A Semi-Passive Permeable Reactive Barrier (PRB) Remediation Technology Using Membrane-Attached Biofilms

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A Semi-Passive Permeable Reactive Barrier (PRB)
Remediation Technology Using Membrane-Attached
Biofilms

• Lee Clapp
• Bala Veerasekaran
• Vipin Sumani
• February 5, 2003

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Chlorinated solvents (e.g., PCE TCE) are used
for industrial vapor degreasing
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Problem Improper disposal of chlorinated solvents
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Magnitude of Problem

• DoD
• 22,089 identified contaminated sites (1995)
• 49 contaminated with chlorinated solvents.
• Estimated cost of remediation - 28.6 billion.
• DOE
• 10,500 identified contaminated sites (1996)
• 25 contaminated with chlorinated solvents.
• Estimated cost of remediation - 63 billion
• Estimated time for remediation - 75 years
• NEED - Development of technologies to reduce
  remediation costs.
• (Ref EPA-542-R-96-005)

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Overall Research Goal
To develop a semi-passive membrane permeable
reactive barrier (PRB) remediation technology
that fosters biological destruction of
chlorinated organic compounds by the controlled
delivery of soluble methane oxygen gas into the
subsurface.
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DNAPL Contamination
EPA, 2003
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Recovery of Free Product
EPA, 2003
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Pump Treat
EPA, 2003
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Permeable Reactive Barrier (PRB) Remediation
Technology
Regenesis, 2003
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GeoprobeTM Direct Push Technology
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Passive Membrane PRB System at TCAAP Superfund
Site
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Two processes for chlorinated solvent
biodegradation

• (1) Reductive dechlorination removes one chlorine
  at a time (anaerobic).

• (2) Cometabolic oxidation results in gt99
  mineralization (aerobic).

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• (1) Previous research with reductive
  dechlorination processes

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Using hollow-fiber membranes to supply H2 to
contaminated aquifers
flow
aquaclude
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Problems with enhanced reductive dechlorination
for CAH remediation.

• Accumulation of intermediate transformation
  products (DCE VC).
• Microbial competition for H2.
• MCLs below threshold concentrations required for
  dechlorinator growth.
• Aquifer biofouling.
• Adverse impact on groundwater quality.

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soil column reactors
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Membrane Module (single fiber)
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Concentrations of PCE byproducts in test column
(H2 added) after 1 year
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Concentrations of PCE byproducts in control
column (no H2) after 1 year
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Concentrations of PCE byproducts in test column
after 1 year
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Concentrations of H2 in control column after 1
year
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Model predictions for H2 concentrations over time
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Simulated aquifer studies
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• Previous research with cometabolic (aerobic)
  degradation processes

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What if CH4-utilizing bacteria grew as biofilms
on surface of membranes?

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Biofilm stratification
membrane
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SEM of biofilm cross-section
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Biofilm viability staining
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Other modeling studies

• Olaf Cirpka at Stanford has modeled different
  strategies for minimizing biofouling in aquifers.

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Two obstacles

• How can capture zone for each well be
  increased? - Bala
• Will presence of copper in groundwater repress
  expression of operative TCE-degrading enzyme
  (sMMO)? - Vipin

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Research Topic

• Characterizing effect of superimposed transverse
  flow on well capture zone.

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Decreasing CH4 zone of influence due to
microbial accumulation
GW flow
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Research Objectives

• Phase 1 Characterize relationship between
  well-spacing, inter-well pumping rate, and
  capture zone.
• Phase 2 Characterize relationship between
  well-spacing, inter-well pumping rate, and DCE
  removal efficiency.

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Modeling Methods

• GMS (Groundwater Modeling System)
• ModFlow
• ModPath
• RT3D

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Basic Concepts in Groundwater Flow

• Darcys Law Qx -KxA (h2 h1)/L
• Time taken for a particle to travelt LnA/Q
• t-Time ,L-Length of the Sample, n-Aquifer
  porosity, A-Area, Q-Flow Rate

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Capture Zone

• The capture zone defines the area of an aquifer
  that will contribute water to an extraction well
  within a specified time period.

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Well capture zone
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Assumed Parameter Values

• Grid 20 ft ? 20 ft.
• Aquifer Hydraulic Conductivity 8.42ft/day
• Head Left10ft , Right9.57ft
• Aquifer Porosity0.35
• Well Hydraulic Conductivity842 ft/day
• Well Porosity1.0
• Unconfined Aquifer

ref Wilson MacKay, 1997.
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Isopotential Lines
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Particle Paths (Flow Direction)
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Capture zone without pumping
Unpumped Well
Unpumped Well
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Capture zone with pumping
injection well
extraction well
injection well
extraction well
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Conceptualized flow field capture vs. of
wells pumping rate
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Research Topic

• Characterizing effect of copper loading on sMMO
  expression in membrane-attached methanotrophic
  biofilms.

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Copper Loading Effect on sMMO Expression in
Membrane-Attached Methanotrophic Biofilms

• Methanotrophs - methane oxidizing bacteria.
• They are of two types Type 1 and Type 2.
• Methane is oxidized by methanotrophs to CO2 via
  intermediates like methanol and formaldehyde.
• Two enzymes sMMO and pMMO play an important role
  for the oxidation of CH4.
• sMMO co-oxidizes a wide range of alkanes
  alkenes, including chlorinated hydrocarbons.
• Cu inhibits sMMO activity.

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Problems associated with copper repression of
sMMO
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CH4 Oxidation and TCE Degradation Pathways
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Hypotheses

• Methanotrophic biofilms can express sMMO at
  higher copper loading rates than planktonic
  cultures.
• Copper will adsorb to the inactive biomass near
  the biofilm surface.
• High cell growth rates will dilute copper present
  in the biofilm interior thus sMMO expression
  will not be repressed.

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Copper will adsorb to surface of
counter-diffusional biofilms?
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Research Objectives

• Characterize sMMO expression as function of
• Copper loading.
• CH4/O2 partial pressures.
• Time (hard to predict at this moment).

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Experimental Methods

• Membrane-attached methanotrophic biofilms will be
  cultivated.
• A nitrate mineral salts medium with will be used
  to supply nutrients (N, P, etc.).
• High CH4 and O2 partial pressures will promote
  development of thick biofilms.

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Membrane-attached methanotrophic biofilm formation
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Analytical Methods

• Headspace GC/ECD (electron capture detector) for
  TCE.
• Headspace GC/TCD (thermal conductivity detector)
  for CH4.
• IC for chloride ion.
• DO meter.
• pH meter, etc.

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Expected Results
sMMO
TCE degradation rate
pMMO
YJCH4 /JCU