Adsorption and biological degradation of ammonium and sulfide on peat

A dynamic mathematical and numerical model has been applied to predict concentration profiles over time for adsorption and biological degradation of ammonium and sulfide in a perfusion column with recycle. The model successfully accounts for the high adsorptive capacity of peat (two thirds of ammonium added to the system at pH 6) which makes this medium a useful carrier for engineered biological systems such as biofilters and biotrickling filters. This characteristic of peat gives it significant buffering capacity to protect against surges in loading. Solid/liquid partition coefficients were determined experimentally for adsorption of ammonium and sulfide onto a peat packing under prevailing pH conditions. The dynamics of mass transfer for the same were shown to be at least as fast as the dynamics of transport by bulk flow and probably very much faster. This enabled mass transfer resistance to adsorption and biological degradation to be discounted as negligible. The rate of biological degradation of ammonium on peat was found to vary between 10 and 80 (mg NH4+) (kg dry peat)(-1) h(-1), depending on the alkalinity of the liquid phase. This translated into predicted biological growth rates (based on published yields) of 1 to 7 (mg dry cell mass) (kg dry peat)(-1) h(-1). Measurement of biological degradation rates for sulfide were frustrated by competing chemical oxidation of sulfide by dissolved oxygen. It is suggested that aerobic sulfide removing biofilters and biotrickling filters may remove sulfide by a two step process involving initial chemical oxidation to elemental sulfur followed by slower biological oxidation to sulfate. (C) 1999 Elsevier Science Ltd. All rights reserved.