Benzene aerobic degradation

Benzene is one of a group of related aromatic monocyclic hydrocarbons (BTEX—benzene, toluene, ethylbenzene, and xylene), and since these are water soluble, there has been concern for their dissipation and persistence in groundwater under both aerobic and anaerobic conditions. Although aerobic growth at the expense of benzene was established many years ago, the pathway for its degradation was established only much later. The aerobic degradation of benzene by bacteria is... 

Salanitro (1993) has summarized the aerobic degradation rates for BTEX in laboratory subsoil-groundwater slurries and aquifers. The data indicate that decay rates for benzene are highest (19-52% per day) for benzene concentrations less than 1 ppm when initial dissolved oxygen levels are about 8 ppm. Rates are significantly reduced (0-1.1% per day) when benzene levels are 1-2 ppm, and no degradation was observed when benzene levels were greater than 2 ppb. 

From Table 2-7, an approximate aerobic degradation rate for benzene is 0.11/day. By assuming first-order decay,... 

Therefore, over 10% of the benzene may degrade in a 20-mi. reach. Due to the large uncertainty in the aerobic degradation rate estimate, this calculation provides only a crude approximation of the amount of benzene remaining. It is sufficient, however, to indicate that biodegradation may be significant over this reach of river. 

The pathways for the degradation of toluene and xylene under denitrifying and sulfate-reducing conditions have been studied most extensively, and they take place by reactions quite different from those used by aerobic bacteria. As an example, two anaerobes affiliated with known sulfate-reducing bacteria isolated from enrichments with crude oil were able to grow at the expense of a number of alkylated benzenes—strain oXySl with toluene, o-xylene, and o-ethyltoluene and strain mXySl with toluene, m-xylene, and m-ethyltoluene (Harms et al. 1999). 

The pathways for the aerobic biodegradation of alkylated benzenes have been elncidated in extensive investigations and have been discussed in Chapter 8, Part 1, so that only salient featnres are briefly snmmarized here. The genes for the degradation of toluene may be either chromosomal or... 

Dissolved in groundwater, benzene is gradually degraded by a variety of microorganisms present naturally in the subsurface. Under aerobic conditions, it attenuates by the reaction,... 

Haider, K.,Jagnow, G., Kohnen, R.. and Lim, S.U. Degradation of chlorinated benzenes, phenols, and cyclohexane derivatives by benzene- and phenol-utilizing bacteria under aerobic conditions, in Decomposition of Toxic and Nontoxic Organic Compounds in Soil Overcash. V.R., Ed. (Ann Arbor. MI Ann Arbor Science Publishers, 1981), pp. 207-223. 

Bioventing technology is applicable to contaminants in the vadose zone as well as contaminated regions just below the water table. It is applicable for any contaminant that degrades more readily aerobically than anaerobically. Most applications have targeted the less volatile petroleum hydrocarbons, although the technology has also remediated mixtures that include acetone, benzene, toluene, biphenyl, phenol, methylphenol, naphthalene, and polycyclic aromatic... 

Haider K, Jagnow G, Kohnen R, et al. 1974. [Degradation of chlorinated benzenes, phenols and cyclohexane derivatives by benzene and phenol utilizing soil bacteria under aerobic conditions.]... 

Chemical degradation reactions, primarily reaction with hydroxyl radicals, limit the atmospheric residence time of benzene to only a few days, and possibly to only a few hours. Benzene released to soil or waterways is subject to volatilization, photooxidation, and biodegradation. Biodegradation, principally under aerobic conditions, is the most important environmental fate process for water- and soil-associated benzene. 

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