The influence of protein and humic acid adsorption on the fouling of hydrophilic ultrafiltration membranes

Membrane fouling is caused by macromolecules adsorbing irreversibly onto the surface or within the porous matrix of a membrane. Although many researchers have studied the phenomenon of polymer and protein adsorption onto smooth surfaces, there is very little quantitative research on the adsorption of proteins or polymers onto a rough, porous membrane surface. In this work, the thermodynamic and kinetic aspects of macromolecular adsorption onto a hydrophilic membrane surface under varying solution conditions were studied.; Static adsorption experiments were performed to determine the rate and extent of adsorption onto the membrane surface in the absence of convective flow through the membrane pores. Model organic macromolecules were chosen to mimic the behavior of naturally occurring organic matter, which is known to foul membranes. The protein, bovine serum albumin (BSA), experienced maximum adsorption at its isoelectric point (pH 4.7), where the configuration was in a tightly packed monolayer. As the ionic strength increased, the adsorption decreased at pH 4.7 and increased at pH 10. The rate of adsorption was described by a modified diffusion model, which successfully predicted the rate of adsorption with the inclusion of a rate constant, {dollar}alpha.{dollar} This rate constant is qualitatively smaller for solution conditions which would dictate less adsorption. This model also described the rate and extent of adsorption of a naturally occurring humic acid from the Suwannee River (SRHA). A second model, the reaction-controlled model, also fit the experimental data well. This model includes a rate constant, k.; Flow-through batch ultrafiltration experiments were performed in order to assess whether the conditions for greatest flux decline were the same as the conditions which would dictate maximum adsorption in the absence of convection. The irreversible resistance of the adsorbed macromolecules in the ultrafiltration experiments was compared to the irreversible resistance of the adsorbed macromolecules in the static adsorption experiments. Although the solution conditions which produced maximum adsorption were the same for the static adsorption and the flow through (dynamic) experiments, the irreversible resistance was greater for the dynamic experiments.; Since the hollow fiber UF configuration is frequently used in practice, experiments were conducted to determine how quickly the irreversible fouling resistance would increase in a crossflow configuration. The performance (flux decline, increase in irreversible resistance) in the crossflow experiments was compared to the performance in the batch (stirred cell) configuration. The irreversible resistance in the crossflow configuration was an order of magnitude greater at pseudo steady state conditions than the stirred cell UF case for the conditions which resulted in greater fouling. Membrane material and configuration are important considerations to consider when scaling up from bench to pilot to full scale operation.