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Pilot-scale hybrid constructed wetland treatment systems (CWTSs) were designed to determine their feasibility for the treatment of natural gas storage produced waters (NGSPWs). To accomplish this task, we characterized NGSPWs, designed and constructed pilot-scale hybrid CWTSs, and measured their performance. Characterization of NGSPWs involved the establishment of constituents of concern (based on the National Pollutant Discharge Elimination System permit limits and potential risks to receiving system biota) and allowed for the formulation of simulated waters. The design of the CWTSs was driven by chlorides and metals (cadmium, copper, lead, and zinc) as well as organics. Individual modules were designed and constructed to create a flexible and robust treatment system that could be modified to treat the range of constituents found in NGSPWs. The system focuses on biogeochemical pathways leading to the immobilization of constituents of concern. The CWTSs in this pilot-scale study were capable of removing constituents of concern and toxicity from simulated NGSPWs. For example, in simulated fresh NGSPW, copper and lead were removed from 0.70 and 0.74 mg/L, respectively, to below instrument detection (0.010 and 0.015 μg/L, respectively). The NGSPWs with chloride concentrations greater than the tolerance of freshwater plants (≤4000 mg Cl−/L) require either comanagement with lower chloride waters or additional treatment such as reverse osmosis (hence, a hybrid CWTS). This pilot-scale study provides proof-of-concept data to support the feasibility of hybrid CWTSs for the treatment of NGSPWs. The CWTSs that are properly designed, constructed, and operated can be readily implemented with the potential to reduce the costs of handling water produced from gas storage fields.
Brenda Johnson received her B.S. degree in environmental science from the University of Wisconsin-River Falls in 2004. In 2006, she received her M.S. degree in environmental toxicology from Clemson University, and she is continuing as a Ph.D. student working with Dr. John Rodgers. Her current research involves risk characterization and mitigation.
Laura Kanagy received her B.S. degree in geology in 2003 from Olivet Nazarene University. In 2006, she earned her M.S. degree in hydrogeology from Clemson University. Her master's research focused on the use of constructed wetlands to treat natural gas storage produced waters. Currently she is a project engineer for Goldie & Associates, a civil and environmental consulting firm in Seneca, South Carolina.
John Rodgers received his Ph.D. from Virginia Polytechnic Institute and State University in 1977. Currently, he is a professor at Clemson University, director of the Ecotoxicology Program in the Department of Forestry and Natural Resources, and codirector of the Clemson Environmental Institute. His current research involves a quest for accurate risk characterizations and development of sustainable risk mitigation tactics.
Jim Castle is a professor in the Department of Environmental Engineering and Earth Sciences at Clemson University, where he conducts research on geological and environmental aspects of energy resources. Prior to joining Clemson in 1995, he was employed for 17 years by Cabot Oil & Gas and Chevron. He received his Ph.D. in geology from the University of Illinois.