Date of Award

5-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

College/School

College of Science and Mathematics

Department/Program

Earth and Environmental Studies

Thesis Sponsor/Dissertation Chair/Project Chair

Yang Deng

Committee Member

Huan Feng

Committee Member

Shifeng Hou

Abstract

More than 50% municipal solid waste (MSW) is being disposed of within landfills in the United States. Despite many benefits, landfills inevitably produce highly contaminated wastewater - landfill leachate. Landfill leachate represents one of the most challengeable wastewaters in the world. Refractory organic matters and ammonia nitrogen are two major persistent traditional contaminants in landfill leachate. The contaminants ought to be properly removed prior to discharge into natural water resources.

Ferrate (FeO42-) is a potential water treatment chemical agent in which iron is in its + 6 oxidation state. In engineering practice, Fe(VI) can concurrently function as oxidant, coagulant, adsorbent and disinfectant. Up to date, Fe(VI) has been intensively studied for treatment of drinking water, wastewater, and ballast water. However, few attempts have been made to apply Fe(VI) for treatment of landfill leachate.

The overall objective of this thesis was to evaluate ferrate as a new oxidizing agent for treatment of landfill leachate, with an emphasis on removal of two major leachate contaminants - refractory organic matters and ammonia nitrogen. The central hypothesis is that Fe(VI) has an adequately high oxidation capacity to simultaneously degrade refractory organic matters and ammonia in landfill leachate through oxidation, thereby providing a viable alternative for traditional landfill leachate treatment methods. To achieve the overall objective, bench scale tests were conducted in batch mode to pursue four specific objectives: 1) to evaluate the effects of Fe(VI) dose and pH on COD removal and NH3-N removal; 2) to evaluate the effect of chloride on Fe(VI) treatment of landfill leachate; 3) to evaluate the effect of initial NH3-N on Fe(VI) treatment of landfill leachate; and 4) to determine N transformation pathway during Fe(VI) oxidation of NH3- N under different conditions.

Results show that Fe(VI) could simultaneously reduce COD and NH3-N under different experimental conditions. In this study, up to 60% COD and 70% NH3-N were removed. Generally, the treatment efficiency was increased with the increasing dimensionless oxidant demand (DOD). COD removal was due to Fe(VI)-induced oxidation and iron sludge-induced coagulation/adsorption, while ammonia was reduced as a result of Fe(VI) oxidation, in addition to volatilization at high pH. The oxidized NH3-N was oxidized to nitrogen gas and NO3-N. High pH and high DOD appeared to favor the NO3-N formation. At any condition, little NO2--N was produced. Cl- (2,100 - 14,880 mg/L) played a complex role in the treatment. It somewhat increased COD removal at pH 4-5, but slightly slowed down the COD reduction at pH 9. At pH 4-5, a low Cl- level (2,100 - 5,000 mg/L) could inhibit the NH3-N removal; however, more Cl-improved NH3-N reduction at a high Cl- range (5,000 - 14,880 mg/L). In contrast, at pH 9, more Cl-favored the NH3-N removal. More initial NH3-N could compete with COD for Fe(VI), thereby inhibiting the COD removal. Our results provide valuable information regarding the treatability of Fe(VI) for landfill leachate, and demonstrate that Fe(VI) is a potential treatment chemical for landfill leachate.

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