Degradation of contaminants

Biostimulatioo Any process that increases the rates of biological degradation, usually by the addition of nutrients,oxygen, or other electron donors and acceptors so as to increase the number of indigenous microorganisms available for degradation of contaminants. 

Degradation of Contaminants under Simulated Atmospheric Conditions... 

The microbial degradation of contaminants under anaerobic conditions using humic acids as electron acceptors has been demonstrated. These included the oxidations (a) chloroethene and 1,2-dichloroethene to CO2 that was confirmed using C-labeled substrates (Bradley et al. 1998) and (b) toluene to CO2 with AQDS or humic acid as electron acceptors (Cervantes et al. 2001). The transformation of l,3,5-trinitro-l,3,5-triazine was accomplished using Geobacter metallireducens and humic material with AQDS as electron shuttle (Kwon and Finneran 2006). 

Degradation of contaminants may occur with bacteria that have been isolated from pristine environments without established exposure to the contaminants, and exhibit no dependence on substrate concentration. For example, organisms from a previously unexposed forest soil were able to degrade 2,4,6-trichlorophenol at concentrations up to 5000 ppm, and terminal restriction fragment length polymorphism analysis revealed that at concentrations up to 500 ppm, the bacterial community was unaltered (Sanchez et al. 2004). 

There has been considerable interest in the use of plants for bioremediation and this merits a rather extensive discussion. Plants can play an important role in bioremediation for several reasons (1) they can transport contaminants from the soil, (2) they can metabolize the contaminants after uptake, or (3) they can produce exudes that support microbial activity for degradation of the contaminants. In addition, bacteria can produce metabolites that counter the effect of toxins produced by fungi, and serve as biocontrol agents that diminish the need for the application of agrochemicals. Plant exudates play an important role in supporting the growth and activity of bacteria that carry out the degradation of contaminants in the rhizosphere and rhizoplane (the external surface of roots... 

Endophytic bacteria can colonize plant tissues without bringing about adverse effects on the plant, in contrast to epiphytes that remain in the external environment. Bacteria with the established potential for degradation have been used to improve the tolerance and degradation of contaminants ... 

Phytodegradation (also known as phytotransformation) is the uptake, metabolizing, and degradation of contaminants within the plant, or the degradation of contaminants external to the plant... 

B-blockers Atenolol T. versicolor Degradation of contaminant by 10 mg L-1 80% reached after 6 h of Atenolol hydroxylated [17]... 

When insufficient amounts of hydroxyl radicals are available, incomplete degradation of contaminants may occur. Metals or solids in the influent may reduce process efficiency by costing or scaling the UV light source. 

The SoilTech anaerobic thermal processor (ATP) technology is a physical separation process that thermally desorbs organics such as polychlorinated biphenyls (PCBs) from soil and sludge. The SoilTech system distills organic contaminants from a solid matrix in an anaerobic environment, thus preventing oxidative degradation of contaminants such as PCBs into more harmful reaction products. Contaminants are collected in an oily condensate, which is disposed. 

We use a variety of preservation techniques in order to minimize the degradation of contaminant concentrations in soil and water samples. Preservation methods stem from the chemical nature of each contaminant and from the rate at which it will undergo irreversible changes in a sample. Preservation is achieved by the application of one or more of the following techniques ... 

This review provides information related to the methods which are currently most suitable for the remediation of contaminated soils and water. The development of a deeper understanding of the physical and chemical processes involved in the degradation of contaminants will facilitate the establishment of more cost-effective and efficient remedial action plans that are protective of human health and the environment. 

We focus initially on the photochemical behaviour of complexes of Fe(III) with simple carboxylic acids and give particular attention to oxalic acid. This compound is prevalent in atmospheric aerosols [28], provides a simple example of environmentally important light-mediated ligand-to-metal charge transfer (LMCT) processes which result in ligand decarboxylation [27] and is used to initiate the degradation of contaminants both in the absence and presence of added hydrogen peroxide (via the so-called modified photo-Fenton process [29,30]). In addition, the photochemistry of Fe(III)-oxalate complexes has been studied in detail, as it is the basis of... 

Photolysis of iron carboxylates has been used to initiate the degradation of contaminant species (often via photo-Fenton processes) but the process results in degradation of the carboxylate ligand. Alternate ligands which are more resistant to oxidation (either via LMCT processes or hydroxyl radical attack) would appear necessary if such approaches are to be adopted in practice. 

Biostimulation is the promotion of favourable conditions to facilitate the degradation of contaminants by in situ microorganisms. Stimulation can be achieved... 

Degradation of contaminants by microorganisms in the soil zone that surrounds and is influenced by the roots of plants (i.e., the rhizosphere)... 

Surfactants and microemulsion systems can be used for ex situ treatment of contaminated soil or in situ soil decontamination. In situ remediation is usually preferred if excavation of the contaminated soil is not possible or expensive, e.g. beneath buildings or for contaminations at great depth. Often bioremediation or natural attenuation is used for decontamination. In most cases, these techniques only permit the effective degradation of contaminants in the plume formed by dissolved pollutants which may be very large. However, for the remediation of a contaminated site, it is also necessary to remove the source where the pollutants maybe adsorbed in large quantities or may be present as solid or liquid phases. The latter are called NAPL (non-aqueous phase liquids) and a differentiation is made between LNAPL (light non-aqueous phase liquids) with a lower density than water and DNAPL (dense non-aqueous phase liquids) with a higher density than water (see Fig. 10.1). 

Inappropriate test conditions (volatilisation, degradation of contaminants). 

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