A PILOT-SCALE STUDY OF CONSTRUCTED WETLAND TREATMENT SYSTEMS TO RENOVATE NATURAL GAS STORAGE PRODUCED WATERS

Waters produced as a byproduct from oil and gas operations, including natural gas storage, vary widely in chemical constituents and concentrations. Variations in composition along with large volumes of produced waters signal a need for an ecologically and economically viable approach to treating these waters for either discharge or reuse. Modular, pilot-scale hybrid constructed wetland treatment systems were specifically designed and built to treat natural gas storage produced waters having salt concentrations ranging from nearly fresh to hypersaline. Both organic and inorganic constituents were targeted for treatment in these systems. Removal of inorganics occurring within wetland cells relies on processes involving binding and sorption to sediments. Characterization of the sediments includes analysis of organic matter content, sediment pH, particle size distribution, moisture content, and acid volatile sulfides. In addition, sequential extractions were performed to identify sediment fractions contributing to the removal of Cd, Cu, Pb, and Zn from gas storage produced water. The performance of these pilot-scale constructed wetland treatment systems was measured against National Pollutant Discharge Elimination System (NPDES) permit limits. Based on this performance measure, the pilot-scale systems provide effective treatment of the waters tested.

Pilot-scale systems provide data pertaining to the feasibility of using constructed wetland treatment systems for renovating wastewaters of various origins and compositions. Results of this pilot-scale study are applicable to designing full-scale systems for treatment of gas storage produced water. Constructed wetland treatment systems are reliable, flexible in design, and can be built, operated, and maintained at lower costs compared to current methods of chemical treatment.