A review on disinfection methods for inactivation of waterborne viruses

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

Bioaccumulation and biomagnification effects of nano-TiO2 in the aquatic food chain

The increasing production of nano-TiO₂ has attracted extensive concerns about the ecological consequence and health risk of these compounds in natural ecosystem. However, little is known about its toxicity on zooplankton, especially its possibility to access to the food chain via dietary exposure. To address this concern, the toxic and cumulative effects of nano-TiO₂ on an aquatic food chain were explored through two trophic levels independently or jointly including producer and consumer. The results revealed that exposure to suspensions of nanomaterials had negative effects on both producers and consumers. Specifically, nanoparticles reduced the density of algal cells in a concentration-dependent way, and hatching life expectancy, average lifespan, net reproductive rate, and population intrinsic growth rate of rotifers decreased significantly with the concentration of nanomaterials increased (P < 0.05). Notably, nanoparticles accumulated in algal cells and were transferred to consumers through dietary exposure. Biomagnification of nano-TiO₂ was observed in this simplified food chain, as many of the biomagnification factor (BMF) values in this study were >1. Exposure concentration, exposure time and their interactions play a strong part in the accumulation of nanoparticles in algae and rotifers. Overall, the present findings confirmed that nano-TiO₂ was deleterious to plankton, posing a significant environmental threat to aquatic ecosystems. Graphical abstract.

An approach to the photocatalytic mechanism in the TiO2-nanomaterials microorganism interface for the control of infectious processes

The approach of this timely review considers the current literature that is focused on the interface nanostructure/cell-wall microorganism to understand the annihilation mechanism. Morphological studies use optical and electronic microscopes to determine the physical damage on the cell-wall and the possible cell lysis that confirms the viability and microorganism death. The key parameters of the tailoring the surface of the photoactive nanostructures such as the metal functionalization with bacteriostatic properties, hydrophilicity, textural porosity, morphology and the formation of heterojunction systems, can achieve the effective eradication of the microorganisms under natural conditions, ranging from practical to applications in environment, agriculture, and so on. However, to our knowledge, a comprehensive review of the microorganism/nanomaterial interface approach has rarely been conducted. The final remarks point the ideal photocatalytic way for the effective prevention/eradication of microorganisms, considering the resistance that the microorganism could develop without the appropriate regulatory aspects for human and ecosystem safety.

Electrophoretic deposition of photocatalytic materials

Powdered photocatalytic materials have been successfully applied for the degradation of organic and inorganic pollutants as well as for hydrogen production and CO₂ photo-reduction. However, the development of strategies for the preparation of photoactive coatings is a hot topic since it is a promising step for its use in photocatalytic reactors on an industrial scale. Electrophoretic deposition is a versatile technique capable to produce coatings of nanoparticles at a relative low cost and with an excellent quality and control of the deposited material. This work summarizes the fundamental aspects of the electrophoretic deposition process, as well as the latest contributions in the deposition of several photocatalytic materials including TiO₂ and other UV-photocatalysts like ZnO, ZnS, SrTiO₃ and PbMoO₄ in addition to visible-light-driven photocatalysts such as Bi₂O₃, CdS, CdSe, g-C₃N₄, among others. Furthermore, the morphological features of the coatings along with the repercussion in the photocatalytic performance are issues discussed in the present review, based on the effect of the multiple parameters of the electrophoretic process such as the applied voltage, the deposition time, the inter-electrode distance, the concentration of the particles, the solvents and additives.

TiO2-based photocatalytic disinfection of microbes in aqueous media: A review

The TiO₂ based photocatalyst has great potential for the disinfection/inactivation of harmful pathogens (such as E.coli in aqueous media) along with its well-known usefulness on various chemical pollutants. The disinfection property of TiO₂ is primarily attributed to surface generation of reactive oxygen species (ROS) as well as free metal ions formation. Furthermore, its disinfection capacity and overall performance can be significantly improved through modifications of the TiO₂ material. In this review, we provide a brief survey on the effect of various TiO₂ materials in the disinfection of a wide range of environmentally harmful microbial pathogens (e.g., bacteria, fungi, algae, and viruses) in aqueous media. The influencing factors (such as reactor design, water chemistry, and TiO₂ modifications) of such processes are discussed along with the mechanisms of such disinfection. It is believed that the combined application of disinfection and decontamination will greatly enhance the utilization of TiO₂ photocatalyst as a potential alternative to conventional methods of water purification.

Antifouling activities of pristine and nanocomposite chitosan/TiO2/Ag films against freshwater algae

Adhesion of microalgae or biofouling on submerged artificial surfaces is a universal problem in freshwater environments.

High photocatalytic activity of plasmonic Ag@AgCl/Zn2SnO4 nanocomposites synthesized using hydrothermal method

Ag@AgCl/Zn₂SnO₄ (ZTO) nanocomposites were successfully prepared by a hydrothermal method.