| Ultrasonic treatment of excess sludge has been widely concerned and applied,there are few studies on the mechanism of ultrasonic cavitation in excess sludge treatment.This topic reveals the mechanism of the three typical effects of ultrasonic cavitation(chemical effects,mechanical effects and thermal effects)to crack excess sludge from microscopic angle.Study on chemical effects of ultrasonic cavitation use the ultrasonic to act on pure water,we find the trend of the change of hydrogen peroxide concentration.Escherichia coli and excess sludge were taken as the research object,and ultrasonic cracking was carried out within 0-40 min,the concentrations of nucleic acid,protein,DNA,peptidoglycan,SCOD and hydrogen peroxide in supernatant were detected after ultrasonic disintegration of Escherichia coli and excess sludge.The same amount of hydrogen peroxide produced by ultrasonic cracking was added to Escherichia coli and excess sludge to oxidize,respectively,and compared with ultrasonic method to break Escherichia coli and excess sludge.Research shows that ultrasonic and hydrogen peroxide can make the Escherichia coli and sludge crack,increase the concentration of each index in the supernatant,chemical oxidation effect on Escherichia coli and excess sludge disintegration accounted for about 10%.The elimination of hydroxyl radicals caused by ultrasonic cavitation by add isopropanol and sodium bicarbonate solution in Escherichia coli and the excess sludge，thereby eliminating the chemical effect of ultrasonic cavitation,by continuously pumping in circulating cooling water to control liquid temperature,thereby eliminating the thermal effect of ultrasonic cavitation,the results of ultrasonic cracking and eliminating other effects were compared and analyzed.The results show that isopropanol and sodium bicarbonate solution can effectively eliminate the chemical effect of ultrasonic cavitation,mechanical crack caused by ultrasonic cavitation on Escherichia coli and excess sludge plays a major role，and under the condition of excluding thermal effects,the contribution of mechanical effects on Escherichia coli and excess sludge disintegration is about 90%.The solutions of glucose,acid orange,Escherichia coli and excess sludge were cracked for 30,60,90 and 120 min,contrastively analyzed with and without pumping in circulating cooling water during ultrasonic process.The cracking rate of glucose and acid orange solution is higher under the condition of’ controlling the temperature by pumping the circulating cooling water,the four substances were directly heated by water bath for 30 min,and the water bath heating temperature was 40,50,60,70 and 80℃.Glucose and acid orange solution can degrade effectively when the temperature is lower than 40℃,when the water bath temperature is higher than 50℃,the disintegration rate of Escherichia coli and excess sludge increases.When the temperature rises to 70℃,the thermal effect of ultrasonic cavitation accounts for about 20%. |
