RESUMO
The down-flow hanging sponge [DHS] reactor, which was developed for post-treatment of effluent from up-flow anaerobic sludge blanket [UASB] process treating sewage, uses polyurethane sponge as media to retain biomass. Wastewater is trickled from the top of the reactor and purified by microorganisms retained both inside and outside of the sponge media as the wastewater flows vertically down through the reactor. Three DHS reactors employing different sizes of sponge media with the same total sponge volume were used for the direct treatment of settled sewage. All the reactors exhibited excellent performance in removal of COD, ammonium nitrogen, and fecal coliform at a fixed hydraulic retention time of 2.0 h based on the sponge volume. It was shown that smaller sponge media produced better removal efficiencies for all the parameters listed above. The most reasonable explanation for this might be that smaller sponge media allows better oxygen uptake in the stream flowing down through the reactors