Anaerobic treatment of baker's yeast wastewater: II. Sulfate removal

The effect of sulfate removal from molasses wastewater on anaerobic digestion was studied using two reactors. One was an anaerobic rotating biological contact reactor with an active biomass developed on its support structure before the experiment commenced. The other was a new fixed-film reactor which was started without attached biomass. The experimental results showed that sulfate removal from the wastewater did not improve the gas production and treatment efficiency of the AnRBC reactor. This observation indicated that sulfate-reducing bacteria could not compete with methane-producing bacteria in a well-established active biomass reactor. However, the FF reactor showed significant improvement in gas production (0·17–0·66 liters CH₄ liter⁻¹) and COD reduction (maximum of 44%) as a result of sulfate removal coupled with pH adjustment. Thus, the initial step of sulfate removal from molasses wastewater would appear to be essential to start up a reactor without well-developed biomass in order to enhance the slow-growing methanogens.