As mills increase their fiber replacement and fiber recovery efforts,the lack of fiber in combined primary and waste activated sludges(WASs)can present a major problem when dewatering with a screw press.Some mills have fought this problem with separate dewatering of primary and WASs.Other mills have looked at replacing older dewatering equipment.As the primary to WAS ratio decreases,belt presses-not screw presses-become the favored dewatering equipment choice.In choosing belt presses,there are several important considerations: 1.How is the polymer-sludge contact maximized? 2.How is the sludge distributed across the width of the belt press? 3.What are the crucial factors impacting the gravity dewatering section? 4.What are the ways to gradually increase dewatering pressure? This paper presents a comparison of three approaches to dewatering a sludge with a high percentage of secondary or waste-activated sludge(WAS).
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