Investigation on the spatial filtration performance in spiral-wound membranes – Influence and length-dependent adjustment of the transmembrane pressure

During microfiltration, the length-dependent transmembrane pressure (Δp_TM) causes an inhomogeneous filtration performance along the module. Elimination of this length effect was found to increase the overall filtration efficiency of ceramic membranes significantly. Up to the authors’ knowledge, a systematic investigation on the spatial behavior of polymeric spiral-wound membranes (SWM) during microfiltration and the potential of a homogeneous Δp_TM has not been carried out yet. A modified SWM with permeate pockets divided in four hermetically separated sections was used to assess the length-resolved filtration performance during skim milk fractionation. Along the membrane, flux and fouling resistance decreased, whereas protein permeation increased. By adjusting the permeate pressure comparable to the uniform transmembrane pressure mode in ceramic membranes, the length dependency of Δp_TM along the module was reduced. In turn, the filtration performance was found to be more balanced. The overall whey protein mass flow increased as all sections were operating at the same Δp_TM under optimal condition. For the first time, we have proved with experimental data that SWM behave similar to ceramic membranes with regard to the length dependency of the filtration performance. Thus, the concept of a length-independent Δp_TM seems promising to enhance filtration performance of SWM at industrial scale.