- Copyright ©2011. The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved.
A by-product of petroleum extraction, produced waters (PWs) containing selenium (Se), arsenic (As), and low-molecular-weight organics (LMWOs) may be generated. Pilot-scale constructed wetland treatment systems (CWTSs) were designed and built to evaluate the removal of these constituents from simulated fresh PW (SFPW). Study objectives were to characterize a fresh PW and determine the constituents of concern (COC); formulate an SFPW; design and build a pilot-scale CWTS for SFPW; and measure performance (i.e., COC removal rates and extents). The treatment goals for this study were to decrease Se concentration in SFPW from approximately 50 μg/L to less than 5 μg/L via microbial reduction; decrease As concentration in SFPW from approximately 20 μg/L to less than 5 μg/L via iron coprecipitation; and decrease LMWO concentration in SFPW from approximately 25 mg/L to less than 1 mg/L via biodegradation. To determine COC removal rates and extents and environmental factors, measurements included analysis of Se, As, LMWOs, dissolved oxygen, conductivity, pH, oxidation-reduction potential, alkalinity, hardness, and temperature. Mean outflow Se concentrations ranged from less than 1 to 47.1 μg/L. Mean outflow As concentrations ranged from 5.7 to 9.5 μg/L, and the mean outflow LMWO concentrations were less than 1 mg/L for all treatments and the untreated control. Organic carbon amendments had a significant effect on Se removal and no effect on As or LMWO removal. This pilot-scale study illustrates that CWTSs can enhance Se removal from SFPW and that removal can be achieved to meet stringent discharge limits. More research is needed to advance the techniques of As removal in CWTSs designed to simultaneously target Se.
Michael M. Spacil is a research and technical support scientist for Diamond V. He received both his B.S. degree in aquaculture, fisheries, and wildlife biology and his M.S. degree in environmental toxicology from Clemson University. His interests are in aquatic toxicology, constructed wetlands, ecological risk assessment, and water quality monitoring.
John Rodgers received his Ph.D. from Virginia Polytechnic Institute and State University. Currently, he is a professor at Clemson University and a director of the Ecotoxicology Program in the Department of Forestry and Natural Resources. 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 geologic and environmental aspects of energy resources. Before joining Clemson University in 1995, he was employed for 17 yr by Cabot Oil & Gas and Chevron. He received his Ph.D. from the University of Illinois.
Wayne Chao is a research scientist in the Department of Forestry and Natural Resources at Clemson University. His research involves the chemistry of natural products and the influence of chemical, physical, and biological processes on natural and anthropogenic materials. He received his Ph.D. from Clemson University.