Direct biofiltration pretreatment for fouling control of ultrafiltration membranes

Broader application of ultrafiltration (UF) membranes in drinking water treatment is limited by particulate and organic fouling. This pilot-scale study demonstrated the ability of rapid biofiltration (without prior coagulation or ozonation) to reduce fouling of a UF membrane treating river water over a two-year period. Three biofilter empty bed contact times (EBCTs; 5, 10, and 15 min) were investigated, using parallel dual-media filters followed by a hollow-fiber membrane unit. Using essentially conventional rapid filtration operating conditions, biofiltration pretreatment enabled stable membrane operation with respect to hydraulically reversible and irreversible fouling. Increased biofiltration EBCTs led to lower rates of irreversible fouling. The results were reproducible, and biofiltration was able to provide effective pretreatment during all seasons (T = 1-25 degrees C). The biofilters also contributed to effective turbidity removal. Overall, biofiltration pretreatment for UF is a promising chemical-free alternative to coagulation pretreatment. A particular niche application could be in small or remote systems.