COMBINED PRE-DEGRADATION AND ANAEROBIC-DIGESTION FOR THE TREATMENT OFA BAKERS-YEAST FACTORY EFFLUENT

A Chryseomonas luteola strain was isolated from raw baker's yeast fact ory effluent as the dominant part of the microbial community and evalu ated for its biodegradative activity, using the raw effluent as substr ate. The strain was able to utilise the raw effluent and produce highe r concentrations of energetically favourable metabolites and thereby, could contribute to the first degradation step in an anaerobic biologi cal treatment process. A 3x4x3 factorial design indicated optimal degr adation conditions in a specific environmental framework of 48 h incub ation time, COD concentration of 30 g/l, pH of 6.0 and temperature of 35 degrees C. The C. luteola strain was thereafter used in a pre-degra dation step followed by an anaerobic digestion step in a 5 1 laborator y-scale hybrid digester. With the use of the pre-degraded effluent, si gnificant improvements were found in the overall anaerobic digestion p erformance. These included increased COD (>15%) and TVFA (>50%) remova ls, especially propionic acid (88%) removal, as well as higher biogas yields (18%). The results also showed a prominent improvement in fatty acid utilisation and methanogenesis. The pre-degradation step resulte d in better process control and increased stability of the system, eve n at relatively high organic loading rates (10 kg COD/m(3).d). When th e raw effluent was not pre-treated (control bioreactor), no improvemen t in bioreactor efficiency was observed. (C) 1997 IAWQ. Published by E lsevier Science Ltd.