THE EFFECTS OF ORGANIC-ACIDS ON THE METHANOGENIC DEGRADATION OF THE LANDFILL LEACHATE MOLECULES BUTYRATE AND VALERATE

The effects of elevated volatile fatty acid (VFA) concentrations, as d istinct From pH, on the methanogenic degradation of butyrate and valer ate were determined. Microbial associations capable of degrading butyr ate or valerate were enriched from municipal refuse and stabilised in multi-stage continuous culture systems. The responses of these associa tions to each of the applied acids (100 mmol l(-1) acetate, propionate , or butyrate) indicated that the butyrate-and valerate-degrading asso ciations were characterized by different populations of acetogenic and sulphate-reducing bacteria, despite being enriched from the same refu se source. The sulphate reducing bacteria were generally more suscepti ble to elevated VFA concentrations than the methanogens. Propionate pr omoted methanogenesis in the presence of bacteria capable of metabolis ing this fatty acid, but had an inhibitory effect on butyrate oxidatio n. In most cases, 100 mmol l(-1) acetate indirectly inhibited methane production. It was thus recommended that leachate concentrations of ac etate and propionate should be closely monitored, since the onset of m ethanogenesis in landfill sites may be delayed by elevated levels of t hese volatile fatty acids, rather than the concomitant reduction in le achate pH. (C) 1998 Elsevier Science Ltd. All rights reserved.