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Experimental Study of Biodegradation of Ethanol and Toluene Vapors

Experimental Study of Biodegradation of Ethanol and Toluene Vapors

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The stoichiometry <strong>of</strong> the biomass synthesis from ethanol can be expressed in 1 C-mol <strong>of</strong><br />

biomass formed as:<br />

- .27CH O − 0.2NH<br />

− α<br />

E<br />

ATP − 0.305H<br />

O 1. 81NAD<br />

1<br />

3 0.5<br />

3 1<br />

2<br />

−<br />

+ CH O N + .27CO<br />

+ 1.81NADH<br />

+ α ADP 0 (5-3)<br />

1 .4 0.4 0.2<br />

0<br />

2<br />

2 1E<br />

=<br />

Where CH is the expression <strong>of</strong> 1-C-mol <strong>of</strong> ethanol ( H O ), while<br />

3O 0.5<br />

C 2 6<br />

CH 1.4<br />

O 0.4<br />

N 0. 2<br />

is the expression <strong>of</strong> 1 C-mol <strong>of</strong> biomass (C5H 7 O 2 N). The biomass composition<br />

(C 5 H 7 O 2 N) is based on the formula proposed by McCarty (1975) <strong>and</strong> was used by<br />

Brown (2000) for the composition <strong>of</strong> Pseudomonas putida (ATCC 23973). In Equation<br />

5-3, α 1E represents the amount <strong>of</strong> ATP used in the biomass synthesis reactions <strong>and</strong> is<br />

given by:<br />

mATP<br />

α1 E<br />

= K +<br />

when μ > 0<br />

(5-4)<br />

μ<br />

in which μ is the specific biomass growth rate (h -1 ) <strong>and</strong> m ATP /μ is the amount <strong>of</strong> ATP<br />

consumed by the biomass maintenance processes (Roels, 1983). In this equation,<br />

NADH 2 st<strong>and</strong>s for reducing equivalents in the form <strong>of</strong> NADH 2 or any other equivalent<br />

form <strong>of</strong> metabolic reductant.<br />

(2) Catabolism <strong>of</strong> <strong>Ethanol</strong><br />

The catabolic pathways supply the required ATP <strong>and</strong> NADH for biomass<br />

synthesis. Reactions (5-5) – (5-10) summarize the overall stoichiometry for the<br />

catabolic pathways. Initially, ethanol is oxidized by dehydrogenases to form an<br />

aldehyde (Equation 5-5), then to acetic acid (Equation 5-6), which can be metabolized<br />

to acetyl-CoA through the beta-oxidation pathway with consumption <strong>of</strong> ATP (Equation<br />

83

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