Grantee Research Project Results
1999 Progress Report: The Effects of Aging and Sorbent Decomposition on the Bioavailability of Toluene and Xylene in Solid Waste
EPA Grant Number: R827131Title: The Effects of Aging and Sorbent Decomposition on the Bioavailability of Toluene and Xylene in Solid Waste
Investigators: Barlaz, Morton A. , Knappe, Detlef R.U.
Institution: North Carolina State University
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1998 through September 30, 2001 (Extended to March 31, 2002)
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $425,000
RFA: EPA/DOE/NSF/ONR Joint Program on Bioremediation (1998) RFA Text | Recipients Lists
Research Category: Land and Waste Management , Hazardous Waste/Remediation
Objective:
It was hypothesized that kinetically limited sorption/desorption processes and humification control the bioavailability and leaching of organic contaminants in landfills and that humification may be an endpoint in the fate of toluene and xylene. The overall objective of this research is to develop an understanding of factors controlling the bioavailability and fate of organic contaminants sorbed to components of municipal solid waste (MSW). Specific objectives are to: (1) estimate the expected distribution of sorbed contaminants in MSW by measuring the sorptive capacity of the dominant organic refuse components in fresh and biodegraded form; (2) determine whether the sorptive uptake of organic contaminants in MSW is reduced in the presence of leachate as a result of organic contaminant binding by dissolved organic macromolecules; (3) determine the impacts of aging and leachate composition on contaminant desorption rates; (4) compare rates of desorption and biodegradation to determine whether desorption limits bioavailability; (5) determine the effects of refuse decomposition on bioavailability; and (6) identify whether humification is an important sequestration mechanism for aromatic xenobiotics in solid waste.Progress Summary:
This project is being conducted with individual components of MSW, including polyvinyl chloride (PVC), high-density polyethylene (HDPE), newsprint, office paper, and model food and yard waste (rabbit food). Each of the biodegradable components is to be tested in both fresh and decomposed form. Batch isotherm data were collected in phosphate-buffered organic-free water and in acidogenic leachate, flame-sealed glass ampules were used to minimize volatilization losses, and sodium azide was added to the liquid phase to prevent aerobic biological activity. Acidogenic leachate was prepared by recirculating water through fresh residential MSW, and methanogenic leachate was generated from decomposed refuse. In addition, anaerobically decomposed office paper and newsprint have been prepared, and the generation of anaerobically decomposed rabbit food is ongoing.
Initial tests were conducted to determine the time required to reach short-term sorption equilibria. Short-term sorption equilibria for toluene on HDPE, newsprint, office paper, and rabbit food were reached within 2 days in both organic-free water and acidogenic leachate, while 20 days were required with PVC. Sorption kinetics of toluene on PVC exhibited a rapid initial rate of toluene uptake followed by a slower phase. A slower approach to equilibrium for the glassy polymer PVC was expected, given that diffusion in glassy polymers is orders of magnitude slower than in rubbery polymers such as HDPE. The Freundlich model (q = Kf CN) was employed to describe the isotherm data. Table 1 summarizes Kf and N with 95 percent confidence limits for single-solute toluene sorption on each material. In addition, Table 1 depicts the correlation coefficients (R2), the number of data points for each isotherm (n), and the studied equilibrium liquid-phase concentration ranges (C). As shown in Table 1, PVC exhibited the largest sorptive capacity for toluene. In contrast, the sorption capacity of office paper for toluene was nearly 200 times smaller than that of PVC. The Freundlich N values for the studied materials were generally close to 1, indicating that partitioning dominated toluene uptake. The largest deviations from linearity were observed for office paper and PVC. Similar data are available for toluene sorption from acidogenic leachate. A comparison of Freundlich Kf values for organic-free water with acidogenic leachate shows no statistical difference for HDPE, rabbit food, and newsprint between these sorbates. In contrast, the sorptive capacity of office paper for toluene from acidogenic leachate was approximately 40 percent of that from organic-free water. Given that the single-solute toluene isotherm on office paper was not quite linear (N = 0.92), it is possible that components in acidogenic leachate competed with toluene for adsorption sites on office paper. The single-solute toluene sorption capacity of PVC also was greater than that determined in acidogenic leachate; however, it is unclear at this point whether true equilibrium was attained with PVC. Longer-term isotherm tests with PVC are ongoing. Sorption isotherms with o-xylene on HDPE and rabbit food are complete and indicate that the sorption capacity of these MSW components for o-xylene is about two to three times larger than that for toluene, a result that is consistent with the greater hydrophobicity of o-xylene.
Table 1. Single-solute Freundlich isotherm parameters for toluene sorption on MSW components. The 95 percent confidence intervals for Kf and N are shown in parentheses.
Material | Kf (Fg/kg)(Fg/L)-N | N | R2 | n | C (Fg/L) |
PVC | 804.1 (751.8, 860.0) | 0.93 (0.91, 0.95) | 0.99 | 93 | 1-958 |
HDPE | 66.9 (59.9, 74.8) | 1.01 (0.99, 1.03) | 0.99 | 54 | 4-1078 |
Rabbit food | 28.2 (27.0, 29.4) | 1.00 (0.99, 1.01) | 0.99 | 46 | 2-684 |
Newsprint | 16.6 (15.6, 17.8) | 0.96 (0.94, 0.98) | 0.99 | 44 | 5-740 |
Office paper | 4.4 (3.7, 5.3) | 0.92 (0.89, 0.96) | 0.99 | 30 | 3-890 |
Future Activities:
Outstanding isotherm experiments will be completed in the next few months. Current activity is focused on initiation of a preliminary bioavailability test. For bioavailability experiments, contaminants will be aged for periods of up to 1 year in both acidogenic and methanogenic leachate, after which the leachate will be replaced with a toluene or o-xylene degrading culture. Biodegradation will be measured by monitoring for 14CH4 and 14CO2. In addition, abiotic desorption tests will be conducted following each aging period to determine whether desorption limits biodegradation rates. At the end of the biodegradation tests, solids will be sequentially extracted with organic solvent (benzyl alcohol appears to be suitable based on preliminary tests) and sodium hydroxide to assess the distribution of remaining 14C among sorbed and humic-matter-associated fractions.Journal Articles:
No journal articles submitted with this report: View all 7 publications for this projectSupplemental Keywords:
landfills, solid waste, toluene, o-xylene, humic substances., RFA, Scientific Discipline, Toxics, Waste, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Environmental Chemistry, HAPS, chemical mixtures, Bioremediation, 33/50, fate and transport, Toluene, landfills , Xylenes, kinetic studies, aging, contaminant release, desorption rates, solid waste, humification, Xylene, municipal solid waste, Xylenes (isomers and mixture), leachateProgress 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.