title: Ammonia, a selective agent for methane production by syntrophic acetate oxidation at mesophilic temperature.
abstract: In biogas processes, methane production from acetate proceeds by either aceticlastic methanogenesis or through syntrophic acetate oxidation (SAO). In the present study, the pathway for methane production from acetate was analysed; i) during a gradual increase of the ammonia concentration (final concentration 7 g NH(4)(+) -N/L) in a semi-continuous lab-scale anaerobic digester (4.3 L), operating at mesophilic temperature (37 degrees C) or ii) in diluted enrichment cultures (100 ml) experiencing a gradual increase in ammonia, sodium, potassium and propionic acid. The pathway for methane formation was determined by calculating the (14)CO(2)/(14)CH(4) ratio after incubating samples with (14)C-2-acetate. In the anaerobic digester, as well as in the enrichment cultures, the (14)CO(2)/(14)CH4 ratio clearly increased with increasing ammonium-nitrogen concentration, i.e. as the ammonia concentration increased, a shift from the aceticlastic mechanism to the syntrophic pathway occurred. The shift was very distinct and occurred as the NH(4)(+) -N concentration rose above 3 g/l. No shift in pathway was seen during increasing concentrations of sodium, potassium or propionic acid. The shift to SAO in the biogas digester resulted in a twofold decrease in the specific gas and methane yield.
authors.affiliation: Department of Microbiology, Swedish University of Agricultural Sciences, Box 7025, S-750 07 Uppsala, Sweden. Anna.Schnürer@mikrob.slu.se
authors.forename: A
authors.initials: A
authors.lastname: Schnürer
authors.forename: A
authors.initials: A
authors.lastname: Nordberg
mesh_terms: D000085:Acetates / Q000737:chemistry*; D000641:Ammonia / Q000737:chemistry*; D000693:Anaerobiosis; D002250:Carbon Radioisotopes; D008697:Methane / Q000737:chemistry*; D010084:Oxidation-Reduction; D013696:Temperature
chemical_list: D000085:Acetates; D002250:Carbon Radioisotopes; D000641:Ammonia; D008697:Methane