Thermal decontamination, soil

Risoul, V., Renauld, V., Trouve, G., and Gilot, P. (2002). A laboratory pilot study of thermal decontamination of soils polluted by PCBs. Comparison with thermogravimetric analysis. Waste Manage. 22(1), 61-72. 

Radio frequency (RF) heating is used for in situ thermal decontamination of soil. This process was originally developed in the 1970s for use in recovering hydrocarbons from materials such as oil shales and tar sands. The treatment is effective for volatile and semivolatile organics only. 

Technolt Demonstration of a Thermal Desorption-UV Photolysis Process for Decontaminating Soils Containing Herbicide Orange... 

The effectiveness of thermal desorption to decontaminate soil containing HO and of UV photolysis to destroy HO toxic constituents has been demonstrated in bench- and pilot-scale tests. Some additional technical information is needed for a complete evaluation of the process and to provide the basis for design of a full-scale system for on-site remedial action. This project illustrates the requirements for developing and implementing new process technology for solving contaminated-soil environmental problems. Only through such demonstration efforts can more cost-effective and environmentally sound remedial action alternatives be made available. 

In-situ RF heating offers two alternatives for decontaminating soil. These alternatives are (1) thermal decontamination of soil... 

Thermal processes like pyrolysis use heat to increase the volatility (separation) to burn, decompose, or detonate (destruction) or to melt (immobilization) contaminants in soil. Separation technologies include thermal desorption and hot gas decontamination. Destruction technologies include incineration, open bum/open detonation, and pyrolysis. Vitrification is used to immobilize inorganic compounds and to destroy some organic materials. In contrast, pyrolysis transforms... 

Decontamination techniqnes and processes, involving chemical, mechanical, and thermal methods, have been developed for the removal of hazardons materials from systems, strnctnres, and components (SSCs), to soil and water. The primary objectives of decontamination are to rednce exposnre, rednce the potential release of hazardons materials to clean areas, and enable decontaminated eqnipment and materials to be salvaged and rensed. For J AC ADS closnre, a key objective will be to meet the end-state criteria for the land and the SSCs that are left in place. 

Decontamination of soils using supercritical fluids is an attractive process compared to extraction with liquid solvents because no toxic residue is left in the remediated soil and, in contrast to thermal desorption, the soils are not burned. In particular, typical industrial wastes such as PAHs, PCBs, and fuels can be removed easily [7 to 21]. The main applications are in preparation for analytical purposes, where supercritical fluid extraction acts as a concentration step which is much faster and cheaper than solvent-extraction. The main parameters for successful extraction are the water content of the soil, the type of soil, and the contaminating substances, the available particle-size distribution, and the content of plant material, which can act as adsorbent material and therefore prolong the extraction time. For industrial regeneration, further the amount of soil to be treated has to taken into account, because there exists, so far, no possibility of continuous input and output of solid material for high pressure extraction plants, so that the process has to be run discontinuously. 

Radio frequency thermal soil decontamination (lubricants and solvents)... 

Chemical decontamination is an alternative to thermal processing or landfilling of soils contaminated with polychlorinated dibenzo-p- dioxins (PCDD) or other aromatic halides such as chlorobenzenes or polychorinated biphenyls (PCB). Chemical decontamination, like incineration, involves changes to the chemical structure of the dioxin molecule. While chlorinated dioxins are thermally stable, they readily dechlorinate to water soluble compounds under relatively mild conditions of temperature and pressure. 

The soil used for testing was contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at a concentration of about 200 ppb. Two tests were run at a 48 Ib/hr feed rate and solid phase residence times of 30 minutes and 15 minutes. The primary chamber temperature was 1490 F to 1560°F. The secondary chamber temperature was maintained above 2200°F. The thermal treatment conditions for both tests are listed in Table II. The testing was performed over two days followed by decontamination of the incinerator and trailer. The incinerator was decontaminated by an extended, high temperature bake out. 

The Portable Unit has successfully demonstrated its capability for thermal treatment of hazardous wastes at the source of the material. This type of on-site treatment would eliminate the need of transportation of hazardous materials to a distant site of stationary treatment equipment. The Portable Unit also has demonstrated that it can be moved to a site and be ready to treat material very quickly, a capability which will be very important in operation of full scale equipment. The on-site treatment of the Times Beach dioxin contaminated soil resulted in no dioxin detected in any of the incinerator effluent streams. The product of the testing activity was soil with no detectable level of dioxin. Dioxin contaminated soil thermally treated in this manner will yield soil which can be disposed as non-hazardous material. The decontamination was performed without exceeding RCRA requirements for particulate emissions and with dioxin destruction efficiencies surpassing the required percentage. The overall conclusion was that the infrared incinerator can very effectively remove dioxin from contaminated... 

Laboratory and field testing determined the effectiveness of a new decontamination process for soils containing 2,4-D/2,4,5-T and traces of dioxin. The process employs three primary operations - thermal desorption to volatilize the contaminants, condensation and absorption of the contaminants in a solvent, and photochemical decomposition of the contaminants. Bench-scale experiments established the relationship between desorption conditions (time and temperature) and treatment efficiency. Laboratory tests using a batch photochemical reactor defined the kinetics of 2,3,7,8-TCDD disappearance. A pilot-scale system was assembled to process up to 100 pounds per hour of soil. Tests were conducted at two sites to evaluate treatment performance and develop scale-up information. Soil was successfully decontaminated to less than 1 ng/g... 

Fig. 2-27. Cleaning up mustard agent in the field with bleaching powder and soil. The labor-intensive nature of mustard decontamination is readily apparent. Note that the exercise is being conducted in the winter no doubt the chemical protective garments shown here would have constituted a considerable thermal load. Photograph Chemical and Biological Defense Command Historical Research and Response Team, Aberdeen Proving Ground, Md.

On-site soil treatment is an alternative to excavation, removal, and incineration. The JM Huber Corporation has developed a mobile advanced electric reactor (AER) for decontamination of soil. The pyrolytic process uses thermal radiation (near infrared) at 2473-2773 K and has a PCB destruction efficiency of 99.9999%. Operating under reducing conditions minimizes the possible formation of PCDD and PCDF, and lessens the change of explosion. Costs are about the same as that of rotary kiln incineration. 

---