Sorption Behavior and Persistence of Organic Contaminants in Landfills
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2009-11-01
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Abstract
Sorption and desorption are important processes governing the distribution and fate of hydrophobic organic contaminants (HOCs) in landfills. The principal objectives of this research were to evaluate factors that control the sorption and desorption of HOCs from municipal solid waste (MSW), and to develop quantitative descriptions of sorption and desorption that are sensitive to waste composition.
Desorption rates of toluene, o-xylene and tetrachloroethene from individual MSW components [high-density polyethylene (HDPE); poly(vinyl chloride) (PVC); office paper (OP); newsprint (NP); and rabbit food (RF), a model food and yard waste] were determined. The effects of sorbent and sorbate properties, solvent composition (ultrapure water, acidogenic and methanogenic leachates), and contact time (“aging†) on desorption rates were evaluated. HOC desorption rates from plastics were rapid for HDPE (D = 10-10 cm2/s), a rubbery polymer, but slower for PVC (D = 10-13-10-14 cm2/s), a glassy polymer. For biopolymer composites, a large fraction (45-94%) of sorbed HOCs was rapidly released (Dr = 10-9-10-10 cm2/s) while the remaining fraction desorbed slowly (Ds = 10-11-10-16 cm2/s). The toluene desorption rate from PVC was one order of magnitude faster in acidogenic leachate than in either ultrapure water or methanogenic leachate, a
result that was primarily attributed to the plasticizing effect of volatile fatty acids in acidogenic leachate. Solvent composition did not otherwise influence HOC desorption rates. For biopolymer composites, small increases in the slowly desorbing HOC fraction were observed with increased aging time.
The impact of discarded plastic materials on the fate and transport of HOCs in landfills was also examined. Sorption affinity and (de)sorption rates of toluene were compared for individual MSW post-consumer plastics (drinking water container, prescription drug bottle, soda bottle, disposable cold cup, computer casing, carpet, formica sheet and vinyl flooring) and model polymers (HDPE, PVC) at dilute aqueous concentrations. The studied plastic materials and model polymers were characterized [X-ray diffractometry, differential scanning calorimetry, and C, H, and N analyses] to evaluate the effects of the amorphous fraction (famorphous) and the organic carbon fraction (foc) on toluene sorption, and to determine the rubbery and glassy behavior of post-consumer plastics. Generally, partition coefficients (Kp) of toluene in plastic materials were 1 to 2 orders of magnitude higher than in biopolymer composites such as OP and NP. The Kp of toluene in plastics was affected by famorphous but not foc. The diffusivity (D) of toluene in rubbery plastics (model HDPE, drinking water container, and prescription drug bottle) was similar (D = 10-10 cm2/s). Among glassy plastics (model PVC, soda bottle, computer casing, disposable cold cup), the diffusivity of toluene was also similar (D = 10-12 cm2/s) but two orders of magnitude smaller than for the rubbery plastics.
To predict the solid-liquid partitioning of a range of HOCs, one-parameter linear free energy relationships (op-LFERs) between the organic-carbon-normalized partition coefficients (Koc) and the sorbate octanol-water partition coefficients (Kow) were developed for individual MSW components. Kp estimates for toluene sorption to two solid waste mixtures (i.e. one with and one without a glassy plastic) using the new op-LFERs for individual MSW components were in close agreement with experimentally determined Kp values. Discrepancies were larger when Kp values determined with established op-LFERs that had been derived for soil and sediment organic matter, and a MSW mixture. Correlations between HOC diffusion coefficients in rubbery and glassy plastics and HOC molecular size were also established and confirmed. The ability to predict contaminant sorption as a function of both MSW composition and sorbate properties represents a step forward in describing contaminant fate and transport in solid waste systems.
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plastics in landfills, Sorption, op-LFER, polyparameter-LFER, Desorption, Landfills, Organic Contaminants
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Degree
PhD
Discipline
Civil Engineering
