Sludge Reduction In An Activated Sludge Sewage Treatment Process By Lysis-Cryptic Growth Using ClO₂-Ultrasonication Disruption

Expansion of cities and population would reslult in large amount of sewage that need tobe treated, which in turn result in large amount of excess sludge that need to be safelydisposed of due to its environmental and health risks. However, the disposure of excess sludgeis costly. Therefore, it is important to reduce excess sludge production during the sewagetreatment.Several methods have been explored for excess sludge reduction, including uncouplingmetabolism, predation on bacteria, and lysis-cryptic growth. In a typical lysis-cryptic growthprocess, excess sludge is first lysed and then returned to the aeration tank in whichbiodegradation takes place. Several techniques, including mechanical, chemical, thermal andbiological methods, have been explored for excess sludge lysis.Chemical methods for sludge lysis is economical but may introduce potential biologicalharmful compounds into the aeration tank. Although ultrasonic treatment for sludge disruptionis efficient and will not introduce compounds that may be harmful to the aeration tank, it isenergy intensive and costly. Aiming to find a economical way with low risk, ClO₂coupledwith ultrasonication was proposed.The optimal parameters of the ClO₂-ultrasonic process were determined by sequencingbatch jar experiment and orthogonal jar experiments. The result showed that the optimalparameters for sludge disruption is: ClO₂treatment time of60min, ClO₂dosage of4mg/gdry sludge, ultrasonic intensity of0.5W/ml and ultrasonic time was6min. The order ofimpact, from high to low level, for sludge disruption are ultrasonic time, ClO₂dosage andultrasonic intensity. Compounds released by sludge disruption was rich in nutrient, theTP:TN:COD of which was1:2:20. The enzymatic activity of disintegrated sludge dropped by96.5%, and most of the disintegrated sludge was inactivated and turned into biodegradablematter，BOD/COD of which was as high as0.4Runing data from1.8m³/d pilot SBRs showed after ClO₂-ultrasonic disruption,70%ofexcess sludge can be returned to the aeration tank and achieved52.4%reduction ofdischarged sludge. COD and N-NH4⁺removal was almost not affected while TN and SSremoval was affected slightly. TP removal was affect significantly, an increase of0.15mg/LTP was observed in the lysis-cryptic growth system, increased by40.5%. All of the effluent indexes met the first-class B discharge standards for sewage treatment plants in China. Sludgeactivity was decreased a little but not much.Compareing ClO₂-ultrasonic disruption with ClO₂lysis and ultrasonic disruption, it wasfound that ClO₂-ultrasonic disruption was most efficient and achieved best sludge reduction.However, the most economical way was ClO₂lysis.Scale up application of lysis-cryptic growth using ClO₂lysis was designed and the sludgereduction was estimated. It is supposed that using lysis-cryptic growth process, dischargedsludge could be decreased by2.22t/d and save342.5yuan/d.