From Ground Water Currents, July 1995, Issue No. 12

Metal-Enhanced Abiotic Degradation of VOCs

By Chien T. Chen, EPA's National Risk Management Research Laboratory, Edison, N.J.

EnviroMetal Technologies, Inc. (ETI) of Canada has developed the metal-enhanced abiotic degradation technology to treat halogenated volatile organic compounds (VOCs) in water. The ETI technology can be installed and operated above ground in a reactor or in situ as a funnel and gate system. The above ground reactor can be an alternative to the air stripper and activated carbon as methods of remediating halogenated organic compounds. The Superfund Innovative Technology Evaluation (SITE) Program evaluated an above ground reactor for remediation of ground water from the SGL Printed Circuits site in Wayne, New Jersey for three months during 1994 and 1995. The technology was designed to lower chlorinated VOC concentrations below regulatory limits after one pass through the reactive iron medium. A reactive, zero-valent, granular iron medium conducts reductive dehalogenation of the VOCs, yielding simple organic compounds and halogen salts as by-products.

The above ground reactor design may be used to simulate the treatment process at pilot scale, allowing for measurement, control, modification and optimization of design and operating parameters, or may be operated as a stand-alone treatment unit. Contaminated ground water enters the reactor through an air eliminator, 5-micron water filter (to remove suspended solids that may inhibit water flow through the reactive iron medium), and a flow meter. Water flows by gravity through the reactive iron medium and into the collector line at the bottom of the reactor and then exits through the effluent line. The effluent line is plumbed so that about one foot of influent water remains ponded above the surface of the reactive iron medium. A passive gas vent in the top of the reactor prevents accumulation of excess pressure. A manhole with a sight glass allows observation of the reactive iron surface and access to the tank interior. Reactor materials include the reactive iron medium, pea gravel or well sand, a reactor tank for above ground installations and appropriate ancillary pumps and piping, where necessary.

For the SITE evaluation, about 60,833 gallons of ground water were treated during 13 weeks of the demonstration. The reactor maintained a flow rate of about 0.5 gallons per minute throughout most of the demonstration. The primary objectives of the SITE demonstration were to (1) determine whether or not effluent met New Jersey Department of Environmental Protection (NJDEP) and federal maximum contaminant level (MCL) requirements for all chlorinated VOCs detected and (2) determine the removal efficiency of tetrachloroethene (PCE) and other chlorinated VOCs. Initial contaminant concentrations were: 4,100 to 16,000 micrograms per liter (µg/L) PCE, 54 to 590 µg/L trichloroethene (TCE), up to 1,200 µg/L cis- 1,2-dichloroethene (cDCE). Removal efficiency for both TCE and PCE exceeded 99.98%. Vinyl chloride and cDCE were not detected until week 6 of the demonstration; and, they occasionally exceeded NJDEP regulatory limits, which may be attributed to unexpectedly high levels of PCE in the influent.

The SITE Program examined only chlorinated solvents, primarily TCE and PCE. However, the developer claims that its system is applicable to all halogenated VOCs in water.

For more information about the SITE Demonstration, call Chien Chen at EPAÕs National Risk Management Research Laboratory at 908-906-6985.