Engineered Wetland Design and Applications for On-Site Bioremediation of PHC Groundwater and Wastewater

Summary Engineered wetlands are an emerging technology for the on-site bioremediation of petroleum hydrocarbon-contaminated (PHC) water. The engineering optimization of natural treatment processes shows that engineered wetlands are a viable alternative to mechanical remediation systems. An engineered wetland incorporates a horizontal subsurface flow gravel bed reactor, lined with an impermeable liner and equipped with a Forced Bed Aeration™ system to enhance oxygen delivery. Design parameters include biodegradation rate coefficients for petroleum hydrocarbons such as benzene, toluene, ethylbenzene, and xylenes (BTEX), flowrate, hydraulic residence time, and influent and required effluent concentrations. Three field-scale applications of this technology in North America are presented. The first application is at a pipeline terminal with contact wastewater containing BTEX and ammonia. A horizontal subsurface flow engineered wetland with Forced Bed Aeration™ and a design flowrate of 1.5 m 3 /d treats BTEX and ammonia to non-detect concentrations at 40% and 80% of the gravel bed length, respectively. The second application is at a former refinery, where a cascade aerator and surface flow wetland (for iron removal) and horizontal subsurface flow engineered wetland with Forced Bed Aeration™ were constructed in 2003 to treat 6,000 m 3