Abstract
This paper explores the feasibility of employing drinking water treatment sludge (WTS) mixed with soils, lime, or rock powder in geotechnical applications, as well as discusses the sustainability of the approach based on experimental results, aiming at the beneficial reuse of waste and the preservation of natural geomaterials. The selected materials were two soils largely used in earthworks, two WTSs, a high purity calcium hydrated lime, and rock powder from a granitic–gneissic quarry, all occurring in São Paulo State, Brazil. The mixtures were chemically, mineralogically, and geotechnically characterized, and the geotechnical properties permeability, shear strength, and deformability were investigated. Soil-WTS mixtures showed hydraulic conductivity (10−10–10−6 m/s, depending on soil and WTS), effective cohesion (10–30 kPa), friction angle (34°–40°), undrained strength (>50 kPa), and compression index (0.1–0.4) compatible with those of soils usually employed in earthworks. Lime:WTS and rock powder:WTS mixtures achieved 50 kPa undrained strength for WTS contents lower than 24% and 8%, respectively, and could be used as daily and intermediate covers of waste landfills, as well as in other applications with low soliciting stresses. The possibility of WTS being pumped instead of transported by trucks was analyzed in the light of results from rheological tests.
Highlights
The chemical composition of both Water treatment sludge (WTS) obtained by X-ray fluorescence in terms of soils through which the Taiaçupeba-WTS, collected in a reservoir, major elements is presented in Table 2, while chemical parameters are presented in Table is The mainly composed tests of amorphous with traces of quartz, and kaolinite
The experimental investigation showed that soil:WTS mixtures are sound multipurpose geomaterials from a geomechanical point of view, considering permeability, shear strength, and deformability properties
Lime:WTS and rock powder:WTS mixtures can be used for applications with low soliciting stresses
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Water treatment sludge (WTS) is the residue generated at water treatment plants (WTPs) by the regular washing of decanters and filters. The main treatment processes to transform raw water into potable water in a conventional WTP are coagulation, flocculation, decantation, filtration, pH correction, disinfection, and fluoridation. During these processes, several chemicals are added to the water, e.g., chlorine, coagulants, lime, and fluorine. Coagulants (ferric, alum, polymeric) cause impurities to accumulate at the bottom of sedimentation basins and filters, which are periodically washed, producing WTS
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