Optimization of cobalt, nickel, and iron supplement for mesophilic and thermophilic anaerobic digestion treating high-solid food waste.

The effects of trace metals (iron (Fe), cobalt (Co) + Fe, and Co + nickel (Ni) + Fe) on mesophilic and thermophilic anaerobic digestion of food waste were quantified experimentally. Supplementation with 0 ≤ [Co] ≤ 5 mg/L, 0 ≤ [Ni] ≤ 10 mg/L, or 0 ≤ [Fe] ≤ 200 mg/L can significantly improve the productivity of mesophilic (MD) and thermophilic (TD) digesters. Addition of micronutrients increased biogas production, but excessive addition of trace metals hindered the production. Supplementation with Fe + Co or Fe + Co + Ni increased biogas production more than the addition of only Fe did. Within the design boundaries, the optimal concentrations for supplementation with three trace metals in MD were [Co] = 0.33 mg/L, [Ni] = 0.43 mg/L, and [Fe] = 5.35 mg/L, and in TD were [Co] = 1.41 mg/L, [Ni] = 3.84 mg/L, and [Fe] = 200 mg/L. TD required larger amounts of the trace metals than MD (4.3-37.4 times). The results can give quantitative information on trace metal supplementation for successful anaerobic digestion.