Optimization of combined ultrasonic and thermo-chemical pretreatment of waste activated sludge for enhanced disintegration
XU Hui-min1, QIN Wei-hua1, HE Guo-fu2, DAI Xiao-hu3,4
1. Nanjing Institute of Environmental Sciences, Ministry of Environmental Protection, Nanjing 210042, China;
2. College of Ecological and Environmental Science, East China Normal University, Shanghai 200241, China;
3. National Engineering Research Center for Urban Pollution Control, Shanghai 200092, China;
4. College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China
Optimization of combined ultrasonic and thermo-chemical disintegration of waste activated sludge was carried out using response surface methodology (RSM) and Box-Behnken design of experiment. The combined effects of ultrasonic (4000, 8000, 12000kJ/kg TS), thermal (60, 70, 80℃) and alkaline (0.04, 0.07, 0.10g/g TS) pretreatments on the disintegration degree of soluble COD (DD) were tested. By applying regression analysis, DD was fitted based on the actual value to a second order polynomial equation:Y=-196.87+6.11X1+487.53X2+0.0039X3-1.742X1X2-0.000024X1X3+ 0.0044X2X3-0.0398X12-2488.33X22 -1.33×10-7X32, where X1, X2, and X3 were temperature, alkaline dosage, and specific energy, respectively. The coefficient of determination (R2) was as high as 97.548% confirming that the model used in predicted DD had a good fitness with experimental variables. The optimum DD achieved was 60.411% at temperature of 73.06℃, alkaline dosage of 0.085g/g TS, and specific energy of 9551kJ/kg TS. Economic evaluation showed that combined pretreatment reduced operating costs by ￥20.42/t sludge comparing with conventional anaerobic digestion without pretreatments.
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