Pretreatment for membrane water treatment systems: a laboratory study

The goal of the work was to determine if biological treatment of water containing soil-derived humic substances has the potential for reducing the fouling of membranes used in water treatment. Laboratory scale biological filters containing biologically active carbon or iron oxide coated sand were fed humic-laden water with or without prechlorination. This stream was split, with half being further treated by microfiltration. Treated water was assessed for total organic carbon removal and biofouling potential using a glass bead assay and membrane assay for total cell counts, fouling layer thickness, and flux reduction. A combination of these assays provided more insight than any single measurement. Compared to untreated control water, biological treatment was capable of reducing downstream fouling of membrane systems. For example, fouling layer thickness was reduced by half after biological treatment, and cell counts were reduced four- to five-fold. Biological treatment coupled with microfiltration provided the best reduction of fouling, while prechlorination did not appear to impact the process. These results suggest that biological treatment may be valuable in reducing membrane fouling while reducing the amount of disinfectants used in pretreatment.