Physicochemical Mechanisms and Environmental Benefits of Using Basic Oxygen Furnace Slag for Sewage Sludge Stabilization

Abstract

The increasing demand for inorganic alkalis in industrial processes, coupled with the environmental challenges of their production, has driven interest in sustainable alternatives. This study evaluates the feasibility of basic oxygen furnace (BOF) slag for sewage sludge stabilization by comparing its performance with commercial agents (NaOH and CaO) in batch hydrolysis experiments. The results reveal that BOF slag effectively increases the sludge pH to 12.4 at a dosage of 1.9 g/g of TSS. Although this dosage is higher than that required for NaOH (0.2 g/g) and CaO (1.0 g/g), BOF slag achieves comparable stabilization through a synergistic mechanochemical mechanism. Regarding heavy metals, BOF slag demonstrated superior immobilization capacity compared to caustic treatments; soluble lead (Pb) levels were maintained at 0.52 μg/g, significantly lower than the 9.2 μg/g release observed with NaOH. Pathogen reduction was notably effective, with Salmonella completely inactivated and coliforms reduced to <10 CFU/g using an optimal particle size of 0.6–1 mm. Furthermore, the economic assessment indicates that BOF slag reduces treatment costs by 15–30% compared with those associated with commercial alkalis. From an environmental perspective, the use of this byproduct results in a net carbon footprint reduction of 68–91% per ton of treated sludge, highlighting its potential as a cost-effective and low-carbon alternative for the circular economy in wastewater treatment.