Inactivation of a wild isolated Klebsiella pneumoniae by photo-chemical processes: UV-C, UV-C/H2O2 and UV-C/H2O2/Fe3+

Inactivation of two oyster pathogens by photocatalysis and monitoring of changes in the microbiota of seawater: A case study on Ostreid herpes virus 1 μVar and Vibrio harveyi

The pollution of seawater by both biotic (bacteria, viruses) and abiotic contaminants (biocides, pharmaceutical residues) frequently leads to economic losses in aquaculture activities mostly mortality events caused by microbial infection. Advanced Oxidation Processes (AOPs) such as heterogeneous photocatalysis allow the removal of all organic contaminants present in water and therefore could reduce production losses in land-based farms. Oysters in land-based farms such as hatcheries and nurseries suffer from a large number of mortality events, resulting in significant losses. If photocatalysis has been widely studied for the decontamination, its application for disinfection is still overlooked, especially on seawater for viruses. We therefore studied seawater disinfection using the photocatalysis (UV365/TiO2) method in the context of Pacific oyster mortality syndrome (POMS). POMS has been defined as a polymicrobial disease involving an initial viral infection with Ostreid Herpes Virus 1, accompanied by multiple bacterial infections. We investigated the impact of treatment on Vibrio harveyi, a unique opportunistic pathogenic bacterium, and on a complex microbial community reflecting a natural POMS event. Viral inactivation was monitored using experimental infections to determine whether viral particles were still infectious after. Changes in the total bacterial community in seawater were studied by comparing UV365/TiO2 treatment with UV365-irradiated seawater and untreated seawater. In the case of OsHV-1, a 2-h photocatalytic treatment prevents POMS disease and oyster mortality. The same treatment also inactivates 80% of viable Vibrio harveyi culture (c.a. 1.5 log). Since OsHV-1 and Vibrio harveyi are effectively inactivated without long-term destabilization of the total bacterial microbiota in the seawater, photocatalysis appears to be a relevant alternative for disinfecting seawater in land-based oyster beds.

Inactivation of the waterborne marine pathogen Vibrio alginolyticus by photo-chemical processes driven by UV-A, UV-B, or UV-C LED combined with H2O2 or HSO5. WATER RESEARCH 2023;232:119686. [PMID: 36764105 DOI: 10.1016/j.watres.2023.119686]

Ultraviolet (UV) radiation is a well-implemented process for water disinfection. The development of emergent UV sources, such as light-emitting diodes (LEDs), has afforded new possibilities for advanced oxidation processes. The emission wavelength is considered to be an important factor for photo-chemical processes in terms of both biological damage and energetic efficiency, as the inactivation mechanisms and mode-of-action may differ according to the wavelength that is applied. In addition, these processes merit exploration for inactivating emerging pathogens, such as marine vibrios, that are important bacteria to control in maritime activities. The main goal of this study was to compare the disinfection efficacy of several UV-LED driven processes with different modes of action. First, the effect of UV-LEDs was assessed at different UV ranges (UV-A, UV-B, or UV-C). Second, the possible enhancement of a combination with hydrogen peroxide (H₂O₂) or peroxymonosulfate salt (HSO₅^-) was investigated under two different application strategies, i.e. simultaneous or sequential. The results obtained indicate a high sensitivity of Vibrio alginolyticus to UV radiation, especially under UV-B (k_obs = 0.24 cm²/mJ) and UV-C (k_obs = 1.47 cm²/mJ) irradiation. The highest inactivation rate constants were obtained for UV/HSO₅^- (k_obs (cm²/mJ)=0.0007 (UV-A); 0.39 (UV-B); 1.79 (UV-C)) with respect to UV/H₂O₂ (k_obs (cm²/mJ)=0.0006 (UV-A); 0.26 (UV-B); and 1.54 (UV-C)) processes, however, regrowth was avoided only with UV/H₂O₂. Additionally, the disinfection enhancement caused by a chemical addition was more evident in the order UV-A > UV-B > UV-C. By applying H₂O₂ (10 mg/L) or HSO₅^- (2.5 mg/L) in a sequential mode before the UV, negligible effects were obtained in comparison with the simultaneous application. Finally, promising electrical energy per order (EE_O) values were obtained as follows: UV/HSO₅^- (EE_O (kWh/m³)=1.68 (UV-A); 0.20 (UV-B); 0.04 (UV-C)) and UV/H₂O₂ (EE_O (kWh/m³)=2.15 (UV-A); 0.32 (UV-B); 0.04 (UV-C)), demonstrating the potential of UV-LEDs for disinfection in particular activities such as the aquaculture industry or maritime transport.

Irreversible inactivation of carbapenem-resistant Klebsiella pneumoniae and its genes in water by photo-electro-oxidation and photo-electro-Fenton - Processes action modes

Carbapenem-resistant Klebsiella pneumoniae is a critical priority pathogen according to the World Health Organization's classification. Effluents of municipal wastewater treatment plants (EWWTP) may be a route for K. pneumoniae dissemination. Herein, the inactivation of this microorganism in simulated EWWTP by the photo-electro-oxidation (PEO) and photo-electro-Fenton (PEF) processes was evaluated. Firstly, the disinfecting ability and action pathways of these processes were established. PEO achieved faster K. pneumoniae inactivation (6 log units in 75 min of treatment) than the PEF process (6 log units in 105 min of treatment). PEO completely inactivated K. pneumoniae due to the simultaneous action of UVA light, electrogenerated H₂O_2, and anodic oxidation pathways. The slower inactivation of K. pneumoniae when using PEF was related to interfering screen effects of iron oxides on light penetration and the diffusion of the bacteria to the anode. However, both PEO and PEF avoided the recovery and regrowth of treated bacteria (with no detectable increase in the bacteria concentration after 24 h of incubation). In addition to the bacteria evolution, the effect of treatment processes on the resistance gene was examined. Despite inactivation of K. pneumoniae by PEF was slower than by PEO, the former process induced a stronger degrading action on the gene, conferring the resistance to carbapenems (PEF had a Ct value of 24.92 cycles after 105 min of treatment, while PEO presented a Ct of 19.97 cycles after 75 min). The results of this research indicate that electrochemical processes such as PEO and PEF are highly effective at dealing with resistant K. pneumoniae in the EWWTP matrix.

Insights into Solar Disinfection Enhancements for Drinking Water Treatment Applications

Poor access to drinking water, sanitation, and hygiene has always been a major concern and a main challenge facing humanity even in the current century. A third of the global population lacks access to microbiologically safe drinking water, especially in rural and poor areas that lack proper treatment facilities. Solar water disinfection (SODIS) is widely proven by the World Health Organization as an accepted method for inactivating waterborne pathogens. A significant number of studies have recently been conducted regarding its effectiveness and how to overcome its limitations, by using water pretreatment steps either by physical, chemical, and biological factors or the integration of photocatalysis in SODIS processes. This review covers the role of solar disinfection in water treatment applications, going through different water treatment approaches including physical, chemical, and biological, and discusses the inactivation mechanisms of water pathogens including bacteria, viruses, and even protozoa and fungi. The review also addresses the latest advances in different pre-treatment modifications to enhance the treatment performance of the SODIS process in addition to the main limitations and challenges.

Visible light plays a significant role during bacterial inactivation by the photo-fenton process, even at sub-critical light intensities

The aim of this research is to clarify the contribution of sunlight wavelengths, irradiance and Fe²⁺/H₂O₂ during bacterial disinfection by the photo-Fenton process in clear surface waters. We considered different solar spectrum distributions (visible, UVA-Visible), sub-critical irradiances (0-400 W/m²), focusing on the action modes of E. coli inactivation by the constituents involved in the composite process, at low μM reactants concentration (Fe²⁺/H₂O₂) in in ultrapure (MQ) water. We report that solar disinfection improved with Fenton reagents (photo-Fenton process) is a reality from very low light irradiance values (200 W/m²), and made possible even without the presence of UVA radiation, even when using low quantities of the Fenton reagents (0.5 mg/L Fe²⁺, 5 mg/L H₂O₂). Under light exposure, H₂O₂ was found to augment the intracellular Fenton process and Fe²⁺ to initiate further, distinct oxidative actions. Finally, validation was performed in Lake Geneva water over a wider irradiance range, where the photo-Fenton process was found to be reagent-dependent in low irradiance, shifting to light-driven in the higher values.

Microorganisms in ballast water: Disinfection, community dynamics, and implications for management

Increasing concerns have accelerated the development of international regulations and methods for ballast water management to limit the introduction of non-indigenous species. The transport of microorganisms with ballast water has received scientific attention in recent years. However, few studies have focused on the importance of organisms smaller than 10 μm in diameter. In this work, we review the effects of ballast water transport, disinfection, and the release of microorganisms on ecosystem processes with a special focus on heterotrophic bacteria. It is important to evaluate both direct and indirect effects of ballast water treatment systems, such as the generation of easily degradable substrates and the subsequent regrowth of heterotrophic microorganisms in ballast tanks. Disinfection of water can alter the composition of bacterial communities through selective recolonization in the ballast water or the recipient water, and thereby affects bacterial driven functions that are important for the marine food web. Dissolved organic matter quality and quantity and the ecosystem status of the treated water can also be affected by the disinfection method used. These side effects of disinfection should be further investigated in a broader context and in different scales (laboratory studies, large-scale facilities, and on the ships).

Total coliform inactivation in natural water by UV/H2O2, UV/US, and UV/US/H2O2 systems

The presence of pathogens in drinking water can seriously affect human health. Therefore, water disinfection is needed, but conventional processes, such as chlorination, result in the production of dangerous disinfection by-products. In this regard, an alternative solution to tackle the problem of bacterial pollution may be the application of advanced oxidation processes. In this work, the inactivation of total coliforms, naturally present in a Colombian surface water by means of UV/H₂O₂, UV/US, and the UV/US/H₂O₂ advanced oxidation processes, was investigated. Under the investigated conditions, complete bacterial inactivation (detection limit equal to 1 CFU 100 mL^-1) was found within 5 min of treatment by UV/H₂O₂ and UV/US/H₂O₂ systems. UV/US oxidation process also resulted in total bacterial load elimination, but after 15 min of treatment. Bacterial reactivation after 24 h and 48 h in the dark was measured and no subsequent regrowth was observed. This phenomenon could be attributed to the high oxidation capacity of the evaluated oxidation systems. However, the process resulting in the highest oxidation potential at the lowest operating cost, in terms of energy consumption, was UV/H₂O₂ system. Therefore, UV/H₂O₂ advanced oxidation system can be used for disinfection purposes, enabling drinking water production meeting the requirements of regulated parameters in terms of water quality, without incurring extremely high energy costs. Nonetheless, further researches are required for minimizing the associated electric costs.

Study on the Inactivation of Pseudomonas sp and the Degradation of Trichloroethylene by Fenton-Like Reaction

The present work intended to use goethite, one of the main compositions of pipe deposit, to combine with H2O2 to degrade TCE or disinfect drinking water. Goethite exhibited excellent degradation performance for TCE, outstanding inactivation ability for Pseudomonas and the disinfection effect for filter water of water treatment plants. The TCE degradation efficiency could reach 87.4%, while the inactivation efficiency of Pseudomonas and the bacterial mortality rate in filtered water were more than 99.9% in this study. In order to effectively reduce the disinfection by-products (chlorine-resistant bacteria) and conduct permanent disinfection, the Fenton-like and chlorine combined disinfection method was also investigated. Experimental results indicated that the bacteria could be effectively killed by this combined method and the chlorine residual was 0.41m g/L, ensuring sustainable disinfection. This work verified that the pipe deposit from the water distribution network is multifunctional, which is a potential candidate for pollutant removal and sterilization. The results could also offer theoretical support for water quality security in water distribution networks in the future.