Scaling filtration time initial dependencies of wastewater sludges

The filtration time, tf, during constant pressure dead-end filtration testing of wastewater sludge is dependant on the initial height, h0, and the initial solids concentration, φ0. The theoretical dependencies of these initial conditions are explored: tf varies with h02 and cφ02, where c is a material dependant parameter that is also dependant on φ0 and the applied pressure. Empirical values for c relative to a given φ0 are determined from phenomenological filtration theory to give a qualitative scaling method to compare the filtration behaviour of highly compressible materials under differing initial conditions. The method is validated using filtration testing of municipal wastewater sludge. This new scaling method is applied to the filtration results of a range of different wastewater sludges, additives and treatments to illustrate its application for plant comparisons, polyelectrolyte comparisons, dose optimisation of polyelectrolyte and ferric chloride and combinations thereof, and the effects of two physicochemical treatments.