Process dependent contaminants

Standard genotoxicity studies are in general not considered necessary. Also testing of production process dependent contaminants is not considered necessary (ICH 1997). 

Dimethylphenol [95-65-8] M 122.2, m 65°, b 225°/757mm, pK 10.36. Heated with an equal weight of cone H2SO4 at 103-105° for 2-3h, then diluted with four volumes of water, refluxed for Ih, and either steam distd or extracted repeatedly with diethyl ether after cooling to room temperature. The steam distillate was also extracted and evaporated to dryness. (The purification process depends on the much slower sulfonation of 3,5-dimethylphenol than most of its likely contaminants.). It can also be crystd from water, hexane or pet ether, and vacuum sublimed. [Kester Ind Eng Chem (Anal Ed) 24 770 1932 Bernasconi and Paschalis J Am Chem Soc 108 29691986.]... 

U.S. EPA has shown that 90% of process water can be recycled to the front end of the system for slurry preparation, and the rest must be treated on site or transported to an off-site facility.80 During the aerobic process, some contaminated air may be formed and emitted from the reactor. Depending on the air characteristics, a compatible air pollution control device may be used, such as activated carbon. Slurry biodegradation has been shown to be successful in treating soils contaminated with soluble organics, PAHs, and petroleum waste. The process has been most effective with contaminant concentrations ranging from 2500 mg/kg to 250,000 mg/kg. 

Contaminant removal processes depend on the type and source of secondary fiber to be pulped. Mill paper waste can be easily repulped with minimal contaminant removal. Recycled postconsumer newspaper, on the other hand, may require extensive contaminant removal, including deinking, prior to reuse. Secondary fiber is typically used in lower-quality applications such as multiply paper-board or corrugating paper. 

A number of important processes depend on the permanence of particle attachment to surfaces by Van der Waal forces in the presence of flowing fluids. These include enzyme fixation, particle filtration, oil production, nuclear reaction excursions, migration of surface contaminants, etc. The release of particles attached to a surface plays an important role in these processes. 

The vendor claims that the TDR process can be used to treat soil and sludge contaminated with polychlorinated biphenyls, polynuclear aromatic compounds, solvents, dioxins, furans, organic pesticides and herbicides, solvents, petroleum wastes, as well as nonhalogenated volatile and semivolatile compounds. The treated residuals from the process include recovered water, oil that can be used for recycling as an alternative fuel or for recycling or can be disposed, and clean soil that can be used as backfill. The volume of treated sludge is reduced by as much as 95% by this thermal process, depending on the initial level of contaminants. 

The treatment costs for the GHEA Associates process depend on the soil matrix, properties, chemical composition of the contaminants, and other site-specific factors. The commercial-scale, integrated process, consists of the extraction and wash liquor purification steps. The estimated costs for the process range from 50 to 80 per ton of soil treated. Other separation processes have estimated treatment costs ranging from 90 to 200 per ton (D13377H, pp. 793, 799). 

According to the vendor, the technology is site dependent. Contaminants must be accessible to ACT DE CON solution. Certain soils, such as zeolites, may interfere with the process solution. Soils with extremely high target contaminant levels may produce large amounts of secondary waste. 

Hydroperoxides are decomposed readily by multivalent metal ions, i.e., Cu, Co, Fe, V, Mn. Sn, Pb, etc., by an oxidation-reduction or electron-transfer process. Depending on the metal and its valence state, metallic cations either donate or accept electrons when reacting with hydroperoxides. Either one or two electrons may be transferred depending on die metal. With most transition metals, e.g., Cu, Co, and Mn, both valence states react with hydroperoxides via one electron transfer. Thus, a small amount of transition-metal ion can decompose a large amount of hydroperoxide and, consequently, inadvertent contamination... 

The choice of process depends on the level of microbiological contamination of the raw materials and packaging, and the ability of the product to withstand growth of micro-organisms (e.g. preservative levels and sugar content). Also of great importance is the ability of the product to withstand heat. 

The silver dye-bleach process depends on destruction of a dye in a photographic layer in an amount proportional to the quantity of image silver present.94 95 The dye is normally an azo dye in which the azo bond is cleaved. Over the years a variety of metal-complexed azo dyes have been described for use in this process. These dyes must be immobile they must not wander from layer to layer, or color contamination of the final image will result. However, they must be reactive enough in an aqueous environment for the azo bond to break. 

However, the successful use of processes dependent on Langmuir-Blodgett films for semiconductor applications is in doubt due to the presence of water and other detrimental contaminants in the films produced. The internal dislocations required for switching by the molecules may not be facile since the molecules are expected to be packed into semicrystalline phases in the Langmuir-Blodgett films. In addition, new developments in the field may obviate the need for such films as part of the device. 

Chemisorption systems are sometimes used for removing trace concentrations of contaminants, but the difficulty of regeneration makes such systems unsuitable for most process applications so most adsorption processes depend on physical adsorption. The forces of physical adsorption are weaker than the forces of chemisorption so the heats of physical adsorption are lower and the adsorbent is more easily regenerated. Several different types of force are involved. For nonpolar systems the major contribution is generally from dispersion-repulsion (van der Waals) forces, which are a fundamental property of all matter. When the surface is polar, depending on the nature of the sorbate molecule, there may also be important contributions from polarization, dipole, and quadmpole interactions. Selective adsorption of a polar species such as water or a quadrupolar species such as CO2 from a mixture with other nonpolar species can therefore be accomplished by using a polar adsorbent. Indeed, adjustment of surface polarity is one of the main ways of tailoring adsorbent selectivity. 

Spent activated carbon waste streams are generated at facilities employing both the baseline incineration system and the chemical neutralization (hydrolysis) process. Depending on the organic contaminants adsorbed, spent carbon may be classified as hazardous or nonhazardous. Other minor sources of activated carbon will be added to the main carbon filter stream for disposal. 

Whereas in Chapter 4 interactions between suspended particles and dissolved constituents have been described, Chapter 5 focusses on the processes taking place within the sediment or near the sediment/water interface. These processes depend on a large extent on the position of the oxic-anoxic interface. This interface (redoxcline) is within the sediments of well-mixed waterbodies and in the water column of some stratified lakes and basins. Transport processes and changes in the chemical environment determine the behaviour of contaminants (Salomons et al., 1987). ... 

Physical processes separate contaminants from uncontaminated material by exploiting differences in their physical properties (e.g. density, particle size, volatility, by applying some external force (e.g. abrasion) or by altering some physical characteristic to enable separation to occur (e.g. flotation). Depending on the nature and distribution of the contamination within the soil, physical processes may result in the segregation of differentially contaminated fractions (for example a relatively uncontaminated material and a contaminant concentrate based on a size separation) or separation of the contaminants (for example oil or metal particles) from the soil particles. Table 6 summarises the main advantages and disadvantages of physical processes. 

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