A review on disinfection methods for inactivation of waterborne viruses

Why is HSO5- so effective against bacteria? Insights into the mechanisms of Escherichia coli disinfection by unactivated peroxymonosulfate

This study examined the antimicrobial efficacy of peroxymonosulfate (PMS) against bacteria, using Escherichia coli (E. coli) as a model organism. Our investigation delineates the complex mechanisms exerted by unactivated PMS. Thus, an initial redox reaction between PMS and the target biomolecules of bacteria generates SO4•- as the pivotal reactive species for bacterial inactivation; to a lesser extent, •OH, 1O2, or O2•- may also participate. Damage generated during oxidation was identified using an array of biochemical techniques. Specifically, redox processes are promoted by PMS and SO4•- targets and disrupt various components of bacterial cells, predominantly causing extracellular damage as well as intracellular lesions. Among these, external events are the key to cell death. Finally, by employing gene knockout mutants, we uncovered the role of specific gene responses in the intracellular damage induced by radical pathways. The findings of this study not only expand the understanding of PMS-mediated bacterial inactivation but also explain the ten-fold higher effectiveness of PMS than that reported for H2O2. Hence, we provide clear evidence that unactivated PMS solutions generate SO4•- in the presence of bacteria, and consequently, should be considered an effective disinfection method.

A critical review of advances in tumor metabolism abnormalities induced by nitrosamine disinfection by-products in drinking water

Intensified sanitation practices amid the recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak might result in the increased release of chloramine disinfectants into surface water, significantly promoting the formation of nitrosamine disinfection by-products (DBPs) in drinking water. Unfortunately, these nitrosamine DBPs exhibit significant genotoxic, carcinogenic, and mutagenic properties, whereas chlorinating disinfectants remain in global practice. The current review provides valuable insights into the occurrence, identification, contamination status, exposure limits, and toxicity of the new unregulated disinfection by-products (nitrosamine DBPs) in drinking water. As a result, concentrations of nitrosamine DBPs far exceed allowable limits in drinking water, and prolonged exposure has the potential to cause metabolic disorders, a critical step in tumor initiation and progression. Importantly, based on recent research, we have concluded the role of nitrosamines DBPs in different metabolic pathways. Remarkably, nitrosamine DBPs can induce chronic inflammation and initiate tumors by activating sphingolipid and polyunsaturated fatty acid metabolism. Regarding amino acid and nucleotide metabolism, nitrosamine DBPs can inhibit tryptophan metabolism and de novo nucleotide synthesis. Moreover, inhibition of de novo nucleotide synthesis fails to repair DNA damage induced by nitrosamines. Additionally, the accumulation of lactate induced by nitrosamine DBPs may act as a pivotal signaling molecule in communication within the tumor microenvironment. However, with the advancement of tumor metabolomics, understanding the role of nitrosamine DBPs in causing cancer by inducing metabolic abnormalities significantly lags behind, and specific mechanisms of toxic effects are not clearly defined. Urgently, further studies exploring this promising area are needed.

Retention of Virus Versus Surrogate, by Ultrafiltration in Seawater: Case Study of Norovirus Versus Tulane

In the field of chemical engineering and water treatment, the study of viruses, included surrogates, is well documented. Often, surrogates are used to study viruses and their behavior because they can be produced in larger quantities in safer conditions and are easier to handle. In fact, surrogates allow studying microorganisms which are non-infectious to humans but share some properties similar to pathogenic viruses: structure, composition, morphology, and size. Human noroviruses, recognized as the leading cause of epidemics and sporadic cases of gastroenteritis across all age groups, may be mimicked by the Tulane virus. The objectives of this work were to study (i) the ultrafiltration of Tulane virus and norovirus to validate that Tulane virus can be used as a surrogate for norovirus in water treatment process and (ii) the retention of norovirus and the surrogate as a function of water quality to better understand the use of the latter pathogenic viruses. Ultrafiltration tests showed significant logarithmic reduction values (LRV) in viral RNA: around 2.5 for global LRV (i.e., based on the initial and permeate average concentrations) and between 2 and 6 for average LRV (i.e., retention rate considering the increase of viral concentration in the retentate), both for norovirus and the surrogate Tulane virus. Higher reduction rates (from 2 to 6 log genome copies) are obtained for higher initial concentrations (from 101 to 107 genome copies per mL) due to virus aggregation in membrane lumen. Tulane virus appears to be a good surrogate for norovirus retention by membrane processes.

Underlying the mechanisms of pathogen inactivation and regrowth in wastewater using peracetic acid-based disinfection processes: A critical review

Peracetic acid (PAA) disinfection is an emerging wastewater disinfection process. Its advantages include excellent pathogen inactivation performance and little generation of toxic and harmful disinfection byproducts. The objective of this review is to comprehensively analyze the experimental data and scientific information related to PAA-based disinfection processes. Kinetic models and modeling frameworks are discussed to provide effective tools to assess pathogen inactivation efficacy. Then, the efficacy of PAA-based disinfection processes for pathogen inactivation is summarized, and the inactivation mechanisms involved in disinfection and the interactions of PAA with conventional disinfection processes are elaborated. Subsequently, the risk of pathogen regrowth after PAA-based disinfection process is clearly discussed. Finally, to address ecological risks related to PAA-based disinfection, its impact on the spread of antibiotic-resistant bacteria and the transfer of antibiotic resistance genes (ARGs) is also assessed. Among advanced PAA-based disinfection processes, ultraviolet/PAA is promising not only because it has practical application value but also because pathogen regrowth can be inhibited and ARGs transfer risk can be significantly reduced via this process. This review presents valuable and comprehensive information to provide an in-depth understanding of PAA as an alternative wastewater disinfection technology.

Effect of NaOCl and ClO2 on seawater desalination using reverse osmosis with cartridge filtration as the pretreatment during the algal bloom

Increased seawater temperature leads to harmful algal blooms (HABs), which releases toxic materials and extracellular polymeric substances (EPS) that are harmful to both humans and the environment. Reverse osmosis (RO) with cartridge filter (CF) as the pretreatment process is often used for desalination process. However, the EPS causes severe fouling on the CF, and RO membrane. Disinfectants, such as NaOCl and ClO2, are commonly used to remove biofouling, because they can oxidize and kill microorganisms. Therefore, our study aims to utilize NaOCl and ClO2 during the CF-RO process to minimize the algal growth within the system and minimize the fouling induced by EPS. Results from this study show that CF can remove more than 50% of protein and 14% of polysaccharides but is not effective in removing toxins. However, with disinfectants, toxic materials were completely oxidized. Improved removal of EPS with CF improved overall performance. The flux reduction in RO process without disinfection was over 60%, however, the flux decline was about 44% and 10% with NaOCl and ClO2, respectively. Both disinfectants were found to be effective, however use of ClO2 is recommended because it is less damaging the membrane, yet more effective in enhancing the performance.

Safeguarding drinking water: A brief insight on characteristics, treatments and risk assessment of contamination

Water pollution stands as a critical worldwide concern, bearing extensive repercussions that extend to human health and the natural ecosystem. The sources of water pollution can be diverse, arising from natural processes and human activities and the pollutants may range from chemical and biological agents to physical and radiological contaminants. The contamination of water disrupts the natural functioning of the system, leading to both immediate and prolonged health problems. Various technologies and procedures, ranging from conventional to advanced, have been developed to eliminate water impurities, with the choice depending on the type and level of contamination. Assessing risks is a crucial element in guaranteeing the safety of drinking water. Till now, research is continuing the removal of contaminates for the sake of supplying safe drinking water. The study examined physical, inorganic, organic, biological and radiological contaminants in drinking water. It looked at where these contaminants come from, their characteristics, the impact they have and successful methods used in real-world situations to clean the contaminated water. Risk assessment methodologies associated with the use of unsafe drinking water as future directives are also taken into consideration in the present study for the benefit of public concern. The manuscript introduces a comprehensive study on water pollution, focusing on assessing and mitigating risks associated with physical, inorganic, organic, biological and radiological contaminants in drinking water, with a novel emphasis on future directives and sustainable solutions for public safety.

Effects of alternative disinfection methods on the characteristics of effluent organic matter and the formation of disinfection byproducts

The characteristics of effluent organic matter (EfOM) and the type of disinfection methods are closely related to the formation of disinfection byproducts (DBPs) in reclaimed water. In this study, five disinfection methods, i.e., chlorination, ultraviolet (UV) followed by chlorination (UV + Cl), UV/chlorine (UV/Cl), chloramination, and chlorine dioxide (ClO2), were applied to investigate the changes in the properties of EfOM, the formation of DBPs, and the relationship between EfOM properties and DBP formation during the disinfection of four secondary biological effluents. The results showed that EfOM with medium molecular weight (MW) (0.5-6 kDa) was the dominant fraction for all WWTPs. From a fluorescence perspective, the EfOM of the AAO process was rich in humic matter, while the EfOM of the oxidation ditch (OD) process was rich in protein matter. Disinfectants tended to transfer EfOM with high molecular weight (MW) (>6 kDa) to those with low MW (<0.5 kDa). Chlorination, UV + Cl and UV/Cl were more reactive to humic matter, while chloramination and chlorine dioxide were more reactive to protein matter. The formation of known DBPs was mainly dependent on humic matter, while protein matter was more likely to generate unknown DBPs. N-DBPs only accounted for 5.7%-17.7% of the total DBPs, but contributed more than 70% of the calculated toxicity, among which bromochloroacetonitrile (BCAN), dichloroacetonitrile (DCAN), and monobromoacetamide (MBAcAm) were the most important contributors to the calculated cytotoxicity. Monobromoacetic acid (MBAA) and MBAcAm were the primary drivers of the calculated genotoxicity. Overall, UV + Cl was the suggested optimal disinfection method for WWTPs.

Pressure-driven membrane filtration technology for terminal control of organic DBPs: A review

Disinfection by-products (DBPs), a series of undesired secondary contaminants formed during the disinfection processes, deteriorate water quality, threaten human health and endanger ecological safety. Membrane-filtration technologies are commonly used in the advanced water treatment and have shown a promising performance for removing trace contaminants. In order to gain a clearer understanding of the behavior of DBPs in membrane-filtration processes, this work dedicated to: (1) comprehensively reviewed the retention efficiency of microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) for DBPs. (2) summarized the mechanisms involved size exclusion, electrostatic repulsion and adsorption in the membrane retention of DBPs. (3) In conjunction with principal component analysis, discussed the influence of various factors (such as the characteristics of membrane and DBPs, feed solution composition and operating conditions) on the removal efficiency. In general, the characteristics of the membranes (salt rejection, molecular weight cut-off, zeta potential, etc.) and DBPs (molecular size, electrical property, hydrophobicity, polarity, etc.) fundamentally determine the membrane-filtration performance on retaining DBPs, and the actual operating environmental factors (such as solute concentration, coexisting ions/NOMs, pH and transmembrane pressure) exert a positive/negative impact on performance to some extent. Current researches indicate that NF and RO can be effective in removing DBPs, and looking forward, we recommend that multiple factors should be taken into account that optimize the existed membrane-filtration technologies, rationalize the selection of membrane products, and develop novel membrane materials targeting the removal of DBPs.

Therapeutic potential of ozone water treatment in alleviating atopic dermatitis symptoms in mouse models: Exploring its bactericidal and direct anti-inflammatory properties

Currently, ozone water is utilized for antibacterial and antiviral purposes without any reported safety concerns. Therefore, ozone water may have clinical applications in treating staphylococcal-specific cutaneous diseases, such as atopic dermatitis (AD) and pyoderma. This study aimed to verify the bactericidal effects of ozone water at different concentrations (3 and 11 mg/L) against staphylococcal species in vitro, as well as evaluate the anti-inflammatory effects of ozone water in a mouse model of AD and pyoderma. Initially, the bactericidal properties of several concentrations of ozone water were confirmed with Staphylococcus aureus and methicillin-resistant S. pseudintermedius. Both 3 and 11 mg/L of ozone water exhibited a significant bactericidal effect against staphylococci at less than 100 times dilution. We next examined the cellular cytotoxicity and cytokine production (Interleukin (IL)-6 and IL-8) induced by S. pseudintermedius pre-treated with ozone water, and our findings indicated that cytotoxicity and cytokine production induced by staphylococci were significantly inhibited after ozone water pre-treatment. In vivo experiments showed that ozone water-pre-treated S. pseudintermedius significantly inhibited the development of pyoderma in mice; however, limited effects were observed in a therapeutic setting. Interestingly, ozone water at concentrations of 3 and 11 mg/L exhibits dual bactericidal and anti-inflammatory effects in mice with AD. This observation was corroborated by the significant inhibition of cytokine production in interferon-γ/tumor necrosis factor-stimulated human epidermal keratinocyte cells exposed to ozone in vitro. These findings indicate that administering ozone can be a novel therapeutic approach for managing allergic skin diseases, such as AD.

Bibliometric analysis of electrochemical disinfection: current status and development trend from 2002 to 2022

The removal of waterborne pathogens from water is critical in preventing the spread of waterborne diseases. Electrochemical methods have been extensively researched and implemented for disinfection, primarily owing to their simplicity, efficiency, and eco-friendliness. Thus, it is essential to conduct a review about the research progress and hotspots on this promising technique. In this paper, we provided a comprehensive bibliometric analysis to systematically study and analyze the current status, hotspots, and trends in electrochemical disinfection research from 2002 to 2022. This study analyzed literature related to electrochemical disinfection or electrochemical sterilization published in the Web of Science database from 2002 to 2022 using CiteSpace and Biblioshiny R language software packages. The analysis focused on the visualization and assessment of annual publication volume, discipline and journal distribution, collaborative networks, highly cited papers, and keywords to systematically understand the current status and trends of electrochemical disinfection. The results showed that between 2002 and 2022, 1171 publications related to electrochemical disinfection were published, with an exponential increase in the cumulative number of publications (y=17.518e0.2147x, R2= 0.9788). The publications covered 76 disciplines with many articles published in high-impact journals. However, the research power was characterized by a large number of scattered research efforts and insufficient cooperation, indicating the need for further innovative collaboration. The citation analysis and keyword analysis suggest that future development in this field may focus on optimizing electrode materials, investigating the disinfection performance of ·OH based systems, optimizing conditions for actual wastewater treatment, and reducing energy consumption to promote practical applications.

The Virucidal Effect of the Chlorination of Water at the Initial Phase of Disinfection May Be Underestimated If Contact Time Calculations Are Used

For the microbiological safety of drinking water, disinfection methods are used to remove or inactivate microorganisms. Chlorine and chlorine dioxide are often used as disinfectants in drinking water treatment plants (DWTPs). We investigated the effectiveness of these chemicals in inactivate echovirus 30 (E30), simian 11 rotavirus (RV SA11), and human adenovirus type 2 (HAdV2) in purified water from a DWTP. Within two minutes of contact, chlorine dioxide inactivated E30 by 4-log10, RV SA11 by 3-log10, and HAdV2 could not be detected, while chlorine reduced E30 by 3-log10, RV SA11 by 2-3log10, and HAdV2 by 3-4log10. However, viral genomes could be detected for up to 2 h using qPCR. The CT method, based on a combination of disinfectant concentration and contact time, during such a short initial phase, is problematic. The high concentrations of disinfectant needed to neutralize organic matter may have a strong immediate effect on virus viability. This may lead to the underestimation of disinfection and overdosing of disinfectants in water with organic contamination. These results are useful for the selection of disinfection systems for reuse of treated wastewater and in the risk assessment of water treatment processes using chlorine and chlorine dioxide.

Photo-Fenton and TiO2 Photocatalytic Inactivation of Model Microorganisms under UV-A; Comparative Efficacy and Optimization

Photocatalytic inactivation of pathogens in aqueous waste is gaining increasing attention. Several homogeneous and heterogeneous photocatalytic protocols exist using the Fenton's reagent and TiO₂, respectively. A comprehensive study of homogeneous and heterogeneous photocatalysis on a range of microorganisms will significantly establish the most efficient method. Here, we report a comparative study of TiO₂- and Fe⁺³-based photocatalytic inactivation under UV-A of diverse microorganisms, including Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, bacterial spores (Bacillus stearothermophilus spores) and viruses (MS2). We also present data on the optimization of TiO₂ photocatalysis, including optimal catalyst concentration and H₂O₂ supplementation. Our results indicate that both photo-Fenton and TiO₂ could be successfully applied for the management of microbial loads in liquids. Efficient microorganism inactivation is achieved with homogeneous photocatalysis (7 mg/L Fe⁺³, 100 mg/L H₂O₂, UV-A) in a shorter processing time compared to heterogeneous photocatalysis (0.5 g/L TiO₂, UV-A), whereas similar or shorter processing is required when heterogenous photocatalysis is performed using microorganism-specific optimized TiO₂ concentrations and H₂O₂ supplementation (100 mg/L); higher H₂O₂ concentrations further enhance the heterogenous photocatalytic inactivation efficiency. Our study provides a template protocol for the design and further application for large-scale photocatalytic approaches to inactivate pathogens in liquid biomedical waste.