Using bio-based CaCO₃ functionalized sediment to simultaneously remove algae and COD through adsorption and...

In-situ turbidity enhancement can suppress algal growth in reservoirs but often exacerbates chemical oxygen demand (COD) accumulation due to incomplete organic removal. This study presents a biologically synthesized bio-CaCO₃-modified sediment, engineered via Bacillus-induced carbonate precipitation, to simultaneously control algae and reduce COD. The material forms 15-30 nm core-shell clusters with enriched -OH/-COOH groups and mesopores (∼19.76 nm), confirmed by SEM, XRD, FTIR, and BET (+1.02 m² g^-1). Adsorption tests against Microcystis aeruginosa, Chlorella, and Limnothrix showed Langmuir-type monolayer binding (R² > 0.97) and pseudo-second-order kinetics. XDLVO theory and DFT analysis revealed strong EPS-Bio-CaCO₃ interactions (ΔE_AB = 31.28 mJ m^-2; ΔE_ads = -1.07 ev). Optimal conditions (7.5 wt % CaCO₃, 56 % residual Ca²⁺, 85 min) achieved 93.8 % Chl-a removal, 88.6 % COD reduction, and 87.5 % turbidity control (R² = 0.98), with minimal Ca²⁺ leaching. By integrating chemisorption, interfacial adhesion, and pore confinement, this material provides a stable, eco-friendly strategy for dual pollutant control and in-situ sediment remediation.