Syntrophy drives the microbial electrochemical oxidation of toluene in a continuous-flow “bioelectric well”

Microbial electrochemical technologies (MET) are promising for the remediation of groundwater pollutants such as petroleum hydrocarbons (PH). Indeed, MET can provide virtually inexhaustible electron donors or acceptors directly in subsurface environment. However, degradation mechanisms linking contaminants removal to electric current flow still largely unknown, hindering development robust design criteria. Here, we analysed toluene, a model PH, bioelectrochemical reactor known “bioelectric well” operated continuous-flow mode at various influent toluene concentrations. With increasing concentration rate increased while tended plateau, hence columbic efficiency decreased. Operation open circuit confirmed that proceeded via syntrophic pathway involving cooperation between different microbial populations. First all, hydrocarbon degraders quickly converted into metabolic intermediates probably by breaking aromatic ring upon fumarate addition. Subsequently, fermentative bacteria these volatile fatty acids (VFA) and likely also H2, which were then used substrates electroactive microorganisms forming anodic biofilm. As is faster than subsequent conversion steps, increase intermediate could not result increase. This work provides valuable insights on BTEX, essential application system hydrocarbons.