Micropollutant removal in real WW by photo-Fenton (circumneutral and acid pH) with BLB and LED lamps

Abstract

In this study, photo-Fenton treatment was performed to remove a target compound (propranolol, PROP) from wastewaters of secondary effluents coming from WWTP. Two different radiation sources were tested: BLB and UV-A LEDs, which implies low electrical power and no mercury content. The differences observed in the PROP removal with both lamps may be due to the different radiation distribution, absorption inside the reactor, emission angle and wavelength emission, which are key parameters in the radiation field of the photoreactor. Four wastewaters (IFAS, MBR, CAS and CAS-NE) and ultrapure water were tested to determine the influence of water matrix. Instead the propranolol degradation using UV-A LEDs was smaller than using BLB lamps, in ultrapure water the degradation was very similar. The matrices with more organic matter and turbidity achieved low propranolol removals due to the competition for hydroxyl radicals and the effect of the light scattering. In addition, photo-Fenton at neutral pH (to avoid the acidification/basification) was also carried out using two chelating agents (EDDS and EDTA). Two molar ratios ligand-Fe(II) were tested (1:1 and 1.5:1). EDDS with L:Fe(II) molar ratio 1:1 was selected based on studies of MP degradation, biodegradability and toxicity. Comparisons between conventional photo-Fenton and photo-Fenton with EDDS-Fe(II) were performed with UV-A LEDs. For Milli-Q and IFAS best results were achieved in conventional photo-Fenton (32.9% for IFAS instead of 14.3% in EDDS-Fe(II)). Contrary, for the MBR, CAS and CAS-NE the best results were shown for EDDS-Fe(II) photo-Fenton. In IFAS, biopolymers and humic substances were the responsible of the different behavior of IFAS than other WW. Finally, for conventional photo-Fenton, dark Fenton plays an important role during the first 30 s, then, photo-Fenton controls the process. For circumneutral photo-Fenton, dark Fenton is not so important during the initial time. These observations have been corroborated by different kinetic fittings for different reaction times.