Potential reuse of drinking water treatment sludge mixed with additives in landfills covers or other low solicitation applications

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Reusing drinking water treatment sludge (WTS) as cover of sanitary landfills can introduce it into the circular economy and partially replace natural soils. However, even after dewatering, WTS water content is very high, and undrained shear strength (s_u) is very low. The incorporation of additives, such as lime (L) or rock powder (RP), can be an alternative to stabilize WTS. This paper presents the s_u of WTS-additive mixtures at different additive contents and investigates the potential reuse of WTS mixed with L or RP as covers of sanitary landfills based on the acceptance criteria for earthworks. Also, it discusses the influence of additive content, curing time, and mixing process on the s_u obtained by vane, fall-cone, and unconfined compression (UC) tests. Results indicated that s_u values obtained for RP are lower than for L addition. Curing time increases s_u; however, s_u does not increase significantly for times longer than 28 days. Depending on the mixing process, two different textures are created: pasty and granular, which are more important than curing time for s_u increase. Generally, granular textures present higher s_u than pasty textures. The acceptance criteria of 10 and 20 kPa were reached for L content of 230% and 300% and RP content of 950% and 1200% (by dry mass basis of WTS). These high values suggest that WTS-L at L content higher than 230% and WTS-RP at RP content higher than 950% can be used in landfill covers provided that a sustainability analysis indicates the carbon footprint decrease.

9th International Congress on Environmental Geotechnics (ICEG2023)

Sustainability