Influence of acetate and propionate on sulphate-reducing bacteria activity

Sulphate-reducing bacteria (SRB) activity is generally considered as inconvenience in domestic wastewater treatment plants (WWTP), but could also be applied beneficially. The competition between SRB and methanogens is a point of concern for stable process design. As limited attention was given to the effect of varying acetate and propionate concentrations on SRB activity, this study focused specially on these substrates.

The research was performed in sequencing batch reactors operated at 20°C and an SRT of 15 days. In the acetate-fed reactor, methanogens became dominant, while in the propionate reactor, SRB were the dominant population. In the mixed-substrate-fed reactor, both substrates were converted by SRB. The dominant SRB population in the mixed-substrate-fed reactor was different from the propionate-fed reactor, but all operational characteristics such as the substrate consumption rate, yield and growth rate were similar. The sludge adapted to propionate could easily switch to an acetate feed procedure.

These results indicate that under wastewater temperature of 20°C, the SRB are likely to outcompete methanogens more easily as inferred from pure substrate studies on acetate solely.

The present results show that the natural presence of propionate in wastewater allows stable sulphate reduction, which decreases the biogas production, but provides an opportunity for using SRB beneficially in wastewater treatment.