Industrial waste-derived biochar composites for the removal of water-borne 4-nitrophenol: assessing cost-effectiveness and sustainability.

Water pollution remains a critical environmental challenge, necessitating the development of cost-effective treatment methodologies. This study investigates sustainable alternatives to conventional adsorbents, focusing on the synthesis and application of Blast Furnace Slag (BFS)-supported biochar. The composite adsorbent was synthesized through pyrolysis of sewage sludge and wood sawdust combined with BFS for the removal of 4-nitrophenol (4-NP). The composite adsorbents were characterized for their physical and chemical properties. Adsorption studies on 4-NP were performed under various operating conditions such as pollutant dosage, pH, and temperature. The composite demonstrated a maximum adsorption capacity of 12 mg/g at pH 6, using an adsorbent dose of 1.0 g/L, an initial 4-NP concentration of 20 mg/L, a contact time of 90 min, and a temperature of 25 °C. The adsorption process was evaluated using five linear isotherm models, with Langmuir fitting best and pseudo-second-order kinetics governing the mechanism. Economic analysis revealed that the production cost of 1 kg of adsorbent was 3.35 USD. Additionally, the sustainability of the adsorbent was assessed using the sustainability footprint methodology, along with a sustainability score-based approach to examine its impact on all 17 Sustainable Development Goals (SDGs). The study findings support the use of industrial and residential waste materials as viable resources for producing cost-effective adsorbents to combat various water pollutants.