Advanced solar photocatalysis in continuous mode: H2O2-enhanced removal of organic contaminants in simulated and real wastewater

The feasibility of a solar-powered continuous-flow photocatalytic system for the degradation of organic pollutants in aqueous streams was investigated. Fe-doped TiO2 immobilized on polystyrene was tested as a reusable photocatalyst under both batch and continuous operation, using rhodamine B (RB) as a model pollutant. However, the scalability and long-term outdoor performance of Fe-TiO2 photocatalysis remain poorly understood. The system was first optimized in batch experiments under artificial light. Optimization considered H2O2 dosage and addition mode, optical path length, and liquid-to-solid ratio. The system was subsequently validated outdoors over eight months, demonstrating stable performance under varying solar irradiance. The addition of H2O2 significantly enhanced photocatalytic activity. It increased the maximum degradation rate constant from 0.293 h−1 to 1.313 h−1. It also reduced the half-saturation irradiance from 210 to 130 W/m2. These effects result from combined heterogeneous photocatalysis and surface-bound photo-Fenton reactions. Continuous-flow tests confirmed the scalability and predictability of the system: up to 99.8 % RB removal and substantial TOC reduction (from 21.5 to 14.3 mg/L) were achieved in real pharmaceutical wastewater at a residence time of 39 min (4.65 mL/h) under natural solar light (irradiance 700–900 w/m2) with H2O2 addition (0.068 mmol/h). This represents the first demonstration of solar-driven continuous operation using immobilized Fe-TiO2 on polystyrene. The study highlights that the use of a supported photocatalyst, rather than a simple bio-based adsorbent, allows for complete degradation of pollutants via oxidative pathways, rather than mere adsorption. This approach makes the system suitable for low-energy, solar-driven, decentralized water treatment.