The effect of sulphide on the anaerobic degradation of propionate

The anaerobic degradation of propionate in the presence of excess sulphate was studied in an Upflow Anaerobic Sludge Bed reactor inoculated with granular sludge. A stable and efficient propionate degradation could be achieved (space load 5 kg COD m−3 day−1, VFA removal 96%). Only 23% of the added COD was recovered as sulphide in the effluent and biogas. H2S concentrations above approximately 100 mg 1−1 S caused a sharp drop of the VFA removal efficiency and resulted in process instability, possibly aggravated by propionate inhibition. Recovery took 3–4 weeks. Acetoclastic methanogenesis was not the rate limiting step under sulphide inhibition.