Partitioning of VOCs: Why do we care? ä Determines how best to treat a site ä vapor extraction ä pump and treat ä remove contaminated soil ä Determines feasibility of phase changes ä gas stripping tower ä sorption to activated carbon from liquid or gas phase ä Determines how best to treat a site ä vapor extraction ä pump and treat ä remove contaminated soil ä Determines feasibility of phase changes ä gas stripping tower ä sorption to activated carbon from liquid or gas phase FRTR Gas/Liquid partitioning 

Partitioning ä gas-liquid ä Henry’s law constant ä gas-solid ä distribution coefficient ä liquid-solid ä distribution coefficient ä gas-liquid ä Henry’s law constant ä gas-solid ä distribution coefficient ä liquid-solid ä distribution coefficient  = mass of solute sorbed per mass of solid Liquid volume Gas volume Solid mass

Gas-Solid Partitioning soil organic carbon organic carbon VOC molecules in gas phase molecules sorbed to soil molecules sorbed to soil linear inhibition condensation

Linearity of Partitioning ä Linear at low VOC concentrations ä The fraction of VOC that sorbs to soil is independent of the concentration of VOC in the gas or liquid phase ä Interference from previously sorbed VOC molecules is small ä (a reasonable assumption at the concentrations we will be using in the laboratory) ä Linear at low VOC concentrations ä The fraction of VOC that sorbs to soil is independent of the concentration of VOC in the gas or liquid phase ä Interference from previously sorbed VOC molecules is small ä (a reasonable assumption at the concentrations we will be using in the laboratory)

Non-linearity of Partitioning ä Non-linear at high VOC concentrations ä partition coef. = f(VOC concentration) ä VOCs prefer sorption to soil over sorbing to previously sorbed VOC molecules (_________) ä Condensation occurs at very high VOC concentrations ä Non-linear at high VOC concentrations ä partition coef. = f(VOC concentration) ä VOCs prefer sorption to soil over sorbing to previously sorbed VOC molecules (_________) ä Condensation occurs at very high VOC concentrations inhibition

gas phase Partitioning during Remediation ä Equilibrium conditions? ä assume the kinetics of partitioning are fast relative to the rate that concentrations change in any of the phases ä Function of temperature ä increase temperature - compounds become more volatile -increased preference for ____ _______ ä Equilibrium conditions? ä assume the kinetics of partitioning are fast relative to the rate that concentrations change in any of the phases ä Function of temperature ä increase temperature - compounds become more volatile -increased preference for ____ _______

organic carbon Partitioning during Remediation ä Reversible reactions ä if the concentration in one phase decreases the concentration in the other phase will decrease to reach a new equilibrium ä Soil type is an important variable! ä VOCs prefer sorption to sites containing _______ ________ over sorption to inorganic soil surfaces ä Reversible reactions ä if the concentration in one phase decreases the concentration in the other phase will decrease to reach a new equilibrium ä Soil type is an important variable! ä VOCs prefer sorption to sites containing _______ ________ over sorption to inorganic soil surfaces

Remediation of VOC Contaminated Site ä Removal techniques ä pump and treat water ä contaminant sticks to soil or is in gas phase ä pump and treat air (vapor extraction) ä contaminant sticks to soil or is in aqueous phase ä Effect of partitioning on transport ä retardation factor ä R = velocity of water/velocity of pollutant, but pollutant when in fluid moves at ______ ________ so R = 1/fraction of pollutant in fluid. ä Removal techniques ä pump and treat water ä contaminant sticks to soil or is in gas phase ä pump and treat air (vapor extraction) ä contaminant sticks to soil or is in aqueous phase ä Effect of partitioning on transport ä retardation factor ä R = velocity of water/velocity of pollutant, but pollutant when in fluid moves at ______ ________ so R = 1/fraction of pollutant in fluid. R R fluid velocity Cause slow removal

Techniques to Measure Partitioning ä Batch Air Stripping (BAS) ä purge dissolved VOC from water using an inert gas ä The concentration of VOC in the gas stream should be related to the partitioning between gas and liquid ä Batch Air Stripping (BAS) ä purge dissolved VOC from water using an inert gas ä The concentration of VOC in the gas stream should be related to the partitioning between gas and liquid

Completely mixed Gas-Liquid equilibrium Batch Air Stripping: Experimental Setup Water jacket Exhaust Aqueous Sample with VOC Saturator Air Supply To Temperature Control Bath To FID detector 6-Way Sampling Valve Assumptions... ________________ ____________________ Assumptions... ________________ ____________________

Equilibrium Partitioning in Closed Systems (EPICS) ä Load two bottles containing different liquid volumes with the same mass of VOC ä Shake the bottles to achieve equilibrium between gas and liquid phase ä Sample the headspace to measure the concentration of VOC in the gas phase ä Use mass balance to determine the amount of VOC in the liquid phase ä Load two bottles containing different liquid volumes with the same mass of VOC ä Shake the bottles to achieve equilibrium between gas and liquid phase ä Sample the headspace to measure the concentration of VOC in the gas phase ä Use mass balance to determine the amount of VOC in the liquid phase

Equilibrium Partitioning in Closed Systems (EPICS) water Add same mass of VOC to both bottles. Equilibrate by shaking. Measure concentration of VOC in gas phase. Add same mass of VOC to both bottles. Equilibrate by shaking. Measure concentration of VOC in gas phase. Measure M by taking sample from control bottle to help account for losses to bottle surfaces. mass VOC added volume gas volume liquid Control

EPICS extended to gas-solid partitioning soil Identical analysis to gas-liquid partitioning

EPICS extended to liquid-solid partitioning water

EPICS Error Analysis water low solubility high solubility ä Assume 10% error in measuring gas concentrations ä What are the maximum and minimum values of mass in liquid phase? ä Assume 10% error in measuring gas concentrations ä What are the maximum and minimum values of mass in liquid phase? (10 ± 1) – (9 ± 0.9) 11 – 8.1 = – 9.9 = -0.9 (10 ± 1) –( 1 ± 0.1) 11 – 0.9 = – 1.1 = 7.9

EPICS Low solubility Limitations ä Henry’s Law constant determination is inaccurate for compounds of low solubility ä Method Detection Limit... ä The fraction of VOC in the liquid phase must be greater than the coefficient of variation of the mass of VOC added ä The fraction in gas phase must be less than 1 minus the coefficient of variation ä Henry’s Law constant determination is inaccurate for compounds of low solubility ä Method Detection Limit... ä The fraction of VOC in the liquid phase must be greater than the coefficient of variation of the mass of VOC added ä The fraction in gas phase must be less than 1 minus the coefficient of variation

EPICS Limitations ä High solubility limitations ä The fraction of VOC in the liquid phase can be accurately determined as long as sufficient VOC is added so that the gas phase concentrations are greater than the GC detection limits ä Similar conclusions for gas-solid partitioning ä High solubility limitations ä The fraction of VOC in the liquid phase can be accurately determined as long as sufficient VOC is added so that the gas phase concentrations are greater than the GC detection limits ä Similar conclusions for gas-solid partitioning

Liquid/Solid partitioning: Error Analysis fraction in gas phase close to 1 (low solubility) High Henry’s law constant fraction in gas phase close to 1 (low solubility) High Henry’s law constant fraction in liquid phase close to 1 (very soluble) Low Henry’s law constant fraction in liquid phase close to 1 (very soluble) Low Henry’s law constant f s = coefficient of variation Lousy data!

gas liquid Expectations based on EPICS limitations Octane Acetone Toluene f s too small? good f s too small good soil Where’s VOC? Where’s VOC?

EPICS Procedure air air + water air + water + soil air + soil Octane Acetone Toluene Test vials each loaded with 3 VOCs VOC Source vials

Batch Air Stripping Expectations C G =f(C L ) Identify the important parameters…