Grantee Research Project Results
1999 Progress Report: Influence of Nonionic Surfactants on the Bioavailability of Chlorinated Benzenes for Microbial Reductive Dechlorination
EPA Grant Number: R825404Title: Influence of Nonionic Surfactants on the Bioavailability of Chlorinated Benzenes for Microbial Reductive Dechlorination
Investigators: Pavlostathis, Spyros G. , Pennell, Kurt D.
Current Investigators: Pavlostathis, Spyros G. , Pennell, Kurt D. , Yeh, Daniel H , Karagunduz, Ahmet , Chang, Eric , Marti, Charlotte A.
Institution: Georgia Institute of Technology
EPA Project Officer: Hahn, Intaek
Project Period: November 12, 1996 through November 11, 1999
Project Period Covered by this Report: November 12, 1998 through November 11, 1999
Project Amount: $333,348
RFA: Environmental Fate and Treatment of Toxics and Hazardous Wastes (1996) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management , Safer Chemicals
Objective:
The objectives of this research project are to: (1) assess the effect of surfactants on the methanogenesis and reductive dechlorination processes; (2) assess the anaerobic biodegradability of different surfactant families and correlation to their properties (e.g., effect of the hydrophobic and hydrophilic moieties); (3) determine the quantification of the effect of surfactants on the solubilization, desorption, and reductive dechlorination of sorbed chlorinated benzenes in batch systems; (4) evaluate surfactant-assisted desorption, biotransformation and transport of hexachlorobenzene (HCB) in column systems; and (5) perform mathematical modeling of the transport, sorption, and biotransformation of both surfactant and chlorinated benzenes.Progress Summary:
Assessment of the biodegradability of the stearic acid-based Tween surfactants (Tween 60, 61, and 65) was completed. The three surfactants were only partially degradable under anaerobic conditions (53, 62, and 62 percent for Tween 60, 61, and 65, respectively, based on total chemical oxygen demand [COD] destruction). They were converted to methane and served as the sole carbon and electron source for the dechlorination of HCB. Abiotic batch assays were conducted to assess surfactant sorption and HCB desorption from a historically contaminated estuarine sediment. For Tween 60, surfactant sorption, coupled with precipitation, resulted in negligible solubilization of sediment sorbed-HCB to the liquid-phase (0.7 percent), even at an initial surfactant concentration of 40,000 mg/L. For Tween 80, the removal of sorbed-HCB was 0.1 and 56.2 percent at initial surfactant concentrations of 10,000 and 40,000 mg/L, respectively. However, the rate and extent of HCB desorption and dechlorination from the solid-phase in surfactant-fed microcosms was not significantly different from that in a glucose-fed microcosm, suggesting that the surfactants were merely used as an electron donor for dechlorination. Therefore, even in the presence of the Tween surfactants, the bioavailability of HCB was still limited as a result of strong contaminant sequestration in the historically contaminated sediment, as well as the high degree of surfactant sorption by the sediment solid-phase. Although Tween surfactants at relatively high concentrations (at or above 40,000 mg/L) facilitated the abiotic release of HCB, the potential surfactant toxicity precluded their use at such high concentrations in a biological system.Micellar solubilization of HCB in aqueous solutions of Tween 80 yielded a weight solubilization ratio (WSR) of 7.0 x 10-4 g HCB/g Tween 80 (r2 = 0.991) over a surfactant concentration range of 250 to 2,000 mg/L, which corresponds to a molar solubilization ratio (MSR) of 3.2 x 10-3 mole HCB/mole Tween 80. HCB solubility measurements made after 2, 7, 11, and 30 days of mixing indicated that micellar solubilization was rate limited, with 70 percent of the solubilization capacity reached after 2 days. Sorption of Tween 80 by the Appling soil (0.75 percent organic carbon) was strongly time dependent, with the limiting sorption capacity increasing from 1.44 to 7.44 mg/g (day 1 and 7, respectively). In the absence of any surfactant, sorption of HCB by Appling soil obtained after 1, 3, 15, and 22 days of mixing yielded linear sorption isotherms, with the observed distribution coefficient (KD) increasing from 385 L/kg to 527 L/kg over the range of mixing times evaluated. These values correspond to HCB distribution coefficients (KOC), expressed on a log scale, of 2.71 to 2.84. The effects of surfactant on HCB sorption by Appling soil then were evaluated as a function of Tween 80 and HCB concentration, as well as mixing time. The presence of Tween 80 at aqueous phase concentrations above the critical micelle concentration reduced the sorption of HCB by Appling soil. Therefore, as the surfactant concentration was increased, the observed HCB distribution coefficient (KD) decreased. In addition, for a given surfactant loading, the value of KD increased with time.
A matrix of one-dimensional column experiments was conducted to assess the transport of three surfactants, Tween 60, Tween 80, and Triton X-100, in Appling soil and a reference Ottawa sand. When 4 pore volumes of Tween 80 (2,100 mg/L) were flushed into a column containing Appling soil, breakthrough of the surfactant occurred after 3 pore volumes of effluent were collected, and ceased after concentrations approached non-detect levels after approximately six pore volumes of solution. Flow was stopped after eight pore volumes for a period of 22 hours and, when resumed, an increase in effluent surfactant concentration was observed, indicative of rate-limited surfactant desorption. Only 41 percent of the injected surfactant mass was recovered after flushing with an additional seven pore volumes of water. Column experiments also were conducted to investigate the simultaneous sorption and desorption of HCB and surfactant (Triton X-100 and Tween 80) with Appling soil. In the case of simultaneous injection of HCB and surfactant, very little HCB was detected in the column effluent, even when the concentration of surfactant eluting from the column was quite high. Solid-phase HCB concentrations were largest near the column inlet, and decreased to essentially zero at the column exit.
A mathematical model was developed to assess the influence of sorbed-phase surfactant on HCB sorption. The overall or apparent solubility of a hydrophobic organic compound in the presence of surfactant was represented as the amount of solute associated with surfactant monomers plus the amount associated with surfactant micelles. This approach can be extended to include the effect of sorbed-phase surfactant on the distribution of solute between the solid and aqueous phases. Good agreement was obtained between measured and predicted values of the apparent soil-water distribution coefficient (K*). Because the critical micelle concentration (CMC) of Tween 80 is very low (13 mg/L), the value of K* decreased almost immediately when the surfactant concentration was increased. Once the CMC of Tween 80 was exceeded, the value of K* decreased exponentially as the micellar surfactant concentration increased.
Future Activities:
Until the completion of this research project in May 2000, research efforts will focus on: (1) developing and testing a mathematical model describing the phase distribution and reductive dechlorination of HCB in the presence of a degradable surfactant, (2) completing three column studies designed to assess the desorption of HCB from contaminated Appling soil in the presence of surfactant, and (3) testing of the one-dimensional numerical model developed to simulate surfactant and HCB transport, rate-limited sorption and desorption of HCB and surfactant, rate-limited micellar solubilization of HCB, and biodegradation of HCB and surfactant.Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 13 publications | 3 publications in selected types | All 2 journal articles |
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Type | Citation | ||
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Yeh DH, Pennell KD, Pavlostathis SG. Toxicity and biodegradability screening of nonionic surfactants using sediment-derived methanogenic consortia. Water Science and Technology 1998;38(7):55-62. |
R825404 (1999) R825404 (Final) |
not available |
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Yeh D, Pavlostathis SG, Pennell KD. Effect of tween surfactants on methanogenesis and microbial reductive dechlorination of hexachlorobenzene. Environmental Toxicology and Chemistry 1999;18(7):1408-1416. |
R825404 (1997) R825404 (1999) R825404 (Final) |
not available |
Supplemental Keywords:
bioavailability, chlorinated compounds, sorption, surfactants, transport, bioremediation, modeling., Scientific Discipline, Toxics, Waste, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Environmental Chemistry, Chemistry, HAPS, Fate & Transport, Bioremediation, 33/50, fate and transport, microbiology, bioremediation model, surfactant-aided desportion, sorption kinetics, benzene, chemical transport, kinetic studies, hazardous waste, biotechnology, hazardous waste cleanup, geochemistry, environmental toxicant, mobility, biotransformation, chemical releases, contaminant release, waste chemicals, Benzene (including benzene from gasoline), chlorinated benzenes, nonionic surfactants, microbial reductive dechlorination, chlorinated solvents, transportProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.