Food waste and sewage sludge co-digestion amended with different biochars: VFA kinetics, methane yield and digestate quality assessment.

This work investigated the impact of the addition of different biochar types on mitigation of volatile fatty acid (VFA) accumulation, methane recovery and digestate quality in mesophilic food waste-sludge co-digestion. Four biochars derived from agricultural and sludge residues under different pyrolysis temperatures were compared. Specific biochar properties such as pH, surface area, chemical properties and presence of surface functional groups likely influenced biochar reactions during digestion, thereby resulting in a varying performance of different biochars. Miscanthus straw biochar addition led to the highest specific methane yield of 307 ± 0.3 mL CH 4 /g VS added versus 241.87 ± 5.9 mL CH 4 /g VS added from control with no biochar addition over 30 days of the co-digestion period. Biochar supplementation led to enhanced process stability which likely resulted from improved syntrophic VFA oxidation facilitated by specific biochar properties. Overall, a 21.4% increase in the overall methane production was obtained with biochar addition as compared to control. The resulting digestate quality was also investigated. Biochar-amended digester generated a digestate rich in macro- and micro-nutrients including K, Mg, Ca, Fe making biochar-amended digestate a potential replacement of agricultural lime fertilizer. This work demonstrated that the addition of specific biochars with desirable properties alleviated VFA accumulation and facilitated enhanced methane recovery, thereby providing a means to achieve process stability even under high organic loading conditions in co-digestions. Moreover, the availability of biochar-enriched digestate with superior characteristics than biochar-free digestate adds further merit to this process. [Display omitted] • Effect of various biochar on mesophilic food waste/sludge co-digestion was compared. • Biochar properties influenced their reactions during digestion. • Miscanthus straw biochar resulted in 21.4% increase in specific methane yield. • Biochar-amended (co)digestate was rich in macro- and micro-nutrients. [ABSTRACT FROM AUTHOR]