Green valorisation of alum sludge using ionic liquid for industrial dye effluent treatment

Green amino acid ionic liquid choline glycine ([Ch][Gly]) was prepared and applied as an effective conditioning agent for alum sludge (Al-S) to enhance its suitability as a sustainable adsorbent for wastewater treatment. The structural and morphological characteristics of the conditioned sludge were examined using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX). The modified Al-S was subsequently evaluated for dye adsorption of from both synthetic wastewater containing Methylene Blue Dye (MBD) and real industrial effluent containing Dispersed Yellow Dye (DYD). Adsorption performance was optimised through contact time and operational parameter studies. The maximum adsorption capacity of Al-S reached 14.2 mg g−1 for MBD (30 ppm) after 21 h at a dosage of 1.0 g L−1 and pH 5.6, while a higher capacity of 16.3 mg g−1 was obtained for DYD (20 ppm) after 24 h using 0.5 g L−1 of Al-S at pH 7.0. Thermodynamic analysis indicated that the adsorption process was endothermic and non-spontaneous. Isotherm modelling showed that the Langmuir model provided the best fit, while kinetic studies confirmed a pseudo-second-order mechanism. These findings demonstrate a sustainable valorisation pathway for dewatered alum sludge, offering a low-cost and environmentally benign solution for treating dye-contaminated wastewater within an industrial ecology framework.