Enhanced dechlorination of 1,2-dichloropropane to propene in a bioelectrochemical system mediated by Dehalogenimonas

Highlights: • A bioelectrochemical system degraded 1,2-dichloropropene to nontoxic propene. • Graphite brush as electrode exhibited higher degradation rate than carbon cloth. • Dehalogenimonas 16S rDNA sequences increased two orders of magnitude. • Application of pulsed voltage increased the coulombic efficiency of the process. Bioelectrochemical systems (BES) are promising technologies to enhance the growth of organohalide-respiring bacteria and to treat chlorinated aliphatic hydrocarbons. In this study, two carbon-based cathodic electrode materials, a graphite brush and a carbon cloth, were used as hydrogen suppliers to couple growth of Dehalogenimonas and dechlorination of 1,2-DCP to nontoxic propene in the cathode vessel. The BES with graphite brush electrode consumed ~4000 µM 1,2-DCP during 110 days and exhibited a degradation rate 5.6-fold higher than the maximum value obtained with the carbon cloth electrode, with a cathode potential set at −0.7 V. Quantitative PCR confirmed that Dehalogenimonas gene copies increased by two orders of magnitude in the graphite brush BES, with an average yield of 1.2·10⁸±5·10⁷ cells per µmol of 1,2-DCP degraded. The use of a pulsed voltage operation (cathode potential set at −0.6 V for 16 h and −1.1 V for 8 h) increased the coulombic efficiency and degradation of 1,2-DCP when compared with a continuous voltage operation of −1.1 V. Bacterial cell aggregates were observed in the surface of the graphite brush electrodes by electron scanning microscopy, suggesting biofilm formation. This study expands the range of chlorinated compounds degradable and organohalide-respiring bacteria capable of growing in BES.