Pilot Study On OSA Sludge Reduction Process

At present,the sludge reduction technology has increasingly become a research hotspot.The OSA(Oxic-Settling-Anaerobic)process as a proven sludge reduction process can significantly reduce sludge production.However most of the research on the sludge reduction process of OSA adopts the small-scale test of artificial water distribution,and there are few on-site pilot test data reports about OSA technology at home and abroad,and lack of long-term experimental data.Therefore,an oxygen-aerobic process(AO process)was coupled to the OSA process,and a Membrane Bio-Reactor(MBR)was used to improve the outflow mode to form the OSA-MBR Pilot Plant.The aim is to investigate the operational stability of the OSA-MBR sludge reduction process under actual sewage treatment plant conditions and the long-term sludge reduction effect.The OSA-MBR pilot plant was directly introduced into the effluent from the grit chamber of the sewage treatment plant.During the operation period,the sludge age in the main reaction zone was 15 days,and the residence time of the anaerobic sludge reactor was 10 days.In the first 80 days,there was no anaerobic sludge recirculation during the sludge stabilization phase,and a sludge reduction phase after 80 days.The pilot plant was cumulatively operated for 430 days.Research indicates:(1)During the operation of the OSA-MBR pilot plant,after the anaerobic sludge in the anaerobic reactor was refluxed into the system,which basically did not have a significant impact on the removal efficiency of COD,TN and NH4+.The removal efficiency of TP was significantly improved,and the effluent water quality indicators all reached Level 1B.After anaerobic recirculation,the dewatering performance of the reacted sludge was also not affected.In this study,using 37%HCl solution and 30%NaClO solution to clean the membrane module can effectively reduce membrane fouling.The MLSS of OSA-MBR activated sludge system was slightly increased by anaerobic sludge sludge,which was 5787±1566 mg/L.It could be operated stably for a long time and had a certain impact resistance.(2)The average daily excess sludge production of the OSA-MBR process before anaerobic sludge recirculation was 925.94 g,Yobs was 0.4246 g MLSS/gCOD;the average daily residual sludge production after anaerobic sludge recirculation was 633.86 g,Yobs is 0.2526 gMLSS/gCOD.Under the actual sewage treatment plant conditions,the excess sludge reduction rate reached 40.51%and the sludge reduction effect was significant.(3)The anaerobic sludge return of OSA-MBR process will greatly increase the aerobic respiration rate of activated sludge in the system.The balance analysis of carbon element and phosphorus element shows that after the OSA-MBR process is in normal operation,the proportion of carbon elements discharged through the excess sludge decreases from 45.53±13.06%to 19.82±2.37%,which is significantly lower than that before the anaerobic sludge reflow;The proportion of phosphorus released from excess sludge rose from 28%to 42%,which was significantly higher than before anaerobic reflow.(4)Sludge decay test results showed that the activated sludge MLSS in OSA-MBR process and A2/O system decreased by 3.98%and 2.17%,respectively,after 7 days without substrate anaerobic reaction,and the activated sludge in OSA-MBR system was reduced.The reduction effect is slightly higher than that of activated sludge in the wastewater treatment plant A2/0 system;the OSA-MBR process activated sludge is more capable of releasing phosphorus in the anaerobic reactor than the activated sludge in the A2/O system.(5)The method for calculating the sludge age of OSA process was established in this study.The average SRT of OSA-MBR process was calculated to be 28.14±7.94d based on the operating data.The actual average reflux ratio during the operation period was 0.43±0.13.The amount of sludge returned from the sludge anaerobic reactor per day was only 2.79%of the total amount of sludge in the main reaction zone.The sludge age of the OSA-MBR system is nearly double that of the conventional activated sludge process and it does not affect the system's treatment of pollutants.(6)Relevant calculation parameters determined by designing batch small-scale experiments:OSA process sludge yield coefficient is 0.89 gMLSS/gCOD,and endogenous attenuation coefficient is 0.089 d-1.OSA process activated sludge system has smaller sludge yield coefficient,larger endogenous attenuation coefficient and longer sludge age than traditional activated sludge process resulting in activated sludge decrease.The OSA process only needs to add a sludge storage tank on the basis of the common activated sludge process.Through the anaerobic and aerobic coupling method,sludge reduction can be achieved without affecting the quality of the effluent water;The rate and low energy consumption of new urban sewage treatment with advanced levels have broad application value and social benefits.