Pretreatments to control membrane fouling in membrane filtration of secondary effluents

Membrane processes have been used as a key technology for water reclamation and reuse of secondary effluent discharged from municipal wastewater treatment plants. However, its extensive practices are limited due to membrane fouling. To control and manage the membrane fouling properly, pretreatment methods were compared and evaluated. Prior to direct membrane filtration of secondary effluent, the effect of coagulation with alum and ferric sulfate on membrane fouling was investigated using two different ultrafiltration membranes (YM30 and PM30). Membrane filterability was enhanced by addition of alum and ferric sulfate respectively. This was due to the effective destabilization of colloidal particles, which was confirmed by measuring particle size distribution. Soluble foulants present in secondary effluents were entrapped to coagulated floes. This reduced the concentration of soluble foulants, which lead to a decrease in R-f values. The hydrophobic membrane (PM30) showed high flux declines, whereas the hydrophilic membrane (YM30) showed relatively low flux decline. For the purpose of controlling membrane fouling, a pretreatment using coagulation is more efficient for hydrophobic than hydrophilic membranes. This could give us a good criterion for selecting membrane materials for water reuse practices.