title: Treatment of oil and grease in produced water by a pilot-scale constructed wetland system using biogeochemical processes.
abstract: Constructed wetland treatment systems (CWTSs) can effectively remove many constituents that limit beneficial use of oilfield produced water. The objectives of this investigation were: (1) to assess the effect of mass loadings of oil and grease (O & G) on treatment performance in pilot-scale subsurface flow and free water surface CWTS series having sequential reducing and oxidizing cells, and (2) to evaluate effects on treatment performance of adding a pilot-scale oil-water separator. Increase in O & G mass loading from 5 to 20 mg min(-1) caused decreases in both dissolved oxygen concentration and sediment redox potential, which affected treatment performance. Biogeochemical pathways for removal of O & G, iron, and manganese operate under oxidizing conditions, and removal rate coefficients for these constituents decreased (0.905-0.514 d(-1) for O & G, 0.773-0.452 d(-1) for iron, and 0.970-0.518 d(-1) for manganese) because greater mass loading of O & G promoted reducing conditions. With increased mass loading, removal rate coefficients for nickel and zinc increased from 0.074 to 0.565 d(-1) and from 0.196 to 1.08 d(-1), respectively. Although the sequential reducing and oxidizing cells in the CWTS were very effective in treating the targeted constituents, an oil-water separator was added prior to wetland cells to enhance O & G removal at high inflow concentration (100 mg L(-1)). The oil-water separator removed approximately 50% of the O & G, and removal extents and efficiencies approximated those observed at 50 mg L(-1) inflow concentration during treatment without an oil-water separator.
authors: Department of Environmental Engineering and Earth Sciences, Clemson University, 340 Brackett Hall, Clemson, SC 29634, USA.
authors: Michael J
authors: MJ
authors: Pardue
authors: Department of Environmental Engineering and Earth Sciences, Clemson University, 340 Brackett Hall, Clemson, SC 29634, USA. Electronic address: jcastle@clemson.edu.
authors: James W
authors: JW
authors: Castle
authors: School of Agricultural, Forest and Environmental Sciences, Clemson University, 261 Lehotsky Hall, Clemson, SC 29634, USA.
authors: John H
authors: JH
authors: Rodgers
authors: SynTerra, 148 River Street, Suite 220, Greenville, SC 29601, USA.
authors: George M
authors: GM
authors: Huddleston
mesh_terms: D006838:Hydrocarbons / Q000302:isolation & purification*; D008670:Metals / Q000302:isolation & purification; D061329:Oil and Gas Fields; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*; D053833:Wetlands
chemical_list: D006838:Hydrocarbons; D008670:Metals; D014874:Water Pollutants, Chemical
keywords: Constructed wetland; Metals; Oil and grease; Produced water