Abstract
Many countries have implemented stringent regulatory standards for discharging produced water (PW) from the oil and gas extraction process. Among the different chemical pollutants occurring in PW, surfactants are widely applied in the oil and gas industry to provide a barrier from metal corrosion. However, the release of these substances from the shale formation can pose serious hazardous impacts on the aquatic environment. In this study, a low-cost and eco-friendly microalgae laboratory-scale technology has been tested for biotransformation of benzalkonium chloride (BACC12 and BACC14) in seawater and PW during 14-days of treatment (spiked at 5 mg/L). From the eight microalgae strains selected, Tetraselmis suecica showed the highest removal rates of about 100% and 54% in seawater and PW, respectively. Suspect screening analysis using liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) allowed the identification of 12 isomeric intermediates generated coming from biotransformation mechanisms. Among them, the intermediate [OH-BACC12] was found as the most intense compound generated from BACC12, while the intermediate [2OH-BACC14] was found as the most intense compound generated from BACC14. The suggested chemical structures demonstrated a high reduction on their amphiphilic properties, and thus, their tendency to be adsorbed into sediments after water discharge. In this study, Tetraselmis suecica was classified as the most successful specie to reduce the surfactant activity of benzalkonium chloride in treated effluents.
Highlights
Over the last decade, the horizontal drilling and hydraulic fracturing techniques have been motivated by a rapid increase of conventional and unconventional energy production such as oil and gas extraction (Patterson et al, 2017)
Microalgae strains were incubated in seawater for 7 days in sterile seawater with the addition of the growth media presented in Supplementary Material, S1
Non-spiked light control experiments showed an increase on cell concentration for most of the microalgae selected up to 155% in R. salina, 103% in E. huxleyi, 169% in T. suecica, 76% in D. salina, and 16% in P. tricornotum after 14 days of treatment (Fig. 1a)
Summary
The horizontal drilling and hydraulic fracturing techniques have been motivated by a rapid increase of conventional and unconventional energy production such as oil and gas extraction (Patterson et al, 2017). Operational discharges from the offshore industry have created public concern since they may represent a potential and continuous input of hazardous pollutants entering in the aquatic environment (Bakke et al, 2013). Numerous pollutants such as organic compounds, heavy metals, salts and chemical additives such as biocides and corrosion inhibitors are used during drilling, fracturing and operating process of the well (Al-Ghouti et al, 2019; Jiménez et al, 2018). Advanced water treatments should be developed for the removal of these pollutants prior to wastewater discharge and/or water reuse (Fakhru'l-Razi et al, 2009; Nasiri et al, 2017)
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