Stufy On Improved Type Of A~2/O Process For Biological Pshosphoru Removal In Rainy Season

One year is clearly divided into dry and wet seasons in Kunming according to theamount of precipitation distribution in time. From May to October is wet season, theamount of precipitation is85%of a year;from November to next April is dry season,the amount of precipitation is85%of a year. Because of the “separate drainage system”planned clearly has not yet been implemented and the drainage system is not perfect, inthe rainy season, there is still a lot of rain flowing into the sewage treatment plant,increase the operating costs of sewage treatment and affect the treating effect ofsewage treatment plant. Compared to the dry season, sewage treatment plant influentwater becomes large, and BOD5, COD, TN, TP, NH3-N of the inlet diverse in wetseason. So this research is very important and great significant to guarantee stableand efficient operation of the Luolong river city sewage treatment plant and improve thewater environment quality of Dianchi lake.The research is using0.2m3/d scale test model of improved A2/O process to studyon nitrogen and phosphorus removal in the view of the feature wet season and wetseason diverse clearly and inlet water quality are significantly different in differentseason. The main results are:①Through the analysis of the inlet water quality weighted average data fromKunming fifth sewage treatment plant and Chengong sewage treatment plant in dryseason and wet season,at the same time combined the design inlet water quality ofLuolong river sewage treatment plant,predict the inlet water quality of this plant:COD,TN,TP,NH3-N are respectively300mg/L、30mg/L、5mg/L、30mg/L in dryseason；COD、TN、TP、NH3-N are respectively230mg/L、25mg/L、4mg/L、25mg/Lin wet season.compared with dry season,every index concentration of inlet water alldecrease in wet season.②Simulating the condition of the inlet water quality in dry season,throughorthogonal test find that the modified A2/O process reached the best phosphorus removeeffect and energy consumption is reasonable in the condition: MLSS is3000~4000mg/L;return sludge ratio is40%;DO is2.5~3mg/L in aerobic pond; internal reflux ratio is200%.③Simulating the condition of the inlet water quality in wet season, through singlefactor test, adjusting internal reflux ratio、return sludge ratio、DO and the COD/P of the inlet water，research the changes of the phosphorus removal performance and thecontaminant removal in every stage in modified A2/O process, and get the bestoperating condition of this process in wet season: DO is2.5`3mg/L in aerobic pond;internal reflux ratio is200%; return sludge ratio is40%; MLSS is3500mg/L; sludge ageis18d.④DO almost not affect the COD removal but affect the phosphorus removal andsludge sedimentation significantly.when2.0mg/L<DO<4.0mg/L, the TP concentrationof outlet water increases with the DO reducing, but the phosphorus removalperformances are all better. when DO<1.0mg/L, Phosphorus removal efficiencysignificantly decreases, phosphorus removal ability deteriorates significantly. Sorecommended keeping DO2~3mg/L in aerobic pond. with the DO reducing in aerobicpond,SVI increases and the sludge sedimentation is more and more poor.⑤In different COD/TP conditions, the system keeps stable COD removal ratio.When the COD/P of inlet water is40~100，TP removal rising gradually with theincreasing of COD/P. But when COD/P>100，TP removal declines slightly. The reasonis the competition of glucose accumulating organisms （GAOs） and phosphorusaccumulating organisms （PAOs）,which causes PAOs are less in sludge compared to inthe condition of low COD/P, so TP removal ratio declines.