Competition between methanogenesis and sulfidogenesis in anaerobic wastewater treatment

Abstract

This study was conducted to investigate the methanogenic and sulfidogenic activities of biomass in a UASB reactor treating wastewater containing benzoate (680 mg l-1) and sulfate (increased from 1080 to 2680 mg l-1) at 37°C and 12 hours of hydraulic retention. Results showed that after 120 days of acclimation, sludge consistently removed 99.5% of benzoate regardless of increased sulfate concentrations. Sulfidogenesis gradually out-competed methanogenesis during the acclimation phase, as indicated by the increase of sulfate-reducing efficiency (up to 99%) accompanied by the decrease of methane production. Overall sulfate removal efficiency was limited after the reactor had reached its maximum sulfate reduction rate of 2.1 g S (l d-1). Further increasing sulfate concentration from 1080 mg l-1 to 2680 mg l-1 lowered the sulfate-reducing efficiency from 85% to 39%. Flow of available electrons toward sulfidogenesis increased with the decrease of benzoate concentration, and was only slightly affected by the sulfate concentration or the benzoate/SO4 2--S ratio.