The Identification Of Bulking Sludge In Beishiqiao Wastewater Treatment Plant, Xi'an

DE-oxidation ditch is employed in Beishiqiao WWTP which serving the south and southwestem suburban of the industrial wastewater and sewage in Xi'an,China.The DE-oxidation ditch suffered seriously sludge bulking since the year of 2005.This research lasted 12 months,Through monitoring the quality of the influent and effluent,and the action of the cells(especially the selector),in order to find the sludge bulking reason.The results were showed as follows:(1) Based on the measurement the quality of influent in Beishiqiao WWTP,COD influent surpassed 60%of the designed influent concentration in the total frequency;and SS surpassed 50%;and TN surpassed 75%;NH₄⁺-N surpassed 68%;TP surpassed 75%,ranged from 4 mg/L to 17 mg/L;NO₃^--N was between 0.3～5.6 mg/L;NO₂^--N between 0.02～0.7mg/L;and PO₄^3--P was 2～10.4 mg/L.Obviously,the influent measurement of Beishiqiao WWTP was over the designed measurement.So Beishiqiao WWTP was usually in overloaded condition,this was one major reason of the filamentous bulking.(2) Removal rate of contaminant was stable in Beishiqiao WWTP,such as COD, NH₄⁺-N,TN.Removal rate of COD≥87.6%,the biggest was 92.6%;The NH₄⁺-N was≥95.4%;The TN was between 85.4～92.9%;The SS was beyond 74.8%;The removal rate of TP was not stable,it between 33.8～93.4%.So we can see Beishiqiao WWTP worked well except TP.But the SV of oxidation ditch effluent in Beishiqiao WWTP was beyond 96%,the biggest was 99%.SVI was between 246～394mL/g.(3)The denitrification rate of returned activated sludge(RAS) in selector was 7.11mg (NO₂^--N)/g(SS)·h in Beishiqiao WWTP,higher than the 3th WWTP in Xi'an which also used oxidation ditch.According to the static test about the removal rate of the contaminant (such as COD,NO₃^--N,NO₂^--N,NH₄⁺-N,PO₄^3--P) in different time,the best hydraulic retention time(HRT) was 30min in the selector.The short HRT in the selector was another reason of filamentous bulking.