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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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slide1

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

Lee Clapp

Bala Veerasekaran

Vipin Sumani

February 5, 2003

slide3
Problem:

Improper disposal of chlorinated solvents

magnitude of problem
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)

overall research goal
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.

slide8
Pump & Treat

EPA, 2003

passive membrane prb system at tcaap superfund site
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
two processes for chlorinated solvent biodegradation
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).
using hollow fiber membranes to supply h 2 to contaminated aquifers
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
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.
slide16
soil

column

reactors

slide25
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

slide26
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?

biofilm stratification
growing cells utilizing CH4

non-growing cells cometabolizing TCE

inactivated cells

CH4 & O2

continuous flux of new cells

erosion

Biofilm stratification

membrane

slide30
flux of new cells

SEM of biofilm cross-section

other modeling studies
Other modeling studies
  • Olaf Cirpka at Stanford has modeled different strategies for minimizing biofouling in aquifers.
two obstacles
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
Research Topic:
  • Characterizing effect of superimposed transverse flow on well capture zone.
research objectives
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
Modeling Methods:
  • GMS (Groundwater Modeling System)
    • ModFlow
    • ModPath
    • RT3D
basic concepts in groundwater flow
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

Capture Zone:

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

assumed parameter values
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.

slide44
Capture zone without pumping

Unpumped Well

Unpumped Well

slide45
Capture zone with pumping

injection well

extraction well

injection well

extraction well

research topic1
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
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.
hypotheses
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.
copper will adsorb to surface of counter diffusional biofilms
membrane wall

liquid

film

biofilm

CH4

flux of new cells

Cu

TCE

Copper will adsorb to surface of counter-diffusional biofilms?
research objectives1
Research Objectives

Characterize sMMO expression as function of:

  • Copper loading.
  • CH4/O2 partial pressures.
  • Time (hard to predict at this moment).
experimental methods
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.
analytical methods
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
Expected Results

sMMO

TCE degradation rate

pMMO

YJCH4 /JCU

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