In situ biological treatment

The potential for microbial mobility under natural or perturbed conditions clearly has significant implications for in situ bioremediation. Implementation of in situ bioremediation may require inoculating a soil or aquifer with contaminant-degrading microbes, perhaps genetically modified bacteria. For source area cleanup, these microbes either must be introduced in proximity to the contaminants or be capable of migrating toward the contaminants. Understanding microbial mobility may be important in the proper design of in situ bioremediation schemes. 

When explosive concentrations in soils were sufficiently high to produce free product in the soil, solubilization was the dominant mass transfer process. When concentrations were low, desorption, convection, and dispersion controlled solution phase concentrations. Surfactants generally increased solution phase concentrations of explosives however, 

The advantage is the potential for large cost savings. The disadvantages are the following negative data for explosives, mass transfer rates are slow, completeness difficult to verify, and process control is difficult. 

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In cases where in situ biological treatment cannot be applied, the contaminated soil is excavated and transferred to specially prepared areas where bioremediation can be carried out under well-controlled conditions. Some common ex situ biological methods are the landfarming technique and the biopile or biopit treatment options.32... 

The in situ biological treatment technique for organic contaminants is fully discussed in the Chapter 17. An example of a cost estimate for bioremediation is shown in Table 16.5. The data is based on a U.S. EPA study15 of a project performed by Biocraft Laboratories, Waldwick, New Jersey. 

The disadvantages of ex situ biological treatment in comparison to in situ biological treatment are as follows ... 

The technology for in situ biological treatment for soil is similar to that for in situ biological ground-water treatment. The following sections present three newly developed techniques. 

WaterSmart Environmental, Inc. (WaterSmart), has developed the Express process technology for simultaneous treatment of contaminated soil and groundwater. Express, a combination of soil washing/leaching and in situ biological treatment, is an acronym for EXPedited REmediation Site Strategy. 

Zappi, M, Gunnison, D., Pennington, J., Cullinane, J., Teeter, C. L., Brannon, J. M., and Myers, T. (1993) Technical Approaches for In Situ Biological Treatment Research Bench-Scale Experiments, US Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS, August 1993, Technical ReportNo. IRP-93-3. 

Chemical Weapons/Explosive Waste/Unexploded Ordnance 8.6 IN SITU BIOLOGICAL TREATMENT... 

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. 

A convenient HPLC technique known as the Fukushima-Nixon method has been widely used for selective analyses of tetrahydrobiopterin and tetrahy-droneopterin in biological samples [49]. This method allows the estimation of concentrations of tetrahydropterins based on difference in the concentrations of the corresponding aromatic pterins in the samples, which are prepared in situ by treatment with iodine under acidic and basic conditions. The Fukushima-Nixon method does not require special techniques or equipment for the chemical reaction the sample is simply subjected to oxidation just before its injection into the HPLC column. For example, tetrahydrobiopterin (43) was selectively oxidized to biopterin (30) by iodine in the presence of... 

In Situ Biological Degradation Test at Kelly Air Force Base, TX, Volume 1 Site Characterization, Lab Studies, and Treatment System Design and Installation... 

Techniques for in situ sediment treatment are still in an early stage of development, and the very few methods currently commercially available are usually restricted to situations where the low water levels allow for water flow diversion. Potential in situ treatment methods include biological, chemical, and stabilization processes. The main advantage relies upon avoiding sediment removal and, therefore, the related risk of spreading the contamination. However, technical limitations to the application of in situ treatments still exist, mainly because the effective delivery of such process reagents as substrates, nutrients, and chemicals, as well as mixing with the contaminated material, may be problematic. 

This chapter will present the principles governing thermal desorption and from this, the changes in chemical and biological reactions that occur during in situ thermal treatment. 

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. 

Ex situ bioremediation may use various biological wastewater treatment processes, soil piles, or land appHcation. With in situ bioremediation, the basic process is the same microbes, soil, and water working together as a bioreactor. Where the in situ techniques differ are in how contaminants and microbes are brought in contact and how oxygen, nutrients, and other chemical supplements ate distributed in the soil—water—air matrix. Typical in situ bioremediation techniques include natural or intrinsic attenuation, air sparging, and bioventing. 

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