Salinity-induced effect on biomethane production and microbial community in anaerobic digestion of food waste components

Food waste holds significant potential for the production of advanced biofuels, including biomethane. This study systematically assessed the impact of salt on biomethane production from different components of food waste. The highest biomethane yields of 258.89 ± 10.96, 337.52 ± 16.36, and 448.49 ± 23.375 mL/g VS (equivalent to biodegradability indexes of 75.75%, 88.92% and 92.66%) were achieved from cellulose-rich, starch-rich and protein-rich components, respectively, at a salt concentration of 3 g NaCl/L. The biomethane yield was improved by 9.69–31.24% with low-concentration salt compared with no salt addition, but it was inhibited by high salinity. Inhibition degree caused by high salinity (15 g NaCl/L) on biomethane production followed the order of protein (15.50%) < starch (28.03%) < cellulose (42.92%). Co-digestion of different components effectively mitigated the inhibitory effect of salt on biomethane production. Microbial community analysis revealed that archaea were significantly affected by high salinity. With a high concentration of salt (15 g/L), acetoclastic methanogens (Methanosatea) predominated in the digestion of starch-rich components, whilst hydrogenotrophic methanogens (Methaonmassiliicoccus and Methanobacterium) predominated in the digestion of cellulose-rich and protein-rich components. Additionally, some salt-tolerant microorganisms (SC103, Thermovirga and Methanosarcina) were selectively enriched at high salinity.