Factors Controlling Hydrophobic Organic Contaminant Sorption to and Desorption from Municipal Solid Waste

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Title: Factors Controlling Hydrophobic Organic Contaminant Sorption to and Desorption from Municipal Solid Waste
Author: Wagner, Travis Brandon
Advisors: Dr. Joel J. Ducoste, Committee Member
Dr. Morton A. Barlaz, Committee Member
Dr. Detlef R. U. Knappe, Committee Chair
Abstract: The objectives of this research were to (1) determine the sorption capacity of individual municipal solid waste (MSW) components for tetrachloroethylene (PCE) and cis-1,2-dichloroethylene (DCE), (2) evaluate the importance of the amorphous fraction of sorbent organic matter on HOC sorption to polyethylenes, (3) measure the toluene sorption capacity of newsprint samples collected at the Norman, OK, landfill (NLF), (4) determine sorbate and sorbent characteristics that affect HOC sorption, and (5) determine PCE desorption kinetics from individual MSW components. PCE and toluene were selected as model HOCs because they frequently occur in landfill leachates. DCE was of interest because it is a product that forms during the reductive dehalogenation of PCE. The MSW components that were tested included high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), poly(vinyl chloride) (PVC), a model food and yard waste (rabbit food), office paper, and newsprint. Biodegradable sorbents were evaluated in both fresh and anaerobically degraded form. In addition, the toluene sorption capacity was measured for newsprint samples that were collected from three depths at the NLF. Isotherm experiments were conducted to determine the HOC sorption capacity of individual MSW components in ultrapure water, acidogenic leachate, and methanogenic leachate. Batch desorption tests were conducted in the same liquid phases. The sorbents had been characterized in previous research [i.e., cellulose, hemicellulose, and lignin contents, elemental analysis, solid-state 13C-nuclear magnetic resonance (NMR) spectra, and BET surface areas]. Single-solute isotherm results showed that PVC had the largest HOC sorption capacity of the MSW components while fresh office paper had the lowest. In general, changes in sorption capacity were negligible when HOC isotherm experiments were conducted in acidogenic and methanogenic leachates. However, organic constituents in acidogenic leachate appeared to have a plasticizing effect on PVC such that HOC sorption capacity decreased and isotherm linearity increased. The importance of the amorphous fraction of sorbent organic matter on HOC sorption capacity was tested by conducting toluene isotherm experiments with three polyethylenes (HDPE, MDPE, and LDPE). Among the polyethylenes, LDPE, the sorbent with the highest amorphous fraction, exhibited the highest sorption capacity while HDPE, the sorbent with the lowest amorphous fraction, exhibited the lowest. For NLF newsprint, the most degraded sample, which was collected near the landfill bottom, exhibited the largest toluene sorption capacity. With respect to sorbent characteristics that control HOC sorption, the increases in the O-alkyl/alkyl ratio of biopolymer composites effectively predicted decreases in HOC sorption capacity. The usefulness of the O-alkyl/alkyl ratio for the prediction of HOC sorption capacities was further demonstrated using literature data for phenanthrene and pyrene sorption to sorbents that were less polar than those evaluated in this study. A comparison of fresh and anaerobically degraded MSW components showed that the O-alky/alkyl ration decreased during degradation. Thus, the overall results of the isotherm study show that the affinity of sorbent organic matter for HOCs increases with increasing extent of MSW decomposition because of the preferential degradation of polar biopolymers and the recalcitrance of plastics. Batch desorption tests after an aging time of 30 days showed that PCE desorption from PVC was slowest while that from newsprint and degraded office paper was fastest. Toluene desorption rate predictions for simulated mixed MSW were made for two landfill scenarios: (1) a 1960 MSW composition with a low plastics content and (2) a 1997 MSW composition containing a larger proportion of plastics. Experimental results for the 1960 scenario showed that the model prediction closely matched the experimental data. Additional experiments are required to verify the model prediction for simulated mixed refuse with a 1997 composition. Overall, the results of the desorption tests illustrated that the presence of plastics decreases HOC release rates. Therefore, HOC release rates should be smaller in landfills containing sizable quantities of synthetic polymers.
Date: 2003-07-25
Degree: MS
Discipline: Civil Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/2005


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