Oxygen Injection System Rids Groundwater of MTBE

AirSep Corporation Environmental Technologies Inc. has demonstrated what it believes to be the first successful full-scale remediation of a site contaminated by MTBE. The company said it had used a biodegradation-enhancing oxygen-injection system. (The system incorporated <%=company%> Pressure Swing Adsorption [PSA] compressed-air, oxygen-generating equipment.) AirSep Corporation said that the same system has been used at a number of petroleum-release sites to remediate groundwater contaminated with volatile organic compounds (VOCs) other than MTBE. The process appears to be most cost-effective for contaminant levels of less than 10 to 15 parts per million (ppm). However, geological conditions--such as groundwater velocity, soil porosity, and other factors--may extend its use to higher levels. In addition, at sites with high levels of VOCs, air sparging and/or vapor extraction can be used to supplement the oxygen-generating system.

The concentration at the MTBE-contaminated site comprised less than 1 ppm of benzene/toluene/ethylbenzene/xylene (BTEX) and 0.5 to 2.8 ppm methyltertiarybutylether (MTBE). Oxygen was injected at seven suitably spaced points directly down gradient from the former source area. The injection rate was 7 scfh (standard cubic feet per hour) per point. Following approximately one year's operation, the MTBE concentration in water from one monitoring well was less than the 50-ppb state drinking-water standard. (The samples contained no BTEX.) The concentration of MTBE in the water from another monitoring well had decreased by two orders of magnitude. Microbial analysis identified Pseudomonas fluorescens, type G and other hydrocarbon degraders.

The relatively low oxygen rate per injection point and high transfer efficiencies into the groundwater are key aspects of the system's cost-effectiveness compared with alternatives, according to Sean R. Carter, Matrix's president.

Carter said that, although roughly 80% of the contaminant could typically be removed by using air, getting the last 20% was cost-prohibitive due to the diffusion limitations of conventional air sparging. He therefore considered using concentrations of oxygen greater than the 21% available in air. He reasoned that with higher adsorption values, higher rates of biodegradation could be achieved, and contaminated groundwater could be remediated more rapidly. Consequently, Carter approached AirSep, which had developed the pressure swing adsorption equipment. In operation, oxygen purity typically has been 95%, and groundwater oxygen concentrations have been measured at up to 40 mg/l.

The oxygen system also has been used to prevent off-site migration in the aquifer. Moreover, it reportedly has worked effectively with a variety of subsurface conditions and groundwater depths. Matrix said that it hopes to extend the application to vinyl chloride as well as to other aerobically biodegradable, halogenated compounds. AirSep Corporation's patent-pending process for groundwater remediation is being marketed for routine conditions as well as for sites featuring such difficult aspects as shallow groundwater, steep groundwater gradient, and fractured bedrock.

AirSep Corporation, 260 Creekside Drive, Buffalo, NY 14228-2075. Tel: 716.691.0202, 800-320-0303; Fax: 716-691-8304.