Microwave Soil Vapor Treatment

Contaminated Site Remediation

Enhanced Recovery Inc. and CHA Corporation are currently combining microwave technologies developed by two companies for contaminated site remediation. The microwave-enhanced soil vapor extraction is applied to increase the VOC removal rate from soils, which significantly reduces the time required for a complete site cleanup. The on-site microwave carbon regeneration system is applied to recover or destroy VOCs in the soil vapor, which eliminates the need for a catalytic oxidizer to destroy any secondary air pollutants and greenhouse gases. The microwave water treatment system is applied to treat ground water contained in the contaminated site without creating any air pollution or greenhouse gas. This combined microwave technology provides a significant environmental benefits and cost savings.

A microwave injection is drilled in the center of contaminated site and prepared for lowering a leaky wave guide microwave applicator. The bottom of the leaky wave guide should be closed to the bottom of the contaminated soil layer. The microwave injection or energy well should be cased to prevent ground water intrusion into the microwave applicator. Soil vapor extraction wells are prepared to withdraw soil vapors. Existing SVE wells can also be used. The distance between the microwave injection well and SVE well is dependent on the soil permeability but could be approximately 10-30 feet.

The soil vapor treatment system consists of two GAC beds in series for the adsorption unit, a GAC regeneration reactor, a microwave generator and its accessories, a vapor condensing and recovery unit, a nitrogen generator, and a microwave oxidizer. The soil vapor from the SVE blower flows into the vapor/liquid separator and then into the first stage GAC adsorber. Most of the VOCs are removed in the 1st stage GAC bed. Almost all of the VOC free air flowing out of the 1st stage GAC adsorber enters into the 2nd stage GAC adsorber to remove any remaining VOCs. The 1st stage GAC adsorber operates as a moving bed but the 2nd stage GAC adsorber operates as a fixed bed. The VOC free air from the 2nd stage GAC is vented into the atmosphere.

The ground water is pumped into the oil/water separator to separate the oil from the water. The water is then pumped out from the oil/water separator into the water storage tank that supplies the feed water to the water treatment system. The oil is pumped from the oil/water separator to the oil storage tank. The filter is inserted in the pump discharge line to remove solid particulates in the ground water. Oil-free water is pumped from the ground water storage tank into the 1st stage ACF adsorber (Guard bed) and then into the 2nd stage ACF adsorber. Cleaned water from the 2nd ACF adsorber enters into the clean water storage tank. Cleaned water is either discharged into the municipal wastewater treatment pipeline or re-injected into the underground soil.

When the ACF bed in the 1st adsorber is saturated with VOCs, it will be isolated from the system and regenerated with microwaves. Nitrogen from the nitrogen generator flows into the ACF bed in the 1st adsorber during microwave regeneration to sweep desorbed VOCs. When the ACF bed in the 1st adsorber is regenerated, contaminated water flows directly into the 2nd adsorber that becomes the guard bed. After the ACF bed in the 1st adsorber is regenerated, water flowing out the 2nd adsorber enters into the 1st adsorber. The nitrogen carrying the VOCs is desorbed from the saturated ACF bed and enters into the water knockout pot to separate the water from the gas and then into the microwave oxidizer. VOCs are oxidized in the microwave oxidizer by oxygen-rich air produced from the nitrogen generator. The VOC-free gas from the oxidizer is then discharged into the atmosphere. The following presents the main advantages of applying the microwave technology for contaminated soil remediation:

  • Water is an excellent microwave absorbent but dried soil does not absorb microwave energy. If microwave energy is applied to contaminated soil, the moisture contained in the soil evaporates quickly. This steam generated in-situ strips, VOCs and other chemicals adsorbed in the soil. This accelerates the chemical desorption and as a result the soil vapor extraction is increased.
  • Microwave energy breaks hydrocarbon-water emulsion and also soil-water-hydrocarbon emulsions. Consequently, hydrocarbons are separated from the ground water when the microwaves are applied to the ground water in the contaminated site.
  • Activated carbon is an excellent microwave absorbent and increases the chemical desorption rate significantly. Consequently, microwave energy can be used for the on-site carbon regeneration.
  • Silicon carbide (SiC) is an excellent microwave absorbent and is also a chemically inert material. The microwaves combined with SiC can be used to initiate low temperature oxidation to oxidize VOCs desorbed during the microwave regeneration of saturated carbon.

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