The role of hydrochar on the production of biogas and volatile fatty acids during anaerobic digestion of cheese whey wastewater

The food production industry on Lesvos island generates a significant amount of liquid biowaste, including olive mill wastewater, cheese whey wastewater, and wine sludge. Co-utilizing different food waste sources supports the Circular Economy concept and offers alternative routes in the waste valorization field. Hydrothermal treatment was applied to produce hydrochar from highphenolic sources, and the phenolic hydrochar was used in Anaerobic Digestion of cheese whey wastewater to study the effect on biogas and volatile fatty acids production. The hydrothermal carbonization of olive mill wastewater and wine sludge was studied, and the biogas quality was assessed using various parameters. In addition, this study focused on the effect of hydrochars on the quality of the products, i.e. biogas and volatile acids. Hydrochars from wine sludge and olive mill wastewater had high calorific values (28.05 MJ/kg and 26.55 MJ/kg respectively), and the addition of hydrochar from wine sludge led to the highest biogas production (up to 211 ml/g VS) but mitigated biogas production at higher concentrations. The total phenolic content of the digestates increased with the addition of hydrochar from both sources. The highlight of this study was that hydrochar assisted in the production of medium-chain VFAs, specifically isocaproic and caproic heptanoic acid and by means of ANOVA, this effect was proved to be statistically significant.