Research On Sludge Dewatering With Feeble Ultrasonic And Electrical Field

The difficult of deeply dewatering is bottleneck problem for sewage sludge resource use and reducing volume. The electro-dewatering(EDW) is a feasible way to reduce more sludge water, which can save more energy than heat drying, but it needs farther research to improve more performance.The paper reasearched the process of sludge dewatering under the low frequency(20kHz) vibrating ultrasonic generator and the DC constant electric field. The main contents included the impact of the ultrasonic coupling with the electric field on the property of sludge, the impact of the ultrasonic pretreatment on the property of sludge and the parameters optimization of the former laboratory through the response surface method(RSM).The experiment of the ultrasonic coupling with the electric field showed that ultrasonic can cooperate electric fields which can reduce water content of the sludge. In the experiment, the constant mechanical pressure is 0.1MPa, the constant DC voltage is 60 V ande sludge thickness is 1.8cm. It had positive effect on the EDW under the optimal conditions of ultrasonic frequency of 20 k Hz, ultrasonic power of 20 W, ultrasonic intensity of 0.255W/cm2 and ultrasonic treatment time of 3.5min, water content of sludge was 72.90%. The result showed that the appropriate ultrasonic energy can destroy sludge floc structure, release part of vicinal water and improve dehydration performance of sludge. While sludge particle size is moderate.When ultrasonic power is high, it may cause that particle is too small, increase surface area,enhance water-binding capacity of sludge particle and hinder the experimental process.The experiment of the ultrasonic pretreatment showed that ultrasonic pretreatment may make a positive effect on the EDW. The electricity parameter of this experiement was the same as the experiment of the ultrasonic coupling with the electric field. It had positive effect on the EDW under the optimal conditions of ultrasonic frequency of 20 kHz, ultrasonic power of 40 W, ultrasonic intensity of 0.510W/cm2 and ultrasonic treatment time of 3.5min, water content of sludge was 74.64%.According the former experiment, it concluded that the ultrasonic coupling with the electric field had the better technicality. With the response surface methods(RSM), the paper optimized parameters, built mathematical model and obtain the optimum parameters and the corresponding response value. The results showed that the optimum parameter of the ultrasonic coupling with the electric field was constant voltage of 60 V, ultrasonic power of 21.31 W, ultrsonic intensity of 0.272W/cm2 and ultrasonic treatment time of 3.28 min under constant mechanical pressure of 0.1MPa. Predicted values of water content of sludge was 63.18%. Experiments verified that the predicted values was highly consistent with the measured values. Water content of sludge which was tested by the EDW was 74.15%.