Research On The Operation Effect Of Sludge Bulking Control And Upgrading In Oxidation Ditch In Cold Area

In this paper,aiming at the serious sludge bulking problem in the oxidation ditch of a sewage treatment plant in Changji,the bulking sludge in oxidation ditch was collected,and the main microbial community causing the sludge bulking was studied by using the metagenomic sequencing technology.The causes of sludge bulking in oxidation ditch were analyzed according to water quality and operating conditions.High-throughput diversity sequencing of bacteria and fungi in aerobic and anaerobic sludge was carried out,and the differences of microbial community structure between aerobic and anaerobic sludge were compared to study the control of anaerobic selection tank on sludge bulking.At the same time,the operation effect of the advanced treatment process after the upgrading was studied.The main research achievements of the thesis are as follows:（1）During the period from February 2018 to June 2019,the influent concentration of COD,BOD₅,SS,TP and TN was far more than 2～3 times that of the designed influent concentration in a sewage treatment plant in Changji,and the effluent quality had reached the secondary standard of Pollutant Discharge Standard of Municipal Wastewater Treatment Plant.Plenty of filamentous bacteria were observed by microscopic examination after gram staining,indicating that filamentous sludge bulking occurred in the plant.（2）Metagenomic sequencing showed that the dominant bacterial phylum were Proteobacteria and Bacteroidetes,and the dominant fungal phylum were Ascomycota and Basidiomycota in bulking sludge;Candidatus＿Accumulibacter（2.45%and 2.51%）,Pseudomonas（0.79%and 0.75%）,Nitrospira（1.22%and 0.47%）,Sulfuritalea（1.10%and 1.49%）,Pedobacter（0.56%and 0.82%）,Thauera（0.59%and 0.54%）and Azoarcus（0.50%and 0.55%）were the main denitrifying phosphorus-removing bacteria in bulking sludge;Saprospira（1.91%and 2.20%）,Haliscomenobacterter（1.15%and1.28%）,Flavobacterium（1.10%and 1.41%）,Candidatus＿Microthrix（1.05%and1.54%）,Trichosporon（2.25%and 2.37%）,Fusarium（1.83%and 2.58%）,Penicillium（1.47%and 1.59%）and Geotrichum（1.11%and 1.02%）were the main filamentous bacteria and fungi responsible for sludge bulking in the plant.（3）The important causes of sludge bulking were imbalanced ratio of influent carbon,nitrogen and phosphorus,oxidation ditch ultra-low sludge loading operation and long sludge age.（4）The effect of anaerobic selective pool on filamentous fungi was greater than that of filamentous bacteria,which had certain inhibition on Candidatus＿Microthrix,Trichosporon,Galactomyces and Geotrichum.However,there was no significant inhibitory effect on norank f Saprospiraceae,Tetrasphaera,Flavobacterium and Trichococcus.It can promote phosphorus accumulation bacteria and denitrifying bacteria,and inhibit nitrifying bacteria.（5）The anaerobic selection tank in this plant had a certain control effect on sludge bulking,but the control effect was not obvious,the reason may be that the dissolved oxygen concentration of sludge returning to the anaerobic tank was too high,and the hydraulic retention time in the anaerobic selection tank was short.（6）After the process upgrading of high-density sedimentation tank and deep-bed filter tank,the effluent COD,NH₄⁺-N,TN and TP in summer and autumn can reach the first grade A standard stably.After entering the winter,the effluent NH₄⁺-N and TNcannot reach the standard stably,it may be that the filter is unstable in the trial run stage.The reasons why the plant failed to improve the denitrification effect after adding carbon source may be that the dosage of sodium acetate was not insufficient,the dissolved oxygen was too high and too many backwash times.