An elemental iron reactor for arsenic removal from groundwater

Summarization: A prototype in-situ flow-through reactor was constructed and operated to treat groundwater affected by arsenic at a former pesticide manufacturing site in New Jersey. Elemental iron is employed as the reactive medium. Perched groundwater beneath the site is affected by arsenic at concentrations of up to 10 mg/l. A series of field treatability tests using flow-through vessels packed with a mixture of iron and quartz sand were performed. Constant flow rate tests were conducted over periods of one to several days with residence times ranging from 1 minute to 5 hours. The mean influent arsenic concentration was 3.0 mg/l. Steady-state effluent concentrations were generally less than 0.01 mg/l for retention times greater than 40 minutes, and increased with decreasing residence time. In the treatability tests, more than 99.8% of the influent arsenic was removed. Arsenic removal in the reactors follows pseudo first-order kinetics, but actually depends on the rate of iron corrosion. A full-scale reactor was designed to treat up to 10 gallons per minute of shallow groundwater collected from railroad sub-drains at the site. An in-situ, passive (gravity flow) system was designed that is capable of isolating the flow stream from surrounding groundwater for performance monitoring. The reactor consists of a concrete-walled vessel in which a 1.8 cubic meter reactive zone is emplaced between upstream and downstream gravel chambers. The reactor also is equipped with an influent-side CO2 injection system for pH control. The treatment unit was operated between July and November 2001. More than 280,000 gallons of perched groundwater were treated and 3 kg of arsenic were removed over a 16 week period. Arsenic removal, initially greater than 99%, began to decline after the first month, eventually leveling off at 94% removal by the third monthΠαρουσιάστηκε στο: 3rd International Conference on Remediation of Chlorinated and Recalcitrant Compound