Propensity and reversibility of membrane fouling in pressure retarded osmosis (PRO) process

Abstract

Pressure retarded osmosis (PRO) process has become an acknowledged system to generate energy from salinity gradient, but still membrane fouling has been recognized as a problematic issue on improving performance of PRO operation. This study aimed at elucidation of fouling mechanisms by investigating propensity and reversibility of fouling. As implementing fouling tests with organic matters (alginate, humic acid, and bovine serum albumin), colloid particles (silica and carboxylate-modified latex), and microorganisms (pseudomonas aeruginosa), this study could find several factors to influence on fouling. When it comes to fouling propensity, the foulants showing a low development in fouling were characterized as either bigger size than that of pores on membrane support or strong negative charge causing high repulsive interactions. Speaking of fouling reversibility, the most cases correlated with exposure time to the foulants

the longer exposure time brought the lower reversibility of fouling. Apart from the factors abovementioned, the foulants that accompany with accumulation at inner support layer triggered drastic decline in water flux, incurring low reversibility as well since the massive accumulation generally possesses bigger size than that of pores on membrane support. For instance, in case of alginate, aggregation with calcium ion inside support layer was promoted by reverse salt diffusion from draw solution, thereby leading to far severer fouling. As for biofouling, fouling right after inoculating microorganisms into the feed solution has progressed very slowly. However, after the sufficient development of biofilm into the membrane support, hardly did osmotic backwashing work since extracellular polymer substances (EPS) secreted by microorganisms, encroaching into the support layer and growing up in mass.