Graduation Year

2004

Document Type

Thesis

Degree

M.S.E.V.

Degree Granting Department

Environmental Engineering

Major Professor

Levine, Audrey D.

Keywords

Waste-to-Energy, ash, batch tests, clogging, deposition, precipitates

Abstract

Leachate collection systems consist of a series of pipes installed beneath the waste at the base of a landfill. The liquid drains toward a central location where it is pumped and then treated, discharged, or recirculated. In some landfills, solid precipitates form in the collection system resulting in clogging and malfunctions of the drainage system. The formation of the precipitates is linked to the chemical and biological stability of the leachate generated within the landfill. To control the formation of precipitates and prevent clogging of leachate collection systems, it is important to understand factors that influence leachate characteristics. Ashes from municipal solid waste (MSW) combustion are either placed in monofills or combined with traditional solid waste, and sludges and biosolids from wastewater and drinking water treatment plants when landfilled.

The ashes, depending on the type of combustion process, contain high concentrations of metals and non-biodegradable materials. As the waste degrades, oxygen in the landfill is consumed and the leachate becomes anaerobic. The reducing environment allows for greater solubility of metals. This research tested ashes from three different Waste-to-Energy (WTE) facilities to understand better the role MSW fly ash and MSW bottom ash in the chemical make-up of landfill leachate. Two different types of batch tests were used to analyze the leaching behavior. First, a contact time batch test with a range of different contact times was used to assess the rate at which different elements reach equilibrium. This was followed by a sequential extraction batch test that predicted the total amount of soluble material in the ashes.

The chemical characteristics of the leachate produced by the ashes were understood and the leaching behaviors analyzed, dominant chemical factors that influence the formation of precipitates were identified. This data produced a better understanding of the roles of WTE ashes in the production of precipitates in leachate collection systems.

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