Electrical Energy Consumption of Multiscale UV-AOP Reactors for Micropollutant Removal in Drinking Water: Facilitated Prediction by Reaction Rate Constants Measured on a Mini-Fluidic Photoreaction System

A comparative study of reactive manganese species and electron transfer pathway in oxidation efficiency and environmental impact: Which activation route for potassium permanganate is optimal?

Various methods have been explored to activate potassium permanganate (Mn(VII)) for the elimination of organic compounds, typically by generating highly-reactive manganese species (RMnS) or mediated by electron transfer process (ETP). However, the oxidation selectivity, transformation pathways, toxicity byproduct potential, and efficacy in complicated water matrices associated with RMnS and ETP have not been comprehensively evaluated and compared, which is important for selecting a fit-of-purpose mechanism for water remediation. This study selected Mn(VII)/graphite process and ultraviolet (UV)/Mn(VII) process as the model ETP-dominated system and RMnS-dominated system, respectively. RMnS demonstrated significantly higher degradation efficiency for bromophenols, with oxidation rate constants 2.69-6.28 times higher than ETP. The oxidation efficiency of RMnS could be enhance under alkaline condition, whereas the degradation efficiency of ETP is dependent on the combined effects of solution pH and pKa of compounds. Furthermore, RMnS exhibited a stronger dehalogenation capacity, enabling the almost complete release of bromide ions from bromophenols with the formation of non-brominated organic product. Correspondingly, the RMnS process obviously reduced the brominated disinfection byproducts formation potential (DBPFPs). Mass spectrometry results revealed that the ETP process tended to form more polymeric brominated dimer products during the oxidation of bromophenol, leading to more DBPFPs production. ETP process showed superior degradation efficiency in real water backgrounds due to robustness against complicated water matrices, and displayed lower energy and oxidant consumption. Findings of this study elucidated the efficiency and mechanistic differences between RMnS and ETP, providing guidance for selecting activation methods to enhance KMnO4-based water treatment process.

Water Disinfection with Dual-Wavelength (222 + 275 nm) Ultraviolet Radiations: Microbial Inactivation and Reactivation

Emerging mercury-free ultraviolet (UV) sources, such as krypton chloride excimer (KrCl*) lamps and UV light emitting diodes (UV-LEDs), emit diverse wavelengths with distinct inactivation mechanisms. The combined application has the potential to improve disinfection effectiveness through synergism. In this study, a mini-fluidic photoreaction system equipped with a KrCl* lamp (222 nm) and a strip of UV-LEDs (275 nm) was developed, which could individually/simultaneously deliver accurate UV radiation(s) at 222 nm (0.32 mW cm-2) or/and 275 nm (0.50 mW cm-2). Dual-wavelength UV (DWUV) radiations demonstrated a substantial synergistic effect on Escherichia coli (E. coli) inactivation with synergistic coefficients reaching up to 1.92, while no synergistic effect was observed for PR772 bacteriophage (PR772) inactivation. Moreover, DWUV radiations significantly (p < 0.05) suppressed the reactivation of E. coli and PR772 in the subsequent light/dark treatment. For E. coli, the underlying mechanism could be ascribed to the increased level of reactive oxygen species induced by DWUV radiations, which not only enhanced inactivation by damaging proteins and lipids, but also suppressed the reactivation by damaging DNA repair enzymes. For PR772, although the DNA and protein damages caused by DWUV radiations did not yield a synergistic effect, the protein damage prevented the viral DNA from entering host cells for repair, thereby suppressing reactivation. This study helps develop more effective UV disinfection technologies by using DWUV radiations.

Far-UVC Photolysis of Peroxydisulfate for Micropollutant Degradation in Water

Increasing radical yields to reduce UV fluence requirement for achieving targeted removal of micropollutants in water would make UV-based advanced oxidation processes (AOPs) less energy demanding in the context of United Nations' Sustainable Development Goals and carbon neutrality. We herein demonstrate that, by switching the UV radiation source from conventional low-pressure UV at 254 nm (UV254) to emerging Far-UVC at 222 nm (UV222), the fluence-based concentration of HO• in the UV/peroxydisulfate (UV/PDS) AOP increases by 6.40, 2.89, and 6.00 times in deionized water, tap water, and surface water, respectively, with increases in the fluence-based concentration of SO4•- also by 5.06, 5.81, and 55.47 times, respectively. The enhancement to radical generation is confirmed using a kinetic model. The pseudo-first-order degradation rate constants of 16 micropollutants by the UV222/PDS AOP in surface water are predicted to be 1.94-13.71 times higher than those by the UV254/PDS AOP. Among the tested water matrix components, chloride and nitrate decrease SO4•- but increase HO• concentration in the UV222/PDS AOP. Compared to the UV254/PDS AOP, the UV222/PDS AOP decreases the formation potentials of carbonaceous disinfection byproducts (DBPs) but increases the formation potentials of nitrogenous DBPs.

New solution for predicting the removal efficiency of organic contaminants by UV/ H2O2: From a case study of 1H-benzotriazole

Rapid prediction of the removal efficiency and energy consumption of organic contaminants under various operating conditions is crucial for advanced oxidation processes (AOPs) in industrial application. In this study, 1H-Benzotriazole (BTZ, CAS: 95-14-7) is selected as a model micropollutant, a validated incorporated Computational Fluid Dynamics (CFD) model is employed to comprehensively investigate the impacts of initial concentrations of H2O2, BTZ and dissolved organic carbon (DOC) (i.e., [DOC]0, [BTZ]0 and [DOC]0), as well as the effective UV lamp power P and volumetric flow rate Qv. Generally, the operation performance depends on [DOC]0 and [BTZ]0 in similar trends, but with quantitatively different ways. The increase in [H2O2]0 and P/Qv can promote •OH generation, leading to the elimination of BTZ. It is worth noting that P/Qv is found to be linearly correlated with the removal order of BTZ (ROBTZ) under specific conditions. Based on this finding, the degradation of other potential organic contaminants with a wide range of rate constants by UV/H2O2 is further investigated. A model for predicting energy consumption for target removal rates of organic pollutants is established from massive simulation data for the first time. Additionally, a handy Matlab app is first developed for convenient application in water treatment. This work proposes a new operable solution for fast predicting operation performance and energy consumption for the removal of organic contaminants in industrial applications of advanced oxidation processes.