Abstract
This work presents the comparison of four advanced oxidation processes driven by UVC-LED radiation (278 nm—2 W/m2) for simultaneous bacteria inactivation (Escherichia coli—106 CFU/mL) and microcontaminant removal (imidacloprid—50 µg/L) in simulated wastewater secondary effluent. To this end, the activation of H2O2 and S2O82− as precursors of HO• and SO4•−, respectively, by UVC-LED and UVC-LED/Fe3+–NTA (ferric nitrilotriacetate at 0.1 mM) has been studied at different oxidant concentrations. For the purpose of comparison, conventional chlorination was used as the baseline along with bacterial regrowth 24 h after treatment. Disinfection was achieved within the first 30 min in all of the processes, mainly due to the bactericidal effect of UVC-LED radiation. UVC-LED/H2O2 did not substantially affect imidacloprid removal due to the low HO• generation by UVC irradiation at 278 nm, while more than 80% imidacloprid removal was achieved by the UVC-LED/S2O82−, UVC-LED/Fe3+–NTA/S2O82−, and UVC-LED/Fe3+–NTA/H2O2 processes. The most efficient concentration of both oxidants for the simultaneous disinfection and microcontaminant removal was 1.47 mM. Chlorination was the most effective treatment for bacterial inactivation without imidacloprid removal. These findings are relevant for scaling up UVC-LED photoreactors for tertiary wastewater treatment aimed at removing bacteria and microcontaminants.
Highlights
In developing countries, municipal and industrial wastewater is discharged without treatment, while in developed countries 50–95% of wastewater is treated through conventional wastewater treatment plants (WWTPs) designed mainly to remove nutrients such as nitrogen, phosphorous, and carbon [1]
advanced oxidation processes (AOPs) are based on the generation of hydroxyl radicals (HO ), which are very effective for microcontaminant removal as well as bacterial inactivation due to their tendency to attack pollutants unselectively [5]
These results show that the use of H2 O2 in combination with UVC-light-emitting diodes (LEDs) (278 nm) enhances bacterial inactivation, it does not substantially affect microcontaminant removal
Summary
Municipal and industrial wastewater is discharged without treatment, while in developed countries 50–95% of wastewater is treated through conventional wastewater treatment plants (WWTPs) designed mainly to remove nutrients such as nitrogen, phosphorous, and carbon [1]. The tertiary treatment of wastewater for its subsequent reuse for irrigating crops has become an essential element of the urban water cycle, and one of the best strategies for fighting water scarcity and climate change To this end, the inactivation of pathogenic microorganisms is required, the simultaneous removal of contaminants of emerging concern is gaining greater attention because the accumulation of these compounds implies a potential collateral effect on human populations and the environment [2]. Many researchers have emphasized the need to develop new tertiary treatments—alternatives to classical treatments such as chlorination or ozonation—since it is necessary to prevent the formation of harmful byproducts during treatments In this sense, the advanced oxidation processes (AOPs) have been studied alongside the most efficient tertiary treatment options in order to remove microcontaminants and pathogens present in WWTPs’ secondary effluent [4]. AOPs are based on the generation of hydroxyl radicals (HO ) (a highly oxidative species), which are very effective for microcontaminant removal as well as bacterial inactivation due to their tendency to attack pollutants unselectively [5]
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