The Removal of Organics

Thiophene [110-02-17, C H S, and dibenzothiophene [132-65-OJ C22HgS, are models for the organic sulfur compounds found in coal, as well as in petroleum and oil shale. Cobalt—molybdenum and nickel—molybdenum catalysts ate used to promote the removal of organic sulfur (see Coal CONVERSION... 

The chemical yield of hydrogen peroxide and the anthraquinone per process cycle is very high, but other secondary reactions necessitate regeneration of the working solution and hydrogenation catalyst, and the removal of organic material from the extracted hydrogen peroxide. 

Supercritical CO2 has also beea tested as a solveat for the removal of organic contaminants from sod. At 60°C and 41.4 MPa (6,000 psi), more than 95% of contaminants, such as diesel fuel and polychlotinated biphenyls (PCBs), may be removed from sod samples (77). Supercritical CO2 can also extract from sod the foUowiag hydrocarbons, polyaromatic hydrocarbons, chlotinated hydrocarbons, phenols, chlotinated phenols, and many pesticides (qv) and herbicides (qv). Sometimes a cosolvent is required for extracting the more polar contaminants (78). 

Carbon Adsorption. Carbon adsorption is a well estabflshed and widely used technology for the removal of organics from wastewaters and gaseous streams. Carbon adsorption is a proven technology for potable water treatment and capable of reducing organic concentrations to very low or nondetectable levels. 

Adsorption — An important physico-chemical phenomenon used in treatment of hazardous wastes or in predicting the behavior of hazardous materials in natural systems is adsorption. Adsorption is the concentration or accumulation of substances at a surface or interface between media. Hazardous materials are often removed from water or air by adsorption onto activated carbon. Adsorption of organic hazardous materials onto soils or sediments is an important factor affecting their mobility in the environment. Adsorption may be predicted by use of a number of equations most commonly relating the concentration of a chemical at the surface or interface to the concentration in air or in solution, at equilibrium. These equations may be solved graphically using laboratory data to plot "isotherms." The most common application of adsorption is for the removal of organic compounds from water by activated carbon. 

The effectiveness of activated carbon for the removal of organic compounds from fluids by adsorption is enhanced by its large surface area, a critical factor in the adsorption process. The surface area of activated carbon typically can range from 450 to 1,800 m /g, with some carbons observed to have a surface area up to 2,500 m /g. Some examples are given in Table 6. 

Prechlorination (before the clarifier) significantly improves the removal of organics as well as reducing the coagulant demand. 

Tubular reactors are used for reactions involving a gas and a liquid. In this arrangement, the gas phase is dispersed as bubbles at the bottom of a tubular vessel. The bubbles then rise through the continuous liquid phase that flows downwards as shown in Figure 4-14. An example of this process is the removal of organic pollutants from water by noncatalytic oxidation with pure oxygen. 

The removal of organic compounds such as toxic compounds... 

The main types of cleaners used for the removal of organic contaminants are solvent cleaners, neutral cleaners, acid cleaners and alkali cleaners. 

The removal of organics by industrial detergent cleaners. These products employ several mechanisms, depending on the formulation, but tend to include dissolution (using nonaqueous solvents such as kerosene, petroleum spirits, and naphtha, saponification, by caustic, or emulsification by nonionic detergents. 

Solvent extraction shows effectiveness in the removal of organic wastes such as PCBs, VOCs, halogenated solvents, and petroleum wastes, but is less effective in removing inorganic compounds.39 The removal of organic contaminants depends on the nature of the extracting solvent. Organic bound metals can become a constituent of the concentrated waste, which is undesirable because it can restrict both disposal and recycle options. 

Iron and manganese levels in the influent water may also limit the use of GAC. They will precipitate onto the carbon during treatment. If this happens, head losses will increase rapidly, the removal of organics will be hindered, and the carbon filter may eventually get clogged, making it ineffective and increasing cost substantially, or impractical due to space constraints. If these elements are present at concentration levels above 5 mg/L, they must be removed prior to GAC treatment. 

In addition, the removal of organic matter and Fe oxides from soils and sediments is common practice as a pretreatment for soils prior to physical, chemical and biological analyses. The effects of the removal of these components on physicochemical and surface chemical properties of soils will be discussed as well. 

The effects of the removal of organic matter and iron oxides on Zn adsorption on soils are also influenced by Zn concentration. At low concentrations (5-10 mg L initial concentration), both treated soils (removed organic matter and iron oxides) behaved similarly. At high Zn concentration, however, treated soils behaved differently. When the initial Zn concentration was between 5 and 10 mg kg-1, adsorption of Zn by soils without organic matter and without both organic matter and iron oxides were 2-2.5 times that of the untreated soil. With an increase in initial Zn concentration, the soil without both iron oxides and organic matter adsorbed more Zn than the soil without organic matter. This indicates that the available sites for Zn decrease with increases in the initial Zn concentration. 

Adsorption kinetics of Zn on the untreated soil and the soils with the removal of organic matter and Fe oxides has been studied in detail by Hinz and Selim (1999) using a thin disk flow method. They reported that Zn sorption was highly concentration-dependent. When Zn concentration was... 

The adsorption/desorption kinetics of Zn on soils with the removal of organic matter and Fe oxides were studied by Kingery et al. (1999) using traditional batch experiments on the same soil used by Hinz and Selim (1999). Adsorption of Zn on the three soils was kinetically characterized by three kinetic rates a very fast initial retention process within 30 min, an intermediate retention process from 30 min to 8 hours, followed by the very slow process (Fig. 5.5). About 50% of Zn was adsorbed on the three soils within the initial first 30 min. Initially, Zn desorption increased with time during the first 20 minutes from both the untreated soils and the soils without organic matter and Fe oxides. However, after 20 minutes of adsorption, net Zn adsorption from the whole soil and the soil with the... 

In summary, the removal of organic matter and Fe oxides significantly changes the physicochemical and surface chemical properties of soils. Thus, this pretreatment affects the overall reactivity of heavy metals in soils. The removal of organic matter and Fe oxides may either increase or decrease heavy metal adsorption. The mechanisms responsible for the changes in metal adsorption in soils with the removal of organic matter and Fe oxides include increases in pH, surface area, CEC and electrostatic attraction, decreases in the ZPC, shifts of positive zeta potentials toward... 

Method for the removal of organic sulfur from carbonaceous materials [78],... 

Microbiological conversion in molecular nitrogen by means of nitrification and denitrification, often in combination with the removal of organic pollutants... 

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