Chemical and geotechnical properties of solidified/stabilized MSWI fly ash disposed at a landfill in China

Abstract

The chemical and geotechnical properties of solidified/stabilized (s/s) municipal solid waste incineration (MSWI) fly ash are of prime importance for the design and operation of landfill sites. This study conducted field and laboratory tests to investigate aging effects on the chemical and geotechnical properties of s/s MSWI fly ash. Field investigations included borehole sampling and cone penetration tests (CPTs), and laboratory analyses included the measurement of the chemical, physical, hydrological, and mechanical properties of s/s fly ash with different fill ages. The results showed that: 1) Cl concentrations in landfill leachate were as high as 52,700 mg.L−1, which may present a technical challenge for leachate treatment; 2) specific gravity decreased with fill age, which was attributed to the leaching of metal elements from the s/s fly ash; 3) mean particle size decreased with fill age, resulting in an increase in the gravimetric moisture retention capacity (MRC) and a decrease in the saturated hydraulic conductivity; 4) gravimetric MRC was much higher than the initial moisture content, suggesting water absorption by s/s fly ash after landfilling; and 5) shear strength decreased with fill age, which was consistent with the CPTs results. To improve the design and operation of s/s MSWI fly ash landfill sites, the following suggestions are made: 1) the use of concentrated MSW landfill leachate in the s/s fly ash process should be avoided to reduce the concentrations of subsequent landfill leachate; 2) leachate generation could be further reduced by improving landfill operation practices and by taking advantage of the absorption capacity of s/s fly ash; and 3) the specific geotechnical parameters of s/s fly ash should be obtained prior to the design of landfill sites, and their aging effects should also be taken into consideration.