Evaluation of Partitioning Electron Donors for Enhanced Bioremediation of Chlorinated Solvent Source Zones
Sponsor: National Science Foundation, Division of Earth Sciences:
Hydrologic Sciences Program
Researchers: Natalie L. Cápiro (PI) and Kurt D. Pennell (co-PI)
Overall Project Objective:
Evaluate partitioning electron donors (PEDs) to enhance in-situ
bioremediation of dense non-aqueous phase liquids (DNAPLs)
trichloroethene (TCE) and tetrachloroethene (PCE).
- Determine if PEDs will have longer lifetimes in DNAPL source zones
than currently used soluble electron donors.
- Determine if PEDs will contribute to biologically enhanced
dissolution (increased rate of dissolution due to microorganisms).
Abiotic batches set-up in glass vials
containing aqueous PED and NAPL.
Biotic batches set-up with varying
NAPL and PED concentrations.
Task 1: PED Screening and Identification
Objective: Identify possible PED candidates, measure their mass
transfer rates, and determine if PEDs will support reductive dechlorination.
Approach: Three PED candidates were chosen; n-butyl acetate (nBA),
isopropyl propionate (IPP) and 2-ethyl-1-hexanol (2E1H). A series of
abiotic batches were performed to determine both the equilibrium
NAPL-water partitioning coefficient (Knw) and NAPL-water effective
rate of mass transfer (k). A series of biotic batches are in
progress to determine if PED candidates will be used as electron
donors in bioremediation.
Preliminary results: All PED candidates partition readily into the
NAPL phase. Commercially available PCE/TCE to ethene dechlorinating
consortium is able to degrade nBA for use as an electron donor.
Significance: PED candidates partition into the DNAPL phase and can
provide a source of electron donor.
Task 2: PED Mass Transfer Utilization in Dynamic Systems
Sand packed column injected with NAPL
Sand packed biotic column with emplaced
NAPL (dyed red of the left end) and 11
side ports used for sampling.
Objective: Measure PED partitioning under dynamic flow conditions.
Approach: Columns packed with Federal Fine Ottawa sand or Appling
soil and imbibed with residual NAPL. Abiotic columns were used to
determine the PED lifetime in the NAPL. Results were modeled and
equilibrium partitioning coefficient, effective mass transfer and
retardation factor were determined. Biotic columns will be used to
evaluate the PED partitioning and utilization when microbes are
Preliminary results: A single PED injection could last up to 20
times the injected pore volumes in PCE and 100 times in TCE.
Significance: PED delivery could reduce the need for frequent or
repeated electron donor injections, thereby improving the
effectiveness of bioremediation at chlorinated solvent sites
Task 3: PED Evaluation in Heterogeneous Flow Conditions
2-D aquifer cell used to evaluate PED
delivery under heterogeneous flow
conditions and source zone architectures.
Objective: Evaluate PED technology to treat DNAPL source zones under
heterogeneous flow conditions.
Approach: A 2-D aquifer cell will be packed with 40-50 or 20-30 mesh
Ottawa sand with layers of lower permeability sand (100-140 mesh) to
create a heterogeneous flow field. Microbes will be introduced
through selected side ports and the spatial and temporal changes in
local reductive dechlorination activity, substrate delivery and
consumption, and aqueous geochemistry will be characterized via the
analysis of side ports and effluent samples.
Significance: Results from this experiment will determine if PED
delivery at the DNAPL:water interface will promote microbial
colonization within ganglia and pooled DNAPL regions.
Task 4: Development and Evaluation of Mathematical Models to
Describe PED Deliver and Utilization for Microbial Reductive
Objective: Mechanistically interpret experimental studies, and
provide a means to predict and compare the performance of PEDs as a
function of system parameters.
Approach: Mathematical models using a modified dual Michaelis-Menten
model will be used to describe reaction kinetics of biotic batches.
Code for Estimating Non-Equilibrium Transport Parameters from
Miscible Displacement Experiments (CFITIM) as a part of Studio of
Analytical Models (STANMOD) will be used to stimulate measured PED
and nonreactive tracer effluent breakthrough curves from the abiotic
columns. Biotic columns and aquifer cells will be simulated using
MISER, a two-dimensional, finite element immiscible multiphase,
Significance: Models will be scaled to stimulate field-scale
scenarios that may be able to predict the performance of PEDs at
real world contaminated sites.
Awards, Presentations and Publications:
- Sylvia, D. F., R. D. Meade, K. D. Pennell, N. L. Cápiro.
"Partitioning Electron Donor Delivery for Chlorinated Solvent
Bioremediation" UCOWR-NIWR-CAUHSI conference; Medford, MA. June
- Sylvia, D. F., K.D. Pennell and N.L. Cápiro. "Partitioning
Electron Donor Delivery for Chlorinated Solvent Bioremediation"
Gordon Research Conference; Environmental Sciences: Water;
Holderness, NH, June 22-27, 2014.
- Sylvia, D. F., K. D. Pennell, N. L. Cápiro. "Evaluation of
Partitioning Electron Donors to Improve Chlorinated Solvent Source
Zone Bioremediation" International Conference of Soils, Sediments,
Water, and Energy; Amherst, MA. October 2014.
This material is based upon work supported by the National Science
Foundation under Grant Number (#1215837). Any opinions, findings,
and conclusions or recommendations expressed in this material are
those of the author(s) and do not necessarily reflect the views of
the National Science Foundation.