Intracellular mechanisms of solar water disinfection

Solar water disinfection (SODIS) is a zero-cost intervention measure to disinfect drinking water in areas of poor access to improved water sources, used by more than 6 million people in the world. The bactericidal action of solar radiation in water has been widely proven, nevertheless the causes for this remain still unclear. Scientific literature points out that generation of reactive oxygen species (ROS) inside microorganisms promoted by solar light absorption is the main reason. For the first time, this work reports on the experimental measurement of accumulated intracellular ROS in E. coli during solar irradiation. For this experimental achievement, a modified protocol based on the fluorescent probe dichlorodihydrofluorescein diacetate (DCFH-DA), widely used for oxidative stress in eukaryotic cells, has been tested and validated for E. coli. Our results demonstrate that ROS and their accumulated oxidative damages at intracellular level are key in solar water disinfection

A critical review on application of photocatalysis for toxicity reduction of real wastewaters

Advanced oxidation processes (AOPs) such as photocatalysis are widely studied for degradation of organic pollutants of contaminants of emerging concern (CECs). However, degradation of organic pollutants leads to formation of by-products, which may be more toxic than parental contaminants. The toxicity of wastewater treated by photocatalysis is topical issue. In this review paper recent studies concerned with photocatalytic detoxification of real industrial and municipal wastewater were assembled and critically discussed. Such issues as challenges for application of photocatalytic wastewater detoxification, feasibility of various toxicity tests, reuse of photocatalysts, cost estimation, etc. were considered. Based on reviewed literature it can be suggested that photocatalysis might not always be a promising treatment method for degradation of organic pollutants in real wastewaters and/or wastewater detoxification from the application point of view. (C) 2020 The Authors. Published by Elsevier Ltd.Peer reviewe

Tertiary treatment of urban wastewater by solar and UV-C driven advanced oxidation with peracetic acid: effect on contaminants of emerging concern and antibiotic resistance

Photo-driven advanced oxidation process (AOP) with peracetic acid (PAA) has been poorly investigated in water and wastewater treatment so far. In the present work its possible use as tertiary treatment of urban wastewater to effectively minimize the release into the environment of contaminants of emerging concern (CECs) and antibiotic-resistant bacteria was investigated. Different initial PAA concentrations, two light sources (sunlight and UV-C) and two different water matrices (groundwater (GW) and wastewater (WW)) were studied. Low PAA doses were found to be effective in the inactivation of antibiotic resistant Escherichia coli (AR E. coli) in GW, with the UV-C process being faster (limit of detection (LOD) achieved for a cumulative energy (QUV) of 0.3 kJL−1 with 0.2 mg PAA L−1) than solar driven one (LOD achieved at QUV = 4.4 kJL−1 with 0.2 mg PAA L−1). Really fast inactivation rates of indigenous AR E. coli were also observed in WW. Higher QUV and PAA initial doses were necessary to effectively remove the three target CECs (carbamazepine (CBZ), diclofenac and sulfamethoxazole), with CBZ being the more refractory one. In conclusion, photo-driven AOP with PAA can be effectively used as tertiary treatment of urban wastewater but initial PAA dose should be optimized to find the best compromise between target bacteria inactivation and CECs removal as well as to prevent scavenging effect of PAA on hydroxyl radicals because of high PAA concentration

New trends on photoelectrocatalysis (PEC):nanomaterials, wastewater treatment and hydrogen generation

The need for novel water treatment technologies has been recently recognised as concerning contaminants (organics and pathogens) are resilient to standard technologies. Advanced oxidation processes degrade organics and inactivate microorganisms via generated reactive oxygen species (ROS). Among them, heterogeneous photocatalysis may have reduced efficiency due to, fast electron-hole pair recombination in the photoexcited semiconductor and reduced effective surface area of immobilised photocatalysts. To overcome these, the process can be electrically assisted by using an external bias, an electrically conductive support for the photocatalyst connected to a counter electrode, this is known as photoelectrocatalysis (PEC). Compared to photocatalysis, PEC increases the efficiency of the generation of ROS due to the prevention of charge recombination between photogenerated electron-hole pairs thanks the electrical bias applied. This review presents recent trends, challenges, nanomaterials and different water applications of PEC (degradation of organic pollutants, disinfection and generation of hydrogen from wastewater)

Solar disinfection is an augmentable, in situ-generated photo-Fenton reaction—Part 1: A review of the mechanisms and the fundamental aspects of the process

The present manuscript is a conceptual review concerning the photo-Fenton reaction at near-neutral pH, used for bacterial inactivation. In this first Part, an overview of the mechanisms involved, as well as the fundamental concepts governing the near-neutral photo-Fenton reaction are critically assessed. The two constituents of the process, namely solar light and the Fenton reagents, are dissociated, with their direct and indirect actions thoroughly analyzed. The effects of UVB and UVA on the bacterial cell are firstly discussed, followed by the presentation of the indirect oxidative stress-related inactivation mechanisms initiated into the microorganism, in presence of light. Afterwards, the effect of each Fenton reagent (H2O2, Fe) is analyzed in a step-wise manner, with H2O2 and Fe as enhancements of the solar disinfection mode of action. This approach proves that in fact, the solar photo-Fenton reaction is an enhanced solar disinfection process. Finally, the photo-Fenton reaction is put into context by considering the possible interactions of the separate parts of the combined process with the constituents of the natural environment that can play an important role in the evolution of the bacterial inactivation. (C) 2016 Elsevier B.V. All rights reserved

Nitrogen and Copper doped solar light active TiO2 photocatalyst for water decontamination

A novel class of photocatalytic coating capable of degrading bacterial and chemical contaminants in the presence of visible sunlight wavelengths was produced by depositing a stable photocatalytic TiO2 film on the internal lumen of glass bottles via a sol gel method. This coating was prepared in either undoped form or doped with nitrogen and/or copper to produce visible light-active TiO2 films which were annealed at 600 °C and were characterized by Raman, UV-Vis, and X-ray photoelectron spectroscopy. The presence of doped and undoped TiO2 films was found to accelerate the degradation of methylene blue in the presence of natural sunlight, while copper-doped TiO2 films were found to accelerate bacterial inactivation (of E. coli and E. faecalis) in the presence of natural sunlight