Energy-harvesting bio-electro-dehalogenation for sustainable wastewater treatment

Highlights: • Reductive dehalogenation is powered by a microbial fuel cell. • Energy from dehalogenated products is captured by bacteria and used for dehalogenation. • Energy efficiency is close to that of a fully sustainable dehalogenation process. • Mechanism of cobalt-macrocycle-catalyzed reductive dehalogenation is revealed. The concept of an "energy-harvesting bio-electro-dehalogenation" process is demonstrated, where exoelectrogenic bacteria in an anodic chamber of a microbial fuel cell (MFC) are used to capture and exploit the electrical energy stored in the biodegradable substrate (acetate). The acetate was derived from full electrocatalytic dehalogenation of non-biodegradable halogenated organic compounds (haloacetic acids) in the cathodic chamber. Cobalt(II) meso-tetraphenylporphyrin serves the role as electrocatalyst in the MFC. Cyclic voltammetric analysis shows that full dehalogenation requires a cathodic potential of −1.1 V vs. Ag/AgCl which can be augmented by stacked MFCs powered by the dehalogenated products. Cyclic voltammetric analysis and ion chromatography measurement confirm that electrogenerated cobalt(I) meso-tetraphenylporphyrin is catalyzing the reduction of tri-, di-, and monochloroacetic acids in a sequential dehalogenation processes. The energy harvesting concept is also applicable to other bio-electrochemical processes for treatment of bio-refractory pollutants.