| The scale of wastewater treatment plant enlarges increasingly with the fast development of social economy and the rise of population. But large number of waste bio-sludge was generated from a lot of wastewater treatment plants and the water content of these sludge was very high, always over 95%. Meanwhile, sludge is rotted easily with strong unpleasant smell and contains much pollutant. The new style of sludge pretreating process, which can improve sludge dewatering and subsequent bio-treatment, can not only resolve the problem of sludge treatment and decrease the running cost of wastewater treatment, but also protect environment and reclaim resource. It is essential to society, environment and economy. As a new technique of pollutant treatment, ultrasound has been taken into account gradually. It has shown great potential of the treatment of sewage sludge and refractory wastewater. Effect of promoting dewatering in plate-frame pressure filtration by ultrasound was studied in this paper. Treating wastewater by ultrasound can destroy extracellular polymeric substances (EPS) in sludge and release microorganism particles. It can help flocculation better then get the goal of decreasing sludge water content by dewatering in plate-frame pressure filtration. There are many factors such as ultrasound intensity and treatment time of ultrasound, the control of time and pressure in filtration, both of which have effect on the dewatering. The compression character of the sludge was studied, which showed that the sludge from Yangste Wastewater Treatment Plant was easy to be compressed. The compress coefficient, s, is 0.92. The optimum ultrasound condition for treatment is: ultrasound intensity 410W·m-2, treatment time of ultrasound 2.5min. Under this condition,the water content of sludge decreased to 81%. Comparison of the dewatering effects of the sludge treated with and without ultrasound showed that ultrasound treatment was beneficial to the water content, from 98% to 81%. Meanwhile, the useage of the flocculant was reduced from 7‰(dry base)to 6‰(dry base), which could save the cost. During certain scope of pressure, adding diatomite precoating can improve the rate of filtration effectively. But the filtration pressure must be lower than 0.3MPa. Besides, adding diatomite has no obvious effect on deceasing water content of sludge.
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