Fouling and wetting studies relating to the vacuum membrane distillation process for brackish and grey water treatment
Membrane distillation (MD) has two major problems: wetting and fouling. MD is rarely employed in wastewater reclamation since the active surfactant in the detergents contained in such water promotes feed water penetration through the membrane. Another difficulty is that the membrane lifetime and the performance of the MD process are both influenced by fouling. The main aim of this paper is to determine the effectiveness of the linear alkylbenzene sulfonate (LAS) concentration in the reduction of contact angle and the prediction of the flux decline with variation of the influent salt concentration. Contact angle was measured for different concentrations of LAS solution as well as different samples of brackish and grey water. The tests were performed with three different types of hydrophobic membranes. A simple empirical model was proposed, and related coefficients were calibrated based on experimental data for contact angles measured for different solutions with the hydrophobic membrane. Flux decline trends during pore wetting was investigated by monitoring the permeate quality through the treatment of synthetic grey water. The effect of membrane fouling during vacuum membrane distillation (VMD) was also studied under different operating conditions. A variety of temperature and pressure combinations as well as several salinity concentrations has been examined. The mathematical based model developed for the permeate flux was used to predict the flux rate of different salinity solutions. It was found that the flux decline could be attributed to the mass transfer resistance of the salt crystals.