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

Advanced oxidation technologies for wastewater treatment have been recognized as promising solutionsfor disinfection. Among them, solar photo-Fenton at near neutral pH is being proposed as alternative dis-infecting technology. This study analyses the role of two solar energy parameters, solar UVA irradiance(intensity in terms of W m−2) and accumulated solar UVA energy dose per unit of volume of treatedwater (QUVA, in terms of kJ L−1), on wastewater disinfection by solar photo-Fenton at neutral pH. Forthis 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 irradiancesassayed, was performed under real sun conditions. These parameters were evaluated during the inactiva-tion of E. faecalis by solar photo-Fenton operating at neutral pH with 20 mg Fe2+L−1and 50 mg H2O2L−1insimulated secondary effluent from a municipal wastewater treatment plant, keeping the temperature at25.0 ± 0.2◦C. Results clearly shown that an increase in irradiance improved the bacterial inactivation rategiving rise to the following first order rate constants: 0.025 ± 0.002, 0.057 ± 0.001 and 0.089 ± 0.004 min−1at 10, 20 and 30 W m−2respectively. Furthermore, the hydrogen peroxide consumption rate increasedwith irradiance: (2.3 ± 0.4)·10−3, (4.6 ± 0.8)·10−3and (6.0 ± 0.8)·10−3mM min−1at 10, 20 and 30 W m−2,respectively. These results showed that, under the tested conditions, E. faecalis inactivation rate by solarphoto-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 irradiancevalue used. These results show that it was possible to monitor a solar photo-Fenton plant for waste-water disinfection on a QUVAdose basis instead of treatment time, when microorganism inactivation isphoto-limited.