Characterization of the sulfate-reducing and syntrophic population in granular sludge from a full-scale anaerobic reactor treating papermill wastewater

To gain more insight into the competitive and syntrophic interactions between sulfate-reducing and methanogenic consortia in sulfate-limited anaerobic reactors, the microbial population in granular sludge from a full-scale upflow anaerobic sludge blanket (UASB) reactor was studied, using the 16S rRNA dot-blot hybridization method in combination with most probable number estimates. The wastewater which was treated in the UASB reactor contained mainly starch, acetate, propionate, butyrate and formate, and had a chemical oxygen demand/sulfate ratio of 9.5. Evidence was obtained that acetate was mainly degraded by Methanosaeta-like microorganisms, while propionate was the preferred substrate for sulfate reduction. The Desulfobulbus-like propionate-degrading sulfate reducers in the sludge competed with Syntrophobacter-like bacteria for the available propionate. Hydrogen and formate were probably mainly degraded via methanogenesis by members of the order Methanobacteriales. Hydrogen, formate and butyrate-degrading sulfate reducers could not be characterized with the 16S rRNA probes available to date. The same was true for syntrophic butyrate degraders. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.