Seawater biofiltration pre-treatment system: comparison of filter media performance

Abstract

Biological filtration is an effective pre-treatment method to remove organic matter and particulate matter from seawater. Three biofilter columns were operated packed with granular-activated carbon (GAC), anthracite and sand as a filter media. The biofilters were run for 120 d at a slow filtration velocity of 0.12 m/h. Biofiltration performances were evaluated in terms of turbidity, different fouling indices, and dissolved organic carbon(DOC). The removal efficiencies of turbidity by the three biofilters were similar with low headloss development. The fouling potential of treated seawater (filtrate) was evaluated using three different fouling indices such as microfiltration, ultrafiltration, and microfiltration at a cross flow. The analyses of three different fouling indices showed that the reduction in fouling potential was the following order GAC > sand > anthracite. In terms of DOC removal efficiency, GAC biofilter showed higher and stable removal efficiency (41–88%), than sand biofilter (7–76%) and anthracite biofilter (3–71%). All biofilters used in this study removed most of hydrophobic organic compounds (around 94%). On the other hand, hydrophilic organic removal varied depending on the media filter. GAC biofilter removed more organic biopolymers (51%), humic substances (75%) and building blocks (50%) compared with sand and anthracite biofilters. Therefore, GAC biofiltration can be used as an effective pre-treatment to alleviate organic fouling.