Study On The Control Technology For Filamentous Bulking Of Activated Sludge In Municipal Wastewater Treatment Plant

The activated sludge wastewater treatment method was widely used for wastewater treatment in the world,because of its good treatment efficiency,comprehensive treatment performance,and relatively cheap economic cost.However,the activated sludge process often causes sludge bulking during operation.The occurrence of sludge bulking will lead to incomplete separation of sludge and water in the secondary sedimentation tank,increased turbidity of the effluent,and a large amount of sludge loss.Sludge loss will further affect the pollutant removal capacity of the system,which seriously damages the efficient and stable operation of the sewage treatment system.This article takes Xi’an Third Sewage Treatment Plant as the research object,and studies the sludge bulking control technology from the following aspects: First,the sludge properties were detected and analyzed.Secondly,the filamentous bacteria that caused bulking of the sludge were identified by morphology（microscopic examination and staining）and molecular biology methods（fluorescence in situ hybridization）.Then,the bulking of “Microthrix Parvecella” bulking sludge was controlled by adding sodium hypochlorite,and the control of sludge bulking when different concentrations of sodium hypochlorite was added and the damage of bacterial micelle microorganisms in flocs were investigated.The image and sludge sedimentation ratio were used to characterize the effects of sludge bulking control,aerobic respiration rate and nitrification activity characterize the damage of bacterial micelles.Finally,based on the experimental results,a physical model for controlling the expansion of filamentous sludge by sodium hypochlorite was established.The main conclusions are as follows:（1）The third wastewater treatment plant has an AOB activity（calculated as NH₄⁺-N）of 1.91（mg / g VSS · h）and a NOB activity（calculated as NO₂^--N）of 2.33（mg / g VSS · h）..The nitrification activity of sludge is at a normal level;During the period,the SVI value reached 232（m L /g）,and the activated sludge swelled.The filamentous fungus sludge was judged to be swollen by microscopic examination.The filamentous bacteria in the activated sludge were identified by and fluorescence in situ hybridization（FISH）.（2）morphological observation and fluorescence in situ hybridization analysis were performed on the expanded sludge to confirm that the key bacteria that caused the expansion of the filamentous fungus sludge of the third sewage treatment plant were microfilaments.（3）Sodium hypochlorite has a good killing effect on microfilament.As the amount of sodium hypochlorite added increases,the sludge sedimentation effect gradually improves;but in the short term（30min）,the sludge sedimentation effect is not significantly improved,and the results of microscopic examination are also inconsistent.No obvious microfilament rupture phenomenon was found;with the extension of the running time,the killed microfilament aging and falling off,the sludge sedimentation ratio decreased,and the sedimentation performance could be completely restored.Sodium hypochlorite also affects the microbial micelles in the floc,In this experiment,the aerobic respiration rate and nitrification activity of sludge are measured to reflect the damage to microbial micelles.The optimal dosage of sodium hypochlorite is 5.72 g Cl₂ / kg SS.After the addition of sodium hypochlorite,the SV of the sludge decreased from 81% to 50%;the aerobic respiration rate decreased by 23.93%;the AOB activity decreased by 17.31%;and the NOB activity decreased the most,which was 49.85%.（4）Based on the above experimental results,a physical model for controlling the bulking of microfilament sludge by sodium hypochlorite was proposed,This model can well explain our experimental results,and at the same time allow people to better understand the mechanism of chemical oxidants controlling the filamentous-bulkingsludge.