Removal of sulfamethoxazole in aqueous solution by two activated carbons from secondary sludge and biomass

Abstract

Removal behavior of sulfamethoxazole (SMX) by two carbonaceous materials was studied. The adsorbents were obtained by pyrolysis (550°C, 1 h under nitrogen flow), followed by acid washing of residuals consisting of a biological secondary sludge (SSCM) and a local herbaceous plant (Phragmites communis, RCM). The morphology, elemental composition and chemical properties of the obtained carbonaceous materials were fully characterized. The equilibrium and kinetics of SMX adsorption were studied and modelled, together with the pH and temperature effects. Additional heating of the materials under limited aerobic conditions (800°C, 1 h) improved their adsorption capacity, compared with simple pyrolysis at 550°C only. The uptake rates followed a second-order model, while the adsorption capacities (up to 30.4 and 21.5 mg g–1) were predictable with Freundlich and Langmuir isotherms (heterogeneous vs. homogeneous adsorption, on SSCM and RCM, respectively). Removal of sulfamethoxazole was most effective at acidic pH in both materials. The thermodynamic parameters (ΔG°, ΔH°, ΔS°) indicated that SMX adsorption was spontaneous, favorable, exothermic and reversible. The residuals were turned into promising low-cost sorbents for removal of sulfamethoxazole from water.