Mixtures of Organic Contaminants

Volatilization from mixtures of organic contaminants brings about changes in both the physical and the chemical properties of the residual liquid. We consider data on kerosene volatilization, as summarized in Yaron et al. (1998). Kerosene is an industrial petroleum product composed of more than 100 hydrocarbons, which may become a subsurface contaminant. 

The differential volatilization of neat kerosene components from a liquid phase, directly into the atmosphere during volatilization up to 50% (w/w), is presented in Fig. 8.8. Ten kerosene components were selected, and their composition was depicted as a function of gas chromatograph peak size (%), which is linearly related to their concentration. It may be seen that the lighter fractions evaporate at the beginning of the volatilization process. Increasing evaporation causes additional components to volatilize, which leads to a relative increase in the heavier fractions of kerosene in the remaining liquid. 

These examples indicate that aggregation and pore-size distribution parameters affect volatilization of petroleum products from a contaminated subsurface. Fine and Yaron (1993) report that kerosene volatilization depends on the type of soil. Tests on four soils with a clay content increasing from 0.3% to 74.4%, and organic matter 

Amount volatilized (%) Density (g cm ) Surface tension (Nm- ) Viscosity (Pa s xlO h 

The relative concentration of the light fraction, diminished with time in all 

---

Advanced oxidation processes (AOPs) are a range of water treatments which involve the in situ formation of radicals, particularly hydroxyl radicals, in sufficient quantity to affect chemical or biological contaminants. These include ultrasonic and ultraviolet irradiation but they are sometimes ineffective for the remediation of water which contains a mixture of organic and inorganic compounds. Chemical oxidants can be used to add additional oxidising power to such processes and ozone in conjunction with ultrasound is one such option [31]. 

Contaminants may be adsorbed on the solid phase or on suspended particles in the liquid phase. Environmental factors, such as temperature, pH, and water content in the subsurface prior to contamination, also affect the nature of contaminant adsorption. Other physical processes of retention include precipitation, deposition, and trapping. Under natural conditions, pollutants often consist of more than a single contaminant, comprising a mixture of organic and inorganic toxic compounds. Each of these compounds can react differently with the existing minerals and chemicals in the subsurface. 

Fig. 8.25 Organic compound droplets in saline (30 g/L NaQ) water as captured by optical micrographs (a) benzene (b) toluene (c) xylene (d) TCE (e) benzene and TCE (f) xylene and TCE (g) oiganic compound mixture. Reprinted from Yaron-Marcovich D, Dror 1, Berkowitz B (2007) Behavior and stabihty of organic contaminant droplets in aqueous solutions. Chemosphere, 69 1593-1601, doi 10.1016/j.chemosphere.2007.05.056. Copyright 2007 with permission of Elsevier...

Microbial cleaners (MCs) are a mixture of specially selected microorganisms and biocatalysts designed for the bioremediation of organic contaminants in soil or water. According to the vendor, MCs have been used in multiple full-scale applications and are commercially available from EnviroLogic Engineering. 

The PO WW ER system was developed by Wheelabrator Clean Air Systems, Inc., a subsidiary of U.S. Filter Corporation, to reduce the volume of aqueous waste and catalytically oxidize volatile contaminants. PO WW ER is used to treat complex industrial and hazardous wastewaters containing mixtures of organic, inorganic, and radioactive contaminants. This proprietary, commercial technology combines evaporation with catalytic oxidation to concentrate and remove contaminants, producing a high-quality product water. 

A soln of the crude acid in THF (14 mL) was cooled to — 20 °C and treated with TEA (686 pL, 4.92 mmol) and ethyl chloroformate (470 pL, 4.92 mmol) and stirred for 30 min. A mixture of coned NHtOH (2mL) and THF (lOmL) was added and the mixture was stirred at -20°C for 30min and left standing at 5 °C for 18 h. The mixture was then poured into ice-cold 3 M HC1 and extracted with EtOAc. The combined organic extracts were dried (MgS04) and concentrated under reduced pressure. Partial purification of the residue by flash chromatography (silica gel, 3 x 20 cm, CHCl3/MeOH/AcOH 96 4 0.1) gave carboxamide (553 mg) as a mixture of diastereomers contaminated with ethyl carbamate. 

Geilsbjerg B, Klinge C, Madsen T. 2001. Mineralization of organic contaminants in sludge-soil mixtures. Environ Toxicol Chem20(4) 698-705. 

A substance is said to be chemically pure when it is made up of identical atoms and molecules. This means that the concept of purity can only apply to a single element or compound. As essential oils are made up of mixtures of organic compounds, they cannot be strictly chemically pure. Chemical purity and composition have to be related to an odour profile and be free from any contamination. Standard samples are used for reference when considering the purity of an essential oil, and the analytical techniques of GC-MS, refractive index and other methods previously described are applied. A standard sample or standard oil is a sample of a product that conforms to a specification for that product. It is kept for purposes of comparison with batch samples and used in quality evaluation. 

Haws NW, Ball WP, Bouwer EJ. 2006. Modeling and interpreting bioavailability of organic contaminant mixtures in subsurface environments. J Contain Hydrol 82 255-292. 

If H2O2 is added, the photochemical reduction of the Fe(III)-complex will be coupled to a Fenton reaction (Eq. 37) [56,80]. Thus, the use of illuminated mixtures of H2O2 and FeOx is very efficient for the photodegradation of organic contaminants the energy required to treat the same volume of a selected wastewater is ca. 20% of the energy required by the common photo-Fenton system [56,81,82],... 

Biodegradation of organic contaminants can be carried out by a single microbial species in pure cultures, but in nature the efforts of a mixture of microbes (a consortium) are usually required. The degradation process ranges from only minor structural changes to the parent molecule, known as primary degradation, to complete conversion to mineral constituents, for example C02 or H20, and termed mineralization ... 

Wastewater is often a mixture of organic and mineral pollutants [3], For example, urban sewage contains both anthropogenic and natural contaminants whose size distribution is very wide (Fig. 1). 

---