Impact of Turbidity-Causing Substances on Fluoride Removal and Sludge Properties with a New Integrated Coagulation–Adsorption Fusion Technology in Treating Groundwater

A new integrated fusion technology combining a novel bimetallic fluoride-removing coagulant (BFrC) and coagulation-driven adsorption process is introduced to remove fluoride (F−) from groundwater. The influence of a turbidity-causing substance (TCS) on F− removal and sludge properties are also investigated, and the morphologies of BFrC and flocs are characterized. The results show BFrC exhibits distinct concentration-dependent mesoscopic morphologies, mainly consisting of more diverse small, interconnected floc-like structures at the working concentration, and gives a large surface area microstructure, providing abundant F− adsorption sites. TCS addition reduces BFrC dosage while enhancing sludge settleability, thickening efficiency, and dewaterability. At 0, 0.5, and 2 g/L TCS additions, the ratios of mixed liquor suspended solids (MLSS), apparent sludge volume index (SVIa), water, and solid content are 20.59:5.27:1, 22.9:2.61:1, 1.66:1.2:1, and 0.21:0.757:1, respectively. Increasing TCS addition improves the compactness, size, packing density, and stacking behavior of flocs, fundamentally explaining the variations in sedimentation, compressibility, and dewaterability, demonstrating the dual role of TCS addition in optimizing F− removal and sludge treatment, and supporting the practicality of this integrated technology in removing F− from groundwater.