Fouling minimization with nanofluidic membranes; How electric field may help

Abstract

Researchers have given water purification substantial consideration in recent years as the availability of fresh water supplies has become a worldwide problem. Water treatment is the typical use for membranes. Enhancing membrane performance is thus a much sought after area of study. In this study, we examine a nanochannel that is embedded in a nanofluidic membrane, located between two reservoirs containing KCl electrolyte solution with equal concentrations. The neutral component present in the source reservoir is bovine serum albumin (BSA). A negatively charged polyelectrolyte layer coats the inside of the nanochannel, making the mass transfer more manageable and efficient. By applying an electric field and inducing electroosmotic flow, the electrolyte passes through the nanochannel without a change in concentration, while BSA is concentrated in the feed reservoir. Fouling performance was evaluated by measuring the flux of fluid passing through the nanochannel, the concentration difference CK+-CCl-, the electroosmotic velocity of the flow, and the time average volume flux. The BSA rejection was also monitored as a goal function. The difference between the electrolyte and the soft layer's physical–chemical properties was varied, and the parameters of electrolyte concentration, surface charge density of the soft layer, and type and frequency of the applied electric field, were all altered to determine their impact on membrane fouling. To do this, the Poisson-Nernst-Planck, continuity, and Navier-Stokes equations were numerically solved using the finite element method in an unsteady state. The findings demonstrate that fouling in the nanochannel can be reduced by increasing the charge density of the soft layer and lowering the electrolyte concentration. Using an AC field at intermediate frequencies is far more successful than a DC field in reducing fouling. Nevertheless, the AC field does not outperform the DC field in fouling reduction at either low or high frequencies tested.