Emergence and fate of iodinated organic compounds and disinfection by-products during biological treatment of oil and gas produced water

Abstract

Oil and gas (O&G) development in arid regions throughout the United States has increased water demands for development of industrial, agricultural, and residential sectors. Treating and recycling wastewater generated during O&G production for potential surface discharge and beneficial reuse can help alleviate water demands in several water-intensive sectors. Several treatment technologies to improve water quality for potential surface discharge, live-stock watering, dust suppression, and on-site water reuse can be implemented. Biological active filters (BAFs) are one treatment technology that can be effectively used as pre-treatment of O&G wastewater to remove organic matter and reduce fouling in downstream membrane treatment processes for desalination. Because O&G wastewater is halogen rich, formation and toxicity of treatment byproducts with iodide and bromide constituents is of concern when planning potential treatment management strategies for complex waste streams like O&G produced water. In this study, we investigated the occurrence of iodinated organic compounds (IOCs) in BAFs treating O&G produced water. The occurrence of three IOCs was monitored by quantifying chloroiodomethane, diiodomethane, and triiodomethane in nine BAF treatment systems operated with different granular activated carbon media and nutrient type before and after treatment. Chloroiodomethane, diiodomethane, and triiodomethane were measured by headspace solid-phase microextraction gas chromatography mass spectrometry at concentrations up to 16.6 μg/L, 442 μg/L, and 4,316 μg/L, respectively. Triiodomethane, an iodinated disinfection byproduct (I-DBP), was the IOC that was predominantly measured in treated produced water with more than 90% contribution to the total sum of three quantified IOCs in 21 samples analyzed (n=21). A moderately strong correlation (r=0.59) was established between iodide concentration and the total concentration of the three quantified IOCs (n=26). This relationship indicates the likelihood that the inorganic iodide introduced to the system in PW is converted to IOCs (organic iodine) during treatment. Additionally, organisms belonging to the iodide oxidizing bacterium (IOB) genus were also found at relatively high abundance (51.5%) in water treated through biological active filters but not produced water (0.2%). The occurrence of IOB, IOCs, and I-DBPs during biological treatment of O&G produced water has not been previously reported and can be indicative of an underestimated formation pathway of I-DBPs in complex waste streams.