Abstract
The objective of this study was to investigate the swelling potential of compacted lime-softening sludge for application in landfill liners. The study involved the assessment of the effect of compaction and moulding moisture content (30–40%), corresponding to the Proctor standard compaction test. One-dimensional oedometer swell tests were conducted using distilled water, tap water, and municipal landfill leachate, resulting in the determination of the expansion indices. Moreover, changes in the moisture content and dry density during the swelling process were investigated. The expansion index was significantly influenced by the initial moisture content and liquid chemistry. Subsequently, these factors also affected the sludge dry density decrease, and its moisture content increase, whereas the impact of the initial dry density on expansion was of low importance. An increase in the sludge moulding moisture content, limited swelling in all liquids used. The highest expansion, dry density, and moisture content changes due to swelling were identified for leachate at w < wopt. It should be underlined that the effect of liquid on the swelling potential faded away along with a further increase in the moisture content w > wopt. The novelty of the work lies in identifying a significant plunge of the expansion index at w ≈ wopt for the leachate swelling test. The lime-softening sludge non-swelling moisture content was defined as wnon ≈ (wopt + 4.0%) − (wopt + 4.5%). For practical engineering implications, the moisture content between (wopt + 2.0%) and (wopt + 4.0%) was provided for the most suitable sludge application in landfill liners.
Highlights
The objective of this study was to investigate the swelling potential of compacted lime-softening sludge for application in landfill liners
The research confirmed that lime-softening sludge compacted at a moisture content higher than the optimum moisture content determined by the Proctor standard compaction test, i.e., wopt + (1–2)% could replace mineral soils in landfill liners because it met the requirements of inert waste landfill liners ( k≤ 1.0·10−7 m/s), irrespective of the leachate pH and hazardous and non-hazardous waste landfill sites (< 1.0·10−9 m/s)
The analysis showed the highest amounts of calcium ( Ca2+) (31.27–32.26%), and relatively low concentrations of iron (Fe3+), magnesium (Mg2+), and aluminium (Al3+)
Summary
The objective of this study was to investigate the swelling potential of compacted lime-softening sludge for application in landfill liners. The highest expansion, dry density, and moisture content changes due to swelling were identified for leachate at w < wopt. The research confirmed that lime-softening sludge compacted at a moisture content higher than the optimum moisture content determined by the Proctor standard compaction test, i.e., wopt + (1–2)% could replace mineral soils in landfill liners because it met the requirements of inert waste landfill liners ( k≤ 1.0·10−7 m/s), irrespective of the leachate pH and hazardous and non-hazardous waste landfill sites (< 1.0·10−9 m/s). The sludge compaction in the range of moisture contents between wopt and wopt + 4% at a dry density, which is not less than that indicated via the standard compaction Proctor test method of 0.95·ρds, allows to reach the lowest hydraulic conductivity and enables swelling reduction. This should be performed by following the requirements of the hydraulic permeability, dry density, and shear s trength[12]
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