Filtration performance of a plastic-sand dual-media filter

A plastic raschig ring medium termed as a plastic medium was used to form dual-media filters. This study was to evaluate the performance of dual-media (anthracite-sand and plastic-sand) filters in terms of the filtrate suspended solids (SS) transparency, and color improvement. Results showed that the transparency was mainly affected by SS but color and the removal of SS from the filtrate can increase the transparency significantly. The removal of color was mainly affected by the pH during coagulation but the type of filter media. For both the anthracite-sand filter and the plastic-sand filter, the SS deposition patterns at pH 7 and pH 5 were surface filtration and in-deep filtration, respectively. The anthracite-sand filter exhibited rapid head loss development and SS breakthrough problems at pH 7 and pH 5, respectively. In contrast these problems did not occur in the plastic-sand filter at pH 7. In addition, results based on the calculated filterability number showed that the plastic-sand;filter performed better than the anthracite-sand filter. To comply with stringent effluent standards in enhancing the effluent SS and transparency, the plastic-sand filter can replace the anthracite-sand filter.