Acidogenic fermentation of food waste and sewage sludge mixture: Effect of operating parameters on process performance and safety aspects

The production of added-value bio-products and energy from waste streams while minimizing environ- mental impacts is a crucial aspect within the circular economy’s principles. The biorefinery can be an exit to the constant increasing of organic food waste and sewage sludge to solve the issues of waste disposal. This work deals with the production of volatile fatty acids (VFA) as added-value products from food waste and sewage sludge mixture in a pilot scale acidogenic fermentation process. Moreover, due to the lack of in- formation about safety aspects in the literature, the explosive risk of the fermenter has been assessed by means of the quantification of lower flammability limit (LFL) of the generated flammable gases. Different temperature and feedstock’s composition were tested, as well as the effect of thermal hydrolysis. Mesophilic fermentation (37 °C) on thermally hydrolysed feedstock (48 h at 72 °C) ensured stability in terms of VFA production at high concentration (30 ± 2 gCODVFA/L) and CODVFA/CODSOL ratio (0.86 ± 0.09). Such condition also showed high LFL (28.9%), corresponding to a less hazardous condition compared to the other investigated, especially the thermophilic ones where LFL changed between 18% and 26%.