American Society of Civil Engineers


Cleaning Contaminated Soil Using Electrical Heating and Air Stripping


by H. Michael Buettner, (Group Leader, Electronics Engrg. Dept., Lawrence Livermore Nat. Lab., L-156, 7000 East Ave., Livermore, CA 94550) and William D. Daily, (Proj. Engr., Electronics Engrg. Dept., Lawrence Livermore Nat. Lab., L-156, 7000 East Ave., Livermore, CA)

Journal of Environmental Engineering, Vol. 121, No. 8, August 1995, pp. 580-589, (doi:  http://dx.doi.org/10.1061/(ASCE)0733-9372(1995)121:8(580))

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Document type: Journal Paper
Abstract: In the summer of 1992, a proof-of-concept demonstration of direct electrical heating and air stripping was conducted for enhancing the removal of a volatile organic contaminant, trichloroethylene (TCE), from soil. Six electrodes were buried in shallow boreholes so that a target region 6.1 m in diameter and 3.05 m in height was heated by ohmic dissipation of power-line–frequency electrical currents supplied by a diesel generator. Air stripping of TCE contamination from the same region was accomplished from a single well at the center of the heated volume. The electrical energy used during the demonstration was 3.46 × 10¹0J (9,600 kW·h), and the temperature of the extracted air rose from 16°C to 38°C. An energy balance shows that the input energy is consistent with the temperature rise in the target volume and the amount of water vaporized at the electrodes. Prior to heating the TCE, concentration in the vapor decreased from about 80 parts per million by volume (ppmv) to around 60 ppmv. As soon as electrical heating started, TCE concentrations began to increase. Some concentration data were lost shortly after electrical heating, after which the concentration dropped rapidly to around 5 ppmv over a period of about 25 days. A simple two-dimensional model for calculation of heating rates is also presented and verified experimentally. Finally some of the operational and safety issues associated with electrical heating are discussed.


ASCE Subject Headings:
Hazardous wastes
Heat treatment
Remediation
Soil pollution
Stripping
TCE
Thermal factors
Waste sites