Effect Of Ultrasound-Anaerobic Digestion Of Different Kinds Of Sludge

Currently, the widespread sewage sludge includes: excess activated sludge, coagulated sludge and dewatered sludge. All need to be stabilized or they would seriously endanger ecological environment. In this paper, the mesophilic anaerobic digestion was used to treat the sludge to investigate its anaerobic digestibility, and the ultrasonic pretreatment was adopted to disintegrate the sludge so as to improve the effect of anaerobic digestion.Ultrasonic pretreatment could disintegrate all the sludges. Along with the increase of ultrasound power density and exposure time more and more organic matters were observed transferred from solid phase to liquid phase. However, the effects of the disintegrations of different sludges were different: excess activated sludge performed best in the disintegration cause it, whether the ultrasound power density was high or low, had the most organic matters dissolved; coagulated sludge had a comparable effect of disintegration with that of excess activated sludge when the ultrasound power density was low, yet it performed bad when the ultrasound power density was moderate and high as its effect of disintegration was not improved conspicuously; dewatered sludge which performed worst in the disintegration had least organic matters dissolved no matter how strong the ultrasound power density was.All the sludges were stabilized through the anaerobic digestion of which the dosing rate was 5%, and the TCOD removal efficiency reached 39.5%, 40.98% and 39.2%, respectively. However, the change processes of the organic matters of different sludges were quite different: as to soluble protein, of all the three sludges it increased first and then decreased to be stable, but excess activated sludge had a greater range of variation than the others; as to soluble carbohydrate, of excess activated sludge it increased to be stable while of the others it decreased to be finally stable. From the change process of the SCOD and the corresponding TCOD removal efficiency of the sludges it was found that the rapid degradation of the TCOD was achieved at the posterior segment of the peak time of the SCOD which meant the efficiency of anaerobic digestion could be improved by increasing the SCOD.Compared with the raw sludge, the pretreated sludge performed better in the anaerobic digestion which showed better organic matters removal efficiency. As to excess activated sludge, coagulated sludge and dewatered sludge, the TCOD removal efficiency reached 45%, 44.1% and 40.7%, respectively, higher than that of raw sludge. In addition, of all the sludges, the SCOD, soluble protein and soluble carbohydrate were higher than that of raw sludges during the anaerobic digestion which meant that the released soluble protein and soluble carbohydrate were not completely used by methanogen but discharged from the anaerobic digestion system in the effluent.