Fouling mechanisms in ultrafiltration under constant flux: Effect of feed spacer design

Abstract

The impact of feed spacer design on membrane fouling mechanism in ultrafiltration (UF) process under constant flux mode was systematically investigated. Thecombined intermediate pore blocking and cake filtration model was employed,coupled with experimental crossflow UF experiments of dextran and sodium alginate (SA) in aqueous feed solutions. Filtration resultsofthree different spacer geometries, which included two 3D-printed spacers based on triply periodic minimal surfaces (TPMS) (Gyroid and TCLP) and one commercial net-type spacer, were analyzed. Flux-stepping tests were performed to determine the threshold flux (TF) in each case. Experimental data were fitted using the filtration model and the results were evaluated in terms of cake filtration constant (Kc, m−1), rate of cake erosion (S, kg.m−2.s−1), particle resuspension rate (B, s−1), and specific cake resistance (α, m.kg−1), in order to understand the cake formation and erosionbehavior that is influenced by the spacer geometry. A difference in spacer performance was observed when the solute was changed from SA to dextran. The results demonstrated that spacer design has a significant effect on the fouling mechanism in UF separation. The TCLP spacer is able to operate at the intermediate pore blocking mechanism at higher fluxes compared to the net-type spacer for both solutes tested. The flow hydrodynamics induced by the spacer geometry influenced the re-suspension rate of the deposited particles in the filtration cake. Additionally, combination of spacer surface roughness and solute molecular sizes were found to be the significant factors in cake-buildup on the spacer and the membrane.