A systematic approach towards a zero-waste water treatment: clay-carbon composite adsorbents made from drinking water treatment sludge

Abstract Increasingly stringent water quality standards are forcing more water treatment facilities to implement adsorption steps. Activated carbon is efficient but has a high environmental impact due to CO₂ emissions and energy demand. Adsorbents derived from water treatment residuals offer a potential solution. In this study, a novel laboratory rotary furnace was designed to produce clay-carbon composite adsorbents from drinking water treatment residues. The process was optimized using a statistical design of experiments, representing the first comprehensive statistical analysis of the thermal activation of such residuals. Thermal activation increased the specific surface area almost tenfold (112–201 m²/g). The adsorbents were tested for removal of ibuprofen, caffeine, diclofenac (1 µg/L), and brilliant blue FCF (5 mg/L). Response surface models showed that heating rate (p < 0.003) and ramp duration (p < 0.00002) significantly influenced adsorption capacity. Mass balance calculations suggest on-site production could fully substitute activated carbon and generate surplus material.