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Enhanced dechlorination of chlorinat...

Hoelen, Thomas Peter.

Enhanced dechlorination of chlorinated ethylenes in sulfidogenic aquifers.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Enhanced dechlorination of chlorinated ethylenes in sulfidogenic aquifers.
Author:	Hoelen, Thomas Peter.
Description:	74 p.
Notes:	Adviser: Martin Reinhard.
Notes:	Source: Dissertation Abstracts International, Volume: 66-01, Section: B, page: 0475.
Contained By:	Dissertation Abstracts International66-01B.
Subject:	Engineering, Environmental.
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3162327
ISBN:	0496962140

Enhanced dechlorination of chlorinated ethylenes in sulfidogenic aquifers.
Hoelen, Thomas Peter.

Enhanced dechlorination of chlorinated ethylenes in sulfidogenic aquifers. - 74 p.

Adviser: Martin Reinhard.

Thesis (Ph.D.)--Stanford University, 2005.

In sulfidogenic aquifers dechlorination of perchloroethylene (PCE) and trichloroethylene (TCE) by dehalogenating bacteria (DHB) is often incomplete, causing accumulation of cis-dichloroethylene (cDCE) and vinyl chloride (VC). Research described in this dissertation addresses this problem through coordinated laboratory and field experiments. Laboratory studies demonstrated dechlorination of approximately 100 muM PCE to ethylene in the presence of more than 1.5 mM sulfate over a period of more than three years. Hydrogen concentrations were 1.6 +/- 0.2 nM during dechlorination of cDCE and VC and increased during sulfate reduction to 2.5 +/- 0.3 nM in the absence of dechlorination. These data show that DHB can outcompete sulfate-reducing bacteria at low hydrogen levels. When hydrogen was added in excess, removal of 2 mM sulfate and dechlorination of 130 muM PCE to ethylene occurred simultaneously and were completed in less than 15 days. These results indicated that dechlorination by DHB can be enhanced by depleting sulfate. A protocol was developed by which sulfate was removed biologically with an excess of electron donor. This protocol was evaluated at the pilot scale at a sulfidogenic site (Moffett Federal Airfield, Mountain View, CA) where the groundwater was contaminated with approximately 1000 muM cDCE and 100 muM VC, and contained approximately 200 mg/L sulfate. Microcosm studies indicated that dechlorinating activity was sparse and unevenly distributed across the site. However, dechlorination rates were strongly enhanced when sediment samples from multiple wells and depths were combined in one composite microcosm. This observation suggested that uneven distribution of nutrients and requisite bacteria is a factor limiting contaminant removal. Data obtained in the pilot-scale field test was consistent with this hypothesis. In this test, the groundwater was amended with approximately 150 mg/L propionate and distributed into the subsurface using a recirculating well pair. Sulfate reduction and dechlorination commenced within four days after propionate amendment. Complete sulfate removal and near-complete transformation of cDCE to ethylene without methane formation was observed after two months of operation. Reaction rates increased with time, indicating growth of dechlorinating communities. Increasing water levels in one of the treatment wells suggests aquifer clogging by sulfate-reducing bacteria and insoluble metal sulfides.

ISBN: 0496962140Subjects--Topical Terms:

212478
Engineering, Environmental.

Enhanced dechlorination of chlorinated ethylenes in sulfidogenic aquifers.
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502 $a Thesis (Ph.D.)--Stanford University, 2005.
520 # $a In sulfidogenic aquifers dechlorination of perchloroethylene (PCE) and trichloroethylene (TCE) by dehalogenating bacteria (DHB) is often incomplete, causing accumulation of cis-dichloroethylene (cDCE) and vinyl chloride (VC). Research described in this dissertation addresses this problem through coordinated laboratory and field experiments. Laboratory studies demonstrated dechlorination of approximately 100 muM PCE to ethylene in the presence of more than 1.5 mM sulfate over a period of more than three years. Hydrogen concentrations were 1.6 +/- 0.2 nM during dechlorination of cDCE and VC and increased during sulfate reduction to 2.5 +/- 0.3 nM in the absence of dechlorination. These data show that DHB can outcompete sulfate-reducing bacteria at low hydrogen levels. When hydrogen was added in excess, removal of 2 mM sulfate and dechlorination of 130 muM PCE to ethylene occurred simultaneously and were completed in less than 15 days. These results indicated that dechlorination by DHB can be enhanced by depleting sulfate. A protocol was developed by which sulfate was removed biologically with an excess of electron donor. This protocol was evaluated at the pilot scale at a sulfidogenic site (Moffett Federal Airfield, Mountain View, CA) where the groundwater was contaminated with approximately 1000 muM cDCE and 100 muM VC, and contained approximately 200 mg/L sulfate. Microcosm studies indicated that dechlorinating activity was sparse and unevenly distributed across the site. However, dechlorination rates were strongly enhanced when sediment samples from multiple wells and depths were combined in one composite microcosm. This observation suggested that uneven distribution of nutrients and requisite bacteria is a factor limiting contaminant removal. Data obtained in the pilot-scale field test was consistent with this hypothesis. In this test, the groundwater was amended with approximately 150 mg/L propionate and distributed into the subsurface using a recirculating well pair. Sulfate reduction and dechlorination commenced within four days after propionate amendment. Complete sulfate removal and near-complete transformation of cDCE to ethylene without methane formation was observed after two months of operation. Reaction rates increased with time, indicating growth of dechlorinating communities. Increasing water levels in one of the treatment wells suggests aquifer clogging by sulfate-reducing bacteria and insoluble metal sulfides.
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