MASS-TRANSFER RESISTANCE IN ASFF REACTORS FOR WASTE-WATER TREATMENT

Analysis of mass transfer resistances was performed for an aerated sub merged fixed-film reactor (ASFF) for the treatment of waste water cont aining a mixture of sucrose and ammonia. Both external and internal ma ss transfer resistances were considered in the analysis, and character ized as a function of feed flow-rate and concentration. Results show t hat, over a certain operating regime, external mass transfer resistanc e in the system was greater for sucrose removal than ammonia. This is because the reaction rates for carbon removal were much larger than th ose of nitrogen. As a result, existence of any foam of mass transfer r esistance caused by inadequate mixing or diffusion limitations, strong ly affects the overall removal rates of carbon more than nitrogen. Eff ects of the internal mass transfer resistance were virtually nonexiste nt for ammonia removal. This behaviour was found over two orders of ma gnitude range for the effective diffusivity for ammonia, and one order of magnitude for the film specific surface area. However, over the sa me parameters' range, it is found that sucrose removal was strongly af fected upon lowering its effective diffusivity and increasing the film specific surface area.