Explosives Removal from Groundwater of the Iowa Army Ammunition Plant in Continuous-Flow Laboratory Systems Planted with Aquatic and Wetland Plants

摘要

A 49-day, continuous-flow, laboratory study was performed to evaluate the ability of two submersed and one emergent plant species to phytoremediate explosives-contaminated groundwater from the Iowa Army Ammunition Plant (IAAP), Middletown, IA. Species evaluated were the submersed Ceralophyllum demersum L. (coontail), Potamogeton nodosus Poir. (American pondweed), and the emergent Sagittaria latifolia Willd. (common arrowhead). Plants were rooted in local, IAAP, sediment under continuous-flow conditions at 25 deg C. Unplanted sediment served as control. 2,4,6-trinitrotoluene (TNT), and hexahydro-1,3,5-trinitro-1, 3,5-triazine (RDX) levels in groundwater were 0.8 and 10.7 mg L(exp -1), respectively. The hydraulic retention time (HRT) was 30 days. TNT decrease rates in groundwater did not differ significantly between implanted and planted sediment treatments. Aqueous TNT concentrations decreased exponentially (first- order kinetics). TNT removal constants decreased in the order of arrowhead>pondweed> sediment>coontail, ranging from 0.533 to 0.375 d(exp -1). Using these removal constants, periods to reach a cleanup level of 0.002 mg L(exp -1) of 45 to 1,015 days were calculated for treatments under fully mixed conditions. Cleanup periods were greatly reduced under plug-flow conditions, ranging from 1 to 16 days. Final aqueous TNT and TNT degradation product levels were extremely low or below detection, while they were below detection in plants and sediments. RDX decrease rates in groundwater were significantly higher by planted than by unplanted sediment treatments. RDX decrease was significantly enhanced by amendment with microbes. Aqueous RDX concentrations decreased linearly (zero-order kinetics). RDX removal rates ranged from 0.28 to 0.13 mg L(exp -1) d(exp -1). RDX cleanup levels were not reached under fully mixed conditions. Cleanup periods under plug-flow conditions ranged from 79 to 200 days for submersed species and implanted sediment treatments.