Operational challenges in scaling photo-Fenton at neutral pH: Toward real-scale urban wastewater purification

This study addresses the practical challenges associated with implementing the photo-Fenton process at large-scale under neutral pH conditions using UV lamps as irradiation source. Most studies available in the literature have been conducted with high-purity analytical-grade reagents, which are not economically viable for full-scale applications due to their elevated cost. In contrast, this work identifies and evaluates commercially available alternatives. Although analytical-grade reagents generally show higher pollutant removal efficiency, our results demonstrate that Fe 3+ :NTA, Fe 3+ :Citric acid (CA), and ferrous citrate (commercial-grade) showed similar performance during the first minutes of treatment. However, both Fe 3+ :NTA and ferrous citrate were found to be unstable during storage, limiting their practical use. Based on performance and stability, the Fe³⁺:CA complex emerged as the most promising candidate for scaling up the photo-Fenton process. The lower photo-stability of Fe 3+ :CA results in iron precipitation but not in the lamp sleeve, meaning that fouling is reduced, thereby allowing less frequent cleaning of the UV lamps. Economical assessment of Fe 3+ :CA revealed that, in the large-scale pilot, 31 % of the cost is related to fouling removal. In a full-scale facility with a cleaning in place system the cost-effectiveness is significantly enhanced, facilitating the implementation of photo-Fenton at neutral pH in low solar irradiance regions.