Electricity from methanol using indigenous methylotrophs from hydraulic fracturing flowback water

Abstract

Methanol solvents that are used in hydraulic fracturing often return back to the surface in the form of recalcitrant flowback water. Here, the indigenous methylotrophic bacteria from flowback water were enriched and used to generate electricity from methanol in a two-compartment microbial fuel cell (CH3OH-MFC). An identical MFC based on a tryptone-yeast extract (TY-MFC) was used as a control. CH3OH-MFC yielded a 2.7-fold thicker biofilm dominated by electrogenic species (81%) and higher power density (76 mW/m2) compared with TY-MFC (50 mW/m2). Illumina MiSeq sequencing of the 16S rRNA gene in TY-MFC revealed classes from Actinobacteria, Bacteroidia and γ-proteobacteria. The CH3OH-MFC yielded α-proteobacteria, β-proteobacteria, γ-proteobacteria and Bacteroidia, with a dominant fraction of Rhodobacter sphaeroides (~29%). We discuss the potential pathways used by R. sphaeroides to maintain syntrophic cooperation with other bacterial and archaeal members to sustain CH3OH oxidation. Finally, we establish that a pure culture of R. sphaeroides 2.4.1 generates electricity directly from methanol.