Bioelectrochemical toluene degradation in marine environments

Accidental oil spills can lead to considerable release of toxic petroleum hydrocarbons in marine environments. Due to their recalcitrance under anoxic conditions in the sediment, oxidative bioremediation strategies have been developed. Here we investigated an alternative strategy to remove monoaromatic hydrocarbons from marine environments by stimulating the biodegradation with an electrode as solid electron acceptor. Using toluene as a model compound, degradation was accomplished in BES with simultaneous current production. Glass BES reactors were set up using sediment collected from an hydrocarbon contaminated marine site as microbial inoculum, and artificial ocean water as growth medium. Anode potentials of 0 mV and +300 mV (vs Ag/AgCl) were tested in order to check their influence on current production, enrichment of electrocatalytically active microorganisms and hydrocarbon degradation rate. At the end of the experiment microbial characterization of the communities attached to the electrodes and in the bulk of each reactor was performed by Illumina sequencing of the 16S rRNA. Degradation of toluene was directly linked to current generation up to 431 mA/m, but over time decreasing peak currents were obtained upon renewed toluene spiking. In both the conditions a degradation rate of 1 mg/(L d) was observed. Monitoring of sulfate/sulfide concentrations during bioelectrochemical experiments suggested that sulfur metabolism might play an important role in toluene degradation on a bio-anode, potentially leading to passivation over time. The microbial communities were dominated by sulfate reducing microorganisms, particularly the family Desulfobulbaceae appeared to be linked both with current production and toluene degradation.