Behavior of carbon monoxide as a trace component of anaerobic digester gases and methanogenesis from acetate

Abstract

Carbon monoxide was a normal trace component of the gases produced during anaerobic sludge digestion. The CO concentration increased in response to perturbing the digestion process by increasing organic loading or adding acetate. Reducing the headspace methane level resulted in higher measured CO concentrations. Accordingly, a thermodynamic relationship was developed by dividing the acetoclastic methane reaction into two half-cell reactions, representing production of and subsequent oxidation of CO. A constant fraction of the total free energy available for acetate conversion to methane was assigned to each half-cell based on the basis of experimental observations. It was determined that approximately 54% of the energy available for acetate conversion to methane was consistently associated with the anaerobic oxidation of CO to carbon dioxide. Estimated values compared well for measured concentrations for both mesophilic and thermophilic digesters operating under steady-state conditions.