Effect of μM Fe addition, mild heat and solar UV on sulfate radical-mediated inactivation of bacteria, viruses, and micropollutant degradation in water

Antibiotics removal and antimicrobial resistance control by ozone/peroxymonosulfate-biological activated carbon: A novel treatment process

Biological activated carbon (BAC) is one of the important treatment processes in wastewater and advanced water treatment. However, the BAC process has been reported to have antimicrobial resistance (AMR) risks. In this study, a new BAC-related treatment process was developed to reduce AMR caused by BAC treatment: ozone/peroxymonosulfate-BAC (O3/PMS-BAC). The O3/PMS-BAC showed better treatment performance on the targeted five antibiotics and dissolved organic matter removal than O3-BAC and BAC treatments. The O3/PMS-BAC process had better control over the AMR than the O3-BAC and BAC processes. Specifically, the amount of targeted antibiotic-resistant bacteria in the effluent and biofilm of O3/PMS-BAC was only 0.01-0.03 and 0.11-0.26 times that of the BAC process, respectively. Additionally, the O3/PMS-BAC process removed 1.76 %-62.83 % and 38.14 %-99.27 % more of the targeted ARGs in the effluent and biofilm than the BAC process. The total relative abundance of the targeted 12 ARGs in the O3/PMS-BAC effluent was decreased by 86 % compared to the effluent after BAC treatment. In addition, Proteobacteria and Bacteroidetes were probably the main hosts for transmitting ARGs in this study, and their relative abundance decreased by 9.6 % and 6.0 % in the effluent of the O3/PMS-BAC treatment compared to that in BAC treatment. The relationship analysis revealed that controlling antibiotic discharge was crucial for managing AMR, as antibiotics were closely related to both ARGs and bacteria associated with their emergence. The results showed that the newly developed treatment process could reduce AMR caused by BAC treatment while ensuring effluent quality. Therefore, O3/PMS-BAC is a promising alternative to BAC treatment for future applications.

Small concentrations, big results: μM addition of photoactive iron oxides with PMS, PDS, or H2O2, leads to enhanced removal of viruses at near-neutral pH

The photo-Fenton process is effective for pathogen removal, and its low-cost versions can be applied in resource-poor contexts. Herein, a photo-Fenton-like system was proposed using low concentrations of iron oxides (hematite and magnetite) and persulfates (peroxymonosulfate - PMS, and peroxydisulfate - PDS), which exhibited excellent inactivation performance towards MS2 bacteriophages. In the presence of bacteria, MS2 inactivation was inhibited in H2O2 and PDS systems but promoted in PMS-involved systems. The inactivation efficacy of all the proposed systems for mixed bacteria and viruses was greater than that of the sole bacteria, showing potential practical applications. The inactivation performance of humic acid-incorporated iron oxides mediating photo-Fenton-like processes was also studied; except for the PMS-involved system, the inactivation efficacy of the H2O2- and PDS-involved systems was inhibited, but the PDS-involved system was still acceptable (< 2 h). Reactive species exploration experiments indicated that ·OH was the main radical in the H2O2 and PDS systems, whereas 1O2 played a key role in the PMS-involved system. In summary, hematite- and magnetite-mediated persulfate-assisted photo-Fenton-like systems at low concentrations can be used as alternatives to the photo-Fenton process for virus inactivation in sunny areas, providing more possibilities for point-of-use drinking water treatment in developing countries.

Efficient and sustainable photocatalytic inactivation of E. coli by an innovative immobilized Ag/TiO2 photocatalyst with peroxymonosulfate (PMS) under visible light

A novel catalytic system for effective photocatalytic inactivation of Escherichia coli (E. coli) was constructed by anchoring Ag nanoparticles (AgNPs) on silane coupling agent (SCA) pretreated TiO2 nano-tube arrays (Ag/SCA/TiO2NTAs). Morphology and structural analyses revealed that SCA could disperse AgNPs evenly on TiO2NTAs, thus inducing a superior surface plasmon resonance (SPR) effect. Ag/SCA/TiO2NTAs catalyst exhibited excellent inactivation performance when in the presence of peroxymonosulfate (PMS) and visible light (VL), with 6-log E. coli was completely inactivated within 60 min, which was 5.3, 12.5 and 13.2 times higher than that of Ag/SCA/TiO2NTAs/VL, PMS/VL and Ag/SCA/TiO2NTAs/PMS/dark systems, respectively. Additionally, the photocatalyst exhibited a highly reusable property, with the inactivation performance almost unchanged after ten cycles of uses with minimal Ag leaching. The inactivation mechanism analysis demonstrated that both radical (SO4•-, OH) and non-radical (h+, 1O2) pathways involved in E. coli inactivation, and SCA played a pivotal role in the production of reactive species. Chloride ions (Cl-) greatly enhanced the inactivation efficiency, while bicarbonate (HCO3-) and phosphate (H2PO4-) showed an inhibitory effect. Humic acid (HA) displayed a dual effect on inactivation performance, where the low concentration of HA facilitated the bacteria inactivation, while the higher dose suppressed bacteria inactivation. Moreover, the system exhibited excellent inactivation performance in tap water. This work first used SCA as the binder to fix AgNPs on TiO2NTAs for VL photocatalytic inactivation of bacteria with the assistance of PMS, which was expected to provide some insights into the practical treatment of drinking water.

Enhanced degradation of oxytetracycline in aqueous solution by DBD plasma-coupled vacuum ultraviolet/ultraviolet (VUV/UVC) system

A systematic investigation of coupling dielectric barrier discharge (DBD) plasma and different ultraviolet bands (UVA, UVB, UVC, and VUV) was constructed for antibiotic-contaminant wastewater treatment. Compared with DBD, UV, or other combined DBD/UV systems, the DBD/VUV/UVC system exhibited excellent degradation and mineralization efficiencies for oxytetracycline (OTC), achieving 93.2% removal rate (reaction rate constant 1.05 min^-1) and higher decarbonization efficiency (mineralization rate 0.47 mg C min^-1) within 2.5 min treatment. The radical quenching tests revealed that HO⋅, [Formula: see text] , and ¹O₂ were all involved in the decomposition of OTC in the DBD/VUV/UVC system, among which [Formula: see text] played a dominant role. Possible degradation pathways of OTC in the DBD/VUV/UVC process were proposed using density functional theory and detected intermediates. Four indexes were used to assess the toxicity of OTC and its degraded intermediates. The inorganic anions and HA slightly reduced the degradation efficiency of the DBD/VUV/UVC system. This research provides new ideas to broaden the application of plasma and alleviate the water environment crisis.

Evaluation of the disinfection effect and mechanism of SO4•- and HO• UV/persulfate salts

Although ultraviolet (UV) and persulfate (PS) have been widely used in water disinfection process, their incompleteness of disinfection, such as inducing the production of viable but non-culturable cells (VBNC), has attracted extensive attention. In this study, the disinfection effect of combined UV and PS was evaluated, and the roles of SO₄^•- and HO^• radicals in UV/PS disinfection were also analyzed. UV/PS more effectively inactivated cells and reduced the number of culturable cells. Also, the test of bacterial dark activation suggested that UV/PS disinfection inhibited the recovery of VBNC bacteria. The mechanisms of UV/PS disinfection were the increase of membrane permeability and oxidative stress, where SO₄^•- radicals played more role than HO^• radicals. Furthermore, UV/PS disinfection more significantly perturbed the metabolism of Pseudomonas aeruginosa (p < 0.05), mainly involving glyoxylate and dicarboxylic acid metabolism, aminoacyl-tRNA biosynthesis, Alanine, aspartate and glutamate metabolism, and citric acid cycle (TCA cycle). In short, UV/PS disinfection can not only significantly reduce the number of culturable bacteria (kill bacteria) but also inhibits the recovery of VBNC bacteria.

Pre-exposure of peracetic acid enhances its subsequent combination with ultraviolet for the inactivation of fungal spores: Efficiency, mechanisms, and implications

Waterborne fungi pose a potential threat to water supply safety due to their high resistance to disinfectants. Peracetic acid, as a promising alternative disinfectant to chlorine, has attracted increasing attention in water treatment. In this study, the inactivation of two dominant fungal species (Aspergillus niger and Aspergillus flavus) by sequential application of peracetic acid and ultraviolet (PAA-UV/PAA) was reported for the first time. Results revealed that the pre-exposure of PAA could facilitate the subsequent process of UV/PAA combination and shorten the lag phase in fungi inactivation. After 10 min of PAA pre-exposure, PAA-UV/PAA achieved 3.03 and 2.40 log inactivation of Aspergillus niger and Aspergillus flavus, which were 2- and 4.3-fold higher than that of direct UV/PAA under the same UV and PAA doses. PAA-UV/PAA disinfection also exhibited a stronger regrowth inhibition for incompletely inactivated fungal spores than direct UV/PAA. The increase of pH (5.0-9.0) and humic acid concentration (1.0-5.0 mg L ^- 1) showed an inhibitory effect on PAA-UV/PAA inactivation, but PAA-UV/PAA was more adaptable in a wide pH range and the presence of humic acid compared to direct UV/PAA. The more severe cell membrane damage and higher reactive oxygen species level in PAA-UV/PAA were evidenced for the first time by flow cytometry. The increased hydroxyl radical generation and higher synergism were primarily responsible for inactivation improvement. This study enhances the further understanding of the PAA-UV/PAA process, and the findings are expected to promote the development of PAA as a promising disinfectant for effective fungi control.

Co-doped Fe3O4/α-FeOOH for highly efficient peroxymonosulfate activation to degrade trimethoprim: Occurrence of hybrid non-radical and radical pathways

Trimethoprim (TMP), as a widely used chemotherapeutic antibiotic agent, has caused potential risks to the aquatic environment. In this study, magnetic Co-doped Fe₃O₄/α-FeOOH was fabricated by a facile one-step ageing method and used for activation of peroxymonosulfate (PMS) in TMP degradation. It was found that low catalyst (0.5 g/L) and PMS addition (0.2 mM) led to the high degradation efficiency of TMP (97.2%, k_obs = 0.11211 min^-1) over a wide range of pH. The oxidation of active radical (SO₄·^-) and non-radical singlet oxygen (¹O₂) co-acted on TMP degradation. Besides, PMS was activated through the cycles between Co(II)/Co(III) and Fe(II)/Fe(III). Fifteen degradation intermediates of TMP were identified by LC-MS, and three possible degradation pathways including hydroxylation, demethylation, and cleavage were proposed. The recovered catalysts exhibited high stability and reusability, maintaining 80% TMP removal efficiency with inappreciable metal leaching (0.012 mg/L of Co, 0.113 mg/L of Fe) after six cycles. Besides, the Co-Fe₃O₄/α-FeOOH/PMS system was highly tolerant to inorganic anions and actual water bodies (river water, lake water, tap water, and sewage plant effluent). Overall, this work provided a promising way to the potential application of Fe-based binary metal oxide for PMS activation.

State-of-the-Art on the Sulfate Radical-Advanced Oxidation Coupled with Nanomaterials: Biological and Environmental Applications

Sulfate radicals (SO₄^-·) play important biological roles in biomedical and environmental engineering, such as antimicrobial, antitumor, and disinfection. Compared with other common free radicals, it has the advantages of a longer half-life and higher oxidation potential, which could bring unexpected effects. These properties have prompted researchers to make great contributions to biology and environmental engineering by exploiting their properties. Peroxymonosulfate (PMS) and peroxydisulfate (PDS) are the main raw materials for SO₄^-· formation. Due to the remarkable progress in nanotechnology, a large number of nanomaterials have been explored that can efficiently activate PMS/PDS, which have been used to generate SO₄^-· for biological applications. Based on the superior properties and application potential of SO₄^-·, it is of great significance to review its chemical mechanism, biological effect, and application field. Therefore, in this review, we summarize the latest design of nanomaterials that can effectually activate PMS/PDS to create SO₄^-·, including metal-based nanomaterials, metal-free nanomaterials, and nanocomposites. Furthermore, we discuss the underlying mechanism of the activation of PMS/PDS using these nanomaterials and the application of SO₄^-· in the fields of environmental remediation and biomedicine, liberating the application potential of SO₄^-·. Finally, this review provides the existing problems and prospects of nanomaterials being used to generate SO₄^-· in the future, providing new ideas and possibilities for the development of biomedicine and environmental remediation.

A review on disinfection methods for inactivation of waterborne viruses

Water contamination is a global health problem, and the need for safe water is ever-growing due to the public health implications of unsafe water. Contaminated water could contain pathogenic bacteria, protozoa, and viruses that are implicated in several debilitating human diseases. The prevalence and survival of waterborne viruses differ from bacteria and other waterborne microorganisms. In addition, viruses are responsible for more severe waterborne diseases such as gastroenteritis, myocarditis, and encephalitis among others, hence the need for dedicated attention to viral inactivation. Disinfection is vital to water treatment because it removes pathogens, including viruses. The commonly used methods and techniques of disinfection for viral inactivation in water comprise physical disinfection such as membrane filtration, ultraviolet (UV) irradiation, and conventional chemical processes such as chlorine, monochloramine, chlorine dioxide, and ozone among others. However, the production of disinfection by-products (DBPs) that accompanies chemical methods of disinfection is an issue of great concern due to the increase in the risks of harm to humans, for example, the development of cancer of the bladder and adverse reproductive outcomes. Therefore, this review examines the conventional disinfection approaches alongside emerging disinfection technologies, such as photocatalytic disinfection, cavitation, and electrochemical disinfection. Moreover, the merits, limitations, and log reduction values (LRVs) of the different disinfection methods discussed were compared concerning virus removal efficiency. Future research needs to merge single disinfection techniques into one to achieve improved viral disinfection, and the development of medicinal plant-based materials as disinfectants due to their antimicrobial and safety benefits to avoid toxicity is also highlighted.

Heat-activated persulfate for the degradation of micropollutants in water: A comprehensive review and future perspectives

This work is a critical review of the most important studies that have dealt with heat-activated persulfate to degrade persistent micropollutants in the last six years. The effect of the different operating parameters is discussed, wherein in all cases, the efficiency was favored at higher temperatures and oxidant concentrations. Particular emphasis was given to the effect of the aqueous matrix. Since heat activation is a homogeneous process based on the production of free radicals, in most of the studies presented, the removal of pollutants decreases as the complexity of the aqueous matrix increases except in cases where secondary oxidative species are produced that are selective with specific pollutants. It has also been observed that the change in toxicity usually follows the removal of the parent compound despite the formation of several by-products. Nowadays, combining different processes for the simultaneous activation of persulfate seems to be gaining ground. A hybrid process is an interesting strategy to reduce costs and increase efficiency, especially in real wastewater. In this light, the most interesting studies of hybrid systems for the destruction of micropollutants in recent years based on thermally activated persulfate are also summarized. Finally, some steps are proposed for future research towards the industrial application, including the study of chemical mixtures, the integrated toxicity assessment, the examination of simultaneous disinfection and decomposition of pollutants into real wastewater, the estimation of the required costs, and energy the combination of processes and their coupling with renewable sources, and the design of pilot plants and the scale-up of the hybrid processes.

An Initial Approach to the Presence of Pharmaceuticals in Wastewater from Hospitals in Colombia and Their Environmental Risk

Hospital wastewater (HWW) from three different cities in Colombia was characterized. Wastewater quality indicators and 38 relevant pharmaceuticals were examined. The HWW had pH from 6.82 to 8.06, chemical oxygen demand was between 235.5 and 1203 mg L−1, and conductivity ranged from 276.5 to 717.5 µS cm−1. Additionally, most of the target pharmaceuticals (20 of 38) had 100% occurrence frequency in the samples due to their high and continuous consumption in the hospitals. Indeed, acetaminophen, diclofenac, azithromycin, ciprofloxacin, sulfamethoxazole, losartan, metoprolol, and omeprazole were present in all samples at concentrations from one up to some hundreds of μg L−1. Once pharmaceuticals are discharged into local sewage systems or rivers, because of the high dilution of HWW, the individual environmental hazards are low (i.e., risk quotients, RQ < 0.1 were determined). The action of conventional treatments on HWW also decreased the individual environmental risks of pharmaceuticals (RQ values < 0.1). However, the mixture of pharmaceuticals in the HWW had potential environmental risks (as RQ > 0.1 were found), remarking the need for efficient processes to eliminate pharmaceuticals from HWW. This work provides an initial view on the characterization of diverse Colombian HWW, which could be useful for the understanding of the current situation of pollution by pharmaceuticals in Latin America.

Activation of sodium persulfate by TiO2@MIL-101(Fe): Boosting the Fenton-like process by interfacial charge transfer

Advanced oxidation processes based on sulfate radicals are considered as a promising approach for environmental remediation. In this study, TiO₂@MIL-101(Fe) is successfully fabricated by a facile impregnation method and is used for sodium persulfate (SPS) activation. TiO₂@MIL-101@SPS combines the advantages of photocatalysis and SPS activation, which shows high removal efficiency for nitrobenzene and methyl orange. In addition, the effect of multiple factors, including light source, SPS amount and catalyst amount, on nitrobenzene degradation have been investigated. Results show that the nitrobenzene degradation efficiency is up to 66.53 % while that of TOC removal is 32.21 % under 4-h visible light irradiation with 30 mg catalyst and 1.6 mM SPS. Moreover, LC-MS have been carried out to study the route of nitrobenzene degradation. Besides, ESR analysis reveals that both ^●SO₄^- and ^●OH radicals are generated sustainably under visible light irradiation, and more ^●OH radicals can be detected owing to the synergic effect of photocatalysis and SPS activation. Interfacial charge transfer effect provides photoinduced electrons for the Fe³⁺/Fe²⁺ cycle in MIL-101(Fe), which boosts the SPS activation process, resulting in high photocatalytic activity.

Advanced Oxidation Processes for Water and Wastewater Viral Disinfection. A Systematic Review

Water and wastewater virological quality is a significant public health issue. Viral agents include emerging and re-emerging pathogens characterized by extremely small size, and high environmental stability. Since the mainly used conventional disinfection methods are usually not able to achieve complete disinfection of viral and other microbial targets, in real water and wastewater matrices, effective strategies for the treatment, use and reuse of water and the development of next-generation water supply systems are required. The scope of the present systematic review was to summarize research data on the application of advanced oxidation processes (AOPs) for viral disinfection of water and wastewater. A literature survey was conducted using the electronic databases PubMed, Scopus, and Web of Science. This comprehensive research yielded 23 records which met the criteria and were included and discussed in this review. Most of the studies (14/23) used only MS2 bacteriophage as an index virus, while the remaining studies (9/23) used two or more viral targets, including phages (MS2, T4, T7, phiX174, PRD-1, S2, ϕB124-14, ϕcrAssphage) and/or Adenovirus, Aichivirus, Norovirus (I, II, IV), Polyomavirus (JC and BK), Sapovirus, Enterovirus, Coxsackievirus B3, Echovirus, and Pepper mild mottle virus. The vast majority of the studies applied a combination of two or more treatments and the most frequently used process was ultraviolet light-hydrogen peroxide (UV/H₂O₂) advanced oxidation. The review is expected to highlight the potential of the AOPs for public health protection from the waterborne viral exposure.

The role of carbonate in sulfamethoxazole degradation by peroxymonosulfate without catalyst and the generation of carbonate racial

Peroxymonosulfate (PMS) can be activated by various catalysts to degrade organic contaminants in wastewater treatment processes. In this research, the co-activation of PMS by sulfamethoxazole (SMX) and carbonate is investigated. The results show that SMX can be degraded in situ, and the main reactive oxygen species are singlet oxygen and carbonate radicals. Only singlet oxygen is detected when SMX is degraded by PMS without carbonate. However, both carbonate radicals and hydroxyl radicals are measured in the presence of carbonate. Among which, hydroxyl radicals are identified by electron paramagnetic resonance spectroscopy method, and carbonate radicals are confirmed by radical quenching experiments, as well as the variation of SMX degradation kinetic and the appreance of carbonyldioxy derivatives by-products in the presence of carbonate anions. Based on this phenomenon, it is proposed that carbonate can enhance the decomposition of PMS and the generation of secondary free radicals (carbonate radicals). Thus carbonate radicals can enhance the oxidizability for sulfonamide antibiotics in the PMS-based advanced oxidation systems. These results suggest that the addition of carbonate is an important enhancement method for the treatment of sulfonamide antibiotics in water.

Enhancing solar disinfection (SODIS) with the photo-Fenton or the Fe2+/peroxymonosulfate-activation process in large-scale plastic bottles leads to toxicologically safe drinking water

Solar disinfection (SODIS) in 2-L bottles is a well-established drinking water treatment technique, suitable for rural, peri‑urban, or isolated communities in tropical or sub-tropical climates. In this work, we assess the enlargement of the treatment volume by using cheap, large scale plastic vessels. The bactericidal performance of SODIS and two solar-Fe²⁺ based enhancements, namely photo-Fenton (light/H₂O₂/Fe²⁺) and peroxymonosulfate activation (light/PMS/Fe²⁺) were assessed in 19-L polycarbonate (PC) and 25-L polyethylene terephthalate (PET) bottles, in ultrapure and real water matrices (tap water, lake Geneva water). Although SODIS always reached total (5-logU) inactivation, under solar light, enhancement by or both Fe²⁺/H₂O₂ or Fe²⁺/PMS was always beneficial and led to an increase in bacterial elimination kinetics, as high as 2-fold in PC and PET bottles with tap water for light/H₂O₂/Fe²⁺, and 8-fold in PET bottles with Lake Geneva water. The toxicological safety of the enhancements and their effects on the plastic container materials was assessed using the E-screen assay and the Ames test, after 1-day or 1-week exposure to SODIS, photo-Fenton and persulfate activation. Although the production of estrogenic compounds was observed, we report that no treatment method, duration of exposure or material resulted in estrogenicity risk for humans, and similarly, no mutagenicity risk was measured. In summary, we suggest that SODIS enhancement by either HO^•- or SO₄^•--based advanced oxidation process is a suitable enhancement of bacterial inactivation in large scale plastic bottles, without any associated toxicity risks.

Simultaneously enhance the inactivation and inhibit the photoreactivation of fungal spores by the combination of UV-LEDs and chlorine: Kinetics and mechanisms

Waterborne fungi have been recognized as an emerging environmental contaminant in recent years. This work was to investigate the inactivation efficiency and mechanisms of ultraviolet light-emitting diodes (UV-LEDs)/chlorine (Cl₂) (265, 280 and 265/280 nm combination) and LPUV/Cl₂ (254 nm) treatments for three fungal species compared with individual disinfection processes. Control of photoreactivation for fungal species inactivated by UV-LEDs/Cl₂ and LPUV/Cl₂ was also evaluated. The results revealed that the combined UV-LEDs/Cl₂ and LPUV/Cl₂ processes, especially UV-LEDs/Cl₂, exhibited better inactivation performance compared to UV alone and Cl₂ alone based on the inactivation rate constants, and an evident synergistic effect was observed. For example, the inactivation rates for Penicillium polonicum in the processes of UV₂₆₅/Cl₂, UV₂₈₀/Cl₂, UV_265/280/Cl₂ and LPUV/Cl₂ was 0.142, 0.168, 0.174 and 0.106 cm²/mJ, respectively, which were all approximately 1.5-fold higher than that of UV alone. The synergistic effect of fungal spores inactivation by UV-LEDs/Cl₂ and LPUV/Cl₂ was due to the high level production of intracellular reactive oxygen species and the reaction of potential extracellular free radicals. Resistance of the tested fungal spores was as follows: Trichoderma harzianum < Penicillium polonicum < Aspergillus niger. In addition, the joint effect of DNA and other cellular damage resulted in the inhibition of photoreactivation of fungal spores inactivated by UV-LEDs/Cl₂ and LPUV/Cl₂ compared with that of fungal spore inactivated by UV alone. This study may provide reference for controlling the dissemination of waterborne fungi utilizing combined UV-LEDs and free chlorine processes.

Employing bacterial mutations for the elucidation of photo-Fenton disinfection: Focus on the intracellular and extracellular inactivation mechanisms induced by UVA and H2O2

The bacterial inactivation mechanisms by solar light and the photo-Fenton process is still a matter of debate. In this study, we bring evidence towards the elucidation of the mechanisms that govern photo-Fenton disinfection at near-neutral pH. With the use of porin-deficient and catalase over-producing E. coli strains, in conjunction with measurements of cell wall oxidation and permeability, we are able to i) highlight the role of the aforementioned components in bacterial inactivation and ii) localize the damages in the intracellular domain, despite the addition of the Fenton reagents in the bulk. We report that H₂O₂ oxidizes cell walls but under light the process is of low significance; UVA initiated an intracellular oxidation process based on excess accumulated H₂O₂, while the UVA+H₂O₂ and UVA+H₂O₂+Fe²⁺ processes have the same effect with light, albeit enhanced, as shown by malondialdehyde (MDA) production and ONPG hydrolysis rates. Finally, compared to the UVA-assisted photo-Fenton process, its solar counterpart is enhanced by the direct UVB effects on bacterial DNA. In conclusion, we have sufficient evidence to postulate that the photo-Fenton process is intracellular and propose the pathways that form the integrated bacterial inactivation mechanism by photo-Fenton.

Insights into the Photocatalytic Bacterial Inactivation by Flower-Like Bi2WO6 under Solar or Visible Light, Through in Situ Monitoring and Determination of Reactive Oxygen Species (ROS)

This study addresses the visible light-induced bacterial inactivation kinetics over a Bi2WO6 synthesized catalyst. The systematic investigation was undertaken with Bi2WO6 prepared by the complexation of Bi with acetic acid (carboxylate) leading to a flower-like morphology. The characterization of the as-prepared Bi2WO6 was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), specific surface area (SSA), and photoluminescence (PL). Under low intensity solar light (<48 mW/cm2), complete bacterial inactivation was achieved within two hours in the presence of the flower-like Bi2WO6, while under visible light, the synthesized catalyst performed better than commercial TiO2. The in situ interfacial charge transfer and local pH changes between Bi2WO6 and bacteria were monitored during the bacterial inactivation. Furthermore, the reactive oxygen species (ROS) were identified during Escherichia coli inactivation mediated by appropriate scavengers. The ROS tests alongside the morphological characteristics allowed the proposition of the mechanism for bacterial inactivation. Finally, recycling of the catalyst confirmed the stable nature of the catalyst presented in this study.

VUV/Fe(II)/H2O2 as a novel integrated process for advanced oxidation of methyl tert-butyl ether (MTBE) in water at neutral pH: Process intensification and mechanistic aspects

Vacuum UV (VUV) technologies have recently attracted high interest due to their high efficacy in generating reactive oxygen species (ROS). To date, no systematic study of the modes of action of the integrated VUV/Fe(II)/H₂O₂ process against contaminants elimination exists; the present study reports the oxidation of MTBE in a new light-assisted Fenton-process, by employing either narrowband UVC (254 nm) or VUV (185 and 254 nm) irradiation, in a comparative evaluation. The processes under investigation were the UVC- or VUV/Fe(II)/H₂O₂ sensitized ones and their constituents, i.e. Fe(II)/H₂O₂, VUV, VUV/Fe(II), VUV/H₂O₂, VUV/Fe(II)/H₂O₂, as well as the UVC, UVC/H₂O₂ and UVC/Fe(II)/H₂O₂. We scrutinize the operational parameters of the VUV-assisted process, its enhancements and synergies, comparison with the UVC-based ones, as well as their inflicted pathways towards MTBE degradation. Complete degradation and 87.8% mineralization of 50 mg/L MTBE was achieved in the VUV/Fe(II)/H₂O₂ process (0.9 mM Fe(II) and 3 mM H₂O₂), at near-neutral pH (reaction times: ∼30 and 60 min, respectively). Irradiation with VUV light was found to act synergistically and in high kinetic rates enhancement compared to the UVC source, sensitizing the Fenton process for effective oxidation of MTBE in the aqueous solution. A scavenger study and degradation by-products investigation has been performed, leading to a mechanistic pathway proposition, elucidating MTBE degradation. The VUV/Fe(II)/H₂O₂ process demonstrated potential applicability in the field since it could efficiently treat (100% degradation and 86.4% mineralization) groundwater spiked with MTBE, operated either under batch or continuous-flow mode. The findings clearly indicates the VUV-assisted Fenton as an emerging and viable technology for field application to treat the MTBE-contaminated effluents or waters.

Application of persulfate salts for enhancing UV disinfection in marine waters

Over the years, industrial activities that generate high salinity effluents have been intensifying; this has relevant potential for causing organic and microbiological pollution which damages both human and ocean health. The development of new regulations, such as ballast water convention, encourage the development of treatment systems that can be feasible for treating seawater effluents. Accordingly, an approach based on the UV activation of persulfate salts has been assessed. In this scenario, two different persulfate sources (S₂O₈^2- and HSO₅^-) were evaluated under UV-C irradiation for disinfection purposes. An optimization process was performed with low chemical doses (<1 mM). In order to extensively examine the applicability on seawater, different water matrices were tested as well as different microorganisms including both fecal and marine bacteria. An enhancement of UV-inactivation with the addition of persulfate salts was achieved in all cases, kinetic rate constant has been accelerated by up to 79% in seawater. It implies a UV-dose saving up to 45% to achieve 4-log reductions. Best efficiencies were obtained with [HSO₅^-] = 0.005 mM and [S₂O₈^2-] = 0.5 mM. Higher effectiveness was obtained with the use of HSO₅^- due to its low stability and interaction with chloride. Also, different responses were obtained according to the specific microorganisms by achieving faster disinfection in Gram-negative than in Gram-positive bacteria, the sensitivity observed was Vibrio spp. > E. coli > E. faecalis ≈ Marine Heterotrophic Bacteria. With an evaluation of regrowth after treatment, greater cell damage was detected with the addition of persulfate salts. The major ability of regrowth for marine bacteria encourages the use of a residual disinfectant after disinfection processes.

Physico-chemical processes

The review scans research articles published in 2018 on physico-chemical processes for water and wastewater treatment. The paper includes eight sections, that is, membrane technology, granular filtration, flotation, adsorption, coagulation/flocculation, capacitive deionization, ion exchange, and oxidation. The membrane technology section further divides into six parts, including microfiltration, ultrafiltration, nanofiltration, reverse osmosis/forward osmosis, and membrane distillation. PRACTITIONER POINTS: Totally 266 articles on water and wastewater treatment have been scanned; The review is sectioned into 8 major parts;  Membrane technology has drawn the widest attention from the research community.

Inactivation of carbapenem-resistant Klebsiella pneumoniae by photo-Fenton: Residual effect, gene evolution and modifications with citric acid and persulfate

The photo-Fenton process application to eliminate carbapenem-resistant Klebsiella pneumoniae, an antibiotic-resistant priority pathogen, was evaluated. Initially, reagents concentration effect was tested and under suitable conditions (5 mg L^-1 of Fe²⁺ and 50 mg L^-1 of H₂O₂) complete bacteria inactivation by action of hydroxyl radical and UVA plus hydrogen peroxide was achieved at 120 min. The process presented a strong residual disinfecting effect when light was turned off at only 20 min. Besides, the cultivability of treated K. pneumoniae in a selective medium containing carbapenem antibiotics was considered. bla-KPC, gene responsible for the resistance, evolution was also assessed. The bacteria response to carbapenem antibiotics was higher as the treatment time increased. In turn, bla-KPC gene remained when K. pneumoniae was completely inactivated (120 min); nevertheless, treatment times longer than 120 min diminished bla-KPC presence. Finally, the photo-Fenton process and its modifications (citric acid addition or persulfate anion instead hydrogen peroxide) were applied to a real hospital wastewater in Colombia. In such complex matrix, the conventional photo-Fenton system reached a moderate disinfection (∼3.5 log-units at 300 min). Meanwhile, in presence of citric acid total inactivation was completed at the same time. Interestingly, the H₂O₂ substitution by persulfate strongly accelerated the microorganism elimination, achieving the 6-log-units reduction after only 60 min of process action. Thus, the effective elimination of K. pneumoniae from water by the modified photo-Fenton evidenced the potential applicability of this process to limit the proliferation of antibiotic resistant bacteria.

Simultaneous atrazine degradation and E. coli inactivation by UV/S2O82-/Fe2+ process under KrCl excilamp (222 nm) irradiation

This study is the first to reveal that the iron-catalyzed photo-activation of persulfate (UV/PS/Fe²⁺system) under mercury-free KrCl excilamp irradiation (222 nm) is capable of simultaneous degradation of an organic pollutant and inactivation of a microorganism in aqueous media using the herbicide atrazine (ATZ) and E. coli as model contaminants, respectively. Deionized water, natural water and wastewater effluents, contaminated with 4 mg/L ATZ and/or 10⁵ CFU/mL E. coli, were sequentially treated by direct UV, UV/PS and UV/PS/Fe²⁺ processes. Lowering the pH to 3.5 accelerated both the degradation and inactivation during the UV/PS/Fe²⁺ treatment of natural water. Comparison of the apparent UV dose-based pseudo first-order rate constants showed the negative effect of E. coli on ATZ degradation by decreasing rates in all of the examined water matrices. This can be due to the competitive effect between ATZ and bacterial cells for reactive oxygen species (ROS). By contrast, E. coli in the presence of ATZ was inactivated faster in natural water and wastewater (but not in deionized water), as compared to the case without ATZ. A scheme of possible synergistic inactivation under ROS exposure in water, containing ATZ, natural organic matter and chloride ions as primary constituents, was proposed. Radical scavenging experiments showed a major contribution of SO₄•^- to ATZ degradation by UV/PS/Fe²⁺ treatment of deionized water and natural water. The UV doses, required for 90% removal of ATZ from natural water and wastewater, achieve 160 mJ/cm² (pH 5.5) and concurrently provide 99.99% E. coli inactivation. These results make the UV/PS/Fe²⁺ system with narrow band UV light sources promising for simultaneous water treatment and disinfection.

Photocatalytic Mechanisms for Peroxymonosulfate Activation through the Removal of Methylene Blue: A Case Study

Industrial activity is one of the most important sources of water pollution. Yearly, tons of non-biodegradable organic pollutants are discharged, at the least, to wastewater treatment plants. However, biological conventional treatments are unable to degrade them. This research assesses the efficiency of photocatalytic activation of peroxymonosulfate (PMS) by two different iron species (FeSO₄ and Fe³⁺-citrate) and TiO₂. These substances accelerate methylene blue removal by the generation of hydroxyl and sulfate radicals. The required pH and molar ratios PMS:Fe are crucial variables in treatment optimization. The kinetic removal is reduced by the appearance of scavenger reactions in acidic and basic conditions, as well as by the excess of PMS or iron. The best performance is achieved using an Fe³⁺-citrate as an iron catalyst, reaching the total removal of methylene blue after 15 min of reaction, with a molar ratio of 3.25:1 (1.62 mM of PMS and 0.5 mM Fe³⁺-citrate). Fe³⁺-citrate reached higher methylene blue removal than Fe²⁺ as a consequence of the photolysis of Fe³⁺-citrate. This photolysis generates H₂O₂ and a superoxide radical, which together with hydroxyl and sulfate radicals from PMS activation attack methylene blue, degrading it twice as fast as Fe²⁺ (0.092 min^-1 with Fe²⁺ and 0.188 min^-1 with Fe³⁺-citrate). On the other hand, a synergistic effect between PMS and titanium dioxide (TiO₂) was observed (S_{PMS/TiO2/UV-A} = 1.79). This synergistic effect is a consequence of PMS activation by reaction with the free electron on the surface of TiO₂. No differences were observed by changing the molar ratio (1.04:1; 0.26:1 and 0.064:1 PMS:TiO₂), reaching total removal of methylene blue after 80 min of reaction.

Disinfection performance using a UV/persulfate system: effects derived from different aqueous matrices

The disinfectant power of UV combined with a persulfate salt has been assessed. The results obtained suggest this system as an attractive alternative to other photochemical processes currently in use for seawater treatment.

Assessment of Sulfate Radical-Based Advanced Oxidation Processes for Water and Wastewater Treatment: A Review

High oxidation potential as well as other advantages over other tertiary wastewater treatments have led in recent years to a focus on the development of advanced oxidation processes based on sulfate radicals (SR-AOPs). These radicals can be generated from peroxymonosulfate (PMS) and persulfate (PS) through various activation methods such as catalytic, radiation or thermal activation. This review manuscript aims to provide a state-of-the-art overview of the different methods for PS and PMS activaton, as well as the different applications of this technology in the field of water and wastewater treatment. Although its most widespread application is the elimination of micropollutants, its use for the disinfection of wastewater is gaining increasing interest. In addition, the possibility of combining this technology with ultrafiltration membranes to improve the water quality and lifespan of the membranes has also been discussed. Finally, a brief economic analysis of this technology has been undertaken and the different attempts made to implement it at full-scale have been summarized. As a result, this review tries to be useful for all those people working in that area.