Anaerobic co-digestion of fish waste and food waste: Synergistic improvement on biogas production

This work evaluated the anaerobic co-digestion of fish waste (FIW) and food waste (FW) to determine the feasibility of co-digestion and the key parameter mixing ratio. The results showed that the cumulative biogas production was significantly improved when the FIW to FW ratios were 80:20, 60:40, 40:60 compared to sole FIW and sole FW, with an optimal ratio of FIW to FW of 60:40. At this ratio, the cumulative biogas yield reached 213.89 NmL/g VS_added, which was 25.35% and 26.57% higher than that of sole FIW and FW groups (170.64 and 168.99 NmL/g VS_added), respectively. It was also found that this ratio not only avoided the high-concentration free ammonia inhibition (>30 mg/L) faced during the digestion of sole FIW, but also prevented the system pH instability (< pH 6.8) caused by the sharp drop in pH during the digestion of sole FW, thus making it more conducive to biogas production. Enzyme activity results showed that the activity of coenzyme F₄₂₀ in the FIW:FW= 60:40 group was ∼1.55 times that of sole FIW and ∼1.61 times that of sole FW. Microbial analysis showed that more hydrolytic microbes, short-chain fatty acids (SCFAs) producer and those facultative microbes, as well as methanogens, were respectively enriched in the FIW:FW= 60:40 group compared to the sole FIW and sole FW. The reported findings can provide an effective strategy for strengthening FIW and FW treatment and energy recovery in fish product processing plants.