evaluation of water distribution and oxygen mass transfer in sponge support media for a down-flow hanging sponge reactor

a down-flow hanging sponge (dhs) reactor has been developed for sewage treatment, mainly in developing countries. this novel reactor employs polyurethane sponge material as a support medium, which promises a proliferation of a large amount of biomass, offering excellent pollutant removal capability. three types of sponge medium were evaluated with respect to water distribution and oxygen mass transfer. water was supplied to the device, which consisted of 40 pieces of sponge media connected in series, and a tracer experiment was carried out. the ratios of actual hydraulic retention time (hrt) to theoretical hrt were in the range of 25-67% depending on the type of support medium. by supplying deoxygenated water from the top of the device, the overall volumetric oxygen transfer coefficient, kla, was evaluated. despite the non-aerated conditions, the kla values of the support media were very high, in the range of 0.56-4.88 (1/min), surpassing those of other mechanically aerated processes. furthermore, it was found that the suspended solids (ss) concentration in the influent played a role in increasing the actual hrt/theoretical hrt ratio, suggesting that managing the influent ss concentration is prerequisite for preventing clogging problems in the dhs.