Dissolved organic compound

The wastewater produced in this process consists mostly of water used in cleanup and propellant conveyance and sorting operations. Techniques such as the use of activated carbon and biological treatment are being investigated for the removal of solvents and dissolved organic compounds (143). 

Hydrofluoric acid is a polar material, as water is, and it behaves as an ionizing solvent when it is scrupulously free of water. Salts that dissolve readily in liquid HF include LiF, NaF, KF, AgF, NaNOs, KNOa, AgNOj, Na2S04, K2S04, and Ag2S04. Liquid HF also dissolves organic compounds and is used as a solvent for a variety of reactions. 

We have seen that molecular substances tend to have low melting points, while network, ionic, and metallic substances tend to have high melting points. Therefore, with a few exceptions, such as mercury, a substance that is liquid at room temperature is likely to be a molecular substance. Liquid solvents are heavily used in industry to extract substances from natural products and to promote the synthesis of desired compounds. Because many of these solvents have high vapor pressures and so give tiff hazardous fumes, liquids that have low vapor pressures but dissolve organic compounds have been sought. 

The dense fluid that exists above the critical temperature and pressure of a substance is called a supercritical fluid. It may be so dense that, although it is formally a gas, it is as dense as a liquid phase and can act as a solvent for liquids and solids. Supercritical carbon dioxide, for instance, can dissolve organic compounds. It is used to remove caffeine from coffee beans, to separate drugs from biological fluids for later analysis, and to extract perfumes from flowers and phytochemicals from herbs. The use of supercritical carbon dioxide avoids contamination with potentially harmful solvents and allows rapid extraction on account of the high mobility of the molecules through the fluid. Supercritical hydrocarbons are used to dissolve coal and separate it from ash, and they have been proposed for extracting oil from oil-rich tar sands. 

Polyurethane foams have been used as sorbents for neutral dissolved organic compounds in water [189,190]. gctraction columns are prepared from sections of cellular (fo Hl) polyurethanes... 

North Sea water at the natural pH has a complexing capacity, probably due to the presence of dissolved organic compounds, in a concentration equivalent to 0.3 M copper. The complexing capacity is zero at pH 2.7. The method of standard addition for the determination of electroactive copper and lead concentrations may lead to erroneous results in samples where complexation of this type occurs. 

Yang et al. [294] determined nanomolar quantities of individual molecular weight amines (and organic acids) in sea water. Amines were diffused from the sample across a hydrophilic membrane to concentrate and separate them from inorganic salts and most other dissolved organic compounds. Methylamine, dimethylamine, and trimethylamine were all found in measurable amounts in sea water. 

Blumer M (1970) Dissolved organic compounds in seawater. Saturated and olefinic hydrocarbons and singly branched fatty acids. In Hood DW (ed) Organic matter in natural waters. Publication no. 1. Institute of Marine Science, University of Alaska, pp 153-167... 

The quality of the purified water and the composition of the concentrate strongly depend on the type of techniques and the applied process conditions. The presence of suspended and colloidal particles or dissolved organic compounds can have a negative effect on the treatment. 

Sorptive reactions of LNAPLs and dissolved organic compounds moving through soil are almost always reversible equilibrium reactions. A concentration equilibrium is established between the concentration of chemical dissolved in water and that which is attached to the soil particles. When concentrations change, the soil may adsorb additional organic molecules or release them to reestablish the equilibrium. 

The physical transport of dissolved organic compounds through the subsurface occurs by three processes advection, hydrodynamic dispersion, and molecular diffusion. Together, these three cause the spread of dissolved chemicals into the familiar plume distribution. Advection is the most important dissolved chemical migration process active in the subsurface, and reflects the migration of dissolved chemicals... 

Additional information is required to determine what is causing this net removal. In the case of iron, research has demonstrated that its solubility decreases with increasing salinity leading to the formation of two types of solids (1) iron oxide minerals, and (2) organic floes. Some iron is also removed by uptake as a micronutrient by plankton. The floes form from the co-precipitation of iron with the high-molecular-weight dissolved organic compounds naturally present in river water. 

Though a great variety of dissolved organic compounds are present in seawater, the functional groups responsible for metal complexation are primarily the anions R-0 ,... 

Iodine has had limited application for disinfection of swimming pools [7] and small public water supplies [8]. One application in a reverse osmosis system has also been reported by Turby and Watkins [9]. Advantages of iodine are greater stability than chlorine, lower residual requirement, and diminished chemical reactivity toward dissolved organic compounds. 

Chlorine dioxide is a very reactive compound and will not exist in the environment for long periods of time. In air, sunlight will quickly break apart chlorine dioxide into chlorine gas and oxygen. In water, chlorine dioxide will react quickly to form chlorite ions. In water treatment systems, chlorine dioxide will not form certain harmful compounds (e.g., trihalomethanes) when it reacts with dissolved organic compounds. Chlorine dioxide does form other disinfection byproducts, such as chlorite and chlorate ions. 

Micellar enhanced ultrafiltration (MEUF) is a recently proposed technique to separate dissolved organic compounds from aqueous streams [256-258]. In this process, surfactant is added to an aqueous stream containing organic solute for forming micelles in order to solubilize the target compound. The subsequent concentration and purification of the target compound is achieved by ultrafiltration by optimizing the process parameters [259-261]. 

Contaminated bed sediments exist at numerous locations in the United States and around the world. These result mainly from past indiscriminate pollution of our aquatic environments and consist of freshwater and marine bodies including streams, lakes, wetlands, and estuaries. The bed sediments contain many hydrophobic organic compounds and metal ions that in the course of time act as sources of pollutants of the overlying aqueous phase. There are a number of transport pathways by which pollutants are transferred to the aqueous phase from contaminated sediments. One of the lesser known, but potentially important, modes of transport of pollutants from bed sediments is by diffusion and advection of contaminants associated with colloidal-size dissolved macromolecules in pore water. These colloids are measured in the aqueous phase as dissolved organic compounds (DOCs). (These are defined operationally as particles with a diameter smaller than 0.45 micrometer.)... 

Note that we make a distinction between a solution and a mixture. When we talk of a solution, we imply that the organic solute is not a major component of the bulk liquid. Therefore, that presence of a dissolved organic compound does not have a significant impact on the properties of the bulk liquid. In contrast, in a mixture we recognize that the major components contribute substantially to the overall nature of the medium. This is reflected in macroscopic properties like air-liquid surface tensions and in molecule-scale phenomena like solubilities of trace constitutents. 

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