial composition and morphological features of activated sludge and biofilm in therunning stage of the system, it is found that the biofacies are abundant of the combinedprocess,and biofacies of biological activated sludge and biofilm sludge are different,then the study analyzed microbial feature in the reactor and microbial immobilizationmechanism. During the test,sludge observed yield of the combined process are basicallybetween0.12and0.21kgMLSS/kgCOD, significantly lower than the activated sludgeprocess. Environmental scanning electron microscope results showed that holes andchannels for the exchange of substances existe in the floc and biofilm, and they createthe material and environmental conditions for simultaneous nitrification anddenitrification of combined process systems. SOUR and DHA of activated sludge andbiofilm of the combined process reactor showed a downward trend, biological activity isaffected by temperature and carbon source, and the sludge activity is proportional toorganic matter concentration in the environment.Through system flora diversity and similarity analysis,comparing biofilm diversityindex of each level of the activated sludge with the biofilm, diversity index of biofilm ishigher than the activated sludge, indicating that microbial populations in the biofilm aremore rich. Simultaneously, similarity of biofilm samples is significantly higher than thatof activated sludge, caused partly by higher diversity of the microbial flora in thebiofilm.Process combining Multi-level A/O with aerobic biofilm is an energy-saving, efficient and stable wastewater treatment process, it can be applied to new constructionand renovation projects, by adjusting the various operating parameters to achieve thebest conditions, and improving water quality. |
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