Effect of Biomass on the Measured Solubility of Trichloroethylene in Aqueous Bioremediation Systems

1
Effect of Biomass on the Measured Solubility of
Trichloroethylene in Aqueous Bioremediation
Systems

• Tayyaba Jatoi
• John W. Barton
• Life Sciences Division
• Oak Ridge National Laboratory
• Oak Ridge, Tennessee

2
TCE

• Nations most common groundwater contaminant
• Almost insoluble in pure water
• Production in the organic chemical industry
  solvent for fats, greases waxes fire
  extinguishers etc.
• Migration of contaminated groundwater plumes
• Leaching out of the contaminant into the living
  systems
• Known to damage liver, kidneys and neurological
  system. Suspected of causing cancer.

3
Henrys Law Constant

• Cheadspace H Cliquid
• Controls the transport and migration of sparingly
  soluble organics.
• Constants are strongly temperature dependent
• A variety of H units are reported, the most
  common of which is atm m3 mol-1
• .

4
Previous Work

• Mackay and Shiu (1981) and many others have
  reported values for dilute organics in pure water
  including many environmentally important
  compounds
• Octanol-air partition constants have been used as
  model systems to describe partitioning from a
  gaseous phase into a biomass phase (Wania and
  Mackay, 1996). Since based upon pure water
  values, presence of active biofilm in active
  environments invalidates such environmental
  models.
• Chawla and McKay (2001) measured effect of
  alcohol cosolvents on the aqueous solubility of
  TCE for some mixures water solubility increased
  by two orders of magnitude

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Microbiology and Materials

• Model species utilized
• - Saccharomyces cerevisiae
• - Rhodopseudomonas palustris
• - Pseudomonas putida
• Cells collected and centrifuged at 5,000 RPM for
  25 minute cycles.
• Pasteurization at 70C for 1hr to eliminate CO2
  production.

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Methods

• Construction of sealed test tubes with precisely
  measured amounts of TCE, biomass and water.
• Up to 8 different biomass densities were used,
  starting from no biomass at all to a very dense
  biomass phase.
• Tubes shaken on a rotary shaker for 1hr to allow
  for equilibration of the organic between the
  three phases.

-Increasing biomass?
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Measurements of Partitioning Behavior

• 2 Types of parameters measured
• Maximum Solubility Measuring Solubility Limit
  when aqueous/biomass phase is in direct contact
  with pure TCE. Samples of aqueous phase extracted
  and TCE concentration measured.
• Partitioning Constants Measuring the ratio of
  TCE concentration in the headspace to the
  concentration in the aqueous phase when no pure
  TCE phase present.

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TCE Solubility and Partitioning

• As the biomass concentration was raised, the TCE
  phase gradually disappeared until only one phase
  was present, which then had a constant TCE
  concentration. TCE in all phases was measured
  and accounted for.

Headspace
Headspace
Pure Water
WaterBiomass
WaterBiomass
Pure TCE
Pure TCE
Pure Water
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Gas Chromatography

• Concentration of the organic in the aqueous phase
  determined by indirect gas chromatography
  (extraction of TCE promoted into a hexane phase).
• Headspace TCE concentrations determined by direct
  gas chromatography.
• Controls were run with each experiment to check
  for unforeseen variables.

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Gas Chromatography
TCE Peak
?
TCE Peak
TCE Peak
?
?
No Yeast
5 mL Yeast
21 mL Yeast

• Increasing TCE peak area due to increasing
  biomass
• Each TCE Peak manually integrated

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TCE Partitioning in Yeast
Henrys Constant (g L-1 L g-1)
Dry Yeast Content (g/mL)
Maximum solubility of TCE in aqueous Yeast
batches increased from 0.93 g/L (no Yeast) to
151 g/L ( pure Yeast).
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TCE Partitioning in RHPAL
Henrys Constant (g L-1 L g-1)
Organic RHPAL content (g/mL)
Maximum solubility of TCE in aqueous RHPAL
batches increased from 0.93 g/L (no RHPAL) to
43.4 g/L (a pure RHPAL phase).
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TCE Partitioning in Putida
1
0
0.05
0.1
.15
0.2
0.25
0.3
0.35
0.1
0.01
Henrys Constant (g L-1 L g-1)
0.001
0.0001
Organic Putida content (g/mL)
Maximum solubility of TCE in aqueous Putida
batches increased from 0.92 g/L (no biomass) to
62.9 g/L (pure biomass).
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Trends

• Greatest solubility change at low concentrations.
• At higher concentrations, the change levels out.
  Might be due to saturation threshold.
• Slight differences in the partitioning data might
  be due to the differences in polysaccharides/prote
  in ratios amongst the three species.

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Conclusion

• TCE solubility can be more than 2.5 orders of
  magnitude higher in aqueous solutions containing
  biomass. Large solubility changes in water were
  noted even when relatively low levels of biomass
  were present
• Increase in solubility appears to be universal
  amongst the 3 species.
• Result is relevant for environmental clean-up
  models.
• Predictive models and management planning must
  consider background biomass levels at
  TCE-contaminated sites.

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Acknowledgements

• - This research was sponsored by Higher
  Education Research Experience (HERE) at ORNL
• - John. W. Barton and Biochemical Engineering
  Research Group at LSD

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Group Photo
My mentor, John
My mentor, John
?
?