The investigation of the sludge reduction efficiency and mechanisms in oxic-settling-anaerobic (OSA) process.

This paper aims to provide a full understanding of the sludge reduction mechanisms in the oxic-settling-anaerobic (OSA) process and presents an evaluation of the sludge reduction efficiencies and sludge characteristics in this process compared to the conventional activated sludge process. Fifty-eight percent reduction in observed yield in the OSA process was achieved compared to the control system at the end of the operational period with no deterioration of effluent quality. The settleability of sludge in the OSA process was also found to be better than that of the control system in terms of sludge volume index. In long-term operation, capillary suction time and specific resistance to filtration values confirmed that the OSA process showed good filterability characteristics. The results of batch experiments showed that higher endogenous respiration in the systems might lead to lower sludge production and that energy uncoupling had only a limited impact on sludge reduction.

Fate of return activated sludge after ozonation: an optimization study for sludge disintegration.

The effects of ozonation on sludge disintegration should be investigated before the application of ozone during biological treatment, in order to minimize excess sludge production. In this study, changes in sludge and supernatant after ozonation of return activated sludge were investigated for seven different ozone doses. The optimum ozone dose to avoid inhibition of ozonation and high ozone cost was determined in terms of disintegration degree as 0.05 g O3/gTS. Suspended solid and volatile suspended solid concentrations of sludge decreased by 77.8% and 71.6%, respectively, at the optimum ozone dose. Ozonation significantly decomposed sludge flocs. The release of cell contents was proved by the increase of supernatant total nitrogen (TN) and phosphorus (TP). While TN increased from 7 mg/L to 151 mg/L, TP increased from 8.8 to 33 mg/L at the optimum ozone dose. The dewaterability and filterability characteristics of the ozonated sludge were also examined. Capillary suction time increased with increasing ozone dosage, but specific resistance to filtration increased to a specific value and then decreased dramatically. The particle size distribution changed significantly as a result of floc disruption at an optimum dose of 0.05 gO3/gTS.

Disintegration of biological sludge: Effect of ozone oxidation and ultrasonic treatment on aerobic digestibility.

The present study deals with disintegration of biological sludge by ozone oxidation and ultrasonic treatment. The effects of ozone and ultrasonic treatment were investigated on aerobic sludge bio-processing as comparatively. 9690kJ/kg TS of specific energy and 0.1g O(3)/kg TS were applied to sludge samples preceding aerobic sludge digestion. In terms of sludge stabilization, the highest volatile solids reduction and protein degradation were obtained with ultrasonic treatment. Moreover, digesters fed with disintegrated sludge had higher bacterial activities in terms of oxygen uptake rate (OUR) and volatile suspended solids (VSS)/ suspended solids (SS) ratio than control one during the operation period. In terms of dewatering characteristics of digested sludge, ultrasonic treatment led to increase the sludge's resistance to dewatering. This negative effect was not observed in ozone oxidation. In addition, disintegration processes used in this study did not contribute to an improvement in cake solids on a crown press application.

Aerobic and anaerobic bioprocessing of activated sludge: floc disintegration by enzymes.

Hydrolytic enzymes such as glucosidases, lipases, and proteases have an imperative function at the hydrolysis stage of complex organic structures in the degradation of biodegradable particulate organic matter. As a key factor, extracellular polymeric substances (EPS) control the extracellular hydrolytic enzymes in this degradation mechanism. A flocculated matrix of EPS bridging with bacteria holds back the dewaterability properties of the bioprocessed sludges. Disruption of the flocculated matrix leads to improved solubilization of sludge solids by attacking the hydrolytic enzymes to polymeric substances forming enzyme-substrate complexes. To determine the floc disintegration mechanisms by enzymes during aerobic and anaerobic bioprocessing of sludges, experimental data obtained from three aerobic digesters and three anaerobic digesters were evaluated. As part of a broader project examining the overall fate and effects of hydrolytic enzymes in biological sludge stabilization, this paper compares the performances of aerobic and anaerobic reactors used in this study and reports significant improvements in enzymatic treatment of activated sludge.