Nitrogen and energy balances of a combined anaerobic digestion and electrochemical oxidation process for dairy manure management

Abstract

Anaerobic digestion and electrochemical oxidation were investigated for their potential to recycle carbon and degrade nitrogen from dairy manure; the energy balance of this combination of treatments was also evaluated. Anaerobic digestion is a sustainable technology that allows recovery of biomass energy and treatment of animal wastes for carbon recycling. Since the anaerobic digestion process performs denitrification poorly, almost all nitrogenous substances are discharged in digested effluent as ammonia. The ammonium nitrogen in anaerobically digested effluent is degraded by electrochemical oxidation with an unsacrificial anode. The electrochemical oxidation requires inputs of electricity. We evaluated the feasibility of using electricity generated by a full-scale biogas plant, producing biogas from dairy manure, for the electrochemical oxidation of ammonium nitrogen in anaerobically digested effluent. Data on the amount of electricity generated by such a plant were compared with data on the electricity requirements of the electrochemical oxidation process to determine the energy balance of the two processes. The results indicated that electricity generated from a biogas plant was able to supply 24 to 33% of the electricity required for the electrochemical oxidation.