Study On The Effect Of Excess Sludge Reduction In A~2/O By Ultrasonic Treatment

With the developing of the urbanization process of our country and the increasingly stringent environmental requirements,the treatment rate of urban sewage and the yield of sludge rose year by year.The water and atmosphere would be polluted severely if the sludge was be discharged into the environment without be treated appropriately,which was very harmful to the environment and the healthy of human being.Meanwhile,the removal rate of nitrogen and phosphorus during the biological process of the sewage plant is not good enough due to the sewage carbon nitrogen ratio is low.However,if ultrasonic wave is used in the process,organic matter,main component of waste activated sludge,could be used as carbon source for biological nutrient removing,and the comprehensive utilization of sludge can be accomplished.In this paper,excess sludge reduction using ultrasonic technology were studied based on the excessive sludge yielded in a lab-scale H2/O reactor.First,the sludge was cultured to make the effluent water quality was stable and satisfy the requirements.Then,the excess sludge yielded in A2/O reactor was treated by ultrasonic wave.Ultrasonic density of 0.62W/mL and sonication time of 4 min was identified as the optimal technical parameters by measuring the optical micrographs and changes of COD,NH4+-N,TP in the sludge supernatant.Finally,w,the influences of sludge reflux ratio on the effluent quality and the production of excess sludge was studied under the best ultrasonic technology parameters condition,if 30%,40%and 50%excess sludge treated by ultrasound was returned into the anaerobic zone of A2/O reactor.The higher sludge recycling ratio was,the fewer the average discharged sludge would be.The effluent COD and NH4+-N were kept almost constant no matter whether the ultrasonic treated sludge was recycled to the system.The effluent TP was 0.46 mg/L if the recycling sludge treated ratio was 30%.However,the effluent TP was 1.27 mg/L in recycling sludge treated ratio of 30%.Combination the results of effluent quality and excess sludge reduction effect,the most appropriate recycling sludge treatment ratio should be 40%and the sludge reduction efficiency could be reach 32.2%.