Stoichiometry of sulphide oxidation with nitrate as electron acceptor

Authotrophic denitrification with sulphide using nitrate as electron acceptor were investigated at bench scale at different HRT (5 and 20 d). The results indicated that the process allows to achieve complete sulphide removal in all testes conditions. Tested sulphide loads were estimated from the H2S produced in a pilot scale anaerobic digester treating vegetable tannery primary sludge; nitrogen loads originated from the nitrification of the supernatant. Average nitrogen removal efficiencies higher than 80% were observed in all the tested conditions once steady state was reached. Due to sulphide limitation, an incomplete denitrification have been observed and nitrite and thiosulphate tend to accumulate especially in the presence of variable environmental conditions. Autotrophic denitrification efficiency and intermediate sulphur compounds production have been simulated using a two step denitrification and three step sulphide oxidation model. The model allowed to estimate those parameters that can affect the production of biomass in a hypotetic real scale Biotrickling filter for biogas desulphurization, as the SOB yield factor (0.6 mgXSOB(COD) mgS-1) and decay coefficients (0.06 d-1).