H 2 initially detected in these wells & a sampling well 6 ft downstream direction of groundwater flow Passive Membrane PRB System at TCAAP Superfund Site hydrogen added to these wells
Two processes for chlorinated solvent biodegradation (1) Reductive dechlorination removes one chlorine at a time (anaerobic). (1) Reductive dechlorination removes one chlorine at a time (anaerobic). (2) Cometabolic oxidation results in >99% mineralization (aerobic). (2) Cometabolic oxidation results in >99% mineralization (aerobic). TCE CO 2 + Cl - O2O2O2O2 CH 4 H 2 HCl H 2 HCl H 2 HCl H 2 HCl PCE TCE cis-DCE VC ETH
(1) Previous research with reductive dechlorination processes
Using hollow-fiber membranes to supply H 2 to contaminated aquifers Geoprobe well ~ 4 cm aquaclude H2H2 flow PCE plume H2H2 HCl PCETCE H 2 gas hollow-fiber membranes TCE DCE VC ETH CH 4 H2H2 HCl DCEVC 4H 2 2H 2 O CO 2 CH 4
Problems with enhanced reductive dechlorination for CAH remediation. Accumulation of intermediate transformation products (DCE & VC). Accumulation of intermediate transformation products (DCE & VC). Microbial competition for H 2. Microbial competition for H 2. MCLs below threshold concentrations required for dechlorinator growth. MCLs below threshold concentrations required for dechlorinator growth. Aquifer biofouling. Aquifer biofouling. Adverse impact on groundwater quality. Adverse impact on groundwater quality.
Biofilm viability staining cells with compromised membranes stained red with propidium iodide viable cells stained green with “Syto 9”
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 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 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 CH 4 “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.
Basic Concepts in Groundwater Flow Darcy’s Law: Q x = -K x A (h 2 – h 1 )/L Time taken for a particle to travel t = 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.
Capture zone with pumping extraction well injection 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 CO 2 via intermediates like methanol and formaldehyde. Two enzymes sMMO and pMMO play an important role for the oxidation of CH 4. sMMO co-oxidizes a wide range of alkanes & alkenes, including chlorinated hydrocarbons. Cu inhibits sMMO activity.
Problems associated with “copper repression of sMMO”
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 biofilm liquidfilm Copper will adsorb to surface of counter-diffusional biofilms? TCE CH 4 flux of new cells Cu
Research Objectives Characterize sMMO expression as function of: 1. Copper loading. 2. CH 4 /O 2 partial pressures. 3. 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 CH 4 and O 2 partial pressures will promote development of thick biofilms.