Biological sulfate removal from tannery wastewater in a two-stage anaerobic treatment

In a long-term study, the process of biological sulfate reduction in anaerobic two-stage pilot plants treating tannery wastewater was investigated with the objective to reduce most of the sulfate in the first stage. Influence of quality and quantity of wastewater on sulfate removal in both stages of the pilot plant was tested simultaneously (multiple regression). Origin of the wastewater, chromium, chloride, sulfide and COD in the influent showed no significant effect on desulfurization. Feed flow and the concentration of sulfate in the influent, however, significantly affected sulfate removal. In the first stage, desulfurization increased with higher feed flow but the desulfurization then decreased in the second stage. The concentration of sulfate in the influent had a significant influence on the desulfurization in both stages of the pilot plants. The removal of sulfate in the first stage was approximately 30%, whereas in the second stage the desulfurization decreased with higher concentrations of sulfate in the influent. Operational parameters were adjusted in order to restrict the biological sulfate reduction to the first stage. The statistical method employed was analysis of variance. Compared to pH 5 or 6 in the influent, a pH of 7 most increased biological sulfate reduction in the first stage. No significant influence on COD removal or volume of gas were observed. For three pilot plants operated parallel to each other, no significant difference in desulfurization was noticed.