Estimation Of The Growth State Of Activated Sludge During Sludge Bulking And Its Control Periods

The good growth status of the microbial community is the essential for the normal operation of sewage treatment plants,but in the actual operation of the plants will be inevitably subjected to unpredictable faults,for example the failure of sewage treatment plant power or aeration equipment and the fluctuations in their diurnal and seasonal variations of pollutant components,temperature,concentrations and flow rates,which would cause a certain shock on the activated sludge system.However,conventional effluent quality monitoring method can only be used as a method of post judgment,cannot be early warning.Therefore,it is necessary to monitor the microorganisms which play a key role in the wastewater treatment.In this study,the monitoring methods of microbial survival and growth were summarized from five aspects: effluent quality and sludge routine,the microbial respirogram,kinetic parameters,microbial morphology observation and metabolic products EPS.Using the SBR system to simulate the sludge bulking caused by the shock of low dissolved oxygen in the sewage treatment plant and the periods of controlling the filamentous bulking by adding sodium hypochlorite.The physiological adaptability of microorganisms in the process of sludge bulking and controlling was discussed from the aspects of survivability,recoverability and sensitivity of microorganisms.The following results were obtained:(1)Autotrophic bacteria are most sensitive to shock of low DO,which the characteristics are the rapid deterioration of effluent ammonia nitrogen,the sharp drop of SOURn,and the decrease of protein content in EPS.However,maintaining low DO,SOURn gradually restored,which means autotrophic bacteria can restore the ability to remove ammonia nitrogen.But the effluent ammonia nitrogen in the system couldn't reach the standard due to the DO in aeration tank is insufficient,which cannot guarantee the completion of microbial metabolism.(2)Ko and SOURe increased abruptly at low DO,accompanied by an increase in LB-EPS and a decrease in TB-EPS,which might be a symbol to a shock of low DO.After physiological adaptation,Ko and SOURe were gradually restored,and microbes could adapt to low DO environment.At the same time,Ks and Kn were significantly reduced,and the respiration rates of microbial community remained at a high level.It means that microorganisms could adapt to the low DO condition through adaptability,which verified the feasibility of “Low oxygen aeration theory” from the respirogram and kinetic parameters.(3)When the concentration of NaClO was lower than 4mg/gSS/d,although the microbial community could restore its activity after short-term inhibition,it could not effectively control filamentous bulking.When the concentration was increased to 8mg/gSS/d,the sludge bulking could be controlled,and the activity of the microbial community could be affected,but the activity could be restored by physiological adaptation.Therefore,the accurate dosage of NaClO to control filamentous bulking is about 8mg/gSS/d,and the time of setting up the dosage can be set according to the abundance and variety of filamentous bacteria.(4)The microorganisms were in shocked by increasing the dosage of NaClO,which showed that the proportion of living cells and respiratory rates decreased,and the yield coefficient Yh increased.Maintaining the environment,microorganisms rapidly grow to ensure the balance of microbial systems through physiological adaptation.Therefore,the change of Yh and the ratio of living cells can be used to characterize the survival rate and recoverability of sludge microorganisms under the shock.(5)The trend of endogenous respiration ratio RI(SOURe/SOURenc)can be used to indicate whether the microorganism can be recovered by shock.When RI suddenly increased,indicating that the microbial system has been shocked by the external environment.If the RI can be gradually restored,it shows that the microbial system can adapt to the new environment through physiological adaptation.When the RI continues to increase more than 0.35,the microbial system cannot adapt to the new environment,facing the disintegration.