Microbial sulphate reduction during anaerobic digestion: EGSB process performance and potential for nitrite suppression of SRB activity

The present study investigated mesophilic anaerobic treatment of sulphate-containing wastewater in EGSB reactors and assessed the inclusion of nitrite in the reactor influent as a method for control of biological sulphate reduction. Two EGSB reactors, R1 and R2, were operated for a period of 581 days at varying volumetric loading rates, COD/SO₄²⁻ ratios and influent nitrite concentrations (R2 only). COD removal efficiencies of >93% were achieved in both reactors at influent sulphate concentrations of up to 3,000 mg l⁻¹. A two-fold increase in the influent sulphate concentration, giving an influent COD/SO₄²⁻ ratio of 2, resulted in a reduction in reactor COD removal efficiency to 84% and 89%, in R1 and R2, respectively. Despite inclusion of nitrite in the R2 influent at concentrations up to 500 mg NO₂-N l⁻¹, sulphate reduction proceeded similarly in R2 and R1, suggesting the ineffectiveness of nitrite as a potential inhibitor of SRB activity.