Biochar–calcium peroxide composite for sustained tebuconazole removal via adsorption and surface-mediated oxidative degradation

Constructed wetlands and other nature-based solutions (NBS) are widely used to mitigate pesticide runoff from agricultural landscapes, but their performance is often limited by short hydraulic retention times and fluctuating environmental conditions. To enhance the pollutant removal capacity of NBS, we developed a biochar-calcium peroxide (CaO₂) composite material designed to combine adsorption with oxidative degradation. The composite was fabricated by embedding biochar and CaO₂ into a cement matrix and achieved up to 76.8 % removal of tebuconazole after 30 days of static incubation, which was 2-6 times higher than CaO₂ alone (10-20 %), depending on biochar loading and solution pH. Notably, under acidic conditions (initial pH ∼5.6), the oxidative degradation contribution of the composite (35-47 %) increased by approximately 20-30 times compared with the composite without biochar (1.9 %). Moreover, incorporating CaO₂ into biochar moderated its consumption and reduced CaO₂ loss by nearly 50 % after 30 days of incubation in water, enabling a more sustained release of reactive oxygen species (ROS). The material maintained stable performance under both acidic and unbuffered conditions, demonstrating applicability under variable field environments. These findings demonstrate the potential of biochar-CaO₂ composites to improve the robustness and effectiveness of NBS for decentralized water treatment of pesticide-contaminated runoff.