Analysis of the incorporation of sludge from a water treatment plant (WTP) into soil for use in impermeable layers of a sanitary landfill

The collection and treatment of water are crucial to ensure the provision of safe drinking water for the population. Raw water is treated using physical and chemical processes to produce treated water for distribution to cities, but the processes also generate waste. The waste from Water Treatment Plants (WTP) is known as WTP sludge. Disposing of WTP sludge in an environmentally friendly manner is crucial. In order to minimize the environmental impact, waterproof barriers are designed in landfills to prevent the contamination of underground water resources provoked by the percolation of generated liquids. This study assessed the geotechnical feasibility of using WTP sludge as a waterproofing material in landfills. The benefits of this process include a decrease in soil extraction from quarries and the environmentally sound disposal of waste. The approach is based on the growing demand for sustainable practices in the treatment and disposal of waste, while also seeking a technical alternative to partially replace soil in geotechnical structures, aiming for resource conservation. The study characterized the sludge from the WTP and conducted tests on compaction, hydraulic conductivity, and oedometric consolidation. Two different fractions of the soil-sludge mixture (2.5% and 5%) were used, with moisture contents ranging from 17.62 to 46.71%. The results showed that the addition of sludge either maintained (2.5%) or improved (5%) the permeability characteristics of the residual soil under study. In optimal conditions, the permeability was approximately 10-9 m/s, which renders it suitable for use in waterproofing layers for landfills.