Treatment In Situ

Where there are large volumes of contaminated water under a small site, it is sometimes most convenient to treat the contaminant in a biological reactor at the surface. Considerable research has gone into reactor optimization for different situations and a variety of stirred reactors, fluidized-bed reactors, and trickling filters have been developed. Such reactors are usually much more efficient than in situ treatments, although correspondingly more expensive. 

They may be favored over in situ treatment where they will reduce cleanup times, their operation and capabiHties are considered more reHable or better understood, or they can achieve lower cleanup levels. Both in situ and ex situ treatment for soil and ground water rely on a combination of unit processes, which often include biological degradation of organics. 

C. D. Chambers and co-workers. In Situ Treatment of Hacyardous Waste-ContaminatedSoils, Noyes Data Corporation, Park Ridge, N.J., 1991. 

Delineation/Verification of Gross Contamination Sampling and Analysis Interceptor Trench/Sump/Subsurface Drain Pump and Treat In-situ Treatment Temporary Cap/Cover... 

Applicability/Limitations. In-situ treatment can be used when it is uneconomical to haul or when infeasible or uneconomical to dig or pump the contaminated waste matrix for treatment in a reactor. This approach should be used whenever excavation or removal causes an increased threat to human health. It can reduce the cost of a remediation program. Because chemicals are applied to the contaminated waste matrix, specifically soil and groundwater, a potential exists for reaction with the soil. Permeability problems can occur as the result of precipitate formation. This can result in inadequate mixing of the contaminant with the treatment chemical. Gas generation may also occur. 

The extent of cleanup that is necessary to protect human health and welfare aries with different use ctitegories. Residential development is probably the most sensiti e type of land use because of the long-term and multiple e.xposure routes and because of potential e.xposure to the most sensitive population segments (e.g., children and elderly persons). E.xcavation and removal appears to be the remedial tiction alternative selected at most sites where there is redevelopment. This is because no one can guaratitee tliat a site is stife (i.e., offers zero risk) unless all contaminants are removed. Neitlier a developer nor a municipality can accept responsibility for site safety as long as haznrdous materials remain there. In situ treatment approtiches are seldom iewed is the best option because they are unproven and because 100% detoxification or stabilization caimot be achieved. 

Only two processes, high-temperature pyrolysis and mobile incineration, have proved effective for soil decontamination and are considered to be commercially viable. Both involve heating the contaminated soil to a high temperatnre, which is costly in terms of energy use and materials handling. There are substantial opportunities for innovation and development of processes for the separation of eontaminants from soils and the in-situ treatment of contaminated soils. Examples of each are given in the following subsections. 

The use of biodegradation for the treatment of dilute waste streams has already been discussed it also has potential for in-situ treatment. The critical need is to learn how to select and control microorgarrisms in a soil environment to achieve the desired degradation of organics. 

Bioremediation methods may be applied either in situ or ex situ. In this section, the most important in situ treatment methods will be examined. 

U.S. EPA, Recent Developments for In Situ Treatment of Metal Contaminated Soils, EPA-542-R-97-004, Technology Innovation Office, Washington, 1997. 

U.S. EPA, Recent developments for in-situ treatment of metal contaminated soils, U.S. EPA, Office of Solid Waste and Emergency Response, Technology Innovation Office, EPA Contract No. 68-W5-006, 1997, pp. 1-47. 

To pump out the contaminated groundwater or perform in situ treatment to halt the source of contamination... 

In situ groundwater treatment is an alternative to the conventional pump-and-treat methods. In situ treatment uses biological or chemical agents or physical manipulations that degrade, remove, or immobilize contaminants. In situ treatment technologies can usually treat both contaminated groundwater and soil. In many instances a combination of in situ and aboveground treatment will achieve the most cost-effective treatment at an uncontrolled waste site. 

The main advantage of in situ thermal methods is that they allow soil to be treated without being excavated and transported, resulting in significant cost savings however, in situ treatment generally requires longer time periods than ex situ treatment, and there is less certainty about the uniformity of treatment because of the variability in soil and aquifer characteristics and because the efficacy of the process is more difficult to verify. 

Electroosmotic soil processing is an in situ separation/removal technique for extracting heavy metals and organic contaminants from soils.17 55 89 The fluid between the soil particles moves because a constant, low DC current is applied through electrodes inserted into the soil mass. The electroosmosis (EO) remedial method provides an advantage over conventional pumping techniques for in situ treatment of contaminated fine-grained soils and is more efficient in saturated conditions. 

Metallic electrodes may dissolve as a result of electrolysis and may introduce corrosion products into the solid mass. However, if the electrodes are made of carbon or graphite, no residue will be introduced in the treated soil mass as a result of the process. The energy expenditure for Pb removal has been estimated to in the range 30 to 60 kWh/m1 2 3 4 of soil. The EO method also provides an advantage over conventional pumping techniques for in situ treatment of contaminated finegrained soils. 

If an in situ treatment method is not feasible, a soil excavation and treatment method should be conducted. The soil excavation and treatment method is usually more cost-effective for small sites and shallow contamination. Before excavation, planning is needed regarding the following steps of the treatment, among others ... 

Ellis, W.D. and Payne, J.R., Chemical Counter Measures for In Situ Treatment of Hazardous Material Releases, U.S. EPA, Edison, NJ, 1983. 

For practitioners of in situ technologies, note that U.S. EPA has issued a policy statement that reinjection of contaminated groundwater is allowed under Resource Conservation and Recovery Act (RCRA)35 36 as long as certain conditions are met. This policy is intended to apply to remedies involving in situ bioremediation and other forms of in situ treatment. Under this policy, groundwater may be reinjected if it is treated aboveground prior to reinjection. Treatment may be by a pump-and-treat system or by the addition of amendments meant to facilitate subsurface treatment. Also, the treatment must be intended to substantially reduce hazardous constituents in the groundwater (either before or after reinjection) the cleanup must be protective of human health and the environment and the injection must be part of a response action intended to clean up the environment.37... 

In general, aboveground treatment systems can be more readily controlled and monitored to optimize the removal of MTBE and other oxygenates than in situ treatment systems. 

U.S. EPA, Cost of In Situ Treatment of Fuel Oxygenate, Site Closure and the Total Cost of Cleanup, Conference on Remediation, National Ground Water Association, New Orleans, November 13-14, 2003. 

U.S. EPA, Applicability of RCRA Section 3020 to In-Situ Treatment of Groundwater, Memorandum from Elizabeth Cotsworth, Director, Office of Solid Waste, United States Environmental Protection Agency, Washington, DC, December 27, 2000. Available at www.cluin.org, 2009. 

In-situ treatment, on the other hand, uses existing polymer processing equipment to apply the desired fluorine-containing gas to the polymer in question. Of course, there has to be some modifications of the processing equipment. The... 

Aeropak process—simultaneous blow-molding and inner-surface fluorination of polymeric containers—is the most well-known example of an in-situ treatment process. 

Consequently, the granular iron hydroxide seems to be suitable for an on site or in situ treatment of arsenic contaminated surface waters. However, the experiment is not yet finished and some more experiments (influence of the dissolved iron, regeneration of the material, and surface characterization) are required before the material can prove its efficiency in a pilot test in the filed. 

The Co 2p XPS spectra from in situ treatments of the catalysts are shown in Figures 2-5. The Co 2p BE, line shape, and satellite intensity vary noticeably among the samples. The variation of these three spectral features has been shown to be useful in identifying the different Co species present in a sample (4). For the Co V /2 line> the metallic peak is located near 778 eV, the +2 and +3 oxide peaks are near 781 eV, and +2 satellite peak is near 787 eV. The Co V /2 features are located at 15-16 eV higher BE than the corresponding Co V /2 peaks. 

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