Product inhibition by sulphide species on biological sulphate reduction for the treatment of acid mine drainage

It is well recognised that the product of sulphate reduction, i.e. the sulphide species formed, may inhibit the biological process. In this paper, we further the kinetic study of biological sulphate reduction using the mixed population of complete oxidisers growing on acetate for which kinetic data has been reported previously as a function of sulphate concentration, temperature, dilution rate and volumetric sulphate loading using chemostat culture by Moosa et al. to provide kinetic insight into this inhibition.The effect of a feed sulphide concentration in the range 0.50 to 1.25 kg m− 3 on the biological sulphate reduction process is established using chemostat culture at pH 7.0 ± 0.2. Further, the chemical speciation of sulphide as undissociated H2S or dissociated HS− on process inhibition is reported through the variation of operating pH across the range pH 6.0 to pH 7.5 at a sulphate feed concentration of 2.5 kg m− 3. It is clearly shown that inhibition is chiefly mediated by the undissociated H2S sulphide species, rather than the total sulphide concentration. This inhibition was shown to affect the maximum specific growth rate constant and the death rate constant in the Contois rate equation presented previously while having negligible effect on KS describing substrate affinity.