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In our country, sewage sludge is generally dewatered to reduce its volume. Conventionally, filter presses required large spaces and centrifugal dehydrators needed large powers for dewatering sewage sludge. Recently, the increased performance of flocculants has enabled even screw presses to dewater sewage sludge, and various models of low-power, space-saving screw presses have been introduced. Sumitomo Heavy Industries Environment Co.,Ltd. (SHI|EV) lately developed a screw press designed for sludge dewatering. This equipment is characterized by its mechanism for constant control of the internal pressure to stabilize the properties of the dehydrated cake produced by the screw press. It maintains a constant internal pressure and stabilizes the moisture content of the dehydrated cake by controlling the discharge from the dehydrator outlet. Specifically, it increases the discharge if the internal pressure rises, and reduces the discharge if the pressure lowers. As a result of conducting a demonstration test, SHI|EV confirmed that the screw press achieves a moisture content of 82% or less and an SS recovery rate of 95% or higher.
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