Naphthalene aerobic degradation

Fig. 3. Initial steps in the aerobic degradation of naphthalene, as a representative multiringed aromatic, and toluene. The different initial steps of toluene...

The bacterial aerobic degradation of pyrene is initiated by the formation of cfi-pyrene-4,5-dihydrodiol. Analysis for this metabolite was used to demonstrate the biodegradability of pyrene in an environment in which there was continuous input of the substrate, when it was not possible to use any diminution in its concentration as evidence for biodegradation (Li et al. 1996). The corresponding metabolite from naphthalene—cfi-naphthalene-1,2-dihydrodiol—has been used to demonstrate biodegradation of naphthalene both in site-derived enrichment cultures and in leachate from the contaminated site (Wilson and Madsen 1996). 

The aerobic degradation of naphthalene and its derivatives has been extensively examined, so that the pathway, biochemistry, and genetics are well established. 

Benzothiophene is isoelectronic with naphthalene, dibenzothiophene with anthracene, and benzothiazole with quinoline, and this is reflected in their aerobic degradation that is initiated by dioxygenation. The diversity of pathways for the degradation of dibenzothiophene is illustrated by the following examples ... 

Much less is known about the enzymes or the pathways used for anaerobic PAH degradation than about those used for aerobic degradation. Naphthalene, however, is usually metabolized anaerobically via 2-naphthoic acid (Meckenstock et al., 2004). 

Biological. In activated sludge, 9.0% of the applied amount mineralized to carbon dioxide after 5 d (Freitag et al, 1985). Under certain conditions. Pseudomonas oxidized naphthalene to cis-1,2-dihydro-1,2-dihydroxynaphthalene (Dagley, 1972). This metabolite may be oxidized by Pseudomonasputida to carbon dioxide and water (Jerina et ah, 1971). Under aerobic conditions, Cunninghamella elegans degraded naphthalene to 1-naphthol, 2-naphthol, trans-l, 2-A hyAxoxy-... 

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... 

The aromatic degradative pathways receiving the most attention include those for toluene, benzoate, PCBs, and naphthalene. Five completely independent routes of toluene catabolism have been well characterized for aerobic bacteria (Figure 11.1). To date, all five pathways have been described in Pseudomonas and Burkholderia, despite the fact that at least two have been shown to be encoded by broad-host-range degradative plasmids. 

The available knowledge about transformation processes of chlorinated naphthalenes is very limited. Only few investigations on the aerobic metabolism have been conducted and have revealed hydroxylation to be the most important initial transformation reaction (Jacobson and Asplund 2000, and references cited therein). Information on anaerobic degradation... 

State, types of functional groups), redox potential, pH, nutrient and carbon availability, contaminant bioavailability and concentration, electron acceptors, temperature, salinity, and microbial consortia and biomass (D Angelo, 2002). Reaction rates can vary over several orders of magnitude depending on these environmental factors. Studies have documented the effects of several of these factors on rates of mineralization of contaminants in wetland substrates. Redox potential, a measure of the electron availability and an indirect measure of the oxygen status, has been used to show certain compounds degrade favorably under aerobic conditions (e.g., naphthalene), others under anaerobic conditions (e.g., DDT), and still others under moderately anaerobic conditions (e.g., polychlorobi-phenyls [PCBs]). 

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