Study On Low Carbon Source Wastewater Treatment In Multiple Anoxic And Aerobic Process

Organic carbon shortage in wastewater is a common problem for municipalwastewater treatment, and the multiple anoxic and aerobic (AO) process is one ofeffective biological nitrogen removal processes.Multiple anoxic and aerobic（AO） process were operated in anoxic and aerobicintermittently which have obvious advantage in aeration save and nitrogen removalefficiency.It can obviously enhanced nitrogen removal efficiency by step feed inanoxic stage of multiple anoxic and aerobic process since effective utilizing carbonsource.Besides,simultaneous nitrogen and phosphorus removal can be realize byinstalling anaerobic zone in front of the multistage AO process within theenrichment of denitrifying phosphorus accumulating.In this study,multistage AOprocess was used to treat low carbon wastewater with a caobon source to nitrogenratio5.The main content and results of this paper are as follows：Two multiple AO processes were operated under sludge retention times（SRTs）of169days and9days,respectively, and characteristics of enhanced biologicalnitrogen removal was examined so as to provide some clues for stable operation andoptimization of the process. Long-term operation showed that the effluent wastewaterquality was well under both SRTs, with the total nitrogen removal percentages of63.2%and64.9%, respectively. For nitrifiers, sludge retention times did not affect theactivities of ammonia oxidizing bacteria, but affected the activities of nitrite oxidizingbacteria with a lower activity occurred at the low sludge retention time. Based onactivities of denitrifiers utilizing different types of organic carbons, in the multiple AOprocess, denitrifiers mainly utilized external and internal organic carbon for nitrogenremoval, while endogenous denitrification contributed little to the biological nitrogenremoval.Two step feed multiple AO processes were operated under sludge retention times(SRT) of169days and9days, respectively, and the influent flow distribution was5:3:2. The aims of this study were to examine the characteristics of enhancedbiological nitrogen removal of the step feed multiple AO process.Long-term operationshowed that the effluent wastewater quality was well under both SRTs,with the totalnitrogen removal percentages of76.5%and74.2%, respectively. At high SRTs,theactivities of ammonia oxidizing bacteria was affected but a high nitrificationefficiency in reactor was obtained. However, at low SRT condition,the activities ofnitrite oxidizing bacteria was affected.Based on activities of denitrifiers utilizeddifferent types of organic carbons, in the step feed multiple AO process,denitrifiersacclimated at low SRTs had a higher activity than those at high SRTs.It could beneglected when denitrifiers utilized endogenous carbon or endogenous respirationcompare to external carbon for nitrogen removal.Characteristics of biological nitrogen and phosphorus removal in the multipleAO process with one-feed and step-feed modes were examined. The total inorganic nitrogen removal percentages were79.4%and64.4%, and the phosphorus removalpercentages were37.1%and33.3%under the one-feed and step-feed mode,respectively, indicating enhanced nitrogen removal in the step-feed mode. Under bothconditions, ammonia oxidizing bacteria and nitrite oxidizing bacteria were affected bythe step-feed mode, and the later was inhibited in a greater degree. Denitrifying ratewas not affected by the feeding mode, while high nitrite accumulated under theone-feed mode.Step-feed benefited enrichment of denitrifying phosphateaccumulating organisms, while a low phosphate accumulating organisms activitiesexisted.