Contributions of biotic and abiotic pathways to anaerobic trichloroethene transformation in low permeability source zones

Erin C. Berns, Robert A Sanford, Albert J Valocchi, Timothy J. Strathmann, Charles E. Schaefer, Charles J. Werth

Research output: Contribution to journalArticle

Abstract

Low permeability source zones sustain long-term trichloroethene (TCE)groundwater contamination. In anaerobic environments, TCE is transformed by both biological reductive dechlorination and abiotic reactions with reactive minerals. Little is known about the relative contribution of these two pathways as TCE diffuses from low permeability zones (LPZs)into high permeability zones (HPZs). This study combines a flow cell experiment, batch experiments, and a diffusion-reaction model to evaluate the contributions of biotic and abiotic TCE transformation in LPZs. Natural clay (LPZ)and sand (HPZ)from a former Air Force base were used in all experiments. In batch, the LPZ material transformed TCE and cis-1,2-dichloroethene (cis-DCE)to acetylene with pseudo first-order rate constants of 8.57 × 10−6 day−1 and 1.02 × 10−6 day−1, respectively. Biotic and abiotic pathways were then evaluated together in a bench-scale flow cell (16.5 cm × 2 cm × 16.5 cm)that contained a LPZ layer, with a source of TCE at the base, overlain by a HPZ continuously purged with lactate-amended groundwater. Diffusion controlled mass transfer in the LPZ, while advection controlled migration in the HPZ. The mass discharge rate of TCE and its biotic (cis-DCE and vinyl chloride)and abiotic (acetylene)transformation products were measured over 180 days in the flow cell effluent. Depth profiles of these compounds through the LPZ were determined after terminating the experiment. A one-dimensional diffusion-reaction model was used to interpret the effluent and depth profile data and constrain reaction parameters. Abiotic transformation rate constants for TCE to acetylene, normalized to in situ solids loading, were approximately 13 times greater in batch than in the flow cell. Slower transformation rates in the flow cell indicate elevated TCE concentration and/or further degradation of acetylene to other reduced gas compounds in the flow cell LPZ (thereby partially masking TCE abiotic transformation). Biotic and abiotic parameters used to interpret the flow cell data were then used to simulate a field site with a 300 cm thick LPZ. Abiotic processes contributed to a 2% reduction in TCE flux after 730 days. When abiotic rate constants were changed to that observed in batch, or to rate constants previously reported for a pyrite rich mudstone, the TCE flux reduction was 21% and 53%, respectively, after 730 days. Though biotic processes dominated TCE transformation in the flow cell experiment, the simulations indicate that abiotic processes have potential to significantly contribute to TCE attenuation in electron donor limited environments provided suitable reactive minerals are present.

Original languageEnglish (US)
Article number103480
JournalJournal of Contaminant Hydrology
Volume224
DOIs
StatePublished - Jul 2019

Fingerprint

Trichloroethylene
trichloroethylene
permeability
Acetylene
acetylene
Rate constants
experiment
Experiments
Minerals
Groundwater
Effluents
effluent
Fluxes
Vinyl Chloride
Dechlorination
groundwater
Advection
dechlorination
mineral

Keywords

  • Abiotic
  • Back diffusion
  • Biotic
  • Low permeability
  • Numerical model
  • Trichloroethene

ASJC Scopus subject areas

  • Environmental Chemistry
  • Water Science and Technology

Cite this

Contributions of biotic and abiotic pathways to anaerobic trichloroethene transformation in low permeability source zones. / Berns, Erin C.; Sanford, Robert A; Valocchi, Albert J; Strathmann, Timothy J.; Schaefer, Charles E.; Werth, Charles J.

In: Journal of Contaminant Hydrology, Vol. 224, 103480, 07.2019.

Research output: Contribution to journalArticle

@article{fd6a602298d44bf9909647a9c8001d31,
title = "Contributions of biotic and abiotic pathways to anaerobic trichloroethene transformation in low permeability source zones",
abstract = "Low permeability source zones sustain long-term trichloroethene (TCE)groundwater contamination. In anaerobic environments, TCE is transformed by both biological reductive dechlorination and abiotic reactions with reactive minerals. Little is known about the relative contribution of these two pathways as TCE diffuses from low permeability zones (LPZs)into high permeability zones (HPZs). This study combines a flow cell experiment, batch experiments, and a diffusion-reaction model to evaluate the contributions of biotic and abiotic TCE transformation in LPZs. Natural clay (LPZ)and sand (HPZ)from a former Air Force base were used in all experiments. In batch, the LPZ material transformed TCE and cis-1,2-dichloroethene (cis-DCE)to acetylene with pseudo first-order rate constants of 8.57 × 10−6 day−1 and 1.02 × 10−6 day−1, respectively. Biotic and abiotic pathways were then evaluated together in a bench-scale flow cell (16.5 cm × 2 cm × 16.5 cm)that contained a LPZ layer, with a source of TCE at the base, overlain by a HPZ continuously purged with lactate-amended groundwater. Diffusion controlled mass transfer in the LPZ, while advection controlled migration in the HPZ. The mass discharge rate of TCE and its biotic (cis-DCE and vinyl chloride)and abiotic (acetylene)transformation products were measured over 180 days in the flow cell effluent. Depth profiles of these compounds through the LPZ were determined after terminating the experiment. A one-dimensional diffusion-reaction model was used to interpret the effluent and depth profile data and constrain reaction parameters. Abiotic transformation rate constants for TCE to acetylene, normalized to in situ solids loading, were approximately 13 times greater in batch than in the flow cell. Slower transformation rates in the flow cell indicate elevated TCE concentration and/or further degradation of acetylene to other reduced gas compounds in the flow cell LPZ (thereby partially masking TCE abiotic transformation). Biotic and abiotic parameters used to interpret the flow cell data were then used to simulate a field site with a 300 cm thick LPZ. Abiotic processes contributed to a 2{\%} reduction in TCE flux after 730 days. When abiotic rate constants were changed to that observed in batch, or to rate constants previously reported for a pyrite rich mudstone, the TCE flux reduction was 21{\%} and 53{\%}, respectively, after 730 days. Though biotic processes dominated TCE transformation in the flow cell experiment, the simulations indicate that abiotic processes have potential to significantly contribute to TCE attenuation in electron donor limited environments provided suitable reactive minerals are present.",
keywords = "Abiotic, Back diffusion, Biotic, Low permeability, Numerical model, Trichloroethene",
author = "Berns, {Erin C.} and Sanford, {Robert A} and Valocchi, {Albert J} and Strathmann, {Timothy J.} and Schaefer, {Charles E.} and Werth, {Charles J.}",
year = "2019",
month = "7",
doi = "10.1016/j.jconhyd.2019.04.003",
language = "English (US)",
volume = "224",
journal = "Journal of Contaminant Hydrology",
issn = "0169-7722",
publisher = "Elsevier",

}

TY - JOUR

T1 - Contributions of biotic and abiotic pathways to anaerobic trichloroethene transformation in low permeability source zones

AU - Berns, Erin C.

AU - Sanford, Robert A

AU - Valocchi, Albert J

AU - Strathmann, Timothy J.

AU - Schaefer, Charles E.

AU - Werth, Charles J.

PY - 2019/7

Y1 - 2019/7

N2 - Low permeability source zones sustain long-term trichloroethene (TCE)groundwater contamination. In anaerobic environments, TCE is transformed by both biological reductive dechlorination and abiotic reactions with reactive minerals. Little is known about the relative contribution of these two pathways as TCE diffuses from low permeability zones (LPZs)into high permeability zones (HPZs). This study combines a flow cell experiment, batch experiments, and a diffusion-reaction model to evaluate the contributions of biotic and abiotic TCE transformation in LPZs. Natural clay (LPZ)and sand (HPZ)from a former Air Force base were used in all experiments. In batch, the LPZ material transformed TCE and cis-1,2-dichloroethene (cis-DCE)to acetylene with pseudo first-order rate constants of 8.57 × 10−6 day−1 and 1.02 × 10−6 day−1, respectively. Biotic and abiotic pathways were then evaluated together in a bench-scale flow cell (16.5 cm × 2 cm × 16.5 cm)that contained a LPZ layer, with a source of TCE at the base, overlain by a HPZ continuously purged with lactate-amended groundwater. Diffusion controlled mass transfer in the LPZ, while advection controlled migration in the HPZ. The mass discharge rate of TCE and its biotic (cis-DCE and vinyl chloride)and abiotic (acetylene)transformation products were measured over 180 days in the flow cell effluent. Depth profiles of these compounds through the LPZ were determined after terminating the experiment. A one-dimensional diffusion-reaction model was used to interpret the effluent and depth profile data and constrain reaction parameters. Abiotic transformation rate constants for TCE to acetylene, normalized to in situ solids loading, were approximately 13 times greater in batch than in the flow cell. Slower transformation rates in the flow cell indicate elevated TCE concentration and/or further degradation of acetylene to other reduced gas compounds in the flow cell LPZ (thereby partially masking TCE abiotic transformation). Biotic and abiotic parameters used to interpret the flow cell data were then used to simulate a field site with a 300 cm thick LPZ. Abiotic processes contributed to a 2% reduction in TCE flux after 730 days. When abiotic rate constants were changed to that observed in batch, or to rate constants previously reported for a pyrite rich mudstone, the TCE flux reduction was 21% and 53%, respectively, after 730 days. Though biotic processes dominated TCE transformation in the flow cell experiment, the simulations indicate that abiotic processes have potential to significantly contribute to TCE attenuation in electron donor limited environments provided suitable reactive minerals are present.

AB - Low permeability source zones sustain long-term trichloroethene (TCE)groundwater contamination. In anaerobic environments, TCE is transformed by both biological reductive dechlorination and abiotic reactions with reactive minerals. Little is known about the relative contribution of these two pathways as TCE diffuses from low permeability zones (LPZs)into high permeability zones (HPZs). This study combines a flow cell experiment, batch experiments, and a diffusion-reaction model to evaluate the contributions of biotic and abiotic TCE transformation in LPZs. Natural clay (LPZ)and sand (HPZ)from a former Air Force base were used in all experiments. In batch, the LPZ material transformed TCE and cis-1,2-dichloroethene (cis-DCE)to acetylene with pseudo first-order rate constants of 8.57 × 10−6 day−1 and 1.02 × 10−6 day−1, respectively. Biotic and abiotic pathways were then evaluated together in a bench-scale flow cell (16.5 cm × 2 cm × 16.5 cm)that contained a LPZ layer, with a source of TCE at the base, overlain by a HPZ continuously purged with lactate-amended groundwater. Diffusion controlled mass transfer in the LPZ, while advection controlled migration in the HPZ. The mass discharge rate of TCE and its biotic (cis-DCE and vinyl chloride)and abiotic (acetylene)transformation products were measured over 180 days in the flow cell effluent. Depth profiles of these compounds through the LPZ were determined after terminating the experiment. A one-dimensional diffusion-reaction model was used to interpret the effluent and depth profile data and constrain reaction parameters. Abiotic transformation rate constants for TCE to acetylene, normalized to in situ solids loading, were approximately 13 times greater in batch than in the flow cell. Slower transformation rates in the flow cell indicate elevated TCE concentration and/or further degradation of acetylene to other reduced gas compounds in the flow cell LPZ (thereby partially masking TCE abiotic transformation). Biotic and abiotic parameters used to interpret the flow cell data were then used to simulate a field site with a 300 cm thick LPZ. Abiotic processes contributed to a 2% reduction in TCE flux after 730 days. When abiotic rate constants were changed to that observed in batch, or to rate constants previously reported for a pyrite rich mudstone, the TCE flux reduction was 21% and 53%, respectively, after 730 days. Though biotic processes dominated TCE transformation in the flow cell experiment, the simulations indicate that abiotic processes have potential to significantly contribute to TCE attenuation in electron donor limited environments provided suitable reactive minerals are present.

KW - Abiotic

KW - Back diffusion

KW - Biotic

KW - Low permeability

KW - Numerical model

KW - Trichloroethene

UR - http://www.scopus.com/inward/record.url?scp=85064315699&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85064315699&partnerID=8YFLogxK

U2 - 10.1016/j.jconhyd.2019.04.003

DO - 10.1016/j.jconhyd.2019.04.003

M3 - Article

C2 - 31006532

AN - SCOPUS:85064315699

VL - 224

JO - Journal of Contaminant Hydrology

JF - Journal of Contaminant Hydrology

SN - 0169-7722

M1 - 103480

ER -