Effect of temperature and photon absorption on the kinetics of micropollutant removal by solar photo-Fenton in raceway pond reactors

- The activated iron Fe3+∗ is proposed to explain irradiance saturation of photo-Fenton.
- The photo-Fenton model fits irradiance and temperature effects on reaction rate.
- Model parameters were obtained at lab scale and validated at pilot plant scale.
- Light absorption coefficient of ferric iron increases with temperature.
- High treatment capacity of 135 mg/m2 h was achieved for 90% acetamiprid removal.

Solar driven photocatalysis is considered as an environmental friendly treatment for micropollutant removal from secondary wastewater treatment plant effluents. The photo-Fenton process is efficient in persistent organic pollutant degradation and the use of low cost reactors with variable light path length such as raceway pond reactors (RPR) has been recently proposed. The aim of the study was to develop a simplified kinetic model predicting micropollutant removal rate as a function of environmental variables (irradiance and temperature), geometrical variables (light path length) and operating variables (reactant concentration). The parameters were obtained by fitting the model to 36 experimental conditions in 1.25-L cylindrical reactors at lab scale and then validated in a 360-L RPR at pilot plant scale. In the studied range, 10-40 °C, temperature enhances the photo-Fenton reaction rate by: i) accelerating the oxidation of ferrous iron with hydrogen peroxide (thermal Fenton); and ii) making the light absorption coefficient of ferric iron higher, that is the VRPA. The proposed photo-Fenton model takes into account both effects and properly fit experimental data. Considering 90% removal of the pesticide acetamiprid at an initial concentration of 100 μg/L, a treatment capacity of 135 mg/m2 h was achieved with low reactant concentrations, 10 mg/L Fe2+ and 50 mg/L H2O2. The presented results encourage the application of this modeling strategy for process optimization, design and operation of raceway pond reactors for micropollutant removal by solar photo-Fenton.