Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1056638 | Journal of Environmental Management | 2012 | 9 Pages |
Volatile fatty acid (VFA) profile is an important parameter in anaerobic reactors because it enables the assessment of metabolic pathways. Volatile fatty acids were monitored during sulfate reduction in a UASB (upflow anaerobic sludge blanket) reactor treating 2 g/L sulfate concentration and with the organic loading increasing from 3.5 kg COD/m3 d to 5.9 kg COD/m3 d, for a 1-day residence time. In the absence of recirculation, the best outcome (65% reduction) was noticed with the lowest organic loading (3.55 kg/m3 d). When recirculation was applied, sulfate reduction yields increased to 89%, corresponding to a sulfate removal rate of 1.94 kg SO42−/m3 d. The reactor performance was discussed in relation to microbial diversity and metabolic pathways. At high organic loading, two metabolic pathways account for lactate degradation: (i) lactate is oxidized to acetate and carbon dioxide by the incomplete-oxidizer SRB (sulfate-reducing bacteria) Desulfomonas, Desulfovibrio, Desulfolobus, Desulfobulbus and Desulfotomaculum spp.; (ii) lactate is converted to acetate by fermenting bacteria such as Clostridium sp. High propionate concentrations imply that there are low sulfate reduction efficiencies.
► In UASB reactors improved mass transfer enhances SRB activity. ► Clostridium competes with SRB for lactate at high COD/sulfate ratios. ► High propionate levels suggest fermentation as main mechanism of lactate oxidation. ► Recirculation can improve the performance of UASB reactors treating sulfate. ► Control of the COD/sulfate ratio is key for sulfate reduction in UASB reactors.