Emergence and fate of volatile iodinated organic compounds during biological treatment of oil and gas produced water.

Oil and gas (O&G) production in the United States is expected to grow at a substantial rate over the coming decades. Environmental sustainability related to water consumption during O&G extraction can be addressed through treatment and reuse of water returning to the surface after well completion. Water quality is an important factor in reuse applications, and specific treatment technologies must be utilized to remove different contaminants. Among others, biological active filtration can remove dissolved organic matter as a pre-treatment for surface discharge or to facilitate reuse in such applications as hydraulic fracturing, dust suppression, road stabilization, and crop irrigation. Yet, the formation of byproducts during treatment of O&G wastewater remains a concern when evaluating reuse applications. In this study, we investigated the previously unnoticed biotic formation of iodinated organic compounds (IOCs) such as triiodomethane during biological treatment of O&G wastewater for beneficial reuse. Iodide and several IOCs were quantified in O&G produced water before and after treatment in biological active filters filled with different media types over 13 weeks of operation. While iodide and total IOCs were measured at concentrations <53 mg/L and 147 μg/L, respectively, before biological treatment, total IOCs were measured at concentrations close to 4 mg/L after biological treatment. Triiodomethane was the IOC that was predominantly present. IOC formation had a negative strong correlation (r = -0.7 to -0.8, p < 0.05, n = 9) with iodide concentration in the treated O&G wastewater, indicating that iodide introduced to the biological active filter system was utilized in various reactions, including biologically mediated halogenation of organic matter. Additionally, iodide-oxidizing bacteria augmented in the treated produced water pointed towards potential negative environmental implications when releasing biologically treated halide-rich wastewater effluents to the aquatic environment.