Sulfide removal from industrial wastewaters by lithotrophic denitrification using nitrate as an electron acceptor

Sulfide is present in wastewaters as well as in biogas and can be removed by several physicochemical and biotechnological processes. Nitrate is a potential electron acceptor, readily available in most wastewater treatment plants and it can replace oxygen under anoxic conditions. A lab-scale reactor was operated for treatment of sulfide containing wastewater with nitrate as an electron acceptor and is used to evaluate the effects of volumetric loading rates, hydraulic retention time (HRT) and substrate concentrations on the performance of the lithotrophic denitrification process for treating industrial fermentation wastewaters. Sulfide is removed more than 90% at the loading rates between 0.055 and 2.004 kg S⁻²/m³ d, when the influent sulfide concentration is kept around 0.163 kg/m³ and the HRT decreased from 86.4 to 2 h. Nitrogen removal differed between 23 and 99% with different influent NO₃⁻-N concentration and loading rates of NO₃⁻/S⁻² ratio. The stoichiometry of sulfide oxidation with nitrate is calculated assuming different end-products based on thermodynamic approach and compared with experimental yield values. The calculated maximum volumetric and specific sulfide oxidation rates reached 0.076 kg S⁻²/m³ h and 0.11 kg S⁻²/kg VSS h, respectively. The results are obtained at industrially relevant conditions and can be easily adapted to either biogas cleaning process or to sulfide containing effluent streams.