Sludge ozonation and its effect on performance of submerged membrane bio-reactor

To investigate the effects of ozonation on minimizing the excess sludge and enhancing the nitrogen removal in an effluent,batch and continuous experiments in two MBRs with and without sludge ozonation (namely combined and reference run) were carried out. Through ozonation at a dose of 0.16 mg O3/mg MLVSS,53.1% of the treated MLVSS was solubilized,and soluble SCOD/TN ratio of ozonized sludge (OS) was about 8.6 due to the release of cellular nitrogen-contained materials and SCOD loss by ozone mineralization. In addition,the results of batch nitrification and denitrification tests with OS supernatant indicated that solubilized sludge could act as a reducing power for denitrification and a nitrogen source for nitrification. 40-day operation of two MBR systems demonstrated that the recirculation of OS into a bioreactor enabled the combined system have two advantages over the control one. The observed sludge yield (Yobs) was decreased from 0.13 to 0.06g MLSS/g COD,while the nitrogen removal was increased from 64.6% to 72.3%. And sludge ozonation elevated the inorganic fraction of MLSS,but did not impact sludge activities.