Liquid-soil heating

The system must be operated properly so the vadose zone does not become completely saturated with water, thus reducing the effective permeability to the point that gases and vapors cannot be recovered. When the soil-heating process has progressed to the extent that gaseous steam reaches the recovery wells, all the water within the soil zone has been vaporized. At this juncture, S VE becomes the primary removal mechanism. A blower or vacuum pump can be used to induce airflow in the subsurface, which will facilitate the removal of any remaining residual liquids. 

The released ammonia forms a pool of refrigerated liquid which evaporates by heat transfer from the soil. A constant mass value was assumed for the evaporation rate and a heavier-than-air gas dispersion model was used. 

Heat and reflux a 5-g portion of soil sample with 50 mL of methanol-phosphate buffer (pH 7)-water (15 7 28, v/v/v) solvent mixture in a round-bottom flask for 1 h. After cooling, transfer a 10-mL portion of the supernatant to a test-tube and mix with 11 mL of 0.02M H3PO4 solution. Load this solution on to a silica-based SPE cartridge (Analytichem International Clin-Elut 1020) at a flow rate of 1-2 drops per second. Discard this fraction. Elute the analytes with 30 mL of dichloromethane. Concentrate the eluate to dryness with air in a water-bath at a temperature of 40 °C (do not use vacuum). Dissolve the residues in 5mL of HPLC injection solution [900 mL of water - - 50 mL of phosphate buffer (pH 7) 4-50 mL of ACN 4-4 g of TBABr]. Pinal analysis is performed using liquid chromatography/ultraviolet detection (LC/UV) with a three-column switching system. 

Sonication helps improve solid-liquid extractions. Usually a finely ground sample is covered with solvent and placed in an ultrasonic bath. The ultrasonic action facilitates dissolution, and the heating aids the extraction. There are many EPA methods for solids such as soils and sludges that use sonication for extraction. The type of solvent used is determined by the nature of the analytes. This technique is still in widespread use because of its simplicity and good extraction efficiency. For example, in research to determine the amount of pesticide in air after application to rice paddy systems, air samples collected on PUF were extracted by sonication, using acetone as the solvent. The extraction recoveries were between 92% and 103% [21]. 

Injection of steam or heated air into the subsurface provides large amounts of thermal energy, which speeds the mobilization of adsorbed organic contaminants and results in their removal as either a vapor or liquid phase. Elevated temperature increases the vapor pressure of the chemicals involved and promotes transfer of constituents across the air-water interface, which results in the increased removal of contaminants in high-humidity or nearly saturated soil systems. Additionally, the presence of high-temperature water sometimes results in oxidation or hydration of organic contaminants. 

Supercritical fluid extraction (EPA 3540, for total recoverable petroleum hydrocarbons EPA 3561 for polynuclear aromatic hydrocarbons) is applicable to the extraction of semivolatile constituents. Supercritical fluid extraction involves heating and pressuring a mobile phase to supercritical conditions (where the solvent has the properties of a gas and a liquid). The supercritical fluid is passed through the soil sample, and the analytes are concentrated on a sorbent or trapped cryogenically. The analytes are eluted with a solvent and analyzed using conventional techniques. Carbon dioxide is the most popular mobile phase. 

Hexachlorobutadiene does not occur naturally in the environment. It is formed during the processing of other chemicals such as tetrachloroethylene, trichloroethylene, and carbon tetrachloride. Hexachlorobutadiene is an intermediate in the manufacture of rubber compounds and lubricants. It is used as a fluid for gyroscopes, a heat transfer liquid, or a hydraulic fluid. Outside of the United States it is used to kill soil pests. 

In order to obtain rapid metabolism and rapid heat generation from aromatic compounds related to lignin, several soil isolates were used. P. putida ATCC 11172 did not grow easily on compounds such as syringic acid and certain other compounds more lignin-like. However, soils collected locally yielded bacteria, first from enrichment cultures and then grown on plates or defined liquid culture, were able to combust the compounds listed in Table... 

ISOTEC was chosen to treat soils contaminated with dense non-aqueous-phase liquids (DNAPLs) at a Superfund site in Florida. With a projected cost of 340,000, ISOTEC was cheaper than the alternative technologies considered. The estimated cost for implementing six-phase heating at the site was 535,000, and the estimated cost for excavation and ex situ treatment was 835,000 (D21478I, pp. 10, 11). 

Mercury Recovery Services, Inc. (MRS), has developed the Mercury Removal/Recovery Process (MRRP) to treat media contaminated with mercury. The ex situ process uses medium-temperature thermal desorption to remove the mercury from contaminated wastes. Process wastes are heated in a two-step process to recover metallic mercury in a 99% pure form. MRS claims MRRP can be applied to soils, activated carbon, mixed waste, catalysts, electrical equipment, batteries, lamps, fluorescent bulbs, mercurous and mercuric compounds, mercury-contaminated waste liquids, and debris. 

The electric infrared incineration technology is a mobile thermal processing system that is suitable for soils or sediments contaminated with organic compounds, polychlorinated biphenyls (PCBs), and metals. Liquid organic wastes can be treated after mixing with sand or soil. Electrically powered silicon carbide rods heat organic wastes to combustion temperature while any remaining combustibles are incinerated in an afterburner. 

Terra Vac s dense non-aqueous-phase liquid (DNAPL) vaporization involves heating the subsurface, including both groundwater and soil, to vaporize the DNAPL. According to the vendor, this technology is appropriate for medium and large sites with separate pools of dense chlorinated solvents, such as chloroform, dichloroethane, dichloroethene, Freons, methylene chloride, and vinyl chloride. This technology is commercially available. 

The base-catalyzed decomposition (BCD) technology is a chemical dechlorination technology for the ex situ treatment of soils, sludges, and liquids contaminated with PCBs and other chlorinated compounds. In the two-step process, chlorine atoms on chlorinated molecules are removed and replaced by hydrogen atoms, using heat and commonly available chemicals in the presence of a catalyst. 

In extraction, analyte is dissolved in a solvent that does not necessarily dissolve the entire sample and does not decompose the analyte. In a typical microwave-assisted extraction of pesticides from soil, a mixture of soil plus acetone and hexane is placed in a Teflon-lined bomb (Figures 28-8 and 28-13) and heated by microwaves to 150°C. This temperature is 50° to 100° higher than the boiling points of solvents at atmospheric pressure. Pesticides dissolve, but the soil remains behind. The liquid is then analyzed by chromatography. 

The liquid waste is stored for at least 6 y prior to solidification to reduce the decay heat (Fig. 16.8) by a factor of 10 or more. The first U.S. military fuel reprocessing wastes were stored as neutralized waste in mild steel tanks at the Hanford reservation in eastern Washington. These steel-lined, reinforced-concrete tanks were 500,000-1,000,000 gal in capacity with provisions for removal of waste heat and radiolysis products. Corrosion of several tanks occurred with the release of waste. Fortunately, the soil around these tanks retarded nuclide transport. A better (and more expensive) design for storage tanks was implemented at the Savannah River site in South Carolina consisting of a second steel tank inside of a Hanford-style tank. The storage of acid waste in these tanks has not encountered the corrosion problems seen with the Hanford tanks. 

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