Effect of some physical and chemical parameters on the fermentation of cellulose to methane by a coculture system

Abstract

In the fermentation of cellulose to methane by the triculture of Acetivibrio cellulolyticus – Desulfovibrio sp. – Methanosarcina barkeri, methanogenesis was the rate-limiting step. The optimal temperature was 35 °C. In the presence of initially added hydrogen, initiation of cellulose hydrolysis was delayed until most of the hydrogen was metabolized, and then the fermentation which followed was comparable with the N₂: CO₂ control. Increased CH₄ yields and rates of formation were stoichiometrically related to the utilization of the hydrogen initially present. Added acetate had no effect on cellulolysis. The increased yields of CH₄ observed could be accounted for by utilization of the added acetate. When Methanobrevibacter sp. was included in the coculture (without added H₂ or acetate), no hydrogen accumulated and lower rates of acetate utilization and subsequent CH₄ evolution were observed. These results suggest a requirement for hydrogen by M. barkeri for efficient acetate utilization. Controlling the pH at 6.8 increased the amount of cellulose degraded, but CH₄ yields were lower and no acetate was used. Increasing sulfate levels altered the ratio of fermentation products but had no effect on cellulose degradation. Lower CH₄ yields were obtained at elevated sulfate concentrations.