article · Scientific Reports
Alum sludge generated during drinking water purification presents a major disposal challenge because of its high water content and bulky volume. Conditioning this sludge with a synthesised choline-glycine ionic liquid significantly enhances dewatering performance, achieving an efficiency of 47 percent under optimised conditions. This improvement is driven by partial charge neutralisation and the creation of an improved floc structure, as evidenced by notable shifts in zeta potential. In addition to improving dewatering, the conditioned sludge can be repurposed directly or following thermal treatment as an adsorbent for industrial wastewater. When tested on Synozol KHL dyes, the modified material showed high adsorption capacities of 43.6 milligrams per gram for red dye and 90.1 milligrams per gram for blue dye, offering a circular waste-to-resource solution.
Water treatment plants generate massive amounts of alum sludge that are costly and difficult to dry and dispose of safely. Using an ionic liquid to improve dewatering while simultaneously converting the dried waste into an effective dye adsorbent addresses two environmental challenges at once: reducing treatment plant waste volumes and producing low-cost materials for industrial wastewater clean-up.
This process could enable drinking water utilities to cut disposal volumes and industrial textile processors to source low-cost adsorbents for dye removal. The research represents an applied, laboratory-tested concept demonstrating technical feasibility in small-scale batches. Moving toward commercialisation would require pilot-scale validation, cost analyses of the ionic liquid, and testing on complex, real-world industrial effluents.
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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.
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DOI: 10.1038/s41598-026-65696-x
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