The effect of leachate seepage on the mechanical properties and microstructure of solidified sludge when used as a landfill temporary cover material

Abstract

In this study, the effect of leachate seepage on the strength properties of a landfill temporary cover material: sewage sludge solidified with soda residue, ground granulated blast furnace slag, and quicklime, was investigated using small-scale column tests. The strength of the solidified sludge was reflected by penetration resistance with a micro penetrometer. The results showed that the penetration resistance increased at first, but then decreased with the increase in duration. The peak value for penetration resistance appeared at around the 75th day under the effect of leachate seepage. In contrast, without leachate seepage, penetration resistance increased at first as duration increased and then remained stable. The main hydration products were calcium silicate hydrate, ettringite and hydrocalumite. Some pollutants, such as copper, chromium, and arsenic, were also stabilized by the solidified sludge. The nuclear magnetic resonance results showed that the sample with highest penetration resistance had a reduced pore volume, especially macropore volume. Furthermore, leachate corrosion and the removal of some substances contributed to the decrease in penetration resistance after long-term seepage. The strength performance of temporary cover in laboratory short-term seepage and leachate soaking environments might be different from that in a landfill leachate seepage environment. This study improves understanding about the performance of temporary cover materials in landfill.

Keywords: Leachate seepage; Microstructure; Penetration resistance; Solidified sludge; Temporary cover material.