PAHs Dissolved in nDodecane Standard Emulsion

An interesting question regarding the biodegradation of n-dodecane droplets (standard emulsion, Section 9.4.2) and the biodegradable PAHs dissolved inside the droplets is: will both be oxidized at the same reaction rate?

Indeed, the results published by Cuno (1996) seem to confirm this assumption. Although n-dodecane, acenaphthene and anthracene are biodegraded by bacteria at different growth rates (Tables 9.7 and 9.8), the results in Fig. 9.5 can be described approximately by Eqs. (9.2) and (9.3), using the same kinetic coefficients for all three substrates.

A possible model to gain insight into these results is the transfer of very small oil droplets with dissolved PAHs into the bacterial cell. PAHs such as pyrene, dissolved in non-biodegradable, and in water-insoluble substances such as heptame-thylnonane, can be used by bacteria such as Rhodococcus sp. at a considerably higher rate than those dissolved in the aqueous medium (Bouchez et al. 1997). PAHs need a solving agent which may be biodegradable (n-alkanes) or not (heptamethyl-nonane). Naphthalene and phenanthrene as well as the solving agent hexadecane can also be mineralized by sulfate-reducing bacteria, which could be proven with 14C-labeled substances (Coates et al. 1997; Zhang and Young 1997).

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