Sustainable char production from pyrolysis of refuse-derived fuel for nitrate removal from water

This study explores a sustainable approach to simultaneously valorising municipal solid waste and remediating nitrate-contaminated water by generating an engineered adsorbent from refuse-derived fuel (RDF) via a thermochemical pathway. RDF feedstock was pyrolysed at 500 °C in a pilot-scale rotary kiln to produce RDF500 char, subsequently modified using zinc chloride in 2:1 wt.% ratio (RDF500-2) to enhance surface functionality and adsorption performance. Modification with ZnCl₂ has been extensively studied, and when handled properly, it does not pose greater environmental risks, thereby supporting sustainability aspects. Furthermore, characterisation through FTIR, BET, and SEM confirmed the introduction of oxygenated groups (-OH, -COOH, -C=O), increased surface heterogeneity, and the development of a micro-mesoporous structure conducive to nitrate adsorption. Fixed-bed column experiments were performed under varying operational conditions, including bed height (5-10 cm), influent flow rate (3-7 mL min^-1), and initial nitrate concentration (67-185 mg L^-1) utilising RDF500-2, to determine breakthrough behaviour and adsorption kinetics. The maximum adsorption capacity was 21.32 mg g^-1, corresponding to 89% nitrate removal efficiency under optimal conditions. The kinetic modelling using Thomas, Yoon-Nelson, Adams-Bohart, Wolborska, and Dose-Response models exhibited an excellent correlation (R² > 0.98), with the Dose-Response and Thomas models showing the best predictive accuracy for column optimisation. A scale-up analysis for a 100 L min^-1 continuous flow system predicted 80% removal efficiency, confirming the practical applicability of modified RDF char (RDF500-2).