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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. Chlorinated solvents (e.g., PCE & TCE) are used for industrial vapor degreasing. Problem:

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Lee Clapp Bala Veerasekaran Vipin Sumani February 5, 2003

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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


Chlorinated solvents (e.g., PCE & TCE) are used for industrial vapor degreasing


Problem:

Improper disposal of chlorinated solvents


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)


Hollow-Fiber Membrane

Semi-Passive

Permeable Reactive Barrier

DCE

CO2 + Cl-

VC

CO2 + Cl-

CH4

Water Table

CH4

Groundwater

flow

CH4

Confining

Contaminant

Biofilm

Bacterium

Layer

Plume

Hollow Fiber

Membrane

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.


DNAPL Contamination

EPA, 2003


Recovery of “Free Product”

EPA, 2003


Pump & Treat

EPA, 2003


Wells loaded with HRC or ORC

Permeable Reactive Barrier (PRB) Remediation Technology

Regenesis, 2003


GeoprobeTM Direct Push Technology


hydrogen added to these wells

H2initially detected in these wells

& a sampling well 6 ft downstream

direction of groundwater flow

Passive Membrane PRB System at TCAAP Superfund Site


H2 HCl H2 HCl H2 HCl H2 HCl

PCE TCE cis-DCE VC ETH

O2

TCE  CO2 + Cl-

CH4

Two processes for chlorinated solvent biodegradation

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

  • (2) Cometabolic oxidation results in >99% mineralization (aerobic).


(1) Previous research with reductive dechlorination processes


H2 gas

4H2

2H2O

Geoprobe

well

H2

HCl

H2

HCl

hollow-fiber

membranes

PCE

plume

CO2

CH4

CH4

H2

DCE

VC

PCE

TCE

TCE

DCE

VC

ETH

~ 4 cm

Using hollow-fiber membranes to supply H2 to contaminated aquifers

flow

aquaclude


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.


soil

column

reactors


Membrane Module (single fiber)


Concentrations of PCE & byproducts in test column (H2 added) after ~1 year


Concentrations of PCE & byproducts in control column (no H2) after ~1 year


Concentrations of PCE & byproducts in test column after ~1 year


Concentrations of H2 in control column after ~1 year


Model predictions for H2 concentrations over time


Simulated aquifer studies


Previous research with cometabolic (aerobic) degradation processes


atmospheric discharge

blower

air

compressor

vapor treatment

compressed

CH4 tank

CH4 explosion hazard,

vapor-phase TCE

gas extraction well

TCE

Cl-

TCE plume

gas-channeling

thru porous media

CH4

CO2


air

compressor

compressed

CH4 tank

TCE

Cl-

TCE plume

CH4

CO2

CH4

O2

What if CH4-utilizing

bacteria grew as

biofilms on surface

of membranes?


growing cells utilizing CH4

non-growing cells cometabolizing TCE

inactivated cells

CH4 & O2

continuous flux of new cells

erosion

Biofilm stratification

membrane


flux of new cells

SEM of biofilm cross-section


cells with compromised membranes stained red with propidium iodide

viable cells stained green with “Syto 9”

Biofilm viability staining


Other modeling studies

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


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


Research Topic:

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


Decreasing CH4 “zone of influence” due to microbial accumulation

GW flow


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.


Modeling Methods:

  • GMS (Groundwater Modeling System)

    • ModFlow

    • ModPath

    • RT3D


Basic Concepts in Groundwater Flow

  • Darcy’s 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


Capture Zone:

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


Well capture zone


Assumed Parameter Values

  • Grid: 20 ft  20 ft.

  • Aquifer Hydraulic Conductivity =8.42ft/day

  • Head: Left=10ft , Right=9.57ft

  • Aquifer Porosity=0.35

  • Well Hydraulic Conductivity=842 ft/day

  • Well Porosity=1.0

  • Unconfined Aquifer

ref: Wilson & MacKay, 1997.


Isopotential Lines


Particle Paths (Flow Direction)


Capture zone without pumping

Unpumped Well

Unpumped Well


Capture zone with pumping

injection well

extraction well

injection well

extraction well


Conceptualized flow field % capture vs. # of wells & pumping rate


Research Topic:

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


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.


Problems associated with “copper repression of sMMO”


CH4 Oxidationand TCE Degradation Pathways


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.


membrane wall

liquid

film

biofilm

CH4

flux of new cells

Cu

TCE

Copper will adsorb to surface of counter-diffusional biofilms?


Research Objectives

Characterize sMMO expression as function of:

  • Copper loading.

  • CH4/O2 partial pressures.

  • Time (hard to predict at this moment).


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.


Membrane-attached methanotrophic biofilm formation


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.


Expected Results

sMMO

TCE degradation rate

pMMO

YJCH4 /JCU


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