Using slaughterhouse waste in a biochemical-based biorefinery - results from pilot scale tests.

A novel biorefinery concept was piloted using protein-rich slaughterhouse waste, chicken manure and straw as feedstocks. The basic idea was to provide a proof of concept for the production of platform chemicals and biofuels from organic waste materials at non-septic conditions. The desired biochemical routes were 2,3-butanediol and acetone-butanol fermentation. The results showed that hydrolysis resulted only in low amounts of easily degradable carbohydrates. However, amino acids released from the protein-rich slaughterhouse waste were utilized and fermented by the bacteria in the process. Product formation was directed towards acidogenic compounds rather than solventogenic products due to increasing pH-value affected by ammonia release during amino acid fermentation. Hence, the process was not effective for 2,3-butanediol production, whereas butyrate, propionate, γ-aminobutyrate and valerate were predominantly produced. This offered fast means for converting tedious protein-rich waste mixtures into utilizable chemical goods. Furthermore, the residual liquid from the bioreactor showed significantly higher biogas production potential than the corresponding substrates. The combination of the biorefinery approach to produce chemicals and biofuels with anaerobic digestion of the residues to recover energy in form of methane and nutrients that can be utilized for animal feed production could be a feasible concept for organic waste utilization.

Volatile fatty acids as an added value from biowaste.

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.