Sludge reduction in an activated sludge sewage treatment process by lysis-cryptic growth using ClO2-ultrasonication disruption

A lysis-cryptic growth system, which combined chlorine dioxide and ultrasonication for sludge disruption (ClO2-ultrasonication disruption), was proposed to reduce the excess sludge in an activated sludge process. The optimal parameters of the ClO2-ultrasonication disruption were determined by sequencing batch jar experiment and orthogonal jar experiments. Subsequently, a ClO2-ultrasonication disruption system was combined with a 1.8 m(3)/d pilot SBR for lysis-cryptic growth. The results indicated that most of the disintegrated sludge was inactivated and turned into biodegradable material at the optimal parameters of a ClO2 dosage of 4 mg/g dry sludge, a ClO2 treatment time of 60 min, an ultrasonic intensity of 0.5 W/mL and an ultrasonication time of 6 min. The enzymatic activity of the disrupted sludge decreased by 96.5% and the value of ROD/COD reached 0.4. The operating data from the pilot SBRs showed that the discharged excess sludge was reduced by 55% by returning 70% of the excess sludge pretreated by the ClO2-ultrasonication disruption. Although lysis-cryptic growth resulted in an increase of 0.11 mg/L TP and 1.1 mg/L TN in the effluent, the impacts on the COD, ammonium and SS present in the effluent, as well as the sludge activity, were minimal. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.