Evaluating Sludge from Landfill Leachate Treatment as a Soil Conditioner Using the Analytic Hierarchy Process: Balancing Soil Health, Toxicity, and Cost

This study evaluates the potential of raw sludge (RS) and pyrolyzed sludge (PS), derived from landfill leachate treatment, as sustainable soil conditioners by examining their impacts on soil health, toxicity, and cost-effectiveness. Soil health indicators—including pH, EC, organic carbon, and nutrient levels—were monitored over incubation, while toxicity was assessed through cytotoxicity tests on HepG2 cells and phytotoxicity assays using maize germination. Cost analysis incorporated amendment dosages and energy requirements for pyrolysis. RS demonstrated higher nutrient content and greater improvements in soil fertility, whereas PS exhibited reduced cytotoxicity and enhanced phytotoxicity performance, reflecting the detoxifying effect of pyrolysis. However, PS incurred significantly higher production costs. To integrate these multifaceted criteria, the Analytic Hierarchy Process (AHP) was employed. Toxicity emerged as the most critical criterion, followed by soil health and cost. AHP results identified 5 g kg⁻¹ RS as the most practical and balanced option due to its favorable nutrient profile, low toxicity at this dosage, and cost-efficiency. These findings underscore the environmental and economic benefits of valorizing landfill leachate sludge in agriculture, promoting resource recovery, circular economy strategies, and reduced dependence on synthetic fertilizers.