Photocatalytic inactivation of Cryptosporidium parvum on nanostructured titanium dioxide films

Wilderness Medical Society Clinical Practice Guidelines on Water Treatment for Wilderness, International Travel, and Austere Situations: 2024 Update

To provide guidance to medical providers, wilderness users, and travelers, the Wilderness Medical Society convened an expert panel to develop evidence-based guidelines for treating water in situations where the potability of available water is not assured, including wilderness and international travel, areas impacted by disaster, and other areas without adequate sanitation. The guidelines present the available methods for reducing or eliminating microbiological contamination of water for individuals, groups, or households; evaluation of their effectiveness; and practical considerations. The evidence base includes both laboratory and clinical publications. The panel graded the recommendations based on the quality of supporting evidence and the balance between benefits and risks/burdens according to the criteria published by the American College of Chest Physicians.

Current Trends in the Application of Nanomaterials for the Removal of Emerging Micropollutants and Pathogens from Water

Water resources contamination has a worldwide impact and is a cause of global concern. The need for provision of clean water is becoming more and more demanding. Nanotechnology may support effective strategies for the treatment, use and reuse of water and the development of next-generation water supply systems. The excellent properties and effectiveness of nanomaterials make them particularly suitable for water/wastewater treatment. This review provides a comprehensive overview of the main categories of nanomaterials used in catalytic processes (carbon nanotubes/graphitic carbon nitride (CNT/g-C₃N₄) composites/graphene-based composites, metal oxides and composites, metal–organic framework and commercially available nanomaterials). These materials have found application in the removal of different categories of pollutants, including pharmaceutically active compounds, personal care products, organic micropollutants, as well as for the disinfection of bacterial, viral and protozoa microbial targets, in water and wastewater matrices. Apart from reviewing the characteristics and efficacy of the aforementioned nanoengineered materials for the removal of different pollutants, we have also recorded performance limitations issues (e.g., toxicity, operating conditions and reuse) for their practical application in water and wastewater treatment on large scale. Research efforts and continuous production are expected to support the development of eco-friendly, economic and efficient nanomaterials for real life applications in the near future.

Introduction

The last 50 years have witnessed a growing awareness of the fragile state of most of the planets’ drinking water resources. Access to freshwater will become even more important in the near future, as the world’s population rises from 7 billion today to 9 billion by 2050. The World Health Organization (WHO) has estimated that 80 % of illnesses in the developing world are water related, resulting from poor water quality and lack of sanitation [1]. There are 3.3 million deaths each year from diarrheal diseases caused by bacteria such as Escherichia coli, Salmonella sp. and Cholera sp., parasites and viral pathogens. In the 1990s, the number of children who died of diarrhoea was greater than the sum of people killed in conflicts since World War II [2]. It is also estimated that around 4 billion people worldwide experience to have no or little access to clean and sanitized water supply, and millions of people died of severe waterborne diseases annually [3, 4].

A review of heterogeneous photocatalysis for water and surface disinfection

Photo-excitation of certain semiconductors can lead to the production of reactive oxygen species that can inactivate microorganisms. The mechanisms involved are reviewed, along with two important applications. The first is the use of photocatalysis to enhance the solar disinfection of water. It is estimated that 750 million people do not have accessed to an improved source for drinking and many more rely on sources that are not safe. If one can utilize photocatalysis to enhance the solar disinfection of water and provide an inexpensive, simple method of water disinfection, then it could help reduce the risk of waterborne disease. The second application is the use of photocatalytic coatings to combat healthcare associated infections. Two challenges are considered, i.e., the use of photocatalytic coatings to give “self-disinfecting” surfaces to reduce the risk of transmission of infection via environmental surfaces, and the use of photocatalytic coatings for the decontamination and disinfection of medical devices. In the final section, the development of novel photocatalytic materials for use in disinfection applications is reviewed, taking account of materials, developed for other photocatalytic applications, but which may be transferable for disinfection purposes.

Disinfection of urban wastewater by solar driven and UV lamp - TiO₂ photocatalysis: effect on a multi drug resistant Escherichia coli strain

The effect of TiO₂ photocatalysis on the inactivation of an antibiotic resistant Escherichia coli strain selected from an urban wastewater treatment plant (UWWTP) effluent was investigated. Different light sources including a 250 W wide spectrum lamp, a 125 W UV-A lamp and solar radiation, as well as, photocatalysts loadings (TiO₂ Degussa P25) in the range from 0.05 to 2.00 g TiO₂ L(-1) were evaluated. The higher efficiency (total bacterial inactivation after 10 min of irradiation) was observed in the absence of TiO₂ when the wastewater was irradiated using the 250 W lamp. In the presence of TiO₂ a decreasing inactivation trend was observed (99.76% and 72.22% inactivation after 10 min irradiation at 0.10 and 2.00 g TiO₂ L(-1) respectively). Under solar simulated conditions the highest inactivation efficiency (93.17%) after 10 min of irradiation was achieved at the lower photocatalyst loading (0.05 g TiO₂ L(-1)). The concept of "reactor optical thickness" was introduced to explain the rates of disinfection observed. The optimum photocatalyst loading estimated by radiation absorption-scattering modeling was found to be 0.1 g TiO₂ L(-1) for all lamps. The difference between experimental tests and modeling may be due to TiO₂ particles aggregation. Comparative kinetic tests between solar and solar simulated photocatalytic (SSP) processes using 0.05 g TiO₂ L(-1) in suspension showed a quite similar inactivation behavior up to 30 min of irradiation, but only the SSP process resulted in a total inactivation of bacteria after 60 min of exposure. Antibiotic resistant test (Kirby-Bauer) on survived colonies showed that the SSP and SP processes affected in different ways the resistance of E. coli strain to the target antibiotics.

Bacterial inactivation in water, DNA strand breaking, and membrane damage induced by ultraviolet-assisted titanium dioxide photocatalysis

The effects of UV-assisted TiO2-photocatalytic oxidation (PCO) inactivation of pathogenic bacteria (Escherichia coli O157:H7, Listeria monocytogenes, Salmonella typhimurium) in a liquid culture using different domains of UV irradiation (A, B and C) were evaluated. Structural changes in super-coiled plasmid DNA (pUC19) and genomic DNA of E. coli were observed using gel electrophoresis to demonstrate the photodynamic DNA strand breaking activity of UV-assisted TiO2-PCO. Membrane damage in bacterial cells was observed using both a scanning electron microscope (SEM) and a confocal laser scanning microscope (CLSM). Both UVC-TiO2-PCO and UVC alone resulted in an earlier bactericidal phase (initial counts of approximately 6 log CFU/mL) in 60 s and 90 s, respectively, in liquid culture. UVC-TiO2-PCO treatment for 6 min converted all plasmid DNA to the linear form; however, under UVC irradiation alone, super-coiled DNA remained. Prolonged UVC-TiO2-PCO treatment resulted in structural changes in genomic DNA from E. coli. SEM observations revealed that bacteria suffered severe visible cell damage after UVC-TiO2-PCO treatment for 30-60 min. S. typhimurium cells showed visible damage after 30 min, which was confirmed using CLSM. All treated cells were stained red using propidium iodide under a fluorescent light.

Bisanthracene bis(dicarboxylic imide)s as potential photosensitizers in photodynamic therapy: a theoretical investigation

The electronic structures and spectroscopic properties of four bisanthracene bis(dicarboxylic imide)s (M1-M4) have been investigated theoretically by using density functional theory (DFT) and its time-dependent extension (TDDFT) in view of their potential use as photosensitizers in photodynamic therapy (PDT). The optimized geometries, electronic absorption transitions, singlet-triplet energy gaps, spin-orbit matrix elements, ionization potentials, and electron affinities have been determined in gas phase and in solvent. Both type I and II PDT mechanisms have been considered. In addition, the variation of a series of relevant properties upon heavy atom substitution (Br and I) have been determined and discussed. Results show that only M4 is able to support the type I reaction, and one of its brominated and iodinated derivatives can produce cytotoxic singlet oxygen (type II reaction).

Inactivation and injury assessment of Escherichia coli during solar and photocatalytic disinfection in LDPE bags

Solar disinfection (SODIS) of Escherichia coli suspensions in low-density polyethylene bag reactors was investigated as a low-cost disinfection method suitable for application in developing countries. The efficiency of a range of SODIS reactor configurations was examined (single skin (SS), double skin, black-backed single skin, silver-backed single skin (SBSS) and composite-backed single skin) using E. coli suspended in model and real surface water. Titanium dioxide was added to the reactors to improve the efficiency of the SODIS process. The effect of turbidity was also assessed. In addition to viable counts, E. coli injury was characterised through spread-plate analysis using selective and non-selective media. The optimal reactor configuration was determined to be the SBSS bag (t(50)=9.0min) demonstrating the importance of UVA photons, as opposed to infrared in the SODIS disinfection mechanism. Complete inactivation (6.5-log) was achieved in the presence of turbidity (50NTU) using the SBSS bag within 180min simulated solar exposure. The addition of titanium dioxide (0.025gL(-1)) significantly enhanced E. coli inactivation in the SS reactor, with 6-log inactivation observed within 90min simulated solar exposure. During the early stages of both SODIS and photocatalytic disinfection, injured E. coli were detected; however, irreversible injury was caused and re-growth was not observed. Experiments under solar conditions were undertaken with total inactivation (6.5-log) observed in the SS reactor within 240min, incomplete inactivation (4-log) was observed in SODIS bottles exposed to the same solar conditions.