Biogeochemical-Based Design for Treating Ammonia Using Constructed Wetland Systems

Abstract

Constructed wetlands have been used to treat contaminants, including ammonia and nitrate, with varying degrees of success; however, no study has been performed to evaluate ammonia treatment performance of a constructed wetland specifically designed to promote biogeochemical conditions controlling nitrification and denitrification. Therefore, this research aims to improve the design of treating ammonia using constructed wetlands by targeting biogeochemical conditions needed for nitrification and denitrification. A pilot-scale constructed wetland was designed and constructed to meet targeted ranges of dissolved oxygen concentration, hydrosoil redox potential, pH, alkalinity, and organic carbon availability to enhance nitrification and denitrification. Design features included aeration, sucrose, and oyster shell addition. The constructed wetland decreased ammonia-N from *20 mg/L in inflow to nondetectable levels ( < 0.1 mg/L) in outflow during three of the four treatment months. Measured biogeochemical conditions indicate that nitrification continued to occur while hydrosoil redox potential, dissolved oxygen concentration, and pH were lower than the targeted ranges. Conversely, denitrification continued to occur while pH was lower than the targeted range, and dissolved oxygen concentration was higher than the targeted range. The success of the constructed wetland in removing ammonia and nitrate under conditions outside of target ranges was attributed to the existence of heterogeneous macro-and microenvironments within individual wetland cells that allow both reactions to occur simultaneously under a wider range of conditions than previously expected. Results from this study demonstrated the advantage of designing constructed wetlands to promote biogeochemical conditions for improved ammonia treatment and also provide the basis for treatment of ammonia-contaminated produced waters.

Biological treatment of oil and gas produced water: a review and meta-analysis

“…In the studies reviewed, wetland treatment was often used for nitrogen and metals removal in addition to reduction of oxygen demand. Beebe et al (2015) observed both nitrification and denitrification when supplemental aeration and carbon were added in pilot-scale surface and subsurface wetlands treating a simulated produced water (TDS < 1000 mg L −1 ). Pardue et al (2014) observed removal of O&G, iron, and manganese under oxidizing conditions as well as removal of nickel and zinc under reducing conditions; iron removal was variable.…”

“…Most of the wetland studies reviewed used large containers to construct and simulate wetlands. Beebe et al (2015) used a series of plastic containers (265 L) planted with cattails. Pardue et al (2014) also used a series of plastic containers (378 L each) planted with reeds to simulate subsurface wetlands; free surface wetlands were simulated by planting the containers with bulrush and cattails.…”