Performance And Mechanism Of Ultrasonic Disintegration For Waste Activated Sludge

In the case of sewage sludge digestion, the biological hydrolysis has beenidentified as the rate-limiting step. If some methods are applied as pretreatment todisintegrate the sludge flocs and disrupt bacterial cells' wall, the hydrolysis can beimproved a lot, so that the residence time can be shortened, fermenter volume bereduced, methane production be significantly increased .In this paper, the pretreatmentof waste sludge by ultrasonic disintegration on a laboratory-scale is studied .Thesludge disintegrated in the research is cultivated using synthetic water. This studycovers the following: the effect of changing ultrasonic density, intensity, sludgeconcentration and disintegration time on the disintegration result; the mechanism ofultrasonic disintegration by adding NaHCO3 to eliminate the contribution of hydroxyl;the improvement of disintegration by combining ultrasonic and alkaline; theestablishment and validation of the dynamics model based on the gained data. It has been found that applying ultrasonic as pretreatment to disintegrate sludgeis an effective method which can break up sludge flocs and disrupt bacterial cells'wall and lead to the release of intracellular material into the sludge supernatant. Afterbeing disintegrated, the SCOD in the sludge supernatant is increased greatly. Theincrement of SCOD is enhanced with the augment of ultrasonic density, intensity,sludge concentration and disintegration time. Under a certain ultrasonic density andintensity, the increment of SCOD is enhanced lineally with the extending of time.That is to say, during the disintegration in this experiment, the reaction of ultrasonicsludge disintegration is a one-order reaction. However, under low sludgeconcentration and high ultrasonic density, the increment of SCOD would notenhanced lineally with the extending of time but turn slow as time extending.Combining ultrasonic and alkaline can improve the effect of disintegration a lot. By adding NaHCO3 to eliminate the hydroxy contribution to the ultrasonic sludgedisintegration, the mechanism of disintegration is investigated. It has been inferredthat the contribution of hydroxyl becomes less and less as the increment of ultrasonicintensity. When the applied ultrasonic intensity is 0.096W/ml, the main contributionto the disintegration is hydraulic shear force and the hydroxy oxidation is almost of noeffect on the disintegration; when the sludge is disintegrated under 0.0384W/ml, the - ii -contribution of hydraulic shear force and the hydroxy oxidation is 80.85ï¼…and 19.15ï¼…, respectively.; when the ultrasonic intensity is 0.72W/ml ,the contribution of thetwo factors is 74.14ï¼…and 25.86ï¼…, respectively. Based on the test data, the dynamics model for ultrasonic sludge disintegrationhas been established. The multi-variables linear regression method is used toestablishment and validation of relation equations, which express the change ofincrement of SCOD and release percent of SCOD with the variation of ultrasonicintensity,ultrasonic density,sludge concentration and disintegration time .