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.