Bioelectrochemical BTEX removal at different voltages: assessment of the degradation and characterization of the microbial communities

BTEX compounds (Benzene, Toluene, Ethylbenzene and Xylenes) are toxic hydrocarbons that can be found in groundwater due to accidental spills. Bioelectrochemical systems (BES) are an innovative technology to stimulate the anaerobic degradation of hydrocarbons. In this work, single chamber BESs were used to assess the degradation of a BTEX mixture at different applied voltages (0.8 V, 1.0 V, 1.2 V) between the electrodes. Hydrocarbon degradation was linked to current production and to sulfate reduction, at all the tested potentials. The highest current densities (about 200 mA/m2 with a maximum peak at 480 mA/m2) were observed when 0.8 V were applied. The application of an external voltage increased the removal of toluene, m-xylene and p-xylene. The highest removal rate constants at 0.8 V were: 0.4 ± 0.1 days−1, 0.34 ± 0.09 days−1 and 0.16 ± 0.02 days−1, respectively. At the end of the experiment, the microbial communities were characterized by high throughput sequencing of the 16S rRNA gene. Microorganisms belonging to the families Desulfobulbaceae, Desulfuromonadaceae and Geobacteraceae were enriched on the anodes suggesting that both direct electron transfer and sulfur cycling occurred. The cathodic communities were dominated by the family Desulfomicrobiaceae that may be involved in hydrogen production.