Performance Factors Single Stage Two Stage
Single or First Stage
Usage of polymer, lb/tn of dry solids 8-12 0
Solids recovery, % 90 50
Solids in cake, % 12-13 13-14 Second Stage
Usage of polymer, lb/tn of dry solids 0
Overall solids recovery, % 97
Solids in combined (first and second stage) cakes, % 10-11
preconcentration of the feed at 6 or 7% solids is economically advantageous.
Wastewater treatment facilities can preconcentrate the feed by combining gravity-settled primary sludge with disc-centrifuged secondary sludge concentrate or by partially dewatering cosettled primary and secondary sludges in a conveyor or knife (basket) centrifuge depending on the flow rates. Sludge concentrations higher than 7% are difficult to pump and require an increase in the heat transfer surface. Conveyor centrifuges and RDVFs can dewater the treated sludge to cakes containing 35 to 45% solids without chemical addition.
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