Evaluation of Water Flow and Oxygen Uptake of Sponge Support Media in DHS Reactor Developed for Sewage Treatment in Developing Countries

Down-flow hanging sponge (DHS) reactor has been developed mainly for sewage treatment in developing countries. The novel rector employs polyurethane sponge material as support media, which promises a proliferation of a large amount of biomass, and thus an excellent capability of removing pollutants. The characterization of the three types of sponge support media is conducted in respect of water flow and oxygen uptake ability. Water was supplied to the device which consisted of 40 sponge media connected in series, and then tracer experiment was carried out. The ratios of actual hydraulic retention time (HRT) per theoretical HRT were in the range of 25-67% depending on the type of support media, meaning that short circuit flow occurs in this type of reactor. By supplying deoxygenized water from the top of the device, overall volumetric oxygen transfer coefficient, KLa, was evaluated. In spite of the non-aerated conditions, the KLa values were so high, 0.56-4.88 (1/min), surpassing those of other mechanically aerated aerobic processes. Furthermore, it was found that the suspended solids (SS) concentration in the influent played a role to increase the ratio of actual HRT/theoretical HRT, meaning that management of the influent SS concentration is prerequisite for preventing the clogging problem in the DHS.