Cocalcination of Drinking Water Sludge with Calcium Carbide Residue for Sustainable Clay Stabilization: Potential Circular Strategy

Abstract

Drinking water sludge (DWS), a major byproduct of urban water treatment, faces growing pressure for sustainable recycling. This study explored a circular approach to DWS management by cocalcining it with calcium carbide residue (CCR), blending the product with ground granulated blast furnace slag (GGBS), and applying it in clay stabilization. The results indicate that the optimized DWS–CCR–GGBS system enabled stabilized clay to reach a 56-day unconfined compressive strength (UCS) of 470 kPa, a 31.2% improvement over that of ordinary portland cement (OPC)-stabilized clay. This enhancement is attributed primarily to the additional aluminum introduced by DWS, which promotes the formation of ettringite and C–A–S–H gels, thereby enhancing the microstructural integrity of the stabilized matrix. DWS–CCR mixtures exhibited optimal performance when calcined at 1,000°C, with effective dosages ranging from 20% to 30% within the GGBS binder system. Moreover, the DWS–CCR–GGBS binder offered substantial environmental and economic benefits, including a 65.2% reduction in carbon emissions, a 22.9% decrease in material cost, and a break-even price approximately 43% lower than that of OPC. These advantages highlight its potential as a sustainable and cost-effective alternative for large-scale soft clay stabilization.