Predicting cake filtration using specific filtration flow rate

Abstract

The filterability parameters obtained from laboratory testing of cake filtration are discussed. A high‐quality filterability parameter for predicting full‐scale equipment operation should only exhibit a small change in parameter value with changing test conditions. An important factor is the test pressure applied, so, the discussion is based on the relationship between the filterability parameter and the test pressure. The traditionally used specific resistance to filtration (SRF) is shown to be highly dependent on the applied pressure when the compressibility of the investigated material is high. Therefore, in this case SRF looses its property as a material constant and a new parameter denoted the specific filtrate flow rate (SFF) is suggested as a possible alternative to SRF. A test coefficient (T) is derived to quantify the constancy of SRF and SFF in relation to changing test pressure. Data obtained from the literature are discussed in relation to SRF and SFF, and it is found that SFF is constant and thus the best alternative in case of biological wastewater solids and highly compressible inorganic slurries. However, for non‐ or slightly compressible solids SRF is more constant than SFF, and therefore, still the relevant filtration parameter. In the range of moderate compressibility neither SRF or SFF can be claimed constant.