also called pump and treat techology. pump and treat involves pumping out contaminated groundwater with the use of a submersible or vacuum pump, and allowing the extracted groundwater to be treated by different water clean-up technologies such as air stripping, teratments based on photodegradation, biodegradation, chemical oxidation or reduction, precipitataion, sorption, etc. in order to eliminate contaminant from water. Technologies used for cleaning ground-water and other sub-surface waters are similar to waste-water and drinking-water treatment technologies. The treated water can be discharged into surface waters or canalisation accordig to its contaminant content. recycling into soil ot groundwater is also a technological option.
It is often difficult to REACH sufficiently low concentrations to satisfy remediation standards, due to the equilibrium of partition between soil solid and liquid phases. For those contaminants which has low solubility in water and prefer sorption on solid phase, pump end treat technology has extremely low efficiency.
treatment of contaminated or otherwise damaged environmnetal compartments or phases such as soil, groundwater, soil gas, surface water and sediment after excavation, dredging or extraction. The remedial treatment may be executed on site or off-site by applying physical, chemical, thermal, biological or ecological technologies.
see also ex situ soil treatment
thermal desorption is the process whereby wastes are heated so that organic contaminants and water volatilize. Typically, a carrier gas or vacuum system transports the volatilized water and organics to a gas treatment system, such as a thermal oxidation or recovery system. Based on the operating temperature of the desorber, thermal desorption processes can be categorized into two groups: high temperature thermal desorption (320 to 560°C or 600 to 1000°F) and low temperature thermal desorption (90 to 320°C or 200 to 600°F).
ex situ thermal treatment of soil contaminants generally involves the destruction or removal of contaminants through exposure to high temperature in treatment cells, combustion chambers, or other means used to contain the contaminated media during the remediation process. The main advantage of ex situ treatments is that they generally require shorter time periods, and there is more certainty about the uniformity of treatment because of the ability to screen, homogenize, and continuously mix the contaminated media; however, ex situ processes require excavation of soils, which increases costs and engineering for equipment, permitting, and materials handling worker safety issues.
Thermal processes use heat to separate, destroy, or immobilize contaminants. Thermal desorption and hot gas decontamination are separation technologies. Pyrolysis and conventional incineration destroy the contaminants. Vitrification destroys or separates organics and immobilizes some inorganics.
Incineration is a heat-based technology that has been used for many years to burn and destroy contaminated materials. Because it is considered to be a conventional rather than an innovative technology, its treatment here is limited to information listed under "Additional Resources."
EX SITU THERMAL DESORPTION involves the application of heat to excavated wastes to volatilize organic contaminants and water. Typically, a carrier gas or vacuum system transports the volatilized water and organics to a treatment system, such as a thermal oxidation or recovery unit. Based on the operating temperature of the desorber, thermal desorption processes can be categorized as either high-temperature thermal desorption (320 to 560ºC or 600 to 1,000ºF) or low-temperature thermal desorption (90 to 320ºC or 200 to 600ºF).
HOT GAS DECONTAMINATION involves raising the temperature of contaminated solid material or equipment to 260ºC (500ºF) for a specified period of time. The gas effluent from the material is treated in an afterburner system to destroy all volatilized contaminants. This method will permit reuse or disposal of scrap as nonhazardous material.
PLASMA HIGH-TEMPERATURE RECOVERY uses a thermal treatment process applied to solids and soils that purges contaminants as metal fumes and organic vapors. The vapors can be burned as fuel, and the metals can be recovered and recycled.
PYROLYSIS is defined as chemical decomposition induced in organic materials by heat in the absence of oxygen. Pyrolysis typically occurs under pressure and at operating temperatures above 430ºC (800ºF). The pyrolysis gases require further treatment. The target contaminant groups for pyrolysis are SVOCs and pesticides. The process is applicable for the separation of organics from refinery wastes, coal tar wastes, wood-treating wastes, creosote-contaminated soils, hydrocarbon-contaminated soils, mixed (radioactive and hazardous) wastes, synthetic rubber processing wastes, and paint waste.
THERMAL OFF-GAS TREATMENT is one of several approaches that can be used to cleanse the off-gases generated from primary treatment technologies, such as air stripping and soil vapor extraction. In addition to the established thermal treatments, organic contaminants in gaseous form can be destroyed using innovative or emerging technologies, such as alkali bed reactors.
VITRIFICATION technology uses an electric current to melt contaminated soil at elevated temperatures (1,600 to 2,000ºC or 2,900 to 3,650ºF). Upon cooling, the vitrification product is a chemically stable, leach-resistant, glass and crystalline material similar to obsidian or basalt rock. The high temperature component of the process destroys or removes organic materials. Radionuclides and most heavy metals are retained within the vitrified product. Vitrification can be conducted in situ or ex situ.
Source: US-EPA, Clu-In: