AimsSulphate-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. Methods and ResultsThe research was performed in sequencing batch reactors operated at 20 degrees C and an SRT of 15days. 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. ConclusionsThese results indicate that under wastewater temperature of 20 degrees C, the SRB are likely to outcompete methanogens more easily as inferred from pure substrate studies on acetate solely. Significance and Impact of the StudyThe 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.