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1. Emerging investigators series: the efficacy of chlorine photolysis as an advanced oxidation process for drinking water treatment

   https://doi.org/10.1039/C6EW00029K  

   Remucal, C. K.; Manley, D. (January 2016, Environmental Science: Water Research & Technology)

   null (Ed.)

   The photolysis of hypochlorous acid (HOCl) and hypochlorite (OCl − ) produces a suite of reactive oxidants, including hydroxyl radical (˙OH), chlorine radical (Cl˙), and ozone (O 3 ). Therefore, the addition of light to chlorine disinfection units could effectively convert existing drinking water treatment systems into advanced oxidation processes. This review critically examines existing studies on chlorine photolysis as a water treatment process. After describing the fundamental chemistry of chlorine photolysis, we evaluate the ability of chlorine photolysis to transform model probe compounds, target organic contaminants, and chlorine-resistant microorganisms. The efficacy of chlorine photolysis to produce reactive oxidants is dependent on solution and irradiation conditions ( e.g. , pH and irradiation wavelengths). For example, lower pH values result in higher steady-state concentrations of ˙OH and Cl˙, resulting in enhanced contaminant removal. We also present the current state of knowledge on the alteration of dissolved organic matter and subsequent formation of disinfection by-products (DBPs) during chlorine photolysis. Although the relative yields of DBPs during chlorine photolysis are also dependent on solution conditions ( e.g. , higher organic DBP yields at low pH values), there is conflicting evidence on whether chlorine photolysis increases or decreases DBP production compared to thermal reactions between chlorine and dissolved organic matter in the dark. We conclude the review by identifying knowledge gaps in the current body of literature. 

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2. Operando investigation of the synergistic effect of electric field treatment and copper for bacteria inactivation

   https://doi.org/10.1038/s41467-024-45587-3  

   Jarin, Mourin; Wang, Ting; Xie, Xing (February 2024, Nature Communications)

   Abstract As the overuse of chemicals in our disinfection processes becomes an ever-growing concern, alternative approaches to reduce and replace the usage of chemicals is warranted. Electric field treatment has shown promising potential to have synergistic effects with standard chemical-based methods as they both target the cell membrane specifically. In this study, we use a lab-on-a-chip device to understand, observe, and quantify the synergistic effect between electric field treatment and copper inactivation. Observations in situ, and at a single cell level, ensure us that the combined approach has an enhancement effect leading more bacteria to be weakened by electric field treatment and susceptible to inactivation by copper ion permeation. The synergistic effects of electric field treatment and copper can be visually concluded here, enabling the further study of this technology to optimally develop, mature, and scale for its various applications in the future. 

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3. Smartphone-powered efficient water disinfection at the point of use

   https://doi.org/10.1038/s41545-020-00089-9  

   Zhou, Jianfeng; Yang, Fang; Huang, Yuxiong; Ding, Wenbo; Xie, Xing (October 2020, npj Clean Water)

   Abstract Clean water free of bacteria is a precious resource in areas where no centralized water facilities are available. Conventional chlorine disinfection is limited by chemical transportation, storage, and the production of carcinogenic by-products. Here, a smartphone-powered disinfection system is developed for point-of-use (POU) bacterial inactivation. The integrated system uses the smartphone battery as a power source, and a customized on-the-go (OTG) hardware connected to the phone to realize the desired electrical output. Through a downloadable mobile application, the electrical output, either constant current (20–1000 µA) or voltage (0.7–2.1 V), can be configured easily through a user-friendly graphical interface on the screen. The disinfection device, a coaxial-electrode copper ionization cell (CECIC), inactivates bacteria by low levels of electrochemically generated copper with low energy consumption. The strategy of constant current control is applied in this study to solve the problem of uncontrollable copper release by previous constant voltage control. With the current control, a high inactivation efficiency ofE. coli(~6 logs) is achieved with a low level of effluent Cu (~200 µg L⁻¹) in the water samples within a range of salt concentration (0.2–1 mmol L⁻¹). The smartphone-based power workstation provides a versatile and accurate electrical output with a simple graphical user interface. The disinfection device is robust, highly efficient, and does not require complex equipment. As smartphones are pervasive in modern life, the smartphone-powered CECIC system could provide an alternative decentralized water disinfection approach like rural areas and outdoor activities. 

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4. Electrocatalytic generation of reactive species and implications in microbial inactivation

   https://doi.org/10.1016/S1872‐2067(21)63941‐4  

   Nichols, F.; Ozoemena, K. I.; Chen, S. W. (April 2022, Chinese journal of catalysis)

   Controlling microbial proliferation in water systems, including wastewater, recreational water, and drinking water, is essential to societal health. Microbial inactivation through electrochemically generated reactive species (RS) mediated pathways provides an effective route toward this microbial control. Herein we provide an overview of recent progress toward electrocatalytic generation of RS and their application in water disinfection, with a focus on the selective production of RS, the microorganism interactions with RS (including both RS mechanisms of action and innate microorganism responses to RS), and practical implementation of electrochemically generated RS for microbial inactivation. The article is concluded with a perspective where the challenges and opportunities of RS‐based electrochemical disinfection of water are highlighted, along with possible future research directions. 

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5. Sulfite-activated ferrate for water reuse applications

   https://doi.org/10.1016/j.watres.2022.118317  

   Spellman, Charles D.; Da'Er, Sahar; Ikuma, Kaoru; Silverman, Isabella; Goodwill, Joseph E. (June 2022, Water Research)

   Ferrate is a promising, emerging water treatment technology. However, there has been limited research on the application of ferrate in a water reuse paradigm. Recent literature has shown that ferrate oxidation of target contaminants could be improved by “activation” with the addition of reductants or acid. This study examined the impact of sulfite-activated ferrate in laboratory water matrix and spiked municipal wastewater effluents with the goal of transforming organic contaminants of concern (e.g., 1,4-dioxane) and inactivating pathogenic organisms. Additionally, the formation of brominated disinfection byproducts by activated ferrate were examined and a proposed reaction pathway for byproduct formation is presented. In particular, the relative importance of reaction intermediates is discussed. This represents the first activated ferrate study to examine 1,4-dioxane transformation, disinfection, and brominated byproduct formation. Results presented show that the sub-stoichiometric ([Sulfite]:[Ferrate] = 0.5) activated ferrate treatment approach can oxidize recalcitrant contaminants by >50%, achieve >4-log inactivation of pathogens, and have relatively limited generation of brominated byproducts. However, stoichiometrically excessive ([Sulfite]:[Ferrate] = 4.0) activation showed decreased performance with decreased disinfection and increased risk of by-product formation. In general, our results indicate that sub-stoichiometric sulfite-activated ferrate seems a viable alternative technology for various modes of water reuse treatment. 

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