Solar-Driven Degradation of Microcystin-LR in Water Using a TiO₂/Zn-Activated Charcoal/Soil Composite

Abstract This study presents the development and field-scale evaluation of a solar-activated TiO₂/Zinc-Activated Charcoal/Soil (TiO₂/ZAC/Soil) composite for the degradation of microcystin-LR (MC-LR) in water systems impacted by harmful algal blooms (HABs). The composite, synthesized from Miscanthus-derived zinc activated charcoal (ZAC), exhibited combined adsorption and photocatalytic functionality under both artificial (~ 500 W/m 2 ) and natural sunlight (400–600 W/m 2 ). Laboratory experiments achieved 96 ± 2% MC-LR removal, while a 144-L outdoor prototype system reached 92 ± 2.6% MC-LR reduction within 96 h of late-summer solar exposure. Kinetic modeling, corrected for water volume loss, followed pseudo-first-order behavior with an apparent rate constant of 0.058 ± 0.004 h⁻ 1 and a half-life of 11.92 ± 0.82 h. LC–MS analysis confirmed progressive degradation of the parent MC-LR molecule and oxidative modification of the toxic Adda moiety, indicating substantial detoxification during early exposure stages. The Area Under the Curve (AUC) analysis was applied to quantify cumulative toxin burden over time. While field replication and environmental variability impose practical limitations, these results demonstrate the potential of TiO₂/ZAC/Soil composite as a low-cost, solar-driven approach for MC-LR attenuation in surface waters and provide a framework for future optimization and large-scale validation.