Laboratory evaluation of conditioning requirements for sludge dewatering using belt filter press

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Virginia Tech

The purposes of this study were to develop a reliable bench-scale testing procedure to adequately predict polymer conditioning requirements for full-scale belt filter presses, and to determine the additional polymer demand exerted by applied pressure during the expression stage of a dewatering process. Bench-scale experiments performed with anaerobically digested, alum, and secondary sludges used a high-speed mixer to gauge mixing intensity effects, and a wedge zone tester to gauge applied pressure effects on conditioning requirements. Full-scale experiments varied Sludge throughput, belt speed, and polymer dose to evaluate polymer performance.

The polymer requirements to optimize performance of a full-scale belt filter press can be predicted with a bench-scale mixing device, where the shear (Gt) of the mixer matches that of the full-scale press. An estimate of the Gt value of the full-scale belt filter presses used in this study was 10,000. Alternatively, a bench-scale wedge zone tester, operated in an applied pressure range between 5 psi and 20 psi, can predict polymer doses for optimum belt filter press performance.

The range of applied pressures used to simulate the expression phase of a dewatering process did not exert a Significant additional polymer demand for optimum conditioning. The shear (Gt) associated with mixing sludge and polymer during conditioning can exert a greater polymer demand than the expression phase of the wedge zone tester.