Abstract: Anaerobic digestion (AD) of food waste could result in a large amount of biogas residue generation, which needs to be properly disposed. Biogas residue was prepared into hydrochar and pyrochar by hydrothermal and pyrolysis reaction, respectively. The effects of hydrochar and pyrochar on AD of food waste were compared. The results showed that compared with the control group (23.8 mL/g), the methane production of hydrochar group (dosage of 1, 5 and 10 g/L) was 24.0, 38.9 and 34.9 mL/g, which increased by 0.8%, 63.4% and 46.6%, respectively. The methane yield of pyrochar group (dosage of 1,5 and 10 g/L) was 29.7, 35.7 and 31.1 mL/g, which increased by 24.8%, 50.0% and 30.7%, respectively. Hydrochar and pyrochar amendment promoted the solubilization of organic matter. While the total relative abundance of hydrolytic acid-producing bacteria of Fastidiosipila, W5053, Propioniciclava, Actinomyces, and Norank_f__ST-12K33 increased from 73.0% to 84.6% and 82.0%, respectively. After adding hydrochar and pyrochar, the relative abundance of Methanosaeta was as high as 60.3% and 50.6% respectively, while the relative abundance of Methanobacterium was only 26.5% and 36.9%. Biochar from biogas residue could strengthen the AD of food waste, with the increase of dosage, methane production first increased and then decreased, the optimal dosage was 5 g/L. And the hydrochar performed better than pyrochar.

Key words: biogas residue, hydrochar, pyrochar, food waste, anaerobic digestion