Effect of compaction on physical properties of a sewage sludge and red gypsum mixture as intermediate landfill cover

Leaching Behaviour of Synthetic Leachate through a Sewage Sludge and Red Gypsum Composite as Intermediate Landfill Cover

“…Hydraulic conductivity tests were carried out in a series of columns using the constant head technique for 180 days (Figure 1). The column set-up was identical to that of [23]. Each sample was compacted to about 75 mm thick using a caulk gun and sandwiched between two 25 mm thick layers of 5 mm glass beads.…”

“…Sustainability 2023, 15, x FOR PEER REVIEW 4 of 15 [23]. Each sample was compacted to about 75 mm thick using a caulk gun and sandwiched between two 25 mm thick layers of 5 mm glass beads.…”

“…The drop in hydraulic conductivity is attributed to the reduction in porosity; the porosity of samples compacted at 70 and 75% reduced from 60 to 52% and from 57 to 40%, respectively, in 180 days. The porosity of samples was estimated based on the correlation between the degree of compaction and porosity developed in [23]. The initial rapid reduction in hydraulic conductivity within the first 14 days for samples compacted at 75% or more (Figure 2) was due to the particle rearrangement as the leachate percolated through the samples.…”

“…Rosli et al [23] observed that when the mixture was percolated using distilled water, there existed a hydration reaction based on the formation of CSH and CH identified from SEM and EDX. From this finding, the percolation of leachate through the mixture is also expected to form CSH, which is proven by the formation of the lump with an average size of 25 to 30 mm observed in samples extracted from the column after 180 days (Figure 5a).…”

“…With most studies focusing on the hydraulic conductivity and strength properties of the materials [21,22], there is scarce data available on the environmental impact, such as the leaching of hazardous chemicals from the mixtures. A six-month study conducted by the authors of [23] has demonstrated that the hydraulic conductivity of the SS:RG composite can be maintained at 10 −6 cm/s and the leaching of chemicals from the composite is within the regulated limits when flowing distilled water through the composite. Nevertheless, the response of the composite when percolated by synthetic leachate and its effects on the environmental impact are not well understood.…”