Final Report: Sub-Critical Water Extraction of Organic Pollutants

EPA Grant Number: R825394
Title: Sub-Critical Water Extraction of Organic Pollutants
Investigators: Hawthorne, Steven B. , Kubatova, Alena , Lagadec, Arnaud J. , Miller, David J.
Institution: University of North Dakota
EPA Project Officer: Packard, Benjamin H
Project Period: December 24, 1996 through December 23, 1999
Project Amount: $374,925
RFA: Exploratory Research - Water Chemistry and Physics (1996) RFA Text |  Recipients Lists
Research Category: Water , Land and Waste Management , Engineering and Environmental Chemistry


The objectives of the investigations were to: (1) develop the use of subcritical water as an extraction solvent for polar and non-polar organic pollutants from contaminated solids; (2) measure and model fundamental solubility behavior of polar and non-polar organics in subcritical water; (3) investigate the mechanisms controlling the extraction of organic pollutants from model and real-world solids; (4) determine the reactivity of model organics under different subcritical water conditions; and (5) determine the extraction selectivity that can be obtained by controlling water's polarity with temperature.

Summary/Accomplishments (Outputs/Outcomes):

Solubility Determinations. A dynamic (flowing) system for determining the solubility of organic solids in subcritical water was developed in Year 1, and initial modifications to allow its use were performed in Year 2. In Year 3, the new system was used to determine the solubility of several liquid solutes including environmental pollutants (e.g., benzene, chlorinated solvents) and flavor and fragrance compounds. These solubility studies demonstrated that the solubility of many organics can be controlled over ca. five orders-of-magnitude by simply increasing the subcritical water temperature up to 250°C. Peer-reviewed publications describing these results are listed below.

Subcritical Water Extraction Mechanisms. Determining extraction mechanisms requires an analytical system which allows the collection of extracted organics every few minutes so that rate curves (e.g., mass extracted per minute) can be generated. The system was developed and validated for its ability to give quantitative data suitable for kinetic studies in Year 1.

Pollutant pesticides and polycyclic aromatic hydrocarbons (PAHs) on soil were studied for the effects of subcritical water flow rate on extraction rates. For PAHs, the relative extraction rates of spiked deuterated PAHs to environmentally-aged PAHs were compared using both subcritical water and supercritical carbon dioxide. These results have allowed the relative contributions of two rate-limiting steps (initial desorption of the pollutants from the active soil binding sites, and chromatographic elution) to be determined and modeled. Four environmentally-aged soils were collected for these studies including two soils contaminated with PAHs (one soil with high, and one with lower contamination levels) and two soils contaminated with multiple pesticides (one with high and one with lower contamination levels?both soils include the pesticides metolachlor and pendimethalin). Interestingly, we have found that these mechanisms are not as expected based on earlier studies on supercritical carbon dioxide extraction. In essence, the extraction of pesticides and PAHs from the soils with subcritical water did not depend on kinetics, and only appeared to depend on the thermodynamics (soil/water distribution coefficients during the subcritical water extraction) of the system. Also, recently spiked deuterated PAHs extracted at similar rates to the aged PAHs (e.g., spiked deuterated pyrene extracted in a manner similar to aged pyrene). These results are in marked contrast to supercritical carbon dioxide extraction, where there can be great differences in the extraction rates of environmentally-aged and spiked pollutants.

Therefore, we compared the extraction behavior of organic pollutants using supercritical carbon dioxide (which does not significantly modify the soil matrix) with subcritical water (which causes soils to swell and expose pollutants in soil micropores, as well as extracting humic material which may contain sequestered organics). Although the data is now being evaluated, we anticipate that the comparison of supercritical carbon dioxide extraction behavior with subcritical water extraction behavior will provide a powerful tool to understand how pollutant molecules interact and bind to soil matrices.

Initial comparison of the characteristics of these two fluids are the subject of a publication in the Journal of Chromatography (see below). Additional peer-reviewed publications describing these results are currently being prepared.

Reactions in Subcritical Water. In Year 1, initial observations of pesticide degradation during subcritical water extraction was observed. These results were potentially important, since they indicated that subcritical water (with NO additives) could be used to degrade toxic organic compounds. In subsequent investigations, several additional compound classes were tested and shown to undergo degradation reactions in subcritical water at relatively mild temperatures (e.g., <250oC). Degradation has been demonstrated for several aromatic and aliphatic organics (including chlorinated and non-chlorinated), and we are presently studying the mechanism(s) and reaction products. To date, we have demonstrated two dechlorination mechanisms: dehydrohalogenation for aliphatic chlorinated hydrocarbons such as the pesticide lindane (where HCl is removed from the molecule to yield a double bond), and hydride/chloride exchange for chlorinated aromatics (where Cl atoms on the aromatic ring is replaced by H). These observations lead to attempts to destroy chlorinated dioxins on municipal incinerator fly ash. Initial work was successful as described in the attached article, and will be continued in collaboration with our colleagues in Belgium's leading dioxin laboratory.

These investigations also lead to attempts to destroy high explosives (TNT, RDX, and HMX) on highly-contaminated soils (under separate funding by DOE). In these investigations, TNT, RDX, and HMX on contaminated soils were completely (>99.9 percent) destroyed with exposure to subcritical water at 250 C for only 1 hour, even though contaminant concentrations on the soil were as high as 12 weight percent. (These results are described in Environmental Science and Technology 2000;34:3224-3228.)

Subcritical Water as a "Green" Solvent. Our better understanding of organic solubility behavior in subcritical water (discussed above) has lead to investigations into using subcritical water as a replacement for organic solvents used in industrial processing. To date, we have used subcritical water to remediate soils which were highly contaminated with PAHs and pesticides (co-funded by the Department of Energy) as described in the enclosed article accepted for publication in Environmental Science and Technology. As discussed above, subcritical water has also been used to destroy high explosives on soil. Additional experiments have shown that extractions of valuable organics from plant tissue can be performed (e.g., lactones from Kava Kava, flavor compounds from herbs). These investigations are really quite interesting since dealing with extracts that smell good (instead of our normal organic pollutant extracts) is a pleasant change! High selectivity for more polar (and more valuable) flavor compounds over less polar (and less valuable) compounds using intermediate subcritical water temperatures was also demonstrated (see the publication in the Flavour and Fragrance Journal, below). A final area in which initial experiments are promising is the extraction of potentially toxic monomers and reaction products from food- and medical-packaging polymers. For example, subcritical water extracted several contaminants from a polyethylene bread bag including benzene, larger aromatics, and aliphatic aldehydes. Since the bag material was physically the same after extraction, these results indicate that it may be possible to remove potentially harmful contaminants from plastics before their use for food and medical product packaging.

Journal Articles on this Report : 9 Displayed | Download in RIS Format

Other project views: All 10 publications 9 publications in selected types All 9 journal articles
Type Citation Project Document Sources
Journal Article Hawthorne SB, Grabanski CB, Martin E, Miller DJ. Comparisons of Soxhlet extraction, pressurized liquid extraction, supercritical fluid extraction, and subcritical water extraction for environmental solids: recovery, selectivity, and effects on sample matrix. Journal of Chromatography A, September 2000;892(1-2):421-433. R825394 (1999)
R825394 (Final)
not available
Journal Article Kubatova A, Lagadec AJM, Miller DJ, Hawthorne SB. Selective extraction of oxygenates from savory and peppermint using subcritical water. Flavour and Fragrance Journal 2001,16(1):64-73. R825394 (Final)
not available
Journal Article Kubatova A, Miller DJ, Hawthorne SB. Comparison of subcritical water and organic solvents for extracting kava lactones from kava root. Journal of Chromatography A 2001;923(1-2):187-194. R825394 (Final)
not available
Journal Article Kubatova A, Lagadec AJM, Miller DJ, Hawthorne SB. Dechlorination of lindane, dieldrin, tetrachloroethane, trichloroethene, and PVC in subcritical water. Environmental Science & Technology 2002;36(6):1337-1343. R825394 (Final)
not available
Journal Article Lagadec AJM, Miller DJ, Lilke AV, Hawthorne SB. Pilot-scale subcritical water remediation of polycyclic aromatic hydrocarbon- and pesticide-contaminated soil. Environmental Science & Technology 2000;34(8):1542-1548. R825394 (1999)
R825394 (Final)
not available
Journal Article Miller DJ, Hawthorne SB. Method for determining the solubilities of hydrophobic organics in subcritical water. Analytical Chemistry 1998;70(8):1618-1621. R825394 (1999)
R825394 (Final)
not available
Journal Article Miller DJ, Hawthorne SB, Gizir AM, Clifford AA. Solubility of polycyclic aromatic hydrocarbons in subcritical water from 298K to 498K. Journal of Chemical and Engineering Data 1998;43(6):1043-1047. R825394 (1999)
R825394 (Final)
not available
Journal Article Miller DJ, Hawthorne SB. Solubility of liquid organic flavor and fragrance compounds in subcritical (hot/liquid) water from 298K to 473K. Journal of Chemical and Engineering Data 2000;45(2):315-318. R825394 (1999)
R825394 (Final)
not available
Journal Article Yang Y, Belghazi M, Lagadec A, Miller DJ, Hawthorne SB. Elution of organic solutes from different polarity sorbents using subcritical water. Journal of Chromatography A, June 1998;810(1-2):149-159. R825394 (1999)
R825394 (Final)
not available

Supplemental Keywords:

soil, sediments, PAHs, PCBs, dioxins, organics, green chemistry, clean technologies, remediation, environmental chemistry, analytical., Scientific Discipline, Toxics, Geographic Area, Waste, Physics, Remediation, Environmental Chemistry, HAPS, State, Engineering, organic pollutants, clean technologies, hydrocarbon, PCBs, corrosivity, phenols, PAH, PCB, sub critical water extraction, process scale equipment, solvents

Progress and Final Reports:

Original Abstract
  • 1997
  • 1998