Abstract

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.

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