Combined pre-degradation and anaerobic digestion for the treatment of a baker's yeast factory effluent

Abstract

A Chryseomonas luteola strain was isolated from raw baker's yeast factory effluent as the dominant part of the microbial community and evaluated for its biodegradative activity, using the raw effluent as substrate. The strain was able to utilise the raw effluent and produce higher concentrations of energetically favourable metabolites and thereby, could contribute to the first degradation step in an anaerobic biological treatment process. A 3×4×3 factorial design indicated optimal degradation conditions in a specific environmental framework of 48 h incubation time, COD concentration of 30 g/l, pH of 6.0 and temperature of 35°C. The C. luteola strain was thereafter used in a pre-degradation step followed by an anaerobic digestion step in a 5 1 laboratory-scale hybrid digester. With the use of the pre-degraded effluent, significant improvements were found in the overall anaerobic digestion performance. These included increased COD (>15%) and TVFA (>50%) removals, 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 predegradation step resulted in better process control and increased stability of the system, even at relatively high organic loading rates (10 kg COD/m³.d). When the raw effluent was not pre-treated (control bioreactor), no improvement in bioreactor efficiency was observed.