Jatoi

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

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

TCE: 

TCE Nation’s 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.

Henry’s Law Constant: 

Henry’s 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 .

Previous Work: 

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

Microbiology and Materials: 

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 70°C for ~1hr to eliminate CO2 production.

Methods: 

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→

Measurements of Partitioning Behavior: 

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.

TCE Solubility and Partitioning: 

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. Pure Water Pure TCE Water+Biomass Pure TCE Pure Water Headspace Water+Biomass Headspace

Gas Chromatography: 

Gas Chromatography

Gas Chromatography: 

Gas Chromatography Increasing TCE peak area due to increasing biomass Each TCE Peak manually integrated No Yeast 5 mL Yeast 21 mL Yeast → TCE Peak TCE Peak → → TCE Peak

TCE Partitioning in Yeast: 

TCE Partitioning in Yeast Maximum solubility of TCE in aqueous Yeast batches increased from 0.93 g/L (no Yeast) to 151 g/L ( pure Yeast). Dry Yeast Content (g/mL) Henry’s Constant (g L-1 L g-1)

TCE Partitioning in RHPAL: 

TCE Partitioning in RHPAL Organic RHPAL content (g/mL) Henry’s Constant (g L-1 L g-1) 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).

TCE Partitioning in Putida: 

TCE Partitioning in Putida Henry’s Constant (g L-1 L g-1) 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). 0.0001 0.001 0.01 0.1 1 0 0.05 0.1 .15 0.2 0.25 0.3 0.35

Trends: 

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/protein ratios amongst the three species.

Conclusion: 

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.

Acknowledgements: 

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

Slide17: 

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