Lime Sludge Stabilization of Sand for Capping Sanitary Landfills

Abstract

Absence of adequate quantities of suitable capping material, such as clay, is a major problem at many landfill sites. The research presented in this paper was undertaken to develop alternative capping materials by stabilizing river sand with sludge additives. Different percentages of sewage sludge and lime sludge were blended with river sand and the mixtures were evaluated for their suitability as capping materials. An effective capping material, when compacted properly, should maximize density, reduce permeability, and maintain stability with respect to slope failure and volume changes. Results from this evaluation procedure suggest that sewage sludge is not effective in stabilizing sand for capping purposes. The addition of sewage sludge decreases maximum dry density from 102 lbs/ft 3 (1.63 Mg/m 3 ) for pure sand to 76.5 lbs/ft 3 (1.22 Mg/m 3 ) for the 40 percent mixture, whereas the permeability remains in the 10 −4 cm/sec range. Contrary to sewage sludge, lime sludge effectively stabilizes sand and can be used to produce a feasible capping material. With the addition of lime sludge, the maximum dry density increases from 105.6 lbs/ft 3 (1.69 Mg/m 3 ) for pure sand to 108.0 lbs/ft 3 (1.73 Mg/m 3 ) for the 10 percent mixture, and then decreases to 99.6 lbs/ft 3 (1.6 Mg/m 3 ) for the 50 percent mixture. The permeability decreases from an initial value of 8.4 × 10 −4 cm/sec for 0 percent sludge content to a low of 1 × 10 −6 cm/sec at 40 percent sludge content. On the basis of these results, the 20 percent lime sludge mix is considered to provide the best compromise between high density and low permeability in a compacted state. The 20 percent mix is also expected to be stable with respect to volume changes and slope failure as indicated by durability testing, shear strength parameters, and stability analysis.