Microcontaminant removal in secondary effluents by solar photo-Fenton at circumneutral pH in raceway pond reactors

Abstract

This paper deals with raceway pond reactors (RPRs) as an alternative photoreactor for solar photo-Fenton applications. Raceway pond reactors are common low-cost reactors which can treat large volumes of water. The experiments were carried out with Fe3+:EDDS complex in the secondary effluent of a municipal wastewater treatment plant spiked with a mixture of 100 μg/L each of five pharmaceuticals (carbamazepine, flumequine, ibuprofen, ofloxacin and sulfamethoxazole) at circumneutral pH. In a preliminary stage, two operating strategies, sequential addition of iron sulfate and Fe3+:EDDS complex at a 1:2 molar ratio were compared, and Fe3+:EDDS complex was found to be the best option. The effect of liquid depth (10, 15 and 20 cm) was also explored. 90% pharmaceutical removal was achieved with accumulated solar UV energy of around 1kJ/L. Finally, RPRs and tubular photoreactors with compound parabolic collectors (CPC) were compared under realistic conditions. Pharmaceutical removal efficiency was four times higher, increasing from 0.26mg/kJ with CPC reactors to 1.07mg/kJ in the 15-cm-deep RPR. As far as the authors know, this is the first detailed study on the effect of liquid depth in RPRs at circumneutral pH.