Catalyst-free activation of persulfate by visible light for water disinfection: Efficiency and mechanisms

EDTA enables to alleviate impacts of metal ions on conjugative transfer of antibiotic resistance genes

Various heavy metals are reported to be able to accelerate horizontal transfer of antibiotic resistance genes (ARGs). In real water environmental settings, ubiquitous complexing agents would affect the environmental behaviors of heavy metal ions due to the formation of metal-organic complexes. However, little is known whether the presence of complexing agents would change horizontal gene transfer due to heavy metal exposure. This study aimed to fill this gap by investigating the impacts of a typical complexing agent ethylenediaminetetraacetic acid (EDTA) on the conjugative transfer of plasmid-mediated ARGs induced by a range of heavy metal ions. At the environmentally relevant concentration (0.64 mg L-1) of metal ions, all the tested metal ions (Mg2+, Ca2+, Co2+, Pb2+, Ni2+, Cu2+, and Fe3+) promoted conjugative transfer of ARGs, while an inhibitory effect was observed at a relatively higher concentration (3.20 mg L-1). In contrast, EDTA (0.64 mg L-1) alleviated the effects of metal ions on ARGs conjugation transfer, evidenced by 11 %-66 % reduction in the conjugate transfer frequency. Molecular docking and dynamics simulations disclosed that this is attributed to the stronger binding of metal ions with the lipids in cell membranes. Under metal-EDTA exposure, gene expressions related to oxidative stress response, cell membrane permeability, intercellular contact, energy driving force, mobilization, and channels of plasmid transfer were suppressed compared with the metal ions exposure. This study offers insights into the alleviation mechanisms of complexing agents on ARGs transfer induced by free metal ions.

The synergistic effect of periodate/ferrate (VI) system on disinfection of antibiotic resistant bacteria and removal of antibiotic resistant genes: The dominance of Fe (IV)/Fe (V)

The proliferation of antibiotic resistant genes (ARGs) and antibiotic resistant bacteria (ARB) caused by antibiotic abuse has raised concerns about the global infectious-disease crisis. This study employed periodate (PI)/ferrate (VI) (Fe (VI)) system to disinfect Gram-negative ARB (Escherichia coli DH5α) and Gram-positive bacteria (Bacillus subtilis ATCC6633). The PI/Fe (VI) system could inactivate 1 × 108 CFU/mL of Gram-negative ARB and Gram-positive bacteria by 4.0 and 2.8 log in 30 min. Neutral and acidic pH, increase of PI dosage and Fe (VI) dosage had positive impacts on the inactivation efficiency of ARB, while alkaline solution and the coexistence of 10 mM Cl-, NO3-, SO42- and 20 mg/L humic acid had slightly negative impacts. The reactive species generated by PI/Fe (VI) system could disrupt the integrity of cell membrane and wall, leading to oxidative stress and lipid peroxidation. Intracellular hereditary substance, including DNA and ARGs (tetA), would leak into the external environment through damaged cells and be degraded. The electron spin resonance analysis and quenching experiments indicated that Fe (IV)/Fe (V) played a leading role in disinfection. Meanwhile, PI/Fe (VI) system also had an efficient removal effect on sulfadiazine, which was expected to inhibit the ARGs transmission from the source.

2D/2D heterojunctions for rapid and self-cleaning removal of antibiotics via visible light-assisted peroxymonosulfate activation: Efficiency, synergistic effects, and applications

Developing eco-friendly and efficient technologies for treating antibiotic wastewater is crucial. Traditional methods face challenges in incomplete removal, high costs, and secondary pollution. Heterogeneous peroxymonosulfate (PMS) activation assisted by visible light shows promise, but suitable activators remain a huge challenge. Here, we synthesized cost-effective carbon nitride/bismuth bromide oxide (CN/BiOBr) heterojunctions. Such a heterojunction achieved rapid PMS activation, achieving over 90.00% tetracycline (TC) removal only within 1 min (kobs of 2.23 min-1), surpassing previous systems by nearly 1-2 orders of magnitude and even remarkably superior to the popular single-atom catalysts. The system exhibited self-cleaning properties, maintaining activity after 8 cycles and stability across a wide pH range (3.01 to 9.03). Quenching experiments and theoretical calculations elucidated the exclusive •O2- species involvement and removal pathways. Eco-toxicity assessment and total organic carbon results confirmed simultaneous degradation, detoxification, and mineralization. This system also showed excellent resistance to environmental factors, e.g., coexisting anions, varying pH, and water sources, and demonstrated potential in coking and medical wastewater purification. This study presents a novel technique for rapidly decontaminating antibiotic wastewater through visible light-assisted PMS activation and introduces innovative bionic catalytic oxidation combining light and darkness for practical applications.

A review of copper-based Fenton reactions for the removal of organic pollutants from wastewater over the last decade: different reaction systems

In recent years, as global industrialization has intensified, environmental pollution has become an increasingly serious problem. Improving water quality and achieving wastewater purification remain top priorities for environmental health initiatives. The Fenton process is favored by researchers due to its high efficiency and ease of operation. Central to the Fenton process is a catalyst used to activate hydrogen peroxide, rapidly degrading pollutants, improving water quality. Among various catalysts developed, copper-based catalysts have attracted considerable attention due to their affordability, high activity, and stable performance. Based on this, this paper reviews the development of copper-based Fenton systems over the past decade. It mainly involves the research and application of copper-based catalysts in different Fenton systems, including photo-Fenton, electro-Fenton, microwave-Fenton, and ultrasonic-Fenton. This review provides a fundamental reference for the subsequent studies of copper-based Fenton systems, contributing to the goal of transitioning these systems from laboratory research into practical environmental applications.

Metal-free synthesis of propargylamines via light-mediated persulfate activation and phase-transfer catalysis

We present a metal-free method to synthesize secondary and tertiary propargylamines from primary and secondary amines and alkynes using light-mediated persulfate activation and phase-transfer catalysis. Our method explores a tandem oxidative coupling/alkynylation reaction for the generation of diverse compounds, highlighting the sustainability of the process and its wide scope.

Progress of disinfection catalysts in advanced oxidation processes, mechanisms and synergistic antibiotic degradation

Human diseases caused by pathogenic microorganisms make people pay more attention to disinfection. Meanwhile, antibiotics can cause microbial resistance and increase the difficulty of disease treatment, resulting in risk of triggering a vicious circle. Advanced oxidation process (AOPs) has been widely studied in the field of synergistic treatment of the two contaminates. This paper reviews the application of catalytic materials and their modification strategies in the context of AOPs for disinfection and antibiotic degradation. It also delves into the mechanisms of disinfection such as the pathways for microbial inactivation and the related influencing factors, which are essential for understanding the pivotal role of catalytic materials in disinfection principles by AOPs. More importantly, the exploratory research on the combined use of AOPs for disinfection and antibiotic degradation is discussed, and the potential and prospects in this field is highlighted. Finally, the limitations and challenges associated with the application of AOPs in disinfection and antibiotic degradation are summarized. It aims to provide a starting point for future research efforts to facilitate the widespread use of advanced oxidation processes in the field of public health.

Potassium permanganate oxidation enhanced by infrared light and its application to natural water

Photocoupled permanganate (PM) is an effective way to enhance the oxidation efficiency of PM, however, the activation of PM by infrared has received little attention. This study aimed to investigate the ability of infrared light to activate PM. When coupled with infrared, the degradation rate of 4-chlorophenol (4-CP) is increased to 3.54 times of PM oxidation alone. The accelerated reaction was due to the formation of vibrationally excited PM by absorbing 3.1 kJ mol-1 infrared energy, which also leads to the primary reactive intermediates Mn(V/IV) in the reaction system. The infrared coupled PM system also showed 1.14-2.34 times promotion effect on other organic pollutants. Furthermore, solar composed of 45% infrared, coupled PM system showed excellent degradation performance, where the degradation of 4-CP in 10 L of tap water and river water was 68 and 23 times faster than in ultrapure water, respectively. The faster-increased degradation rate in natural waters is mainly due to the abundant inorganic ions, which can stabilize the manganese species, and then has a positive effect on 4-CP degradation. In summary, this work develops a energy-efficient photoactivated PM technology that utilizes infrared and provides new insights into the design of novel sunlight-powered oxidation processes for water treatment.

Carbonaceous Materials-Based Photothermal Process in Water Treatment: From Originals to Frontier Applications

The photothermal process has attracted considerable attention in water treatment due to its advantages of low energy consumption and high efficiency. In this respect, photothermal materials play a crucial role in the photothermal process. Particularly, carbonaceous materials have emerged as promising candidates for this process because of exceptional photothermal performance. While previous research on carbonaceous materials has primarily focused on photothermal evaporation and sterilization, there is now a growing interest in exploring the potential of photothermal effect-assisted advanced oxidation processes (AOPs). However, the underlying mechanism of the photothermal effect assisted by carbonaceous materials remains unclear. This review aims to provide a comprehensive review of the photothermal process of carbonaceous materials in water treatment. It begins by introducing the photothermal properties of carbonaceous materials, followed by a discussion on strategies for enhancing these properties. Then, the application of carbonaceous materials-based photothermal process for water treatment is summarized. This includes both direct photothermal processes such as photothermal evaporation and sterilization, as well as indirect photothermal processes that assisted AOPs. Meanwhile, various mechanisms assisted by the photothermal effect are summarized. Finally, the challenges and opportunities of using carbonaceous materials-based photothermal processes for water treatment are proposed.

Interfacial coupling of CuFe2O4 induced hotspots over self-assembled g-C3N4 nanosheets as an efficient photocatalytic bacterial disinfectant

Most bacterial disinfectants contain high levels of extremely toxic and environmental hazardous chemicals, which pose a significant threat to the ecosystem. Semiconductor photocatalysis exhibits attractive prospects as an emerging greener technology for waste water disinfection. However, the fast recombination of charge carriers limits its practical application. Herein, self-assembled polymeric feather-like g-C3N4 (GCN) nanosheets modified with ferromagnetic CuFe2O4 (CFO) nanospheres were successfully applied as a reusable visible light photocatalytic disinfectant. As expected, the g-C3N4/CuFe2O4 (GCF) nanohybrid displayed superior photocatalytic inactivation efficiency of 0.157log within 120 min towards Escherichia coli DH5α (E. coli) compared with pristine GCN and CFO. The characterization results revealed the synergistic heterostructure interfaces, high surface area, and the transformative self-assembly of GCN to feather-like structure providing a rich active site for improved charge separation efficiency, and wide spectral response, therefore the superior performance of GCF. The radical trapping assay proclaimed that both O2•- and •OH radical played major role in the photocatalytic inactivation among the other reactive oxygen species (ROS). Furthermore, the chemical oxygen demand (COD), protein estimation, and DNA estimation assay results validated the cell damage caused by the photocatalyst. Besides that, GCN showed applicability in real-time wastewater samples with improved efficiency than in the saline solution. The excellent magnetic characteristics facilitated the recycling of the catalyst with insignificant leaching, magnetic induction, and distinguished separation. The results of this work signify the well-designed GCF as a high-performance and reusable photocatalyst for real-world pathogenic bacterial disinfection operations.

Catalyst-free persulfate activation by UV/visible radiation for secondary urban wastewater disinfection

This study focuses on the treatment of secondary urban wastewater (W) to improve the effluent quality aiming at the reduction of pathogenic microorganisms for the safe reuse of the treated wastewater (TW). Catalyst-free persulfate activation by radiation-based oxidation was applied as a treatment technology. A parametric study was carried out to select the best operating conditions. Total enterobacteria inactivation (quantified by the log reduction (CFU/100 mL)) was achieved when using [S2O82-] = 1 mM, pH = 8.5 (natural pH of W), T = 25 °C, and I = 500 W/m2. However, storing TW for 3 days promoted the regrowth of bacteria, risking its reutilization. Therefore, in this study, and for the first time, the potential beneficial role of inoculation of wastewater treated by the radiation-activated persulfate process with a diverse bacterial community was evaluated in order to control the regrowth of potentially harmful microorganisms through bacterial competition. For this, TW was diluted with river water (R) in the volume percentages of 5, 25, and 50 (percentages refer to R content), and enterobacteria and total heterotrophs were enumerated before and after storage for 72 h. The results showed total heterotrophs and enterobacteria regrowth for TW and R + TW diluted 5 and 25% after storage. However, for R + TW diluted 50%, only the total heterotrophs regrew. Hence, the treated wastewater generated by the oxidative process diluted with 50% river water complies with the legislated limits for reuse in urban uses or irrigation.

Inactivation of Heterosigma akashiwo under UV/peroxydisulfate advanced disinfection system in marine waters

Heterosigma akashiwo (H. akashiwo) is recognized as a harmful algal bloom (HABs) species with a global distribution, capable of posing significant threats to marine ecosystems, particularly when spread through ship ballast water. This investigation focused on elucidating the inactivation kinetics and underlying mechanism of H. akashiwo through a combined ultraviolet irradiation and peroxydisulfate (UV/PDS) process. The results demonstrated a strong synergistic effect within the UV/PDS system, resulting in an inactivation of 0.78-ln and 2.67-ln within 40 min of UV and UV/PDS processes. The principal agents accountable for inactivation were identified as sulfate radicals (•SO4-) and hydroxyl radical (•OH), which exhibited a synergistic effect in the UV/PDS process. Furthermore, the study observed a negatively impact of seawater pH and salinity on the efficiency of inactivation. UV/PDS caused oxidative stress on algal cells, initially involving the participation of antioxidant enzymes in counteracting cellular damage, but this protective mechanism diminished as the reaction duration extended. The UV/PDS treatment not only inflicted damage upon H. akashiwo's photosynthetic system but also caused the extracellular release of DNA and algal organic matter (AOM) due to damaged cell membranes. Transcriptome analysis provided a molecular biology perspective on the cellular inactivation process. Upregulation of genes linked to photosynthesis and oxidative phosphorylation suggested a potential elevation in energy metabolism. In contrast, genes associated with cellular and metabolic processes, including glycolysis and the tricarboxylic acid cycle (TCA cycle), exhibited downregulation. Moreover, this treatment exerted an inhibitory influence on RNA polymerase and protein synthesis, resulting in the reduced expression of genetic information.

Enhanced Escherichia coli removal from stormwater with bermudagrass-derived activated biochar filtration systems

Stormwater treatment and reuse can alleviate water pollution and scarcity while current sand filtration systems showed low treatment performance for stormwater. For enhancing E. coli removal in stormwater, this study applied the bermudagrass-derived activated biochars (BCs) in the BC-sand filtration systems for E. coli removal. Compared with the pristine BC (without activation), the FeCl3 and NaOH activations increased the BC carbon content from 68.02% to 71.60% and 81.22% while E. coli removal efficiency increased from 77.60% to 81.16% and 98.68%, respectively. In all BCs, the BC carbon content showed a highly positive correlation with E. coli removal efficiency. The FeCl3 and NaOH activations also led to the enhancement of roughness of BC surface for enhancing E. coli removal by straining (physical entrapment). The main mechanisms for E. coli removal by BC-amended sand column were found to be hydrophobic attraction and straining. Additionally, under 105-107 CFU/mL of E. coli, final E. coli concentration in NaOH activated BC (NaOH-BC) column was one order of magnitude lower than those in pristine BC and FeCl3 activated BC (Fe-BC) columns. The presence of humic acid remarkably lowered the E. coli removal efficiency from 77.60% to 45.38% in pristine BC-amended sand column while slightly lowering the E. coli removal efficiencies from 81.16% and 98.68% to 68.65% and 92.57% in Fe-BC and NaOH-BC-amended sand columns, respectively. Moreover, compared to pristine BC, the activated BCs (Fe-BC and NaOH-BC) also resulted in the lower antibiotics (tetracycline and sulfamethoxazole) concentrations in the effluents from the BC-amended sand columns. Therefore, for the first time, this study indicated NaOH-BC showed high potential for effective treatment of E. coli from stormwater by the BC-amended sand filtration system compared with pristine BC and Fe-BC.

Generation and engineering applications of sulfate radicals in environmental remediation

Sulfate radical (SO4•-)-based advanced oxidation processes (AOPs) have become promising alternatives in environmental remediation due to the higher redox potential (2.6-3.1 V) and longer half-life period (30-40 μs) of sulfate radicals compared with many other radicals such as hydroxyl radicals (•OH). The generation and mechanisms of SO4•- and the applications of SO4•--AOPs have been examined extensively, while those using sulfite as activation precursor and their comparisons among various activation precursors have rarely reviewed comprehensively. In this article, the latest progresses in SO4•--AOPs were comprehensively reviewed and commented on. First of all, the generation of SO4•- was summarized via the two activation methods using various oxidant precursors, and the generation mechanisms were also presented, which provides a reference for guiding researchers to better select two precursors. Secondly, the reaction mechanisms of SO4•- were reviewed for organic pollutant degradation, and the reactivity was systematically compared between SO4•- and •OH. Thirdly, methods for SO4•- detection were reviewed which include quantitative and qualitative ones, over which current controversies were discussed. Fourthly, the applications of SO4•--AOPs in various environmental remediation were summarized, and the advantages, challenges, and prospects were also commented. At last, future research needs for SO4•--AOPs were also proposed consequently. This review could lead to better understanding and applications of SO4•--AOPs in environmental remediations.

Co single atoms anchored on straw biochar as an efficient peroxydisulfate activator for ultrafast removal of antibiotics

The removal efficiency of antibiotics decreases at low temperature, which is an urgent problem to be solved in cold regions. This study prepared a low-cost single atom catalyst (SAC) from straw biochar, which can rapidly degrade antibiotics at different temperatures by activating peroxydisulfate (PDS). Co SA/CN-900 + PDS system can degrade 100% of tetracycline hydrochloride (TCH, 10 mg/L) in 6 min. The high concentration of TCH (25 mg/L) was degraded by 96.3% in 10 min at 4 °C. The system was also tested in simulated wastewater and showed a good removal efficiency. TCH was primarily degraded by 1O2 and direct electron transfer pathway. Electrochemical experiments and density functional theory (DFT) calculations showed that CoN4 improved the electron transfer capacity of biochar and thus enhanced the oxidation capacity of Co SA/CN-900 + PDS complex. This work optimizes the application of agricultural waste biochar and provides a design strategy of efficient heterogenous Co SACs to degrade antibiotics in cold regions.

Efficient inactivation of amoeba spores and their intraspore bacteria by solar/chlorine: Kinetics and mechanisms

Amoebae are widespread in water and serve as environment vectors for pathogens, which may threaten public health. This study evaluated the inactivation of amoeba spores and their intraspore bacteria by solar/chlorine. Dictyostelium discoideum and Burkholderia agricolaris B1qs70 were selected as model amoebae and intraspore bacteria, respectively. Compared to solar irradiation and chlorine, solar/chlorine enhanced the inactivation of amoeba spores and intraspore bacteria, with 5.1 and 5.2-log reduction at 20 min, respectively. The enhancement was similar in real drinking water by solar/chlorine under natural sunlight. However, the spore inactivation decreased to 2.97-log by 20 min solar/chlorine under oxygen-free condition, indicating that ozone played a crucial role in the spore inactivation, as also confirmed by the scavenging test using tert‑butanol to scavenge the ground-state atomic oxygen (O(3P)) as a ozone precursor. Moreover, solar/chlorine induced the shape destruction and structural collapse of amoeba spores by scanning electron microscopy. As for intraspore bacteria, their inactivation was likely ascribed to endogenous reactive oxygen species. As pH increased from 5.0 to 9.0, the inactivation of amoeba spores decreased, whereas that of intraspore bacteria was similar at pH 5.0 and 6.5 during solar/chlorine treatment. This study first reports the efficient inactivation of amoeba spores and their intraspore pathogenic bacteria by solar/chlorine in drinking water.

Ultraviolet-based synergistic processes for wastewater disinfection: A review

Ultraviolet (UV) irradiation is widely used for wastewater disinfection but suffers from low inactivation rates and can cause photoreactivation of microorganisms. Synergistic disinfection with UV and oxidants is promising for enhancing the inactivation performance. This review summarizes the inactivation effects on representative microorganisms by UV/hydrogen peroxide (H₂O₂), UV/ozone (O₃), UV/persulfate (PS), UV/chlorine, and UV/chlorine dioxide (ClO₂). UV synergistic processes perform better than UV or an oxidant alone. UV mainly attacks the DNA or RNA in microorganisms; the oxidants H₂O₂ and O₃ mainly attack the cell walls, cell membranes, and other external structures; and HOCl and ClO₂ enter cells and oxidize proteins and enzymes. Free radicals can have strong oxidation effects on cell walls, cell membranes, proteins, enzymes, and even DNA. At similar UV doses, the inactivation rates of Escherichia coli with UV alone, UV/H₂O₂, UV/O₃, UV/PS (peroxydisulfate or peroxymonosulfate), and UV/chlorinated oxidant (chlorine, ClO₂, and NH₂Cl) range from 2.03 to 3.84 log, 2.62-4.30 log, 4.02-6.08 log, 2.93-5.07 log, and 3.78-6.55 log, respectively. The E. coli inactivation rates are in the order of UV/O₃ ≈ UV/Cl₂ > UV/PS > UV/H₂O₂. This order is closely related to the redox potentials of the oxidants and quantum yields of the radicals. UV synergistic disinfection processes inhibit photoreactivation of E. coli in the order of UV/O₃ > UV/PS > UV/H₂O₂. The activation mechanisms and formation pathways of free radicals with different UV-based synergistic processes are presented. In addition to generating HO·, O₃ can reduce the turbidity and chroma of wastewater to increase UV penetration, which improves the disinfection performance of UV/O₃. This knowledge will be useful for further development of the UV-based synergistic disinfection processes.

Dual promoted ciprofloxacin degradation by Fe0/PS system with ascorbic acid and pre-magnetization

As a widely used and hard-to-degrade pharmaceuticals and personal care product (PPCP), ciprofloxacin (CIP) was frequently found in water environment and the detected concentration was gradually increased. Although zero-valent iron (ZVI) has been shown to be effective in destroying refractory organic pollutants, the practical application and sustained catalytic performance is not satisfactory. Herein, introduction of ascorbic acid (AA) and employment of pre-magnetized Fe⁰ was achieved to maintain a high-concentration of Fe²⁺ during persulfate (PS) activation. Pre-Fe⁰/PS/AA system presented the best performance for CIP degradation, achieving almost complete elimination of 5 mg/L CIP within 40 min in the reaction conditions of 0.2 g/L pre-Fe⁰，0.05 mM AA and 0.2 mM PS. The CIP degradation retarded as excess pre-Fe⁰ and AA were added, therefore, the optimum dosages of pre-Fe⁰ and AA were determined to be 0.2 g/L and 0.05 mM, respectively. The CIP degradation gradually decreased as the initial pH increased from 3.05 to 11.03. The presence of Cl^-, HCO₃^-, Al³⁺, Cu²⁺ and humic acid significantly influenced the performance of CIP removal, while Zn²⁺, Mg²⁺, Mn²⁺, and NO₃^- slightly affected the CIP degradation. Combined with the results of HPLC analysis and previous literature, several possible degradation pathways of CIP were proposed.

Autochthonous DOM had solar disinfection effect but nitrate counteracted with them

Pathogens in natural water can pose great threat to public health and challenge water quality. In sunlit surface water, dissolved organic matters (DOMs) can inactivate pathogens due to their photochemical activity. However, the photoreactivity of autochthonous DOM derived from different source and their interaction with nitrate on photo-inactivation remained limited understood. In this study, the composition and photoreactivity of DOM extracted from Microcystis (ADOM), submerged aquatic plant (PDOM) and river water (RDOM) were studied. Results revealed that lignin and tannin-like polyphenols and polymeric aromatic compounds negatively correlated with quantum yield of ³DOM*, whilst lignin like molecules positively correlated with •OH generation. ADOM had highest photoinactivation efficiency of E. coli, followed by RDOM and PDOM. Both the photogenerated •OH and low energy ³DOM* could inactivate bacteria damaging cell membrane and causing increase of intracellular reactive species. PDOM with more phenolic or polyphenols compounds not only weaken its photoreactivity, also increase regrowth potential of bacteria after photodisinfection. The presence of nitrate counteracted with autochthonous DOMs on photogeneration of •OH and photodisinfection activity, as well as increased the reactivation rate of PDOM and ADOM, which might be attributed to the increase of survival bacteria and more bioavailable fractions provided in systems.

Oxidative transformations of olefins employing persulfate/visible light irradiation in water

We present a green and economical approach for the photooxidation of diverse olefins through the use of ammonium persulfate and blue light irradiation, resulting in the formation of vicinal diols from styrenes and aliphatic alkenes, and vinyl esters and diacids from α,β-unsaturated ketones. The involvement of sulfate radicals in the reaction medium was established as the primary species responsible for the selective generation of the products. A significant advantage of the method lies in its broad substrate scope and economic feasibility, making it a promising alternative to conventional transition metal photocatalysis.

An Overview of Recent Developments in Improving the Photocatalytic Activity of TiO2-Based Materials for the Treatment of Indoor Air and Bacterial Inactivation

Indoor air quality has become a significant public health concern. The low cost and high efficiency of photocatalytic technology make it a natural choice for achieving deep air purification. Photocatalysis procedures have been widely investigated for environmental remediation, particularly for air treatment. Several semiconductors, such as TiO₂, have been used for photocatalytic purposes as catalysts, and they have earned a lot of interest in the last few years owing to their outstanding features. In this context, this review has collected and discussed recent studies on advances in improving the photocatalytic activity of TiO₂-based materials for indoor air treatment and bacterial inactivation. In addition, it has elucidated the properties of some widely used TiO₂-based catalysts and their advantages in the photocatalytic process as well as improved photocatalytic activity using doping and heterojunction techniques. Current publications about various combined catalysts have been summarized and reviewed to emphasize the significance of combining catalysts to increase air treatment efficiency. Besides, this paper summarized works that used these catalysts to remove volatile organic compounds (VOCs) and microorganisms. Moreover, the reaction mechanism has been described and summarized based on literature to comprehend further pollutant elimination and microorganism inactivation using photocatalysis. This review concludes with a general opinion and an outlook on potential future research topics, including viral disinfection and other hazardous gases.

Orientated construction of visible-light-assisted peroxymonosulfate activation system for antibiotic removal: Significant enhancing effect of Cl. JOURNAL OF HAZARDOUS MATERIALS 2023;445:130476. [PMID: 36455327 DOI: 10.1016/j.jhazmat.2022.130476]

Antibiotic contaminants can migrate over long distances in the water, thus possibly causing severe detriment to the environment and even potential harm to human health. Heterogeneous activation of peroxymonosulfate (PMS) assisted by visible light is an emerging and promising technology for the purification of such wastewater. This study designed an ultra-efficient and stable PMS activator (FeCN) to restore the typical antibiotic-polluted water under harsh conditions. About 90.94% of sulfamethoxazole (SMX) was degraded in 35 min in the constructed FeCN+PMS/vis system, and the reaction rate constant was nearly 50-fold higher than direct photocatalysis. Electron spin resonance, quenching experiments, LC/MS technique, eco-toxicity assessment, and density functional theory validated that the SMX removal was dominated by the attack of h⁺, ^•O₂^- and ¹O₂ on the active atoms of SMX molecules with high Fukui index, presenting as a simultaneous degradation and detoxification process. Such a visible-light-assisted PMS activation system also had good resistance to the environmental water bodies and a broad spectrum in the degradation of various pollutants. In particular, Cl^- (50 mM) could significantly accelerate the removal of SMX with a 32.6-fold increase in catalytic activity, and the mineralization efficiency could reach 56.6% under identical conditions. Moreover, this Cl^- containing system excluded the degradation products of disinfection by-products, and such a system was also versatile for different contaminants. This work demonstrates the feasibility of the FeCN+PMS/vis system for the remediation of antibiotic-contaminated wastewater in the presence and absence of Cl^-, and also highlights their great potential in WWTPs.

Periodate activation by pyrite for the disinfection of antibiotic-resistant bacteria: Performance and mechanisms

The propagation of antibiotic-resistant bacteria (ARB) greatly endangers the ecological safety and human health. This study employed pyrite (FeS₂, naturally abundant mineral) for periodate (PI) activation to disinfect ARB. FeS₂/PI system could disinfect 1 × 10⁷ CFU mL^-1 of kanamycin-resistant E.coli below the limit of detection in 20 min. Efficient ARB inactivation performance was achieved in pH from 3 to 9, ionic strength from 0 to 300 mM, with HA (0.1-10 mg L^-1) in suspension, and in real water samples including tap water, river water and sewage. FeS₂/PI system could also efficiently disinfect gentamycin-resistant E.coli and Gram-positive B. subtilis. The generated reactive species including Fe(IV), ·O₂^- and ·OH would attack cell membrane and overwhelmed intracellular defense system. The intracellular kanamycin resistance genes in cells would be released and then degraded in FeS₂/PI system. PI preferred to be adsorbed on Fe site of FeS₂ (with lower adsorption energy, more occupancy of bonding state and stronger bonding strength). The subsequent transfer of electron cloud from Fe site to PI would cleave IO bond to generate reactive species. Moreover, FeS₂/PI system could also combine with sand filtration system to efficiently capture and disinfect ARB. Therefore, FeS₂/PI system is a promising approach to inactivate ARB in different scenarios.

Uncovering novel disinfection mechanisms of solar light/periodate system: The dominance of singlet oxygen and metabolomic insights

Disinfection plays an essential role in waterborne pathogen control and disease prevention, especially during the COVID-19 pandemic. Catalyst-free solar light/periodate (PI) system has recently presented great potential in water disinfection, whereas the in-depth chemical and microbiological mechanisms for efficient bacterial inactivation remain unclear. Our work delineated firstly the critical role of singlet oxygen, instead of reported hydroxyl radicals and superoxide radicals, in dominating bacterial inactivation by the PI/simulated sunlight (SSL) system. Multi-evidence demonstrated the prominent disinfection performance of this system for Staphylococcus aureus in terms of culturability (> 6 logs CFU), cellular integrity, and metabolic activity. Particularly, the excellent intracellular DNA removal (> 95%) indicated that PI/SSL system may function as a selective disinfection strategy to diminish bacterial culturability without damaging the cell membrane. The PI/SSL system could also effectively inhibit bacterial regrowth for > 5 days and horizontal gene transfer between E. coli genera. Nontargeted metabolomic analysis suggested that PI/SSL system inactivated bacteria by triggering the accumulation of intracellular reactive oxygen species and the depletion of reduced glutathione. Additionally, the PI/SSL system could accomplish simultaneous micropollutant removal and bacterial inactivation, suggesting its versatility in water decontamination. Overall, this study deciphers more comprehensive antibacterial mechanisms of this environmentally friendly disinfection system, facilitating the technical development and application of the selective disinfection strategy in environmental pathogen control.

Disinfection of treated urban effluents for reuse by combination of coagulation/flocculation and Fenton processes

In this study, a combination of coagulation/flocculation and Fenton processes was studied as tertiary treatment in order to generate treated water susceptible to reuse. The combination of both processes has never been applied in disinfection of real urban wastewater. The best removals of turbidity and enterobacteria were achieved when applying a coagulant (FeCl₃) dosage of 120 mg/L and the natural pH of the effluent (7.14). The following Fenton reaction presented the maximal enterobacteria inactivation after 120 min at 25 °C, when using hydrogen peroxide and added iron concentrations of 100 mg/L and 7 mg/L, respectively. The abundance of antibiotic resistant (amoxicillin and sulfamethoxazole) enterobacteria and total enterobacteria, enterococci, and heterotrophs, and antibiotic resistance genes - ARG - (sul1, bla_TEM and qnrS) was evaluated before and after each step of the treatment. Values below 10 CFU/100 mL were achieved for total and resistant cultivable enterobacteria immediately after treatment and after storage for 72 h, therefore meeting the strictest limit imposed for E. coli. Physico-chemical parameters also met the established limits for water reuse. Despite harbouring a rich and diverse bacterial community, the final stored disinfected wastewater contained high relative abundance of potentially hazardous bacteria. Such results point out the need of a deep microbiological characterization of treated wastewater to evaluate the risk of its reuse in irrigation.

Promoting selective water decontamination via boosting activation of periodate by nanostructured Ru-supported Co3O4 catalysts

The superior catalytic efficiency of ruthenium (Ru)-based nanocomposites in advanced oxidation processes for water decontamination has attracted accumulating attention worldwide. However, rather limited knowledge is currently available regarding their roles in activating periodate (PI), an emerging oxidant with versatile environmental applications. This study firstly delineated that Ru-supported Co₃O₄ (Ru/Co₃O₄), a typical Ru-based nanomaterial, can efficiently accomplish PI activation to eliminate multiple organic micropollutants and inactivate different pathogenic bacteria. Almost all eight micropollutants can be completely removed within 2 min of Ru/Co₃O₄-PI oxidation except sulfamethoxazole (SMX), which was degraded ∼70 % at 2 min with 100 % mineralization after 10 min. The excellent catalytic performance was independent of PI dosages, initial pH, and coexisting water constituents, demonstrating its prominent capability as a selective oxidation strategy. Diverse lines of evidence indicated the dominant role of single oxygen in the Ru/Co₃O₄-PI system, which triggered the generation of five transformation products of SMX with reduced environmental risks. Concurrently, PI was stoichiometrically converted to the eco-friendly IO₃^-. Additionally, Ru/Co₃O₄-PI system achieved 6-log inactivation of different pathogenic bacteria within 1 min, implying the feasibility of rapid water disinfection. Overall, this work demonstrated the excellent promise of Ru-based composites in PI activation for highly efficient and selective water decontamination.

Photodegradation of oxytetracycline by UV-assisted persulfate and percarbonate processes: kinetics, influencing factors, anion effect, and radical species

In this study, the performance of ultraviolet (UV)-assisted persulfate (PS) and percarbonate (PC) oxidation processes in oxytetracycline (OTC) removal was investigated. UVC lamps were used for the photolysis process and the effect of operating parameters (initial pH, oxidant dose, initial OTC concentration, UV intensity) on OTC removal efficiency was determined. Control experiments were carried out at pH 5.5 and 32 W UV power for 60 min by adding a 4 mM oxidant with 10 mg/L initial OTC concentration. The OTC removal efficiency obtained as a result of only photolysis was 17.3% and the removal efficiency obtained by PS and PC oxidation alone was 18.3% and 12.7%, respectively. The OTC removal efficiencies increased in the combined processes and reached 58.1% and 69.9% for the UV-PS and UV-PC processes, respectively. The reaction rates of the processes were ranked as UV-PC > UV-PS > PS > UV > PC. In the UV-PS and UV-PC processes, the highest removal efficiencies were achieved at alkaline pH values. The OTC removal efficiency was increased with the increase in oxidant dose; however, the efficiency decreased after a certain dose due to the scavenging effect. The removal efficiency also increased as the initial OTC concentration decreased. The UV intensity had a positive effect on OTC removal efficiency. The effect of the water matrix on OTC removal efficiency was investigated while the dominant radical types were determined in UV-assisted processes. The EE/O values for the UV-PS and UV-PC processes were calculated as 211 kWh/m³ and 153 kWh/m³, respectively for 60 min of reaction time. Although similar removal efficiencies were obtained with both UV-assisted processes, the UV-PC process steps forward in terms of being a novel, environmentally friendly, more economic, and promising technology for OTC removal.

Inactivation of antibiotic resistant bacteria from stormwater runoff using UVA/LED and its potential risks

Recently, increasing attention has been paid to antibiotic resistance in stormwater runoff. However, there is no available literature about the control of antibiotic resistant bacteria (ARB) through 365 nm ultraviolet light-emitting diode (UVA/LED). In this study, batch experiments were conducted to investigate ARB inactivation kinetics, effects of light intensity and water matrix (including suspended solid (SS) concentration, initial pH and bacteria concentration), and potential transmission risks after UVA/LED irradiation. Results showed that ARB inactivation efficiencies reached 6.31 log reduction at 8 mW/cm² (86 J/cm²) of UVA/LED for 180 min. ARB inactivation efficiencies increased with the increase of light intensity, and showed a linear relationship. ARB inactivation decreased with increasing SS levels, and the largest inactivation efficiencies was 3.56 log reduction at 50 mg/L of SS. Initial pH had slight effect on ARB inactivation through UVA/LED irradiation. A low initial bacteria concentration (10⁵ CFU/mL) was not necessarily associated with good ARB inactivation (3.59 log reduction). After UVA/LED irradiation, ARB was hardly detected during 12 hr of dark repair, and the transfer frequency of kanamycin resistance gene was increased to 5.43 × 10^-4. These suggested that the application of UVA/LED to inactivate ARB in stormwater runoff was feasible and desirable in this study.

Natural organic matters promoted conjugative transfer of antibiotic resistance genes: Underlying mechanisms and model prediction

Dissemination of antibiotic resistance gene (ARG) is a huge challenge around the world. Natural organic matter (NOM) is one of the most commonly components in aquatic systems. Information regarding ARG transfer induced by NOM is still lacking. In this study, experimental exploration and model prediction on RP4 plasmid conjugative transfer between bacteria under NOM exposure was conducted. Compared with no exposure, the conjugative transfer frequency of RP4 plasmid increased 7.1-fold and 3.2-fold under exposure to 10 kDa and 100 kDa NOM exposure, respectively. NOM exposure with a lower molecular weight and higher concentration promoted gene expressions related to reactive oxygen species generation, cell membrane permeability, intercellular contact, quorum sensing, and energy driving force. Concurrently, the expressions of conjugation genes in RP4 plasmid were also upregulated. Moreover, model prediction demonstrated that the maintenance of the acquired plasmid was shortened to 133 h under 10 kDa NOM exposure compared with the control (200 h). Long-term NOM exposure enhanced transfer frequency and transfer rate of ARG. This study firstly theoretically and experimentally revealed the underlying mechanisms for promoting ARG transfer by NOM.

Efficient degradation of Rhodamine B in water by CoFe2O4/H2O2 and CoFe2O4/PMS systems: A comparative study

In this work, a comparative study of efficient degradation of Rhodamine B (RhB) in CoFe₂O₄/H₂O₂ and CoFe₂O₄/PMS systems was performed. Batch experiments indicated that the RhB degradation rate of CoFe₂O₄/H₂O₂ system reached 95.5% at 90 min under the condition of 0.5 g L^-1 of CoFe₂O₄ dosage, 10 mM of H₂O₂ concentration and 3.0 of initial pH. At certain conditions of initial pH = 7.0, 0.3 g L^-1 of CoFe₂O₄ dosage, 7 mM of PMS concentration, CoFe₂O₄/PMS system could completely degrade RhB within 90 min. EPR and quenching experiments indicated that •OH was the main active species of CoFe₂O₄/H₂O₂ system, and •OH, SO₄•^-, •O₂^- and ¹O₂ participated in RhB degradation of CoFe₂O₄/PMS system. The circulate of Co(II)/Co(III) and Fe(II)/Fe(III) on the CoFe₂O₄ surface promoted the formation of free radical species in the two system. In CoFe₂O₄/PMS system, the formed •O₂^- and SO₅•^- realized the generation of non-free radical species (¹O₂). The LC-MS results indicated that N-de-ethylation, chromophore cleavage, opening rings and mineralization were the main steps for the RhB degradation of the two systems. After five cycles of degradation experiment, the CoFe₂O₄/H₂O₂ and CoFe₂O₄/PMS systems still maintained the high degradation rate (85.2% and 92.4%) and low mass loss (2.7% and 3.09%). In addition, CoFe₂O₄/PMS system had better potential value for the actual water and multi-pollutant degradation than CoFe₂O₄/H₂O₂ system. Finally, the toxicity analysis and cost assessment of the two oxidation systems were preliminarily evaluated.

Single-atom Ru loaded on layered double hydroxide catalyzes peroxymonosulfate for effective E. coli inactivation via a non-radical pathway: Efficiency and mechanism

The Fenton-like processes are considered to be one of the most promising strategies for inactivating bacteria due to their capacity to produce reactive oxygen species (ROS). Herein, a catalytic system for efficient inactivation of Escherichia coli (E. coli) was developed by anchoring single-atom Ru on layered double hydroxides (LDH). The Ru/NiFe-LDH catalyst showed excellent performance in activating peroxymonosulfate (PMS) to inactivate E. coli. Under the combined action of the ultra-low concentrations of Ru/NiFe-LDH (40 mg/L) and PMS (5 mg/L), 7 log E. coli can be totally inactivated within 90 s. This was attributed to the combined effect of single-atom Ru adsorption to E. coli and the ROS produced in situ. Mechanism studies indicated that the ¹O₂ with electrophilic properties was the key active species responsible for the rapid inactivation of E. coli. The E. coli inactivation process suggested that the ROS produced first attacked the outer membrane of the cell, then the antioxidant enzymes in the cell were induced, the macromolecule substances were released and mineralized, eventually leading to irreversible cell death. This work firstly loads monoatomic Ru on LDH for bacterial inactivation, providing a feasible method for rapid inactivation of E. coli.

Mechanism insights into bacterial sporulation at natural sphalerite interface with and without light irradiation: The suppressing role in bacterial sporulation by photocatalysis

Unveiling the mechanisms of bacterial sporulation at natural mineral interfaces is crucial to fully understand the interactions of mineral with microorganism in aquatic environment. In this study, the bacterial sporulation mechanisms of Bacillus subtilis (B. subtilis) at natural sphalerite (NS) interface with and without light irradiation were systematically investigated for the first time. Under dark condition, NS was found to inactivate vegetative cells of B. subtilis and promote their sporulation simultaneously. The released Zn2+ from NS was mainly responsible for the bacterial inactivation and sporulation. With light irradiation, the photocatalytic effect from NS could increase the bacterial inactivation efficiency, while the bacterial sporulation efficiency was decreased from 8.1 % to 4.5 %. The photo-generated H2O2 and O2- played the major roles in enhancing bacterial inactivation and suppressing bacterial sporulation process. The intracellular synthesis of dipicolinic acid (DPA) as biomarker for sporulation was promoted by NS in dark, which was suppressed by the photocatalytic effect of NS with light irradiation. The transformation process from vegetative cells to spores was monitored by both 3D-fluerecence EEM and SEM observations. Compared with the NS alone system, the NS/light combined system induced higher level of intracellular ROSs, up-regulated antioxidant enzyme activity and decreased cell metabolism activity, which eventually led to enhanced inactivation of vegetative cells and suppressed bacterial sporulation. These results not only provide in-depth understanding about bacterial sporulation as a new mode of sub-lethal stress response at NS interface, but also shed lights on putting forward suitable strategies for controlling spore-producing bacteria by suppressing their sporulation during water disinfection.

WSe2/g-C3N4 for an In Situ Photocatalytic Fenton-like System in Phenol Degradation

An in situ photo-Fenton system can continuously generate H₂O₂ by photocatalysis, activating H₂O₂ in situ to form strong oxidizing ·OH radicals and degrading organic pollutants. A WSe₂/g-C₃N₄ composite catalyst with WSe₂ as a co-catalyst was successfully synthesized in this work and used for in situ photo-Fenton oxidation. The WSe₂/g-C₃N₄ composite with 7% loading of WSe₂ (CNW2) has H₂O₂ production of 35.04 μmol/L, which is fourteen times higher than pure g-C₃N₄. The degradation efficiency of CNW2 for phenol reached 67%. By constructing an in situ Fenton-system, the phenol degradation rate could be further enhanced to 90%. WSe₂ can enhance the catalytic activity of CNW2 by increasing electron mobility and inhibiting the recombination of photogenerated electron-hole pairs. Moreover, the addition of Fe²⁺ activates the generated H₂O₂, thus increasing the amount of strong oxidative ·OH radicals for the degradation of phenol. Overall, CNW2 is a promising novel material with a high H₂O₂ yield and can directly degrade organic pollutants using an in situ photo-Fenton reaction.

Visible Light-Driven Advanced Oxidation Processes to Remove Emerging Contaminants from Water and Wastewater: a Review

The scientific data review shows that advanced oxidation processes based on the hydroxyl or sulfate radicals are of great interest among the currently conventional water and wastewater treatment methods. Different advanced treatment processes such as photocatalysis, Fenton's reagent, ozonation, and persulfate-based processes were investigated to degrade contaminants of emerging concern (CECs) such as pesticides, personal care products, pharmaceuticals, disinfectants, dyes, and estrogenic substances. This article presents a general overview of visible light-driven advanced oxidation processes for the removal of chlorfenvinphos (organophosphorus insecticide), methylene blue (azo dye), and diclofenac (non-steroidal anti-inflammatory drug). The following visible light-driven treatment methods were reviewed: photocatalysis, sulfate radical oxidation, and photoelectrocatalysis. Visible light, among other sources of energy, is a renewable energy source and an excellent substitute for ultraviolet radiation used in advanced oxidation processes. It creates a high application potential for solar-assisted advanced oxidation processes in water and wastewater technology. Despite numerous publications of advanced oxidation processes (AOPs), more extensive research is needed to investigate the mechanisms of contaminant degradation in the presence of visible light. Therefore, this paper provides an important source of information on the degradation mechanism of emerging contaminants. An important aspect in the work is the analysis of process parameters affecting the degradation process. The initial concentration of CECs, pH, reaction time, and catalyst dosage are discussed and analyzed. Based on a comprehensive survey of previous studies, opportunities for applications of AOPs are presented, highlighting the need for further efforts to address dominant barriers to knowledge acquisition.

Enhancing production of hydrocarbon-rich bio-oil from biomass via catalytic fast pyrolysis coupled with advanced oxidation process pretreatment

This study aims to propose a method for upgrading biomass pyrolysis products based on the combination of sodium persulfate pretreatment and fast catalytic pyrolysis. Combined with the analysis of components and thermogravimetric analysis, the result showed that after pretreatment the biomass structure was gradually depolymerized, the contents of lignin, the reaction of activation energy and the crystallinity of cellulose decreased. Due to the destructive effect of persulfate radicals, in fast pyrolysis, the relative contents of acids and oxygen-containing substances decreased, and the relative content of phenols can significantly increase to 19.20%. The yield of aromatic hydrocarbons and total hydrocarbons had a high value under the catalytic pyrolysis in the best performance which amount of yield reached 28.66% and 33.72%, respectively. Sodium persulfate pretreatment was beneficial in the production of hydrocarbon-rich bio-oils and high-value chemicals since the radicals can effectively depolymerize lignin which promoted the process of pyrolysis.

Layered metal oxides loaded ceramic membrane activating peroxymonosulfate for mitigation of NOM membrane fouling

Catalytic membrane can achieve sieving separation and advanced oxidation simultaneously, which can improve the effluent water quality while reducing membrane fouling. In this study, the catalytic membranes (M²⁺Al@AM) were fabricated by loading different binary layered metal oxides (M²⁺Al-LMO: MnAl-LMO, CuAl-LMO and CoAl-LMO) on alumina ceramic substrate membranes (AM) via vacuum filtration followed by calcination process. The performance of the catalytic membranes was investigated by filtering actual surface water. It was found that the presence of peroxymonosulfate (PMS) could mitigate membrane fouling effectively, as evidenced by the increase of normalized flux from 0.28 to 0.62 in CoAl@AM/PMS system, from 0.25 to 0.52 in CuAl@AM/PMS system, and from 0.22 to 0.31 in MnAl@AM/PMS system, respectively. Correspondingly, the CoAl@AM exhibited the highest removal for UV₂₅₄, TOC and fluorescent components in the surface water, followed by CuAl@AM and MnAl@AM. Quenching effect of phenol and furfuryl alcohol proposed the surface-bound radicals and singlet oxygen were the major reactive oxygen species in the M²⁺Al@AM/PMS systems. Interface free energy calculations confirmed the in-situ PMS activation could enhance the repulsive interactions between NOM and the membranes, thus mitigating membrane fouling. This work provides an original but simple strategy for catalytic ceramic membrane preparation and new insights into the mechanism of membrane fouling mitigation in catalytic membrane system.

One-pot synthesis of a cellulose-supported CoFe2O4 catalyst for the efficient degradation of sulfamethoxazole

Cellulose-supported cobalt ferrite (CoFe₂O₄/RC) was synthesized via a facile one-pot hydrothermal method and demonstrated to be an efficient catalyst to activate peroxymonosulfate (PMS) for the degradation of sulfamethoxazole (SMX). The characterizations of CoFe₂O₄/RC catalysts revealed that an appropriate particle size of the cellulose support could promote the dispersion of CoFe₂O₄ nanoparticles and consequently promote the catalytic activity of the resulting CoFe₂O₄/RC catalysts. The degradation of SMX reached 97.6 % within 20 min at 30 °C with the CoFe₂O₄/RC/PMS system. The mechanism of SMX degradation over CoFe₂O₄/RC-activated PMS was studied via EPR, XPS, and quenching tests. The results suggested that ¹O₂ was the dominant reactive oxygen species and was accompanied by SO₄^-, OH, and O₂^- radicals for SMX degradation. The CoFe₂O₄/RC catalyst exhibited high stability and recyclability and maintained high catalytic activity after five experimental cycles.

Development of novel K0.8Ni0.4Ti1.6O4 nano bamboo leaves, microstructural characterization, double absorption, and photocatalytic removal of organic pollutant

Novel K_0.8Ni_0.4Ti_1.6O₄ (KNTO) nano bamboo leaves were prepared for the first time under a simple hydrothermal method with 3 M KOH at 320 °C over 80 min. Highly pure KNTO possessing layered structure was determined by X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM). Double absorption feature of KNTO semiconductor was revealed at band energies of 1.88 and 2.08 eV by the UV-vis diffuse reflectance spectra and confirmed by the photoluminescence (PL) spectra. The photocatalytic activity was explored by the photodegradation of MB organic dye. KNTO not only exhibits strong adsorptive ability on methylene blue (MB) in dark environment, but also possesses good photodegradation capability of 94% degradation in 60 min. Degradation mechanism revealed that the photogenerated holes play an essential role in the MB degradation process, which is confirmed by trapping experiments. The recycling experiments demonstrated very high recycling ability and durability of KNTO nano bamboo leaves, suggesting KNTO is a potential candidate for high efficiency organic pollutant removal in the wastewater treatment.

Vacancy-rich BiO2-x as a highly-efficient persulfate activator under near infrared irradiation for bacterial inactivation and mechanism study

This study, for the first time, developed a novel defective BiO_2-x based collaborating system, where the near-infrared light (NIR) irradiation (λ > 700 nm) initiated persulfate activation and photocatalytic bacterial inactivation simultaneously. Vacancy-rich BiO_2-x nanoplates possessed impressive NIR absorption and firstly realized persulfate activation under NIR irradiation. In this collaborating system, on one hand, the persulfate can be transformed into sulfate radicals through light/heat activation mode directly, which would be enhanced by the presence of vacancy-rich BiO_2-x owing to its outstanding light and heat absorption ability. On the other hand, the photogenerated electrons can further efficiently react with persulfate and form sufficient reactive sulfate radicals. The sulfate radicals, synergizing with other reactive species (O₂^-, h⁺, etc.), achieved a 7-log Escherichia coli inactivation within 40 min. The systematic investigation of inactivation mechanism revealed that the reactive species caused the dysfunction of cellular respiration, ATP synthesis and bacterial membrane, followed by the severely oxidative damage to the antioxidative SOD and CAT enzymes and the generation of carbonylated protein. The final leakage of DNA and RNA implied the lethal damage to the bacteria cells. This work provided a new insight into the persulfate associated NIR driven remediation technology of controlling microbial contaminants.

Inactivation of E. coli and Streptococcus agalactiae by UV/persulfate during marine aquaculture disinfection

Sulfate radical (•SO₄^-)-based advanced oxidation processes have attracted a great deal of attention for use in water disinfection because of their strong oxidation ability toward electron-rich moieties on microorganism molecules. However, a few studies have focused on the effects of •SO₄^- on pathogenic microorganism inactivation in marine aquaculture water containing various inorganic anions. We employed the gram-negative bacteria E. coli and gram-positive bacteria S. agalactiae as representatives to evaluate the application of UV/persulfate (S₂O₈^2-, PDS), to the disinfection of marine aquaculture water in a comprehensive manner. Total inactivation of 4.13ˍlog of E. coli cells and 4.74ˍlog of S. agalactiae cells was reached within 120 s in the UV/PDS system. The inactivation of pathogenic bacteria in marine aquaculture water increased with the increasing PDS concentration and UV intensity. An acidic pH was beneficial for UV/PDS inactivation. Halogen-free radicals showed a strong influence on the inactivation. Anions in seawater, including Cl^-, Br^-, and HCO₃^- inhibited the disinfection. The inactivation rates of pathogenic bacteria followed the order seawater < marine aquaculture water < freshwater. Pathogenic bacteria could also be effectively inactivated in actual marine aquaculture water and reservoir water. The analysis of the inactivation mechanisms showed that S₂O₈^2- was activated by UV to produce •SO₄^-, which damaged the cell membranes. In addition, antioxidant enzymes, including SOD and CAT, were induced. The genomic DNA was also damaged. Inorganic disinfection byproducts such as chlorate and bromate were not formed during the disinfection of marine aquaculture water, which indicated that UV/PDS was a safe and efficient disinfection method.

Does light-based tertiary treatment prevent the spread of antibiotic resistance genes? Performance, regrowth and future direction

The common occurrence of antibiotic-resistance genes (ARGs) originating from pathogenic and facultative pathogenic bacteria pose a high risk to aquatic environments. Low removal of ARGs in conventional wastewater treatment processes and horizontal dissemination of resistance genes between environmental bacteria and human pathogens have made antibiotic resistance evolution a complex global health issue. The phenomenon of regrowth of bacteria after disinfection raised some concerns regarding the long-lasting safety of treated waters. Despite the inactivation of living antibiotic-resistant bacteria (ARB), the possibility of transferring intact and liberated DNA containing ARGs remains. A step in this direction would be to apply new types of disinfection methods addressing this issue in detail, such as light-based advanced oxidation, that potentially enhance the effect of direct light interaction with DNA. This study is devoted to comprehensively and critically review the current state-of-art for light-driven disinfection. The main focus of the article is to provide an insight into the different photochemical disinfection methods currently being studied worldwide with respect to ARGs removal as an alternative to conventional methods. The systematic comparison of UV/chlorination, UV/H₂O₂, sulfate radical based-AOPs, photocatalytic processes and photoFenton considering their mode of action on molecular level, operational parameters of the processes, and overall efficiency of removal of ARGs is presented. An in-depth discussion of different light-dependent inactivation pathways, influence of DBP and DOM on ARG removal and the potential bacterial regrowth after treatment is presented. Based on presented revision the risk of ARG transfer from reactivated bacteria has been evaluated, leading to a future direction for research addressing the challenges of light-based disinfection technologies.

Photocatalytic Inactivation of Bacillus subtilis Spores by Natural Sphalerite with Persulfate under Visible Light Irradiation

Bacterial spores are highly resistant to be inactivated by conventional water disinfection methods. In this study, the inactivation efficiency and mechanisms of Bacillus subtitles (B. subtilis) spores by natural sphalerite (NS) with persulfate (PS) under visible light (Vis) irradiation were investigated for the first time. The NS was composed of ZnS doped with trace amounts of metal ions, including As, Fe, Cd, and Mn. The results showed that 7 log of B. subtilis spores could be completely inactivated within 5 h in the Vis/NS/PS photocatalytic system, and the inactivation efficiency was about four and seven times higher than that of the NS/PS system and the Vis/PS system, respectively. The photo-generated electrons are generated by the excitation of NS under the illumination activated PS to form PS radicals (∙SO4−) and hydroxyl radicals (∙OH), which are the main active species for spore inactivation. Mechanism studies further showed that spore inactivation was related to physiological responses, including the increase in intracellular reactive oxygen species, the change of induced antioxidant enzyme activity, and the change of total protein. Furthermore, the dynamic changes of cells during spore inactivation were observed by SEM. These results not only clarify the relationship between the cell physiological stress response and inactivation mechanism of spores, but also reveal the interaction between minerals and PS under Vis, which provides technical methods for the inactivation of bacterial spores in the field of water disinfection.

Catalyst-Free Periodate Activation by Solar Irradiation for Bacterial Disinfection: Performance and Mechanisms

Periodate (PI)-based advanced oxidation process has recently attracted great attention in the water treatment processes. In this study, solar irradiation was used for PI activation to disinfect waterborne bacteria. The PI/solar irradiation system could inactivate Escherichia coli below the limit of detection (LOD, 10 CFU mL^-1) with initial concentrations of 1 × 10⁶, 1 × 10⁷, and 1 × 10⁸ CFU mL^-1 within 20, 40, and 100 min, respectively. ^•O₂^- and ^•OH radicals contributed to the bacterial disinfection. These reactive radicals could attack and penetrate the cell membrane, thereby increasing the amount of intracellular reactive oxygen species and destroying the intracellular defense system. The damage of the cell membrane caused the leakage of intracellular K⁺ and DNA (that could be eventually degraded). Excellent bacterial disinfection performance in PI/solar irradiation systems was achieved in a wide range of solution pH (3-9), with coexisting humic acid (0.1-10 mg L^-1) and broad solution ionic strengths (15-600 mM). The PI/solar irradiation system could also efficiently inactivate Gram-positive Bacillus subtilis. Moreover, PI activated by natural sunlight irradiation could inactivate 1 × 10⁷ CFU mL^-1 viable E. coli below the LOD in the river and sea waters with a working volume of 1 L in 40 and 50 min, respectively. Clearly, the PI/solar system could be potentially applied to disinfect bacteria in water.

Enhancement of E. coli inactivation by photosensitized erythrosine-based solar disinfection under weakly acidic conditions

Cost-effective disinfection technology is urgently needed in poor rural areas. Erythrosine (ERY)-based solar disinfection (SODIS) provides a promising solution because of its effective inactivation of viruses and gram-positive bacteria at low cost. However, the poor gram-negative bacteria (G^-, e.g., Escherichia coli) inactivation of photosensitized ERY inhibits its application. Herein, for the first time, the protonation of ERY was found to greatly enhance its G^- inactivation, and 99.99999% (7.0 log) of E. coli were completely inactivated within only 30 s using 2.5 mg/L ERY under 200 mW/cm² visible light irradiation. The inactivation rate constant (k) reached 17.5 min^-1 at pH 4.0, which was 4730 times higher than that at pH 7.0. At a lower pH, more severe cell wall and genomic DNA damage was observed. A linear correlation between k and monoanionic ERY (HE^-) content was obtained, indicating that HE^- rather than dianionic ERY (E^2-) participated in the inactivation at pH 5.0-7.0, which was further explained by the higher production of reactive oxygen species and bacterial adsorption of HE^- than E^2-. Both ¹O₂ and O₂^-• dominated bacterial inactivation, contributing 56.8% and 43.2%, respectively. O₂^-• but not ¹O₂ caused ERY photobleaching. OH• was not involved in either inactivation or photobleaching. Humic acid and salts (NaCl, Na₂SO₄, CaCl₂, and MgCl₂) slightly inhibited inactivation, while NaHCO₃ accelerated inactivation. Complete inactivation (99.9999%) of E. coli was achieved within ∼30 min at pH 5.0 in ERY-based SODIS with good adaptation to various water matrices and weather (sunny or partly cloudy). This work will help to promote the application of ERY-based disinfection especially for SODIS in poor rural areas.

Multi-heteroatom-doped carbocatalyst as peroxymonosulfate and peroxydisulfate activator for water purification: A critical review

Catalytic activation of peroxymonosulfate (PMS) and peroxydisulfate (PDS) (or collectively known as persulfate, PS) using carbocatalyst is increasingly gaining attention as a promising technology for sustainable recalcitrant pollutant removal in water. Single heteroatom doping using either N, S, B or P is widely used to enhance the performance of the carbocatalyst for PS activation. However, the performance enhancement from single heteroatom doping is limited by the type of heteroatom used. To further enhance the performance of the carbocatalyst beyond the limit of single heteroatom doping, multi-heteroatom doping can be conducted. This review aims to provide a state-of-the-art overview on the development of multi-heteroatom-doped carbocatalyst for PS activation. The potential synergistic and antagonistic interactions of various heteroatoms including N and B, N and S, N and P, and N and halogen for PS activation are evaluated. Thereafter, the preparation strategies to develop multi-heteroatom-doped carbocatalyst including one-step and multi-step preparation approaches along with the characterization techniques are discussed. Evidence and summary of the performance of multi-heteroatom-doped carbocatalyst for various recalcitrant pollutants removal via PS activation are also provided. Finally, the prospects of employing multi-heteroatom-doped carbocatalyst including the need to study the correlation between different heteroatom combination, surface moiety type, and amount of dopant with the PS activation mechanism, identifying the best heteroatom combination, improving the durability of the carbocatalyst, evaluating the feasibility for full-scale application, developing low-cost multi-heteroatom-doped carbocatalyst, and assessing the environmental impact are also briefly discussed.

Application of iron-activated persulfate for municipal wastewater disinfection

To address the increasing contamination of aquatic environments and incidence of waterborne diseases, advanced oxidation processes with activated persulfate have emerged as tools to inactivate wastewater microorganisms and contaminants. In this work, the disinfection of a secondary effluent from a wastewater treatment plant by iron-based persulfate activation was studied. Experiments in a batch stirred tank reactor were carried out to evaluate the performance along reaction time and the effect of operational parameters in the oxidative process efficiency (oxidant and iron concentration, pH and temperature). After 60 min of reaction, persulfate and iron concentrations of 3 mM and 0.75 mM, respectively, combined with a neutral initial pH (7.5) and a temperature of 40 °C, allowed to reach values below the detection limit (<10 CFU/100 mL) of enterococci and enterobacteria with and without ciprofloxacin resistance, as well as a 91% inactivation of total heterotrophic organisms and a 70% removal of total organic carbon. Regrowth of microorganisms was evaluated 72 h after treatment and it was only noticed a slight increase in total heterotrophs. Evaluation of physico-chemical characteristics of the treated water showed that it meets the requirements imposed by European and Portuguese legislation for its reuse in irrigation and most urban utilities.

Fe Single-Atom Catalyst for Efficient and Rapid Fenton-Like Degradation of Organics and Disinfection against Bacteria

The Fenton-like reaction has great potential in water treatment. Herein, an efficient and reusable catalytic system is developed based on atomically dispersed Fe catalyst by anchoring Fe atoms on nitrogen-doped porous carbon (Fe SA/NPCs). The catalyst of Fe SA/NPCs exhibits enhanced performance in activating peroxymonosulfate (PMS) for organic pollutant degradation and bacterial inactivation. The Fe SA/NPCs + PMS system demonstrates a high turnover frequency of 39.31 min^-1 in Rhodamine B (RhB) degradation as well as a strong bactericidal activity that can completely sterilize an Escherichia coli culture within 5 min. Meanwhile, the degradation activity of RhB by Fe SA/NPCs is improved up to 28 to 371-fold in comparison with the controls. Complete degradation of RhB can be achieved in 30 s by the Fe SA/NPCs + PMS system, demonstrating an efficiency much higher than most traditional Fenton-like processes. Experiments with different radical scavengers and density functional theory calculations have revealed that singlet oxygen (¹ O₂ ) generated on the N-coordinated single Fe atom (Fe-N₄ ) sites is the key reactive species for the effective and rapid pollutant degradation and bacterial inactivation. This work innovatively affords a promising single-Fe-atom catalyst/PMS system for applying Fenton-like reactions in water treatment.