Definitions of Remediation Technologies
Extracted from EPA REACH IT
The following treatment technologies are used to treat soils, sediments, sludge, solid-matrix waste and groundwater:
This section provides brief definitions of the 19 types of source control (primarily soil) treatment technologies, and 5 types of innovative in situ groundwater technologies.
EX SITU BIOREMEDIATION: This technology uses microorganisms to degrade organic contaminants in excavated soil, sludge, and solids. The microorganisms break down contaminants by using them as a food source. The end products typically are carbon dioxide and water. Ex situ bioremediation includes slurry phase bioremediation, in which the soils are mixed in water to form a slurry, and solid-phase bioremediation, in which the soils are placed in a cell or building and tilled with added water and nutrients. Land farming and composting are types of solid-phase bioremediation.
IN SITU BIOREMEDIATION: In applications of this technology an oxygen source and sometimes nutrients are pumped under pressure into the soil through wells, or they are spread on the surface for infiltration into the contaminated material. Bioventing is a common form of in situ bioremediation. Bioventing uses extraction wells to circulate air with or without pumping air into the ground.
BIOVENTING: This technology is an in situ remediation technology that combines soil vapor extraction methods with bioremediation. It uses vapor extraction wells that induce air flow in the subsurface through air injection or through the use of a vacuum. Bioventing can be effective in remediating releases of petroleum products, such as gasoline, jet fuels, kerosene, and diesel fuel. See also Bioremediation and Soil Vapor Extraction.
CHEMICAL TREATMENT: This technology typically involves reduction/oxidation (Redox) reactions that chemically convert hazardous contaminants to nonhazardous or less toxic compounds that are more stable, less mobile, or inert. Redox reactions involve the transfer of electrons from one compound to another. Specifically, one reactant is oxidated (loses electrons) and one is reduced (gains electrons). The oxidizing agents most commonly used for treatment of hazardous contaminants are ozone, hydrogen peroxide, hypochlorites, chlorine, and chlorine dioxide.
FLUSHING (IN SITU): In this technology large volumes of water, at times supplemented with treatment compounds, are introduced into soil or waste to flush hazardous contaminants from a site. Injected water must be isolated effectively within the aquifer and recovered.
HOT AIR INJECTION: With this technology heated air is injected and circulated through the subsurface. The heated air volatilizes volatile organic compounds so they can be extracted and captured for further treatment or recycling.
INCINERATION: Both on-site and off-site incineration use high temperatures, 970 to 1,200 EC (1,400 to 2,200 EF), to volatize and combust (in the presence of oxygen) halogenated and other refractory organics in hazardous wastes. The destruction and removal efficiency (DRE) for properly operated incinerators exceeds the 99.99 percent requirement for hazardous waste and can be operated to meet the 99.9999 percent requirement for Polychlorinated biphenyls (PCBs) and dioxins.
PHYTOREMEDIATION: This technology typically involves the use of plants to remove, contain, accumulate, or degrade environmental contaminants in soil, groundwater, surface water, sediment, and air. That definition applies to all biological, chemical, and physical processes that are influenced by plants (including the rhizosphere) and that aid in cleanup of the contaminated substances. Plants can be used in site remediation, both through the mineralization of toxic organic compounds and through the accumulation and concentration of heavy metals and other inorganic compounds from soil into aboveground shoots.
PLASMA HIGH-TEMPERATURE METALS RECOVERY: This technology involves a thermal treatment process that purges contaminants from solids and soils such as metal fumes and organic vapors. The vapors can be burned as fuel, and the metal fumes can be recovered and recycled. This innovative treatment technology is used to treat contaminated soil and groundwater.
SLURRY-PHASE BIOREMEDIATION: This technology can be used alone or in conjunction with other biological, chemical, and physical treatments, is a process through which organic contaminants are converted to innocuous compounds. Slurry-phase bioremediation can be effective in treating various SVOCs and nonvolatile organic compounds, as well as fuels, creosote, pentachlorophenols (PCP), and PCBs.
SOIL VAPOR EXTRACTION (SVE): This technology removes volatile organic compounds from the soil in situ through the use of vapor extraction wells, sometimes combined with air injection wells, to strip and flush contaminants into the air stream for further treatment.
SOIL WASHING: This technology is used for two purposes. First, the mechanical action and water (sometimes with additives) physically remove contaminants from the soil particles. Second, agitation of the soil particles allows the more highly contaminated fine particles to separate from the larger ones, thus reducing the volume of material requiring further treatment.
SOLIDIFICATION/STABILIZATION (S/S): This technology reduces the mobility of hazardous substances and contaminants in the environment through both physical and chemical means. Unlike other remedial technologies, S/S seeks to trap or immobilize contaminants within the Ahost@ medium (that is, the soil, sand, and/or building materials that contain them), instead of removing them through chemical or physical treatment. Leachability testing is typically used to measure the immobilization of contaminants. S/S can be in situ or ex situ. In situ S/S techniques use auger/caisson systems and injector head systems to apply S/S agents to in situ soils. Ex situ S/S, however, typically requires disposal of the resulting materials.
SOLVENT EXTRACTION: This technology operates on the principle that, in the correct solvent, organic contaminants can be solubilized (dissolved?) preferentially and removed from the waste. The solvent used will vary depending on waste type.
SURFACTANT FLUSHING: With this technology surfactants are used to increase the solubility and mobility of nonaqueous phase liquids (NAPL), so that the NAPL can be biodegraded more easily in the aquifer or recovered for treatment aboveground by a pump-and-treat system.
THERMAL DESORPTION: With this technology the waste is heated in a controlled environment to volatize organic compounds. The operating temperature for thermal desorption is usually less than 1,0000F (5500C). The volatilized contaminants usually require further control or treatment.
VITRIFICATION: This technology melts contaminated soil at temperatures of approximately 3,0000F (1,6000C). Metals are encapsulated in the glass-like structure of the solidified silicate compounds. Organic constituents may be treated by combustion.
AIR SPARGING: This technology involves injecting air or oxygen into the aquifer to strip or flush volatile contaminants as the air bubbles up through the groundwater and is captured by a vapor extraction system. The entire system acts as an in situ air stripper. Stripped or volatilized contaminants usually will be removed through soil vapor extraction wells and usually require further treatment.
IN SITU GROUNDWATER BIOREMEDIATION: Air sparging often is combined with this technology, in which nutrients or an oxygen source (such as air) are pumped into the aquifer through wells to enhance biodegradation of contaminants in the groundwater. Specific types of in situ bioremediation include biosparging and bioslurping.
DUAL-PHASE EXTRACTION: This technology removes contaminants simultaneously from both saturated and the unsaturated zone soils in situ. This new technology applies soil vapor extraction techniques to contaminants trapped in saturated-zone soils, which are more difficult to extract than those in the unsaturated zone. In some instances, this result may be achieved by sparging the groundwater section of a well that penetrates the groundwater table. Other methods also may be employed.
PASSIVE TREATMENT WALLS: This technology involves the use of in situ walls that act like chemical treatment zones. Contaminated groundwater comes into contact with the wall, which is permeable, and a chemical reaction takes place. Limestone treatment zones increase the pH, which effectively immobilizes dissolved metals in the saturated zone. Another type of passive treatment wall contains iron filings that dechlorinate compounds.