Enrichment of A Mesophilic, Syntrophic Bacterial Consortium Converting Acetate to Methane at High Ammonium Concentrations

Abstract

Nitrogen-rich organic materials, such as swine and poultry manure, slaughterhouse and fish industry waste, etc., generally produce smaller amounts of biogas than similar substrates with lower nitrogen contents. In addition, methane formation rates are lower during fermentation of the nitrogen-rich materials (McCarty & McKinney, 1961; van Velsen, 1979; 1981; Wiegant, 1986). These differences seem to be due to the fact that ammonium, which at high concentrations inhibits methane formation (van Velsen, 1979; 1981; Wiegant, 1986), is formed during the anaerobic degradation of nitrogen-rich substrate and, as in the case of manure, is also added via the urine (cf Fig. 1). Elevated ammonium concentrations can prolong the period necessary for starting up a bioreactor. In addition, longer retention times are necessary in order to obtain a given reduction in COD in nitrogen-rich material as compared with organic matter with a lower nitrogen content. Research within this field has thus far been performed mainly in laboratory reactor systems, where effects of temperature, pH, loading rates and adaptation phenomena have been studied. Present know-ledge within this field is briefly summarized below.