Effect of hydraulic retention time and attachment media on sulfide production by sulfate reducing bacteria

Abstract

The effects of hydraulic retention time (HRT) and attachment media on the rate of microbial sulfate reduction with lactate as a carbon and energy source were investigated for sulfate reducing bacteria (SRB). Laboratory experiments were conducted in semi-continuous and continuous modes by using synthetic feed in three parallel 10-L PlexiglasTM upflow anaerobic reactors. The lactate:sulfate was maintained below 2 for proper SRB activity. Results indicated that 70% of the lactate fed was bio-oxidized and 30% was biosynthesized, which showed that the energy production reaction dominated over the synthesis reaction in non-packed reactors. Continuous mode operation of three upflow anaerobic suspended growth reactors yielded effluent sulfide concentrations as high as 190 mg/L at the optimum conditions of 20 h of HRT, 1.5 m/d of upflow velocity, and an organic loading rate (OLR) of 6 kg d–1 m–3, regardless of the presence of attachment media in the reactor. The critical HRT was 10 h. Lower retention times showed a significant decrease in the effluent sulfide concentration and washout of biomass. When the OLR was doubled, the rate of sulfide production increased proportionately. Key words: sulfate reducing bacteria (SRB), hydraulic retention time (HRT), support media, sulfide production.