BTEX compounds

Preliminary laboratory data demonstrate the feasibility of removing Pb, Cr, Cd, Ni, Cu, Zn, As, TCE, BTEX compounds, and phenol from soils (clays and sandy clayey deposits, and dredged sediments) using EO technology. It has been demonstrated that 75 to 95% of Pb can be removed across the cell, in which a significant amount of the removed Pb can be electroplated at the cathode. 

The monoaromatic compounds benzene, toluene, ethylbenzene and xylene, commonly found in crude oil, are often jointly called BTEX compounds. The most harmful of these compounds is benzene, which is a known carcinogen. BTEX compounds occur naturally near natural gas and petroleum deposits and are detected in the fumes of forest fires. Most of the highly volatile BTEX compounds released by human activity originate from fuel use and end up as pollutants in the air. Inhaling BTEX-polluted air is also the greatest hazard to humans by these compounds. BTEX compounds are water-soluble, and therefore, improper handling can also cause groundwater contamination. 

Jaynes WF, Vance GF (1999) Sorption of benzene, toluene, ethylbenzene and xylene (BTEX) compounds by hectorite clays exchanged with aromatic organic cations. Clays Clay Miner 47 358-365 Johnston CT, De Oliveira MF, Teppen BJ, Sheng G, Boyd SA (2001) Spectroscopic study of nitroaromatic-smectite sorption mechanisms. Environ Sci Technol 35 4767-4772... 

Hexane is contained in a variety of products commonly used in household settings. Given its volatility, this creates possibilities for exposures from inhalation as well as by dermal contact and ingestion. In a study of over 1,000 common household products, -hexanc was detected in 101 products, about the same detection rate as for BTEX compounds (e g., benzene, toluene, xylene or ethylbenzene) and other normal alkanes. -Hexane was detected in more than 10% of the items sampled in the following product categories automotive products oils, greases and lubricants and adhesive-related products (Sack et al. 1992). 

Without appropriate cleanup measures, BTEX often persist in subsurface environments, endangering groundwater resources and public health. Bioremediation, in conjunction with free product recovery, is one of the most cost-effective approaches to clean up BTEX-contaminated sites [326]. However, while all BTEX compounds are biodegradable, there are several factors that can limit the success of BTEX bioremediation, such as pollutant concentration, active biomass concentration, temperature, pH, presence of other substrates or toxicants, availability of nutrients and electron acceptors, mass transfer limitations, and microbial adaptation. These factors have been recognized in various attempts to optimize clean-up operations. Yet, limited attention has been given to the exploitation of favorable substrate interactions to enhance in situ BTEX biodegradation. 

BTEX bioremediation projects often focus on overcoming limitations to natural degradative processes associated with the insufficient supply of inorganic nutrients and electron acceptors. However, other limitations associated with the presence and expression of appropriate microbial catabolic capacities may also hinder the effectiveness of bioremediation. Thus, while subsurface addition of oxygen or nitrate has proven sufficient to remove BTEX below detection levels [134,145,292,315,316], it has been only marginally effective at some sites [6]. Sometimes, the concentration of a target BTEX compound fails to decrease below a threshold level even after years of continuous addition of nutrients and electron acceptors [317]. This phenomenon has also been observed for many other xenobiotic and natural substrates under various experimental conditions [327-332]. 

Except for short-term hazards from concentrated spiUs, BTEX compounds (benzene, toluene, ethylbenzene, and xylenes) have been more frequently associated with risk to humans than with risk to nonhuman species such as fish and wildlife. This is partly because plants, fish, and birds take up only very small amounts, and because this volatile compound tends to evaporate into the atmosphere rather than persisting in surface waters or soils. However, volatiles such as this compound can pose a drinking water hazard when they accumulate in groundwater. See also BTEX entry, and entries for benzene, toluene, ethylbenzene, and xylenes. 

Petroleum refineries are a somce of hazardous and toxic air pollutants, such as BTEX compounds (benzene, toluene, ethylbenzene, and xylene). They are also a major source of criteria air pollutants particulate matter (PM), nitrogen oxides (NO t), carbon monoxide (CO), hydrogen sulfide (H2S), and sulfur oxides (SO ). 

In testing, this technology was effective in treating waste streams contaminated with benzene, toluene, ethylbenzene, and xylenes (BTEX compounds). The technology is not in use at present and is not commercially available. 

The technology is applicable to chlorinated and nonchlorinated VOCs methyl tertiary butyl ether (MTBE) dichloroethylene (DCE), trichloroethylene (TCE), and tetrachloroethylene (per-chloroethylene, PCE) dichloroethane (DCA) vinyl chloride alcohols ethers ketones and halogenated and nonhalogenated paraffinic, olefinic, aliphatic, and aromatic hydrocarbons. It is very effective at treating benzene, toluene, ethylbenzene, and xylene (BTEX) compounds and any oxygenate, such as acetone or isopropanol. 

The quantity of aromatic contaminants that adsorb onto TiO2 surfaces is also relatively low. d Hennezel and Ollis [47] measured the dark adsorption of the BTEX compounds at a gas-phase concentration of 50 mg/m . Benzene displays the lowest dark adsorption, followed by ethylbenzene. Higher dark adsorption was observed for toluene and xylenes. At 50 mg/m, the dark adsorption of m-xylene was nearly 10 times that of benzene (Table 1). 

What are the major sources of the BTEX compounds in the environment Why are these compounds considered to be a problem ... 

Benzene is the simplest aromatic hydrocarbon, perhaps the most recalcitrant of the BTEX compounds, and of greatest regulatory concern because of its associated health impacts. Until recently, benzene was believed to be completely resistant to attack under anaerobic conditions, a view supported by the majority of both field and laboratory investigations (Table 3-1). 

All studies use aquifer sediments and/or groundwater unless otherwise indicated, (ind) - tested individually, rather than as a group of BTEX compounds. 

This work is dedicated to the memory of Dunja Grbif-Galif. Her initial work in this area was critical in demonstrating that the anaerobic transformation of BTEX compounds can occur. Subsequent studies done in her lab, as illustrated in this review, has provided a basis for our general interpretation of the fate of BTEX compounds in the environment. 

Arcangeli,J. P. Arvin, E. (1994). Biodegradation of BTEX compounds in a biofilm system under nitrate-reducing conditions. In Hydrocarbon Bioremediation, ed. R. E. Hinchee, B. C. Alleman, R. E. Hoeppel R. N. Miller, pp. 374—82. Boca Raton, FL Lewis Publishers. 

Barlaz, M. A., Shafer, M. B., Borden, R. C. Wilson, J. T. (1993). Rate and extent of natural anaerobic bioremediation of BTEX compounds in ground water plumes. Symposium on Bioremediation of Hazardous Wastes Research, Development, and Field Evaluations. May 4-6 Dallas, Texas. 

Patterson, B. M., Pribac, F., Barber, C., Davis, G. B. Gibbs, R. (1993). Biodegradation and retardation of PCE and BTEX compounds in aquifer material from Western Australia using large-scale columns. Journal of Contaminant Hydrology, 14, 261-78. 

Suarez and Rifai [31] report first-order and Monod rate constants for the aerobic biodegradation of BTEX compounds in laboratory and field studies. 

It has been demonstrated that BTEX compounds can readily be oxidized using nitrate as an electron acceptor [29,40-42]. With only a few exceptions (for instance, ethylbenzene has not been demonstrated to degrade under sulfate-reducing conditions), BTEX oxidation using sulfate, carbon dioxide, ferric iron,... 

Interaction between the different BTEX compounds is accounted for through the microbial growth term, as follows ... 

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