Predicting dewatering equipment performance from laboratory tests

Abstract

This study was undertaken to evaluate the dewatering characteristics of a bench-scale belt filter press and a full-scale screw press, and to develop a suitable bench-scale test to simulate dewatering in a full-scale screw press. Tests were conducted to determine the effect of pressure and shear on dewatering of anaerobically digested, alum, waste activated, and pulp and paper sludges. The first part of the study involved tests conducted on a bench-scale belt filter press. Pressure was varied to develop performance characteristics with respect to cake and filtrate solids, and polymer demand. The second part of the study consisted of mixing intensity tests conducted to evaluate the effect of shear on dewatering in sludges. The third part of the study involved field evaluation of dewatering performance using a full-scale screw press. Tests were conducted to determine the shear produced in the dewatering process and to assess its effect on polymer conditioning requirements.

The tests indicated that the polymer demand produced by the belt filter press simulator and the screw device was minimal. Rather, a substantial polymer demand was observed as a result of shear in the pipes and pumps during full-scale screw press dewatering operations. A combination of a high speed mixing device and a free drainage tester was capable of predicting polymer conditioning requirements for a full-scale screw press. Individual sludge performance characteristics varied with pressure producing changes in cake solids and filtrate quality.