INFLUENCES OF TYPICAL HYDRAULIC FRACTURING FLUID CONSTITUENTS ON THE STRUCTURE AND ACTIVITY OF IRON REDUCING MICROBIAL COMMUNITIES

Little is known about the impact of hydraulic fracturing fluid (HFF) constituents and unconventional oil and gas wastewater on the environment. We hypothesize that microbial metabolism may mitigate contamination due to produced water (PW) disposal in affected stream systems. We studied a stream running alongside an oil and gas PW disposal facility in West Virginia which was impacted by disposal and storage operations, as indicated by elevated conductivity and TDS and by shifts in microbial populations. The growth potential of iron-reducing bacteria (FeRB) from impacted and unimpacted (background) stream sediments from this site was evaluated in the presence of HFF components. FeRB were cultivated under anaerobic conditions with added FeOOH and either no electron donor, lactate (an easily metabolized carbon source), or one of several HFF additives: guar gum (a gelling agent), ethylene glycol (a petroleum-based scale inhibitor), 2,2-dibromo-3-nitrilopropionamide (DBNPA) or bronopol (both biocides). Microbial iron reduction rates were positively influenced by additives with the potential to act as a carbon source (lactate, ethylene glycol, and guar gum) and were suppressed, but not completely inhibited, by biocides. Fe(II) production was greater in cultures with sediment from the impacted site, consistent with the observation of increased sediment-Fe concentrations. A lag time in Fe reduction was observed in the presence of biocides, possibly due to a shift towards biocide-tolerant communities. Total community analyses suggested shifts towards bacterial communities adapted to high salinity and iron levels, and low oxygen levels. Prior to culture, communities differed between the impacted and background sites, and communities shifted over time and in response to the presence of biocides, guar gum, and lactate. The presence of ethylene glycol had little effect on iron reduction rates and did not cause community shifts in cultures from either site. These data imply that FeRB are present in stream sediments adjacent to the disposal facility and that their activity is influenced by various HFF components and the availability of Fe(III). Additionally, community shifts suggest that some HFF additives have a direct impact on microbial community structure.