Metal stimulation and municipal digester thermophilic/mesophilic activity

Biomass from thermophilic and mesophilic digesters (four temperature-phased anaerobic digesters and one phased thermophilic digester) was assayed for potential methane production rate increases resulting from nutrient (Ni, Co, and Fe) addition. Furthermore, digester operations and biomass activities were compared. The majority (77%) of biomass samples benefited from nutrients, with propionate and acetate utilization rates increasing as much as 50 and 35%, respectively, after nutrient addition. Propionate, utilization rates were more frequently stimulated by nutrient addition, demonstrating increased methane production rates of from 14 to 50% upon nutrient amendment. Others have observed difficulty achieving low propionate concentrations in municipal thermophilic digesters, especially at lower retention times. Trace nutrient supplementation is one method to increase propionate and acetate utilization in some municipal thermophilic as well as mesophilic digesters.