Study On Influencing Factors And Microbial Community Of Activated Sludge Settling Performance

Activated sludge process is often used in municipal wastewater treatment plant,but sludge bulking has always been an important problem that puzzles the development of activated sludge process.When sludge bulking is serious,the effect of wastewater treatment will be affected,and the operation of activated sludge treatment system will be affected.The sequencing batch reactor(SBR)was used to conduct laboratory simulation,and inoculate bulking sludge of wastewater treatment plant.The effects of single factor of water temperature,dissolved oxygen(DO)and sludge retention time(SRT)on sedimentation performance of activated sludge were tested.We analysised the factors affecting the sedimentation performance of activated sludge and the change of the microbial community,by detecting the extracellular polymeric substances(EPS)and microbial community before and after bulking.At the same time,the bulking sludge of Changji wastewater treatment plant in Xinjiang was sampled from January 2016 to January 2018.We found the influence factors that caused the sludge bulking in the wastewater treatment plant by analysising the microbial community,and provided theoretical support for the effective control of sludge bulking in this plant.The main results of this paper are as follows:(1)The SBR reactor laboratory simulation showed that the reduction of water temperature was not conducive to sludge settling.The increase of dissolved oxygen was favorable for sludge settling.Shorting SRT could accelerate the recovery rate of sludge settling performance.(2)High-throughput sequencing indicated that there was rich diversity in the microbial communities of seeding sludge.Generally,during sludge bulking microbial composition was decreased,and after the sludge was remediated diversity gradually increased.The dominant bacteria in the seeding sludge were Saprospiraceae_norank,Comamonadaceae_unclassified and Tetrasphaera,comprising 13.37%,10.54% and 8.59% of the community,respectively.After culturing using sodium acetate as the sole carbon source,Thiothrix and Trichosporon increased significantly from seeding to bulking sludge from ranges of 0.1% to 56.95%~60.14% and 19.60% to 94.82%,respectively.After the sludge bulking was controlled,the relative abundance of Thiothrix and Trichosporon were 0.1% and 2.32%,respectively.Therefore,we postulate that increases in filamentous Thiothrix and Trichosporon were the main cause for the sludge bulking.(3)The total amount of protein in sludge EPS of SBR reactor accounts for 61%~94% of total EPS,which was the main component of EPS.Before SVI down to 150 mL/g,the higher content of tightly bound protein and total protein was,the higher the SVI value was,the worse the sludge settling performance was.(4)Although the sludge bulking of Changji wastewater treatment plant continued,the effect of water treatment was good,and the effluent reach the standard.The microbial community structure of this plant was stable during the study.(5)The microscopic examination of activated sludge showed that the wastewater treatment plant in Changji was filamentous bulking.The results of high-throughput sequencing showed that the total relative abundance of Saprospiraceae_norank,Anaerolineaceae_norank,Tetrasphaera,Flavobacterium and Candidatus_Microthrix was 17.36% ~33.53%.These filamentous bacteria were the main bacteria causing sludge bulking in Changji wastewater treatment plant.The relative abundance of Trichosporon was 17.92%~25.00%,which was the main fungi caused sludge bulking in this plant.