Date of Award

1-1-2011

Document Type

Campus Access Thesis

Department

Civil and Environmental Engineering

First Advisor

Nicole D Berge

Abstract

Escalating production and subsequent incorporation of engineered nanomaterials in consumer products increases the likelihood of nanomaterials being discarded in municipal solid waste (MSW) landfills. Many commonly discarded products have been reported to contain nanomaterials, including plastics, ink jet printer paper, textiles, cosmetics, sunscreens, and sporting goods. Although no direct measurement or inventory of nanomaterial disposal has been documented in the literature, life cycle based studies predict that over 50% of nanomaterials produced will likely eventually reside in MSW landfills. It is possible that nanomaterial fate within landfills will be dictated by leachate composition. Typically, mature landfill leachate contains high concentrations of refractory dissolved organic matter and high electrolyte concentrations. Studies have shown that organic matter and electrolyte concentration and composition greatly influence nanomaterial aggregation and deposition, and thus subsequent material mobility. The purpose of this study was to evaluate the behavior of single walled carbon nanotubes (SWNT) in mature landfill leachate. To achieve this goal, the electrokinetic properties and relative stability of the carbon nanotubes were measured in representative mature landfill leachate. Additionally the mobility of nanomaterials in sand and mixed MSW was evaluated by conducting saturated 1-D column experiments.

Batch experiments were conducted to evaluate the influence of humic acid (HA) concentrations (20 - 800 mg/L as C), ionic strength (NaCl: 50 - 400 mM), and pH (6, 7 and 8) on the electrophoretic mobility and relative stability of SWNTs. Additionally, 1-D saturated column experiments were performed to evaluate carbon nanotube mobility in Ottawa sand (20-30 mesh) and mixed MSW (simulated using representative waste materials) in the presence of a HA (400 mg/L) and ionic strength (200 mM NaCl).

Results from this study indicate the addition of HA (20-800 mg/l) significantly increased the surface charge and stability of the nanomaterials. Thus, the presence of high molecular weight organics (e.g. fulvic acid, HA) present in mature leachate may act to stabilize carbon nanotubes in landfill environments. Furthermore, changes in solution pH (6-8) resulted in negligible changes in SWNT electrokinetic properties and suspension stability. The pH values evaluated in this study are representative of those found in landfill leachate, suggesting that pH will not control nanomaterial behavior in waste environments. Additionally, for all HA concentrations evaluated in this study, an increase in the salt concentration lead to a subsequent reduction in the surface charge of SWNT. Therefore, both ionic strength and organic concentration are dominant factors influencing changes in the surface charge and stability of carbon nanotubes in landfill leachate. Results from one dimensional saturated column experiments showed that the maximum travel distances calculated for carbon nanotubes in sand (1.9 m) and mixed MSW (1.07 m) were significantly greater than those reported in other studies without HA and lower concentrations of monovalent ions. Results from these column experiments suggest mobility of SWNTs, and possibly of other nanomaterials, in waste environments may be significant and should be examined more closely.

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