Reuse of drinking water treatment sludge for the removal of antibiotics: The case study of sulfamethoxazole and trimethoprim based on advanced statistical physics models

• Drinking water treatment sludge (DWTS) adsorbed sulfamethoxazole and trimethoprim. • The sludge achieved uptake capacities higher than 36 mg/g for both antibiotics. • Leaching tests confirmed the chemical stability of the sludge. • The antibiotics removal was due to hydrogen bonding. • In wastewater, DWTS uptake reached 18 mg/g for TMP and 11 mg/g for SMX. This study reports the valorization of drinking water treatment sludge (DWTS) to remove antibiotics from water. Sulfamethoxazole and trimethoprim were used as model antibiotic molecules to analyze the removal capacity of DWTS. A detailed physicochemical characterization of this DWTS was performed including a leaching assay to determine its chemical stability. Kinetic and equilibrium studies were performed at pH 6.5 and 20–40 °C in single and binary aqueous solutions containing the tested antibiotics. Different models including statistical physics theory were applied to correlate and analyze the antibiotic adsorption on DWTS. The application of DWTS to remove the tested antibiotics from real treated wastewater was assessed. The leaching analysis proved that this sludge was chemically stable and can be used safely in (waste)water treatment. The results showed that DWTS can remove both antibiotics with uptake capacities up to 36 mg/g. This sludge displayed better adsorption properties to remove sulfamethoxazole in both single and binary systems. The binary studies indicated the presence of antagonistic removal of both antibiotics. The oxygenated functional groups of the DWTS were involved in the adsorption mechanism of the tested antibiotics via hydrogen bonding. The results in wastewater showed uptake capacities up to 18 mg/g, namely for trimethoprim, despite the presence of chemical species that interfere with their removal. Therefore, DWTS are an alternative that can be used to reduce the costs of treatment systems, namely in the removal of antibiotics, besides contributing to the sustainability and circular economy in the water sector.