Flux and Product Distribution during Biological Treatment of Tetrachloroethene Dense Non-Aqueous-Phase Liquid

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• 作者：David T. Adamson ; Delina Y. Lyon ; and Joseph B. Hughes
• 刊名：Environmental Science & Technology
• 出版年：2004
• 出版时间：April 1, 2004
• 年：2004
• 卷：38
• 期：7
• 页码：2021 - 2028
• 全文大小：114K
• 年卷期：v.38,no.7(April 1, 2004)
• ISSN：1520-5851

文摘

Flux in non-aqueous-phase liquid (NAPL)-contaminatedsystems containing active microbial populations (includingDehalococcoides sp.) was investigated using a quantitativemass balance and phase distribution approach. Batch systemscontaining mixed NAPL with an initial tetrachloroethene(PCE) mole fraction ranging from 0.1 to 0.4 provided a meansfor comparing systems where mass transfer and aqueousconcentration were controlled by the initial NAPLcomposition. Although the use of mixed NAPL withincreasing PCE mole fractions introduced a mass-transfervariable on the abiotic dissolution rate, it was determinedthat biological systems produced flux rates that were similarto each other regardless of the initial PCE mole fraction.Thus, organisms appeared to be dechlorinating near theirmaximum conversion rates, and the result was theaccumulation of cis-1,2-dichloroethene (cDCE) followed byslow conversion to vinyl chloride (VC). Increases in theinitial PCE mole fractions in the NAPL had a negative impacton product distribution due to the presence of a largerconcentration of a more favorable electron acceptor. Becausethe mass converted to cDCE was present largely in thedissolved phase in all systems, the production of thismetabolite was a favorable outcome in terms of NAPLdissolution. The pH dropped as low as 4.9 in active systems,indicating that the amount of HCl released during thereductive dechlorination process was large enough tooverwhelm the buffering capacity. This pH effect was morepronounced in systems that exhibited extensive dechlorination to VC, further suggesting that rapid dechlorinationof PCE NAPL can alter chemical characteristics insource zone regions.