EFFECT OF SMALL-SCALE SOLIDS MIGRATION IN FILTER CAKES DURING FILTRATION OF WASTE-WATER SOLIDS SUSPENSIONS

Upward curved (concave) filtration plots of the inverse filtrate flux as a function of filtrate volume have been investigated using a laboratory-scale filtration device and different wastewater solids suspensions stored anaerobically in the laboratory. Using an empirical approach in which a polynomial expression of arbitrary order was applied for regression analysis on filtration data it was shown that a parabolic expression was able to fit adequately all concave filtration plots. Turbidity measurements on supernatant and filtrate evidenced that the concave behavior of the filtration plots could be explained by migration of small-scale solids into the filter cake pores (blinding). The coefficients of the derived parabolic equation characterized the resistance attributed to blinding, basic cake filtration, and the filter medium, respectively. Based on the coefficients of the derived parabolic equation, a physically comprehensible parameter for characterizing the influence of blinding on filtration was defined.