THE EFFECT OF SULFATE ON PROPIONATE AND BUTYRATE DEGRADATION IN A PSYCHROPHILIC ANAEROBIC EXPANDED GRANULAR SLUDGE BED (EGSB) REACTOR

The effect of sulphate on the anaerobic psychrophilic degradation of p ropionate and butyrate was studied using an expanded granular sludge b ed (EGSB) reactor. The EGSB reactor was operated at organic loading ra tes 7 - 12 kg COD . m(-3). day(-1), at hydraulic retention times of 2. 5 - 1.6 h and at three different sulphate concentrations. The results of the continuous flow experiments and of batch experiments with sludg e from the EGSB reactor reveal that the psychrophilic degradation of p ropionate is strongly affected by the presence of sulphate. Addition o f 0.266 g SO42--S . dm(-3) to the medium resulted in a 35% increase in the propionate conversion rate. In contrast, the butyrate degradation rate decreased by 32% in the presence of sulphate. Syntrophic acetoge nic butyrate-oxidizing consortia seem to compete effectively with sulp hate reducing bacteria.