Dehalogenation of environmental pollutants in microbial electrolysis cells with biogenic palladium nanoparticles.

PURPOSE OF WORK: Hydrodehalogenation of persistent pollutants, such as the groundwater contaminants trichloroethylene and diatrizoate, are catalyzed by biogenic Pd nanoparticles. As H(2) gas supply for the dehalogenation reactions is still the limiting factor, this study examines in situ H(2) production in the cathode of a microbial electrolysis cell. In a biogenic Pd nanoparticle (bio-Pd) free microbial electrolysis cell (MEC), dechlorination of trichloroethylene (TCE) with concomitant chloride and ethane formation was achieved in the cathode compartment at a removal rate of 120 g TCE m(-3) total cathode compartment (TCC) day(-1), applying -0.8 V with a power source. When the cathode granules were coated with 5 mg bio-Pd g(-1) graphite, chloride and ethane formation increased to 151 g TCE m(-3) TCC day(-1) corresponding with a specific removal rate of 48 mg TCE g(-1) Pd day(-1). In both cases, formation of unwanted byproducts, such as vinyl chloride, was not significant. When the same setup was applied for transformation of the iodinated contrast medium diatrizoate (diaI(3)), reduction in a catalyst-free cathode of a MEC resulted in a removal of 48 ± 9% during the first h corresponding to 3 g diaI(3) m(-3) TCC day(-1). Coating the cathodic graphite granules with bio-Pd enhanced the transformation resulting in a 93 ± 4% removal during the first h corresponding to 6 g diaI(3) m(-3) TCC day(-1). These results suggest that MECs can produce H(2) in a sustainable way to provide an economical interesting reactant for bio-Pd catalyzed dehalogenation reactions.