LONG-TERM COMPETITION BETWEEN SULFATE-REDUCING AND METHANE-PRODUCING BACTERIA DURING FULL-SCALE ANAEROBIC TREATMENT OF CITRIC-ACID PRODUCTION WASTE-WATER

The bacterial population structure of sludge present in a full-scale u pflow, fully-packed anaerobic digester treating a sulphate-containing wastewater (12 g COD/l, 4 g SO42-/l) from the citric acid production i ndustry for a period of 5 years was determined: Populations of sulphat e-reducing, methanogenic, syntrophic and homoacetogenic bacteria were found to prevail in the reactor sludge. The degradation patterns of se veral key anaerobic intermediates were studied. Both propionate and H- 2/CO2 were completely metabolised by sulphate reducing bacteria. Metha nogenic bacteria outcompeted sulphate-reducers for acetate, whereas co mpetition took place for butyrate and ethanol. The outcome of competit ion in the sludge was not affected by the location within the reactor or by the cell residence time. (C) 1998 Elsevier Science Ltd. All righ ts reserved.