Bio-electrochemical assisted anaerobic digestion of the liquid fraction of dairy manure in a UASB reactor

Electrochemical assisted anaerobic digestion has been recently introduced as a new alternative to improve the anaerobic digestion process. The implementation of a bio-electrochemical system such as a microbial electrolysis cell (MEC) coupled with a digester can allow in situ (i) the increase biogas energy content and quality and (ii) the precipitation of struvite (MgNH₄PO₄) by applying an electric field. Subsequently, the concentration of hydrogen sulfide (H₂S) in the biogas can be decreased at the cathode following SO₄⁻² +6e⁻ + 8H⁺ -> S⁰ + 4H₂O (E_cat -0.19 V vs NHE) and at the anode following H₂S -> S° + 2 H⁺ + 2e⁻ (E_an +0.27 V vs NHE) and due to the production of micro-aerobic conditions sulphate reducing bacteria (SRB) will reduce sulphide following 2H₂S + O₂ ->S° + H₂O. The objectives of this work were the development and assessment of an improved UASB reactor through the implementation of a bio-electrochemical system. Our results showed that at an applied voltage of 0.5 V, an increase of about 10% of methane content and a removal of 40% of H₂S in the biogas of UASB-MEC reactor was observed. This system has shown the potential implementation for the H₂S removal of digesters.