Wastewater disinfection by neutral pH photo-Fenton: The role of solar radiation intensity

Advanced oxidation technologies for wastewater treatment have been recognized as promising solutions for disinfection. Among them, solar photo-Fenton at near neutral pH is being proposed as alternative disinfecting technology. This study analyses the role of two solar energy parameters, solar UVA irradiance (intensity in terms of Wm(-2)) and accumulated solar UVA energy dose per unit of volume of treated water (Q(UVA), in terms of kJ L-1), on wastewater disinfection by solar photo-Fenton at neutral pH. For this purpose, a systematic study of the influence of three UVA irradiance levels (10, 20 and 30 W m(-2)) and different accumulated energy doses (0.6, 1.4, 1.8, 2.5, 3.2 and 3.7 kJ L-1), achieved at the irradiances assayed, was performed under real sun conditions. These parameters were evaluated during the inactivation of E. faecalis by solar photo-Fenton operating at neutral pH with 20 mg Fe2+ L-1 and 50 mg H2O2 L-1 in simulated secondary effluent from a municipal wastewater treatment plant, keeping the temperature at 25.0 +/- 0.2 degrees C. Results clearly shown that an increase in irradiance improved the bacterial inactivation rate giving rise to the following first order rate constants: 0.025 +/- 0.002, 0.057 +/- 0.001 and 0.089 +/- 0.004 min(-1) at 10,20 and 30 W m(-2) respectively. Furthermore, the hydrogen peroxide consumption rate increased with irradiance: (2.3 +/- 0.4).10(-3), (4.6 +/- 0.8).10(-3) and (6.0 +/- 0.8).10(-3) mM min(-1) at 10,20 and 30 W m(-2), respectively. These results showed that, under the tested conditions, E. faecalis inactivation rate by solar photo-Fenton at neutral pH was limited by solar UVA irradiance. Consequently, first order kinetics for E. faecalis inactivation versus the accumulated energy dose was observed, regardless of the UVA irradiance value used. These results show that it was possible to monitor a solar photo-Fenton plant for wastewater disinfection on a Q(UVA), dose basis instead of treatment time, when microorganism inactivation is photo-limited. (C) 2015 Elsevier B.V. All rights reserved.