Re-engineering alum sludge using choline–glycine ionic liquid for enhanced dewatering and dye adsorption in wastewater treatment

Abstract

Abstract Large quantities of by-product alum sludge (Al-S) generated from drinking water treatment plants pose significant environmental and disposal challenges due to their high water content and large volume. This study aims to develop a sustainable conditioning and valorization strategy for Al-S using a choline–glycine ionic liquid ([Ch]–[AA]). The ionic liquid was synthesized and applied as a sludge conditioner to enhance dewatering performance. Under optimized conditions, the dewatering efficiency reached 47%, accompanied by a notable zeta potential shift, indicating partial charge neutralization and improved floc structure. To enable sludge valorization, the conditioned sludge was reused as an adsorbent, either directly or after thermal treatment. The modified materials exhibited high adsorption capacities toward Synozol KHL dyes, reaching 43.6 and 90.1 mg g⁻ 1 for Red and Blue dyes, respectively. Adsorption behavior was well described by the Langmuir isotherm and pseudo-second-order kinetic model. Thermodynamic analysis indicated an exothermic adsorption process, with spontaneity dependent on operating conditions. Overall, the results demonstrate an effective waste-to-resource approach in which enhanced dewatering facilitates the conversion of alum sludge into a functional adsorbent for wastewater treatment, supporting sustainable sludge management.