Volatile fatty acids as an added value from biowaste

•VFAs were produced using kitchen biowaste and potato peels as co-substrates.•VFAs production and chain elongation was performed under micro-aerobic conditions.•Volatile acids elongation to valeric acid took place within a relatively short time.•High conversion yields, up to 325mg/g TS after 72h of the bioprocess, were achieved.•Achieved conversion rates were higher than the literature values for each of the substrates. The aim of the present work was to provide proof of concept of employing a co-culture of K. mobilis and E. coli for producing short and medium chain volatile fatty acids (VFAs) from kitchen biowaste and potato peels. To this aim, experiments were carried out at pilot-scale installation with a bioreactor of 250L. Different feeding strategies were tested under microaerobic conditions, at pH 6.0–6.5 in order to enhance chain elongation. Acetic acid and ethanol were dominating products in the initial stages of the bioprocess, but in a relatively short time of approx. 20–22h from the process start accumulation of propionic acid took place followed by a chain elongation to butyric and valeric acids. The highest final products yield of 325mg/g TS was achieved for the substrate load of 99.1g TS/L (VS of 91.1g/L) and pH 6.5, with the productivity of 448mg/L/h. However, the highest average VFAs chain length (3.77C) was observed in the process run with the loading of 63.2g TS/L and pH 6.0. In this study, we demonstrated that the existing symbiosis of the co-culture of K. mobilis and E. coli favours formation and chain elongation of VFA, induced most likely by the enhanced ethanol formation. Our finding differs from the previous research which focus mostly on anaerobic conditions of VFAs production. The results provide good basis for further optimisation of VFAs production process.