Conversion of organic waste into volatile fatty acids – The influence of process operating parameters

Abstract The objectives of this study were to investigate the effect of hydraulic retention time (HRT) and organic loading rate (OLR) on the volatile fatty acids (VFAs) production from cheese whey and sludge, and to find the relation between total volatile fatty acids (TVFAs) accumulation at different HRT and OLR and the corresponding bacterial community. The highest concentrations of butyrate (5.0 g COD/L), valerate (3.8 g COD/L), caproate (4.2 g COD/L) and heptate (0.8 g COD/L) were obtained from whey fermentation, where proportion of acetate increased with HRT shortening (from 8.3% to 83.5% for HRT of 20 to 1 day, respectively). The highest concentrations of acetate (1.6 g COD/L), propionate (2.9 g COD/L), iso-butyrate (0.8 g COD/L) and iso-valerate (1.8 g COD/L) were obtained from sludge fermentation, where proportion of acids was independent of HRT. Bacterial communities consisted mostly of the phyla Firmicutes , Cloacimonetes , Proteobacteria and uncultured bacterium clones. The bacterial community originating from the substrate was able to adapt to the applied bioreactor conditions and it had an immense impact on the process performance.