Oil and gas (OG) wastewaters are commonly disposed of by underground injection and previous research showed that activities at a disposal facility in West Virginia affected stream biogeochemistry and sediment microbial communities downstream from the facility. Microorganisms can control the fate and transport of organic and inorganic components of OG wastewater highlighting the need to characterize the effects of OG wastewater components on microbial activity. We conducted a series of aerobic microcosm experiments to assess the influence of high total dissolved solids (TDS) and hydraulic fracturing fluid additives (2,2-dibromo-3-nitrilopropionamide (DBNPA), a biocide, and ethylene glycol, an anti-scaling additive), on microbial community structure and function. Microcosms were constructed with sediment from upstream (background) or downstream (impacted) from the disposal facility in West Virginia and four treatment conditions each with heat-killed controls were tested: 1) brine (high TDS) + DBNPA, 2) brine + ethylene glycol, 3) brine, and 4) unamended control. Microbial terminal electron accepting processes were monitored over time and changes in microbial community composition were characterized. Over the course of the incubation, the sediment layer in the microcosms became anoxic, and addition of DBNPA was observed to inhibit iron reduction.