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Handbook of Solvents - George Wypych - ChemTech - Ventech!

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1588 Hanadi S. Rifai, Charles J. Newell, Todd H. Wiedemeier<br />

23.1.4 BIODEGRADATION RATES FOR CHLORINATED SOLVENTS<br />

Overall, dechlorination is more rapid for highly chlorinated compounds than for compounds<br />

that are less chlorinated. 38,86,87 Figure 23.1.5 qualitatively shows the reaction rate<br />

and required conditions for halorespiration <strong>of</strong> PCE to ethene. PCE (four chlorines) degrades<br />

the fastest under all anaerobic environments, while VC (a single chlorine) will degrade only<br />

under sulfate-reducing and methanogenic conditions, with a relatively slow reaction rate.<br />

At many chlorinated ethene sites, concentrations <strong>of</strong> cis-1,2-DCE are <strong>of</strong>ten higher than<br />

any <strong>of</strong> the parent chlorinated ethene compounds. The reason for the accumulation <strong>of</strong><br />

1,2-DCE may be due to either slower rates <strong>of</strong> DCE halorespiration, or the prevalence <strong>of</strong> organisms<br />

that reduce PCE as far as cis-1,2-DCE over ones that can reduce PCE all the way to<br />

ethene. 48 Although many researchers have commented that reductive dechlorination will result<br />

in the accumulation <strong>of</strong> VC (e.g., see 84, 89), at many field sites VC accumulation is<br />

much lower than cis-1,2-DCE. This may occur because the vinyl chloride in many chlorinated<br />

solvent plumes can migrate to zones that can support direct oxidation <strong>of</strong> VC oxidation,<br />

either aerobically and/or anaerobically.<br />

Suarez and Rifai 90 analyzed data from 138 studies (field and laboratory) to estimate<br />

biodegradation coefficients for chlorinated compounds. Suarez and Rifai 90 found a total <strong>of</strong><br />

thirteen studies that reported Michaelis-Menten kinetics, 28 studies that reported zero-order<br />

rates, and 97 studies that reported first-order constants.<br />

23.1.4.1 Michaelis-Menten rates<br />

The data in Table 23.1.5 present the Michaelis Menten kinetic data from Suarez and Rifai. 90<br />

Half-saturation constants varied from 0.6 mg/L to 29.5 mg/L for TCE and from 0.17 mg/L<br />

to 28 mg/L for DCE. Maximum specific degradation rates were within the ranges<br />

0.038-478.59 mgcompound/mgprotein-day for TCE, and 0-11,115 mgcompound/mgprotein-day for<br />

DCE.<br />

Table 23.1.5. Michaelis-Menten parameters for chlorinated solvents<br />

Compound<br />

Type <strong>of</strong> study<br />

1,1,1-TCA Continuous<br />

reactor<br />

1,1-DCE<br />

1,2-DCA<br />

Growth<br />

reactor<br />

Continuous<br />

reactor<br />

Continuous<br />

reactor<br />

Redox<br />

environment<br />

Aerobic<br />

Aerobic-<br />

Cometabolism<br />

(methane)<br />

Aerobic<br />

Aerobic<br />

Culture<br />

Methylosinus<br />

trichosporium<br />

OB3b<br />

Mixed<br />

methanotrophic<br />

culture<br />

Methylosinus<br />

trichosporium<br />

OB3b<br />

Methylosinus<br />

trichosporium<br />

OB3b<br />

μ max , day -1<br />

Half-saturation,<br />

Ks, mg/L<br />

Yield, Y, mg/mg<br />

Max. spec. degradation<br />

rate,<br />

μ max /Y,<br />

mg/mg-day<br />

Initial concentration,<br />

So,<br />

mg/L<br />

Ref<br />

28.46 4.60 >93.10 92<br />

1.37 0.43 0-11115 0.01 93<br />

0.48 0.84 1.94-2.91 92<br />

7.62 9.26 4.95-6.93 92

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