COMPARISON OF TWO LABORATORY PISTON FILTER PRESS TECHNIQUES FOR SEWAGE SLUDGES

摘要

Sewage sludges are considered difficult to dewater, particularly waste activated sludges and their digested successors. Although the American Public Health Association (APHA) has a range of standard test methods for characterising the dewatering properties of sewage sludges, there is no standard pressure filtration test or standard method for determining the extent of dewatering. In a project funded by the Water Environment Research Foundation, a series of sewage sludges from Hunter Water plants were conditioned and tested in two laboratory piston filter presses. The results from a single-sided filter press were examined by applying pressure filtration theory derived from rheological concepts developed by Melbourne University. The results from a double-sided filter press were examined by applying conventional pressure filtration theory to obtain specific resistance of expression and solidosity compressibility values. These compressibility values appear useful in terms of describing the compressible nature of the sludge and being able to easily compare with other sludges. Attempts to use the specific resistance and solidosity compressibility values to simulate or predict the performance of a belt-press filter were not successful. Further work is required to improve the belt-press filter model and assess its sensitivity to the input parameters. It is proposed that the specific resistance of expression and solidosity compressibility values might be used to predict the type of dewatering device suited to any specific sludge, although this remains to be validated.