Effects of Biowaste-Derived Hydrochar on Anaerobic Digestion: Insights into Hydrochar Characteristics

Abstract

Hydrochar prepared with four typical biowastes, pine wood, food waste, digested sewage sludge, and Chlorella were applied for the promotion of anaerobic digestion. The gas production and substrate composition were analyzed associated with the hydrochar characteristics. The results suggested that Chlorella hydrochar (C-C) showed the highest cumulative yield of methane (approximately 345 mL) with high total organic carbon (TOC) removal efficiency and low volatile fatty acids (VAFs) concentration. Especially, food waste hydrochar (F-C) showed a poor effect on anaerobic digestion and aroused 1.4–1.6 g/L accumulation of VAFs, in which the toxic components may account for the low efficiency. The C-C and sludge hydrochar (S-C) may develop direct interspecific electron transport (DIET) to facilitate the generation of methane by both surface groups and conductivity of the body structure, unlike pinewood hydrochar (P-C), which mainly depended on the aromatic matrix structure of hydro-char body. This work suggested that C-C can be the best candidate for the facilitation of anaerobic digestion, and N-containing biowaste like algae and lignocellulose like pine wood may establish different DIET pathways based on the physicochemical characteristics of hydrochar.