Development of High-Speed and High-Level Reduction Process of Difficult-to-Dewatering Sludge by Combined Reversible Flocculation and Multistage Ultrahigh-Pressure Expression System

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High rate reduction in volume of difficult-to-dewatering sludge was achieved by step-up ultrahigh-pressure expression combined with reversible flocculation. Flocculation with inorganic electrolyte with multivalent cation such as poly aluminum chloride was extremely effective for the increase in the dewatering rate of excess activated sludge, and the water content of the compressed cake was finally reduced to 31wt% by expression under action of ultrahigh-pressure of 15 MPa combined with reversible flocculation. This new method shortened the total dewatering time of activated sludge by 51. 6% compared to the conventional method, and reduced the sludge volume by 99. 83%. The results derived from a series of experiments attained the research goals from the viewpoint of both the rate in dewatering and the water content of the compressed cake.