Effects of Operating Parameters in Tubular Ultrafiltration

A parametric waste-specific study was conducted to develop a more mechanistic understanding of the tubular ultrafiltration system using a surrogate metalworking (MW) fluid as a model waste stream. An average gel layer concentration of 31% oil was calculated and the gel layer concentration was determined to be independent of transmembrane pressure and cross-flow velocity. The thin-film model adequately described limiting flux data collected in this study, due to the use of discrete cross-flow velocity∕MW fluid concentration experiments; thus, an improved mechanistic understanding was achieved. Mass transfer and thus the pressure-independent “limiting” permeate flux were generally comparable to values observed in a high-shear rotary UF system, for oil concentrations <26%. However, a decrease in net permeate flux was observed in the tubular ultrafiltration (UF) system at high feed oil concentrations; thus, a hybrid system (conventional tubular followed by high-shear rotary UF) is proposed for treatment applications where high concentrations are desired.