Free chlorine inactivation of fungi in drinking water sources

The aggregation characteristics of Aspergillus spores under various conditions and the impact on LPUV inactivation: Comparisons with chlorine-based disinfection

Aggregation is the primary step prior to fungal biofilm development. Understanding the attributes of aggregation is of great significance to better control the emergence of waterborne fungi. In this study, the aggregation of Aspergills spores (A. flavus and A. fumigatus) under various salt, culture medium, and humic acid (HA) conditions was investigated for the first time, and the inactivation via low-pressure ultraviolet (LPUV) upon aggregated Aspergillus spores was also presented. The aggregation efficiency and size of aggregates increased over time and at low salt (NaCl and CaCl2) concentration (10 mM) while decreasing with the continuous increase of salt concentration (100 and 200 mM). Increasing the concentration of culture medium and HA promoted the aggregation of fungal spores. Spores became hydrated, swelled, and secreted more viscous substances during the growth period, which accelerated the aggregation process. Results also suggested that fungal spores aggregated more easily in actual water, posing a high risk of biohazard in real-life scenarios. Inactivation efficiency by LPUV decreased with higher aggregation degrees due to the protection from the damaged spores on the outer layer and the shielding of pigments in the cell wall. Compared to chlorine-based disinfection, the aggregation resulted in the extension of shoulder length yet neglectable change of inactivation rate constant under LPUV treatment. Further investigation of cell membrane integrity and intracellular reactive oxygen species was conducted to elucidate the difference in mechanisms between various techniques. This study provides insight into the understanding and controlling of the aggregation of fungal spores.

The improved resistance of germinated spores to ultraviolet irradiation: Comparison with chlorine

Fungi outbreaks in water will include a series of processes, including spore aggregation, germination, biofilm, and finally present in a mixed state in the aquatic environment. More attention is paid to the control of dispersed fungal spores, however, there was little knowledge of the control of germinated spores. This study investigated the inactivation kinetics and mechanism of ultraviolet (UV) treatment for fungal spores with different germination percentages compared with dormant spores. The results indicated that the inactivation rate constants (k) of spores with 5%-45% germination were 0.0278-0.0299 cm2/mJ for Aspergillus niger and 0.0588-0.0647 cm2/mJ for Penicillium polonicum, which were lower than those of dormant spores. It suggested that germinated spores were more tolerant to UV irradiation than dormant spores, and it may be due to the defensive barrier (upregulated pigments) and some reductive substance (upregulated enoyl reductase) by absorbing UV or reacting with reactive oxygen species according to transcriptome analysis. Compared to dormant spores, the k-UV of germinated spores decreased by 18.17%-26.56% for Aspergillus niger, which was less than k-chlorine (62.33%-69.74%). A slighter decrease in k-UV showed UV irradiation can efficiently control fungi contamination, especially when dormant spores and germinated spores coexisted in actual water systems. This study indicates that more attention should be paid to germinated spores.

Rapid Inactivation of Fungal Spores in Drinking Water by Far-UVC Photolysis of Free Chlorine

Effective and affordable disinfection technology is one key to achieving Sustainable Development Goal 6. In this work, we develop a process by integrating Far-UVC irradiation at 222 nm with free chlorine (UV222/chlorine) for rapid inactivation of the chlorine-resistant and opportunistic Aspergillus niger spores in drinking water. The UV222/chlorine process achieves a 5.0-log inactivation of the A. niger spores at a chlorine dosage of 3.0 mg L-1 and a UV fluence of 30 mJ cm-2 in deionized water, tap water, and surface water. The inactivation rate constant of the spores by the UV222/chlorine process is 0.55 min-1, which is 4.6-fold, 5.5-fold, and 1.8-fold, respectively, higher than those of the UV222 alone, chlorination alone, and the conventional UV254/chlorine process under comparable conditions. The more efficient inactivation by the UV222/chlorine process is mainly attributed to the enhanced generation of reactive chlorine species (e.g., 6.7 × 10-15 M of Cl•) instead of hydroxyl radicals from UV222 photolysis of chlorine, which is verified through both experiments and a kinetic model. We further demonstrate that UV222 photolysis damages the membrane integrity and benefits the penetration of chlorine and radicals into cells for inactivation. The merits of the UV222/chlorine process over the UV254/chlorine process also include the more effective inhibition of the photoreactivation of the spores after disinfection and the lower formation of chlorinated disinfection byproducts and toxicity.

Effect of Location, Disinfection, and Building Materials on the Presence and Richness of Culturable Mycobiota through Oligotrophic Drinking Water Systems

Safe drinking water is a constant challenge due to global environmental changes and the rise of emerging pathogens-lately, these also include fungi. The fungal presence in water greatly varies between sampling locations. Little is known about fungi from water in combination with a selection of materials used in water distribution systems. Our research was focused on five water plants located in the Pannonian Plain, Slovenia. Sampled water originated from different natural water sources and was subjected to different cleaning methods before distribution. The average numbers of fungi from natural water, water after disinfection, water at the first sampling point in the water network, and water at the last sampling point were 260, 49, 64, and 97 CFU/L, respectively. Chlorination reduced the number of fungi by a factor of 5, but its effect decreased with the length of the water network. The occurrence of different fungi in water and on materials depended on the choice of material. The presence of the genera Aspergillus, Acremonium, Furcasterigmium, Gliomastix, and Sarocladium was mostly observed on cement, while Cadophora, Cladosporium, Cyphellophora, and Exophiala prevailed on metals. Plastic materials were more susceptible to colonization with basidiomycetous fungi. Opportunistically pathogenic fungi were isolated sporadically from materials and water and do not represent a significant health risk for water consumers. In addition to cultivation data, physico-chemical features of water were measured and later processed with machine learning methods, revealing the sampling location and water cleaning processes as the main factors affecting fungal presence and richness in water and materials in contact with water.

Solar-driven strongly coupled plasmonic Au nanoarrays on mesoporous silica nanodisks enable selective fungal and bacterial inactivation in well water

Well water is an important water source in isolated rural areas but easily suffers from microbial contamination. Herein, we anchored periodic Au nanoarrays on mesoporous silica nanodisks (Au-MSN) to fabricate a solar-driven nano-stove for well water disinfection. The solar/Au-MSN process completely inactivated 3.98, 6.55, 7.11 log10 cfu/mL, and 3.37 log10 pfu/mL of Aspergillus niger spores, Escherichia coli, chlorine-resistant Spingopyxis sp. BM1-1, and bacteriophage MS2 within 5 min, respectively. Moreover, the complete inactivation of various microorganisms (even at a viable but nonculturable state) was achieved in the flow-through reactor under natural solar light in real well water matrixes. Thorough characterizations and theoretical simulations verified that the densely anchoring strategy of Au-MSN's nanoarray worked on broadband absorption via the photon confinement effect, and trace amounts of Au can induce strong electromagnetic fields and collective localized heating. The resulting surge of 1O2 and heat synergically destroyed membranes, dysfunction cellular self-defense and metabolic system, induced intracellular oxidative stress, and ultimately inactivated microorganisms. Additionally, the 1O2-dominated oxidation and cell adhesion facilitated the selective disinfection in real well water matrixes. This study provides a cost-effective and practical solution for efficient well water disinfection, which assists isolated rural areas in getting safe drinking water.

Kinetics and mechanism of sulfate radical-and hydroxyl radical-induced disinfection of bacteria and fungal spores by transition metal ions-activated peroxymonosulfate

Peroxymonosulfate(PMS)-based advanced oxidation process have been recognized as efficient disinfection processes. This study comprehensively investigated the role of sulfate radical (SO4•-) and hydroxyl radical (•OH)-driven disinfection of bacteria and fungal spores by the PMS/metals ions (Me(II)) systems and modeled the CT value based on the relationship between survival and ∫[Radical]dt, with the aim to provide an accurate and quantitative kinetic data of inactivation processes. The results indicated that •OH played a more central role than SO4•- in the inactivation process, and bacteria were more vulnerable to radical attack than fungal spores due to the differences in antioxidant mechanisms and external structures. The k value of •OH -induced inactivation of E. coli was approximately 3-fold higher than that of A. niger, and the shoulder length of •OH -induced inactivation of E. coli was closely 52-fold shorter than that of A. niger after treated with the PMS/Co(II) system. The morphological and biochemical changes revealed that PMS/Me(II) treatment caused membrane damage, intracellular ROS accumulation and esterase activity loss in microorganisms. This study significantly improved the understanding of the contribution of radicals in the process of microbial inactivation by PMS/Me(II) and would provide important implications for the further development of technologies to cope with the highly resistant fungal spores in drinking water.

Study on total residual oxidant decay in long-distance seawater intake pipeline of cooling system

Electrochlorination is often used for biofouling control along the water intake pipeline of seawater cooling system, but with the increasing of pipeline length, this process needs to be further improved. In this study, the dynamic circulation and field pilot test were used to simulate the long-distance seawater intake pipeline, investigating total residual oxidant (TRO) decay and its influencing factors by comparing the bench test. The results showed that intermediate dosing could increase terminal TRO, but also reduce the CT value, resulting in decline of local inactivation effect. The initial concentration of dynamic cycle test was higher than that of bench test under the same terminal TRO, and the difference value between the two was affected by holding time. When the initial concentration was greater than 8.5 mg L-1, TRO decay rate was proportional to the seawater flow rate and inversely proportional to the initial concentration. The initial concentration of 8.5-10 mg L-1 could meet TRO decay requirement under 3 h holding time, and the dosing concentration could be reduced to 6 mg L-1 when the temperature was low. The results provided important guidance for the actual operation of biofouling control in long-distance water intake pipelines of cooling system.

Disruption of Pseudomonas aeruginosa Adherent Cells by NaCl and NaOCl in Drinking Water

The aim of this study was to compare and explain the disruptive effect of sodium chloride and sodium hypochlorite on the adherent cells of P. aeruginosa on glass slides. To this end, the surface characteristics of glass slides and P. aeruginosa were estimated using the contact angle method. In addition, the effects of NaCl and NaOCl on the attachment of the adherent cells were revealed using optical microscopy. The contact angle data showed moderate effects of NaCl and NaOCl on the P. aeruginosa surface, which became faintly more hydrophilic (21.9 mJ/m², 51.1 mJ/m²) and a stronger electrons donor (53.4 mJ/m², 54.3 mJ/m²). NaCl reversed the hydrophobicity of glass, with its surface becoming very hydrophobic (- 31.7 mJ/m²) and a weak electrons donor (7.4 mJ/m²), whereas NaOCl enhanced the hydrophobicity of glass (49.3 mJ/m²) and its electrons donor character (62.7 mJ/m²). The optical microscopy showed that NaCl caused a clear and progressive disruption of the colonization, while NaOCl had no effect. Briefly, this study suggests that a combination of NaCl and NaOCl may solve the problem of P. aeruginosa installation in water tracks.

Identifying Eukaryotes and Factors Influencing Their Biogeography in Drinking Water Metagenomes

The biogeography of eukaryotes in drinking water systems is poorly understood relative to that of prokaryotes or viruses, limiting the understanding of their role and management. A challenge with studying complex eukaryotic communities is that metagenomic analysis workflows are currently not as mature as those that focus on prokaryotes or viruses. In this study, we benchmarked different strategies to recover eukaryotic sequences and genomes from metagenomic data and applied the best-performing workflow to explore the factors affecting the relative abundance and diversity of eukaryotic communities in drinking water distribution systems (DWDSs). We developed an ensemble approach exploiting k-mer- and reference-based strategies to improve eukaryotic sequence identification and identified MetaBAT2 as the best-performing binning approach for their clustering. Applying this workflow to the DWDS metagenomes showed that eukaryotic sequences typically constituted small proportions (i.e., <1%) of the overall metagenomic data with higher relative abundances in surface water-fed or chlorinated systems with high residuals. The α and β diversities of eukaryotes were correlated with those of prokaryotic and viral communities, highlighting the common role of environmental/management factors. Finally, a co-occurrence analysis highlighted clusters of eukaryotes whose members' presence and abundance in DWDSs were affected by disinfection strategies, climate conditions, and source water types.

Occurrence and control of fungi in water: New challenges in biological risk and safety assurance

Recently, the contamination of fungi in water has aroused widespread concern, which will pose a threat to water quality and safety, and raise diseases risk in the immunocompromised individuals. In this review, the characteristics and different physiological state of fungi in water are summarized. A comprehensive evaluation of the control efficiency and mechanism of waterborne fungi by the commonly used disinfection methods is provided as well. During the disinfection processes of chlorine, chlorine dioxide, chloramine and advanced disinfection processes (ADPs) such as O₃-based ADPs and UV-based ADPs, the fungal spores firstly lost their culturability, followed by membrane integrity, and the intracellular reactive oxygen species level increased at the same time, eventually the fungal spores were completely inactivated. The security strategies of drinking water against the contamination of fungi are also discussed in terms of water sources, water treatment plants and pipe network. Finally, future researches need to be explored are proposed: the rapid detection methods, the production laws and control of mycotoxin, and the outbreak conditions of fungi in water. Specifically, exploring efficient, safe and economical technologies, especially ADPs, is still the main direction in the disinfection of fungi in future studies. This review can offer a comprehensive understanding on the occurrence and control of fungi in water to fill the knowledge gap and provide guidance for the future research.

Occurrence of fungal spores in drinking water: A review of pathogenicity, odor, chlorine resistance and control strategies

Fungi in drinking water have been long neglected due to the lack of convenient analysis methods, widely accepted regulations and efficient control strategies. However, in the last few decades, fungi in drinking water have been widely recognized as opportunity pathogens that cause serious damage to the health of immune-compromised individuals. In drinking water treatment plants, fungal spores are more resistant to chlorine disinfection than bacteria and viruses, which can regrow in drinking water distribution systems and subsequently pose health threats to water consumers. In addition, fungi in drinking water may represent an ignored source of taste and odor (T&O). This review identified 74 genera of fungi isolated from drinking water and presented their detailed taxonomy, sources and biomass levels in drinking water systems. The typical pathways of exposure of water-borne fungi and the main effects on human health are clarified. The fungi producing T&O compounds and their products are summarized. Data on free chlorine or monochloramine inactivation of fungal spores and other pathogens are compared. At the first time, we suggested four chlorine-resistant mechanisms including aggregation to tolerate chlorine, strong cell walls, cellular responses to oxidative stress and antioxidation of melanin, which are instructive for the future fungi control attempts. Finally, the inactivation performance of fungal spores by various technologies are comprehensively analyzed. The purpose of this study is to provide an overview of fungi distribution and risks in drinking water, provide insight into the chlorine resistance mechanisms of fungal spores and propose approaches for the control of fungi in drinking water.

The protective role and mechanism of melanin for Aspergillus niger and Aspergillus flavus against chlorine-based disinfectants

Melanin is a critical component of fungal cell wall which protect fungi from adverse environmental tress. However, the role of melanin for fungi during the disinfection with chlorine-based disinfectants has not been elucidated. The results showed that the inactivation rate constants of Aspergillus niger with chlorine and chlorine dioxide decreased from 0.08 to 2.10 min^-1 to 0 after addition of 0.32 mg/L melanin. The results indicated addition of extracted fungal melanin inhibited the inactivation efficiency of chlorine and chlorine dioxide. In contrast, the k of Aspergillus niger after inactivation with monochloramine ranged from 1.50 to 1.78 min^-1 after addition of melanin which indicated effect of melanin on the inactivation efficiency of monochloramine was negligible. In addition, the extracted fungal melanin exhibited high reactivity with chlorine and chlorine dioxide but very low reactivity with monochloramine. The different inactivation mechanisms of chlorine-based disinfectants and different reactivity of melanin with chlorine-based disinfectants led to the different protective mechanism of melanin for A. niger and A. flavus spores against disinfection with chlorine-based disinfectants. The chlorine and chlorine dioxide appeared to react with functional groups of melanin in cell wall of spores, so sacrificial reactions between melanin and disinfectants decreased the available disinfectants and limited the diffusion of disinfectants to the reactive site on cell membrane, which led to the decrease of the disinfection efficiency for chlorine and chlorine dioxide. The monochloramine could penetrate into cell and damage DNA without the effect of melanin due to its strong penetration and low reactivity with melanin. Our results systematically demonstrate the protective roles of melanin on the fungal spores against chlorine-based disinfectants and the underlying mechanisms in resisting the environmental stress caused by chlorine-based disinfectants, which provides important implications for the control of fungi, especially for fungi producing melanin.

Differentiation of DNA or membrane damage of the cells in disinfection by flow cytometry

Recently, the viabilities changes of fungal spores in the water supply system during different disinfection processes have been revealed. SYBR Green I (SG), a nucleic acid stain, its fluorescence intensity is correlated with the amount of double-stranded DNA. This study established a new method through successive SG-SG-PI staining (PI: Propidium Iodide) with flow cytometry (FCM). It could successfully distinguish DNA damage and membrane damage of fungal spores, clearly elucidating the intrinsic disinfection mechanism during the chemical disinfection. This method was briefly described as follows: firstly, (1) the fungal spores were stained with SG and washed by centrifugation; and then, (2) the washed spores were treated with disinfectants and terminated; after that, (3) the disinfected spores were re-stained with SG and analyzed by FCM; finally, (4) the SG re-stained spores were stained with PI and analyzed by FCM. The percentages of spores with DNA damage and membrane damage were determined by the fluorescence intensity obtained from steps (3) and (4), respectively. The repeatability and applicability of this developed method were confirmed. It was further applied to explore the inactivation mechanism during chlorine-based disinfection, and results demonstrated that chloramine attacked the DNA more seriously than the membrane, while chlorine and chlorine dioxide worked in a reverse way.

A Study on Biofouling and Cleaning of Anion Exchange Membranes for Reverse Electrodialysis

This study covers the modification, (bio)fouling characterization, use, and cleaning of commercial heterogeneous anion exchange membranes (AEMs) to evaluate their feasibility for reverse electrodialysis (RED) applications. A surface modification with poly (acrylic) acid resulted in an improved monovalent perm-selectivity (decreased sulfate membrane transport rate). Moreover, we evaluated the (bio)fouling potential of the membrane using sodium dodecyl sulfate (SDS), sodium dodecyl benzenesulfonate (SDBS), and Aeromonas hydrophila as model organic foulants and a biofoulant, respectively. A detailed characterization of the AEMs (water contact angle, ion exchange capacity (IEC), scanning electron microscopy (SEM), cyclic voltammetry (CV), and Fourier Transform Infrared (FTIR) spectra) was carried out, verifying that the presence of such foulants reduces IEC and the maximum current obtained by CV. However, only SDS and SDBS affected the contact angle values. Cleaning of the biofouled membranes using a sodium hypochlorite aqueous solution allows for (partially) recovering their initial properties. Furthermore, this work includes a fouling characterization using real surface and sea water matrixes, confirming the presence of several types of fouling microorganisms in natural streams. A lower adhesion of microorganisms (measured in terms of total bacteria counts) was observed for the modified membranes compared to the unmodified ones. Finally, we propose a cleaning strategy to mitigate biofouling in AEMs that could be easily applied in RED systems for an enhanced long-term process performance.

Inactivation and subsequent reactivation of Aspergillus species by the combination of UV and monochloramine: Comparisons with UV/chlorine

Ultraviolet (UV)/monochloramine (NH₂Cl) as an advanced oxidation process was firstly applied for Aspergillus spores inactivation. This study aims to: i) clarify the inactivation and photoreactivation characteristics of UV/NH₂Cl process, ii) compared with UV/Cl₂ in inactivation efficiency, photoreactivation and energy consumption. The results illustrated that UV/NH₂Cl showed better inactivation efficiency than that of UV alone and UV/Cl₂, and could effectively control the photoreactivation. For instance, the inactivation rates for Aspergillus flavus, Aspergillus niger and Aspergillus fumigatus in the processes of UV/NH₂Cl (2.0 mg/L) was 0.034, 0.030 and 0.061 cm²/mJ, respectively, which were higher than that of UV alone (0.027, 0.026 and 0.024 cm²/mJ) and UV/Cl₂ (0.023, 0.026 and 0.031 cm²/mJ). However, there was no synergistic effect for Aspergillus flavus and Aspergillus fumigatus. As for Aspergillus niger, the best synergistic effect can reach 1.86-log₁₀. This may be due to their different resistance to disinfectants, which were related to the size, an outer layer of rodlets (hydrophobins) and pigments. After UV/NH₂Cl inactivation, the degree of cell membrane damage and intracellular reactive oxygen species were higher than that of UV alone. UV/NH₂Cl had the advantages of high inactivation efficiency and inhibition of photoreactivation, which provides a new entry point for the disinfection of waterborne fungi.

Effective inactivation of fungal spores by the combined UV/PAA: Synergistic effect and mechanisms

Peracetic acid (PAA) can effectively inactivate fungi in water, while may pose a potential risk of regrowth after disinfection. The inactivation kinetic and mechanism of fungal spores by combined UV and PAA (UV/PAA) was investigated in this study. The results showed that synergistic factor of the inactivation of A. niger and A. flavus was 1.44 and 1.37, which indicated significant synergistic effect of UV/PAA. The k of A. niger and A. flavus was similar at pH 5.0 and 7.0, while decreased 60.00% and 39.13% at pH 9.0 compared with that at pH 7.0. The effect of HA concentration on the inactivation efficiency of fungal spores by UV/PAA was negative, while the effect of PAA concentration was positive. The membrane permeabilized cell of A. niger and A. flavus caused by UV/PAA was 17.0% and 31.7%, which was higher than that caused by PAA and UV alone. The changes of morphology of fungal spores and the leakage of intracellular material indicated that the damage of cell structure caused by UV/PAA system was more serious than that of UV or PAA alone. In addition, the four parts that contributed in UV/PAA system was in the following order: UV > radical > PAA > synergistic effect. The inactivation efficiency of combined UV and chlorine (UV/Cl₂) was higher than that of UV/PAA. Furthermore, the typical order of the inactivation efficiency in different matrix was: phosphate buffer solution > surface water > secondary effluent. The regrowth potential of fungal spores after UV/PAA treatment was significantly lower than that by PAA alone, indicating that UV/PAA could decrease the microbial regrowth potential after PAA disinfection alone.

Health Effect of N-Nitroso Diethylamine in Treated Water on Gut Microbiota Using a Simulated Human Intestinal Microbiota System

Chlorination disinfection byproducts (CDBPs) can exert adverse human health effects. Many toxicology-based studies confirmed the health hazards of CDBPs, but little research has been done on gut microbiome. We explored the effect of CDBPs on intestinal microbiota in the Simulator of the Human Intestinal Microbial Ecosystem (SHIME). The results showed that CDBPs slightly inhibited the production of short-chain fatty acids, and the abundance of Actinobacteria decreased in the transverse colon and descending colon. The abundance of Proteobacteria increased in the ascending colon and descending colon, while it decreased in the transverse colon. The abundance of Firmicutes decreased in both the ascending colon and descending colon. In particular, the abundance of Lachnospiraceae members, Bilophila, Oscillospira, Parabacteroides, Desulfovibrio, and Roseburia increased in the ascending colon, while the abundance of Sutterella, Bacteroides, Escherichia, Phascolarctobacterium, Clostridium, Citrobacter, and Klebsiella increased in the descending colon. The Shannon index differed significantly in both the ascending colon and descending colon before and after exposure. Overall, we demonstrate the feasibility of applying the SHIME model to studying the effects of intestinal toxicity on health of chlorinated by-products. The findings of this study improve our understanding of the health impact of CDBPs on the intestinal microbiota and better control of CDBPs in treated water is recommended.

Sequential use of UV-LEDs irradiation and chlorine to disinfect waterborne fungal spores: Efficiency, mechanism and photoreactivation

In this work, sequential applications of light-emitting diodes (UV-LEDs) with two wavelengths and chlorine (Cl₂) were performed for fungal spores disinfection: UV-Cl₂, Cl₂-UV, UV/Cl₂-UV, UV-UV/Cl₂, Cl₂-UV/Cl₂-Cl₂. Overall comparisons of the sequential processes with respect to the inhibitory effect on photoreactivation were also evaluated. According to the evaluation of culturability and membrane permeability, inactivation of fungal spores by UV was not enhanced by prior or post exposure to Cl₂, but in the UV/Cl₂ process with pre or post UV treatment, the inactivation efficiency was greatly enhanced. Take P. polonicum for example, pre-treatments by UV₂₆₅ and UV₂₈₀ (40 mJ/cm²) caused the log count reduction (LCR) of 1.05 log and 0.95 log, then the followed UV₂₆₅/Cl₂ and UV₂₈₀/Cl₂ at the same UV fluence caused additional LCR of 1.80 log and 2.00 log. The permeabilization of P. polonicum was also accelerated in the processes of UV/Cl₂-UV and UV-UV/Cl₂, especially at the wavelength of 280 nm. In the sequential processes, especially those containing UV/Cl₂ or at the wavelength of 280 nm, could promote the formation of intracellular reactive oxygen species (ROS), thus leading to more severe damage to the spores as reflected in the culturability reduction, membrane permeability and inhibition of photoreactivation.

Efficacy of UV-LED based advanced disinfection processes in the inactivation of waterborne fungal spores: Kinetics, photoreactivation, mechanism and energy requirements

The contamination of fungi in water supply systems poses great risks to environment and human health. In this work, UV light-emitting diodes (UV-LEDs)-based advanced disinfection processes (ADPs) including UV-LEDs/hydrogen peroxide (H₂O₂), UV-LEDs/persulfate (PS) and UV-LEDs/peroxymonosulfate (PMS), were adopted for waterborne fungal spores inactivation. Overall comparisons of the UV-LEDs-based ADPs with respect to the control efficiency of photoreactivation and energy consumption were also evaluated. Results showed that culturability reduction of the fungal spores treated by UV-LEDs was not enhanced with the addition H₂O₂, PMS, and PS according to the results of heterotrophic plate counts and reaction rate constants; A. niger was expected to have higher UV resistance followed by T. harzianum and P. polonicum. However, UV-LEDs-ADPs inactivation, especially at the wavelengths of 280 and 265/280 nm, could accelerate the permeabilization of fungal spores as characterized by flow cytometry. Take P. polonicum for example, the percentage of membrane permeabilized spores was 98.0%, 98.7%, 97.6% and 82.6% after treatment by UV₂₈₀/H₂O₂, UV₂₈₀/PS, UV₂₈₀/PMS and UV₂₈₀ alone, respectively at the fluence of 100 mJ/cm². The direct attack of free radicals in the processes of UV-LEDs-ADPs further enhanced the membrane damage and lowered the photoreactivation level, thus improved the inactivation efficiency. UV-LEDs/H₂O₂ was considered as an effective process in the disinfection of fungal spores with the advantages of enhancing the damage of membrane, inhibiting photoreactivation and comparable energy consumption compared with UV-LEDs alone.

Enhanced HClO production from chloride by dual cocatalyst loaded WO3 under visible light

Photocatalytic production of HClO was improved more than twice by co-loading of Mn compared to the standard Pt/WO3.

Automated flow cytometry as a flexible tool for comparing disinfection characteristics of indigenous bacterial communities and pure cultures

Bacterial inactivation efficiency of chlorine varies with organisms and environmental conditions. The comparability of different samples/studies, especially comparing indigenous bacterial communities with pure cultures, is impeded by inconsistent experimental conditions and analytical methods used in various studies. We tested a novel 96-well plate FCM experimental and automated analytical approach, where bacterial communities and pure cultures were suspended in the same natural water matrix prior to chlorination directly in the plate. We demonstrated the ability to rapidly monitor the efficiency of 32 different combinations of chlorine concentration and time (i.e. chlorine exposure) on bacterial pure cultures and indigenous aquatic communities, which enabled correct comparison of the data from different samples under the exact same experimental conditions. In this study, the 96-well plate automated FCM approach enabled large sets (896) of independent chlorination experiments to be carried out in a short time period. To our knowledge, this is the largest dataset of chlorination experiments which consumed least time (within 18 h after sampling) until now. Staining with SYBR Green I (SG) and SG combined with propidium iodide (SGPI) was used to assess cellular damage during chlorination. The results showed that with the same chlorine exposure, a higher chlorine concentration with a shorter contact time is favorable for inactivation of bacteria. Our research provides a promising framework to compare disinfection characteristics of various microorganism and can be further developed to diagnose effect of antimicrobial products.

A comprehensive investigation of the microbial risk of secondary water supply systems in residential neighborhoods in a large city

Secondary water supply systems (SWSSs) are characterized by long water stagnation and low levels of chlorine residuals, which may pose a high microbial risk to terminal users. In this study, the SWSSs of 12 residential neighborhoods in a metropolitan area of 5 million people in southeastern China were seasonally investigated to assess their microbial risks by determining more than 30 physicochemical and biological parameters. Although the microbiological quality of SWSS water met the requirements of the standards for drinking water quality of China, it did deteriorate in various aspects. The heterotrophic plate counts with R2A media were high (> 100 CFU/mL) in some SWSS tank and tap water samples. Propidium monoazide (PMA)-qPCR revealed a one magnitude higher abundance of viable bacteria in the tank and tap water samples (average 10^3.63±1.10 and 10^3.65±1.25 gene copies/mL, respectively) compared with the input water samples, and Enterococcus, Acanthamoeba, and Hartmannella vermiformis were only detected in the tanks. In particular, the high detection frequency of Legionella in 35% tank and 21% tap water samples suggested it is a supplementary microbial safety indicator in SWSSs. The microbial regrowth potential was more obvious in summer, and Illumina sequencing also demonstrated distinct seasonal changes in the relative abundance of bacterial gene sequences at the genus level. Turbidity and residual chlorine were closely connected with total bacterial biomass, and the latter seemed responsible for microbial community structure alteration. The extremely low chlorine residuals associated with a high abundance of total bacteria (as high as 10^6.48 gene copies/mL) and Legionella (as high as 10^6.71 gene copies/100 mL) in the closed valve tanks highlighted the high microbial risk increased by mishandling the operation of SWSSs. This study found that SWSSs possessed a higher microbial risk than the drinking water network, which suggested that the frequency and scope of monitoring the microbial risk of SWSSs in megacities should be strengthened for the purpose of waterborne epidemic disease prevention and control.

Synergistic effect of ozone and chlorine on inactivating fungal spores: Influencing factors and mechanisms

Effective control of fungal contamination in water is vital to provide healthy and safe drinking water for human beings. Although ozone was highly effective in inactivating fungi in water, it was limited by a lack of continuous disinfection ability in water supply system. In present study, the inactivation of fungal spores by combining ozone and chlorine was investigated. The synergistic effects of Aspergillus niger and Trichoderma harzianum spores reached 0.47- and 0.55-log within 10 min, respectively. The inactivation efficiency and the synergistic effect would be affected by disinfectant concentration, pH, and temperature. The combined inactivation caused more violent oxidative stimulation and more severe damage to the fungal spores than the individual inactivation based on the flow cytometry analysis and the scanning electron microscopy observation. The synergistic effect during the combined inactivation process was attributed to the generation of hydroxyl radicals by the reaction between ozone and chlorine and the promotion of chlorine penetration by the destruction of cell wall by ozone. The combined inactivation efficiency in natural water samples was reduced by 26.4-43.8% compared with that in PBS. The results of this study provided an efficient and feasible disinfection method for the control of fungi in drinking water.

The aggregation of Aspergillus spores and the impact on their inactivation by chlorine-based disinfectants

The formation of fungal biofilm goes through some different states, including monodisperse state, aggregated state, germinated state, hyphal and biofilm. The aggregation of spores is a primary step of fungal biofilm development in aquatic systems. Previous studies on the inactivation of fungi were mostly performed in the monodisperse state of fungal spores and biofilm state, however, the inactivation of aggregated fungal spores is still unclear. In this study, the aggregated characteristics of fungal spores (Aspergillus fumigatus and Aspergillus flavus) at different pH values were firstly studied, and the inactivation efficiency of fungal spores at different aggregation degree by chlorine-based disinfectants was also clarified. The results showed that the aggregation degree of Aspergillus fumigatus was the highest at pH 9.0 while it was the lowest at pH 5.0. Aggregation between fungal spores was mainly mediated by occasional adhesin-adhesin interactions and electrostatic interactions. Compared with monodisperse spores, fungal spores were more resistant to chlorine-based disinfectants with the increase of spore aggregation degree. The inactivation rate constants of Aspergillus fumigatus at 30% and 63% aggregation degree were 1.5- and 4-folds lower than that of monodisperse spores, respectively. The lower proportion of membrane damage and higher intracellular reactive oxygen species level for aggregated spores than monodisperse spores was observed according to the flow cytometric results after chlorine-based disinfectants treatment. The reasons for the lower inactivation efficiency of aggregated spores are as following: the protection of outer layer spores and signals between aggregates lead to the increase of resistance for aggregated spores. This study is meaningful for the control of the fungal spores at different states in water.

Impact of the physiological state of fungal spores on their inactivation by active chlorine and hydrogen peroxide

This study aimed at assessing the impact of the physiological state of fungal spores on inactivation by sodium hypochlorite, 0.1% and 0.2% active chlorine, and 3% hydrogen peroxide. In this context, two physiological states were compared for 4 fungal species (5 strains). The first physiological state corresponded to fungal spores produced at 0.99 a_w and harvested using an aqueous solution (laboratory conditions), while the second one corresponded to fungal spores produced under a moderate water stress (0.95 a_w) and dry-harvested (mechanical harvesting without use of any water, mimicking food plant conditions). Aspergillus flavus "food plant" conidia were more resistant to all tested fungicide molecules than the "laboratory" ones. The same phenomenon was observed for Penicillium commune UBOCC-A-116003 conidia treated with hydrogen peroxide. However, this isolate did not exhibit any inactivation difference between "laboratory" and "food plant" conidia treated with sodium hypochlorite. Similarly, the physiological state of Cladosporium cladosporioides conidia did not impact the efficacy of the tested biocides. P. commune UBOCC-A-112059 "food plant" and "laboratory" conidia were more resistant to hydrogen peroxide and sodium hypochlorite, respectively. As for Mucor circinelloides, "laboratory" spores were more resistant to all disinfectant than the "food plant" ones. Noteworthy, regardless of the physiological state, all M. circinelloides and C. cladosporioides conidia were inactivated for 5 min treatment at 0.2% active chlorine and for 2.5 min treatment at 0.1% active chlorine, while the conidia of all the other species remained viable for these treatments. The obtained data indicate that the efficacy of disinfectant molecules depends not only on the encountered fungal species and its intraspecific diversity but also on the spore physiological state.

Inactivation of waterborne fungal spores by 1-bromo-3-chloro-5,5-dimethylhydantoin: Kinetics, influencing factors and mechanisms

Fungal contamination in drinking water source has become a problem worth studying, as waterborne fungi may cause deterioration of water quality and outbreak of diseases. Various disinfection methods have been explored to control fungal spores in drinking water, such as chlor(am)ination, ozonation, chlorine dioxide treatment, but these methods are not appropriate for remote areas, owing to the difficulties in preparation, carriage and storage. In this study, a powdery disinfectant of 1-bromo-3-chloro-5,5-dimethylhydantoin (BCDMH), which facilitated transportation and preservation, was firstly chosen to inactivate opportunistic pathogens of Aspergillus niger (A. niger) and Penicillium polonicum (P. polonicum). The results revealed that the inactivation kinetics of fungal spores by BCDMH fitted to Chick-Watson model well, with the inactivation rate constant of 0.011 and 0.034 L mg^-1 min^-1 for A. niger and P. polonicum, respectively. Acidic condition and high temperature promoted the inactivation by BCDMH. Compared with chlorine, BCDMH showed relative weaker ability on inactivation of fungal spores. However, it was demonstrated that the inactivation efficiency of BCDMH was obviously enhanced by adding halide ions, with 11 or 36 folds for A. niger and 4 or 15 folds for P. polonicum by adding 40 μM Br^- or I^-. The inactivation mechanisms were detected by flow cytometry and scanning electron microscope. Fungal spores lost their culturability firstly, then membrane integrity was damaged. Meanwhile, the esterase activity and intracellular reactive oxygen species level changed, and finally intracellular adenosine triphosphate released.

Inactivation of Aspergillus species in real water matrices using medium pressure mercury lamps

The aim of this work is to understand the inactivation efficiency of medium pressure mercury lamps, measured in terms of growth inhibition as well as cell death, damage and response, using three strains from three different Aspergillus species (A. fumigatus, A. niger and, A. terreus) spiked in filtered surface water. A complete characterization of the effect of the treatment on each strain of the fungal species was assessed considering spores' morphology, cell wall integrity and enzymatic activity, the formation of pyrimidine dimers in the DNA and proteome analysis. Results showed that, when subjected to medium pressure mercury lamps, A. niger is the most resistant to inactivation, that both A. fumigatus and A. niger suffer more morphological changes and present a higher number of damaged spores and A. terreus presented more dead spores. DNA damages detected in A. niger were able to be repaired to some extent, under both light and dark conditions. Finally, proteome analysis showed that the UV radiation treatment triggered different types of stress response, including cell wall reorganization and DNA repair in A. fumigatus and A. terreus, and oxidative stress responses like the increase in production of citric acid and itaconic acid in A. niger and A. terreus, respectively.

Evaluation of the vital viability and their application in fungal spores' disinfection with flow cytometry

More attention was focused on fungi contamination in drinking water. Most researches about the inactivation of fungal spores has been conducted on disinfection efficiency and the leakage of intracellular substances. However, the specific structural damage of fungal spores treated by different disinfectants is poorly studied. In this study, the viability assessment methods of esterase activities and intracellular reactive oxygen species (ROS) were optimized, and the effects of chlorine-based disinfectants on fungal spores were evaluated by flow cytometry (FCM) and plating. The optimal staining conditions for esterase activity detection were as follows: fungal spores (10⁶ cells/mL) were stained with 10 μM carboxyfluorescein diacetate and 50 mM ethylene diamine tetraacetic acid at 33 °C for 10 min (in dark). The optimal staining conditions for intracellular ROS detection were as follows: dihydroethidium (the final concentration of 2 μg/mL) was added into fungal suspensions (10⁶ cells/mL), and then samples were incubated at 35 °C for 20 min (in dark). The cell culturability, membrane integrity, esterase activities, and intracellular ROS were examined to reveal the structural damage of fungal spores and underlying inactivation mechanisms. Disinfectants would cause the loss of the cell viability via five main steps: altered the morphology of fungal spores; increased the intracellular ROS levels; decreased the culturability, esterase activities and membrane integrity, thus leading to the irreversible death. It is appropriate to assess the effects of disinfectants on fungal spores and investigate their inactivation mechanisms using FCM.

The microbial ecology of a Mediterranean chlorinated drinking water distribution systems in the city of Valencia (Spain)

Drinking water distribution systems host extensive microbiomes with diverse biofilm communities regardless of treatment, disinfection, or operational practices. In Mediterranean countries higher temperatures can accelerate reactions and microbial growth that may increase aesthetic water quality issues, particularly where material deposits can develop as a result of net zero flows within looped urban networks. This study investigated the use of flow and turbidity monitoring to hydraulically manage mobilisation of pipe wall biofilms and associated material from the Mediterranean city of Valencia (Spain). Pipe sections of different properties were subjected to controlled incremental flushing with monitoring and sample collection for physico-chemical and DNA analysis with Illumina sequencing of bacterial and fungal communities. A core microbial community was detected throughout the network with microorganisms like Pseudomonas, Aspergillus or Alternaria increasing during flushing, indicating greater abundance in underlying and more consolidated material layers. Bacterial and fungal communities were found to be highly correlated, with bacteria more diverse and dynamic during flushing whilst fungi were more dominant and less variable between sampling sites. Results highlight that water quality management can be achieved through hydraulic strategies yet understanding community dynamics, including the fungal component, will be key to maintaining safe and ultimately beneficial microbiomes in drinking water distribution systems.

Water-Transmitted Fungi are Involved in Degradation of Concrete Drinking Water Storage Tanks

Global warming, globalization, industrialization, and the rapidly growing population at present increasingly affect the production of safe drinking water. In combination with sustainable bio-based or recycled materials, used for water distribution systems, these factors promote emerging pathogens, including fungi. They can proliferate in oligotrophic water systems, affect the disinfection process, degrade building materials, and cause diseases in humans. In this study, we explored fungal-based degradation of modern concrete water storage tanks and the presence of fungi in chlorinated drinking water at the entrance and exit of the tanks. The degradation potential of isolated 52 fungal strains and their growth at different oligotrophic conditions was tested in vitro. Forty percent of strains grew at extremely oligotrophic conditions, and 50% classified as aerophilic. Two-thirds of tested strains produced acids, with Penicillium strains as the best producers. Only 29.7% of the strains were able to grow at 37 °C, and none of them was isolated from drinking water at consumers' taps. Although not yet part of the guidelines for building materials in contact with drinking water, fungi should be taken into consideration in case of visible degradation. Their number of consumers' endpoints should be checked to exclude possible health risks for consumers.

The virus removal in UV irradiation, ozonation and chlorination

The COVID-19 pandemic draws much attention to virus inactivation since the SARS-CoV-2 was detected in miscellaneous environments and the wastewater can be a potential transmitting pathway. UV irradiation, ozonation and chlorination are widely used disinfection processes in water treatment. In this review, the mechanisms and applications of three disinfection processes are introduced, and their inactivation effects on virus as well as other microorganisms are compared and discussed. The resistance of viruses to UV irradiation is generally stronger than that of bacteria. 4-log inactivation of bacteria can be easily obtained within a UV dose of 10 ​mJ/cm². However, the doses to reach the same virus removal rate vary greatly from 10 to 140 ​mJ/cm². The coronaviruses have even stronger UV resistance. Comparatively, ozonation and chlorination are effective methods to inactivate viruses, and the CT values of 4-log removal for most viruses concerned are lower than 1 ​mg·min/L and 10 ​mg·min/L, respectively. Protozoa, fungal spores and bacterial spores are more resistant to disinfection. Temperature, pH, organic matters, turbidity and other parameters all have influences on the disinfection. With a 10 ​°C decrease in temperature, the CT value required for certain removal rates doubles. Generally low pH promotes disinfection and high pH is against it. In drinking water and wastewater treatment process, the resistance properties of microorganisms and other influence parameters should be taken into consideration when choosing disinfection technologies.

Inactivation of fungal spores in water using ozone: Kinetics, influencing factors and mechanisms

Fungal contamination of drinking water sources is increasingly threatening the environment and human health. In this study, the inactivation of three genera of dominant fungi in drinking water sources using ozone was first reported. The inactivation of the fungal spores by ozone could be divided into two distinct stages: first a rapid reduction in survival, and then the inactivation at a slower rate. The secondary stage inactivation fitted the Chick-Watson model well, and there was no significant difference in the second-order inactivation rate constants of the three fungal spores (0.199-0.209 L mg^-1 min^-1). The inactivation rate constants of fungal spores by molecular ozone were much lower than those of viruses, which were equivalent to that of Cryptosporidium. The increase in pH and temperature showed a positive effect on the inactivation rate. Damage to cell membranes, leakage of intracellular compounds, and changes of reactive oxygen species and esterase activity in the spores were detected after inactivation. The results indicated that ozone inactivated fungal spores by firstly destroying cell walls and membranes and then causing the release of intracellular compounds. The fungicidal efficiency of ozone was superior to those of chlorine and chlorine dioxide. In addition, the inactivation efficiency of ozone on fungal spores in real water matrices was reduced to 50.7-91.2% of the efficiency in phosphate buffer. In conclusion, ozone showed high efficiency in the inactivation of fungal spores and could be used as an alternative disinfectant for fungal contamination in drinking water sources.

Simultaneously enhance the inactivation and inhibit the photoreactivation of fungal spores by the combination of UV-LEDs and chlorine: Kinetics and mechanisms

Waterborne fungi have been recognized as an emerging environmental contaminant in recent years. This work was to investigate the inactivation efficiency and mechanisms of ultraviolet light-emitting diodes (UV-LEDs)/chlorine (Cl₂) (265, 280 and 265/280 nm combination) and LPUV/Cl₂ (254 nm) treatments for three fungal species compared with individual disinfection processes. Control of photoreactivation for fungal species inactivated by UV-LEDs/Cl₂ and LPUV/Cl₂ was also evaluated. The results revealed that the combined UV-LEDs/Cl₂ and LPUV/Cl₂ processes, especially UV-LEDs/Cl₂, exhibited better inactivation performance compared to UV alone and Cl₂ alone based on the inactivation rate constants, and an evident synergistic effect was observed. For example, the inactivation rates for Penicillium polonicum in the processes of UV₂₆₅/Cl₂, UV₂₈₀/Cl₂, UV_265/280/Cl₂ and LPUV/Cl₂ was 0.142, 0.168, 0.174 and 0.106 cm²/mJ, respectively, which were all approximately 1.5-fold higher than that of UV alone. The synergistic effect of fungal spores inactivation by UV-LEDs/Cl₂ and LPUV/Cl₂ was due to the high level production of intracellular reactive oxygen species and the reaction of potential extracellular free radicals. Resistance of the tested fungal spores was as follows: Trichoderma harzianum < Penicillium polonicum < Aspergillus niger. In addition, the joint effect of DNA and other cellular damage resulted in the inhibition of photoreactivation of fungal spores inactivated by UV-LEDs/Cl₂ and LPUV/Cl₂ compared with that of fungal spore inactivated by UV alone. This study may provide reference for controlling the dissemination of waterborne fungi utilizing combined UV-LEDs and free chlorine processes.

Broad Diversity of Fungi in Hospital Water

INTRODUCTION

Some studies have reported the occurrence of microorganisms isolated from water. Considering these microorganisms, fungi are known to occur ubiquitously in the environment, including water, and some are pathogenic and may cause health problems, especially in immunocompromised individuals. The aim of this study was to identify fungi in hospital water samples and to correlate their presence with the concentration of free residual chlorine.

METHODS

Water samples (100 mL) were collected from taps (n = 74) and water purifiers (n = 14) in different locations in a university hospital. Samples were filtered through a nitrocellulose membrane and placed on Sabouraud dextrose agar and incubated for 24 hours at 30°C. Fungi were identified according to established methods based on macroscopic and microscopic characteristics (filamentous) and physiological tests (yeasts). Free chlorine residual content was measured at the time of sample collection.

RESULTS

Seventy species of fungi were identified in the water samples and about 56% of the water samples contained culturable fungi. Cladosporium oxysporum, Penicillium spinulosum, and Aspergillus fumigatus were the most common filamentous fungi. Aureobasidium pullulans and Candida parapsilosis were the most common yeasts. Chemical analyses revealed that free residual chlorine was present in 81.8% of the samples within recommended concentrations. Among samples from water purifiers, 92.9% showed low levels of free residual chlorine (<0.2 mg/L). There was no significant association between chlorine concentrations (either within or outside the recommended range) and the presence of filamentous fungi and yeasts.

CONCLUSIONS

This study showed that hospital water can be a reservoir for fungi, some of which are potentially harmful to immunocompromised patients. Free residual chlorine was ineffective in some samples.

Comparison of UV-LEDs and LPUV on inactivation and subsequent reactivation of waterborne fungal spores

Recently, the contamination of fungi in water supply systems has been an area of increasing concern, such as Aspergillus spp. and Penicillium spp. It can cause some waterborne issues such as odor, taste and formation of mycotoxins. Ultraviolet light emitting diodes (UV-LEDs) are considered as a potential alternative to conventional mercury lamps for water disinfection. This study has compared the performance of LPUV (low pressure ultraviolet) and UV-LEDs with emissions at 265, 280 nm and combination emissions at 265/280 nm to test inactivation efficiency, reactivation, viability and electrical energy consumption in the treatment of three water-borne fungal species (Aspergillus niger, Penicillium polonicum, Trichoderma harzianum) at a batch water disinfection system. The results showed that the performances of UV-LEDs were superior for the inactivation of fungal spores compared to the 254 nm (LP), while no statistically differences were observed among the UV-LEDs (p > 0.05). The average photoreactivation rate (k₁) of fungal spores irradiated by UV-LEDs and 254 nm (LP) follows the order: T. harzianum > A. niger > P. polonicum. Compared with LPUV, UV-LEDs irradiation at 280 nm and 265/280 nm more efficiently inhibits photoreactivation, which was attributed to that irradiation of 280 nm and 265/280 nm would cause greater membrane damage and increase intracellular reactive oxygen species level of fungal spores according to the flow cytometric results. The electrical energy consumption of UV-LEDs was higher than that of LPUV, which was due to its lower wall plug efficiency. The results of this study can provide additional and beneficial information for the reasonable exploitation of UV-LEDs in water disinfection.

Biodiversity and ecology of microorganisms in high pressure membrane filtration systems

High-pressure membrane filtration (reverse osmosis and nanofiltration) is used to purify different water sources, including wastewater, surface water, groundwater and seawater. A major concern in membrane filtration is the accumulation and growth of micro-organisms and their secreted polymeric substances, leading to reduced membrane performance and membrane biofouling. The fundamental understanding of membrane biofouling is limited despite years of research, as the means of microbial interactions and response to the conditions on the membrane surface are complicated. Here, we discuss studies that investigated the microbial diversity of fouled high-pressure membranes. High-throughput amplicon sequencing of the 16S rRNA gene have shown that Burkholderiales, Pseudomonadales, Rhizobiales, Sphingomonadales and Xanthomonadales frequently obtain a high relative abundance on fouled membranes. The bacterial communities present in the diverse feed water types and in pre-treatment compartments are different from the communities on the membrane, because high-pressure membrane filtration provides a selective environment for certain bacterial groups. The biofilms that form within the pre-treatment compartments do not commonly serve as an inoculum for the subsequent high-pressure membranes. Besides bacteria also fungi are detected in the water treatment compartments. In contrast to bacteria, the fungal community does not change much throughout membrane cleaning. The stable fungal diversity indicates that they are more significant in membrane biofouling than previously thought. By reviewing the biodiversity and ecology of microbes in the whole high pressure membrane filtration water chain, we have been able to identify potentials to improve biofouling control. These include modulation of hydrodynamic conditions, nutrient limitation and the combination of cleaning agents to target the entire membrane microbiome.

Development of fungal spore staining methods for flow cytometric quantification and their application in chlorine-based disinfection

Fungal contamination in drinking water has been becoming a hot topic. The routine enumeration method of fungal spores is heterotrophic plate counts (HPC). However, this method is time-consuming and labor-intensive and there is also the difficulty of enumerating viable but non-culturable cells. In this study, a rapid, simple and accurate method for quantifying fungal spores and discriminating their viability in water was established using flow cytometry (FCM) combined with fluorescence dyes. The optimal staining conditions are as follows: spores suspensions are sonicated at 495 W for 5 min as pretreatment, and then 10 μL of SYBR Green I (100×) and 30 mM Ethylene diamine tetraacetic acid are added to a 500 μL water sample, which incubate at 35 °C for 20 min in dark. The concentration of fungal spores measured by FCM was highly correlated with HPC results and microscope observations, with correlation coefficient of 0.996 and 0.988, respectively. This staining method can be widely applied to the enumeration and viability evaluation of fungal spores. In addition, chlorine-based inactivation of three genera of fungal spores was assessed by plating and FCM. The result showed that all three genera of fungal spores lost culturability firstly and then membrane integrity decreased, preliminarily revealing the inactivation mechanism. The inactivation rate constants of membrane damage varied in the following order: chlorine dioxide > chlorine > chloramine. This study concluded that FCM is an appropriate and alternative tool to detect fungal spores' viability and can be used for evaluating the fungal inactivation by disinfectants.

Application of a smartphone based spectrophotometer for rapid in-field determination of nitrite and chlorine in environmental water samples

In this paper, a low cost and portable smartphone-based spectrophotometer with the purpose of measuring trace levels of two important anions, chlorine and nitrite ions in water samples, is introduced. This home-made spectrophotometer is made of Plexiglas, equipped with two LEDs as a light source, and a piece of DVD is acted as light dispersing element. Battery of smartphone was used as its power supply and spectral analysis was performed by a free software downloadable from Google Playstore. By using this lightweight spectrophotometer, various environmental samples were analyzed for their NO₂^- and Cl₂ content in field. Good detection limits of 5.00 × 10^-2 mg L^-1 and 8.60 × 10^-3 mg L^-1 were obtained for chlorine and nitrite, respectively. The linear range for chlorine was 1.00-4.00 mg L^-1 and this range for nitrite was 0.05-1.20 mg L^-1. Reproducibility as relative standard deviation for both chlorine and nitrite was better than 8.75%. In order to investigate validity of data, results were compared to standard methods of measuring chlorine and nitrite, using both spectrophotometry and commercial kits which showed no difference between results obtained. This very simple to use and inexpensive device can be used many times, so can be considered as a low-cost alternative to the detection device of commercial kits.

Biofilm formation potential and chlorine resistance of typical bacteria isolated from drinking water distribution systems

Biofilms are the main carrier of microbial communities throughout drinking water distribution systems (DWDSs), and strongly affect the safety of drinking water. Understanding biofilm formation potential and chlorine resistance is necessary for exploring future disinfection strategies and preventing water-borne diseases. This study investigated biofilm formation of five bacterial strains isolated from a simulated DWDS at different incubation times (24 h, 48 h, and 72 h), then evaluated chlorine resistance of 72 h incubated biofilms under chlorine concentrations of 0.3, 0.6, 1, 2, 4, and 10 mg L⁻¹. All five bacterial strains had biofilm formation potential when incubated for 72 h. The biofilm formation potential of Acinetobacter sp. was stronger than that of Bacillus cereus, Microbacterium sp. and Sphingomonas sp. were moderate, and that of Acidovorax sp. was weak. In contrast, the order of chlorine resistance was Bacillus sp. > Sphingomonas sp. > Microbacterium sp. > Acidovorax sp. > Acinetobacter sp. Thus, the chlorine resistance of a single-species biofilm has little relation with the biofilm formation potential. The biofilm biomass is not a major factor affecting chlorine resistance. Moreover, the chlorine resistance of a single-species biofilm is highly related to the physiological state of bacterial cells, such as their ability to form spores or secrete extracellular polymeric substances, which could reduce the sensitivity of the single-species biofilm to a disinfectant or otherwise protect the biofilm.

Biofilms are the main carrier of microbial communities throughout drinking water distribution systems (DWDSs), and strongly affect the safety of drinking water.

Reactivation of fungal spores in water following UV disinfection: Effect of temperature, dark delay, and real water matrices

The occurrence of fungi in water supply systems causes many environmental problems (e.g., odor, taste, turbidity, formation of mycotoxins); it has been an area of increasing concern in recent years. Ultraviolet irradiation can inactivate fungi efficiently. However, its reactivation poses further challenges in water purification. The reactivation characteristics of waterborne fungi under different environmental conditions have rarely been reported. In this study, the effects of temperatures and dark delay on the reactivation of three genera of fungal spores (Trichoderma harzianum, Aspergillus niger, Penicillium polonicum) were evaluated. The reactivation levels among these fungal spores were compared in phosphate buffer solution (PBS) and in real groundwater. It was found that lower temperature can inhibit the photoreactivation of fungi, whereas higher temperatures would promote the process. A long-term dark delay can inhibit the photoreactivation of fungi effectively. The dark repair of fungal spores almost do not occur neither in PBS nor in real groundwater. Finally, the photoreactivation percentage in real groundwater was higher than that in PBS. This study will provide a basis for controlling the reactivation of fungi in water.

Wide diversity of fungal species found in wellwater for human consumption: an analytical cross-sectional study

BACKGROUND

Fungi are ubiquitous in the environment. They are able to grow in water and many of them may be opportunistic pathogens.

OBJECTIVE

The aims were to identify fungi in registered wells (RWs) and nonregistered wells (NRWs) that tap into groundwater; and to correlate the results from physicochemical assays on this water (free residual chlorine and pH) with the presence of fungi.

DATA AND SETTING

Analytical cross-sectional quantitative study on groundwater wells in São José do Rio Preto, São Paulo, Brazil.

METHODS

52 samples of 500 ml of water were collected from RWs and 107 from NRWs. These were sent to a microbiology laboratory to identify any fungi that were present. In addition, free residual chlorine and pH were measured immediately after sample collection. Several statistical analysis tests were used.

RESULTS

Fungal contamination was present in 78.8% of the samples from RWs and 81.3% from NRWs. Filamentous fungi were more prevalent than yeast in both types of wells. There was no significant difference in presence of fungi according to whether chloride and pH were within recommended levels in RWs; or according to whether pH was within recommended levels in NRWs. Furthermore, there was no statistical difference in the levels of fungal contamination between RWs and NRWs.

CONCLUSION

Both RWs and NRWs are potential reservoirs for many types of fungi. Many of these may become opportunistic pathogens if they infect immunosuppressed individuals. Furthermore, this study confirms that fungi are able to grow even when chlorine and pH parameters are within the standards recommended.

Ozone disinfection of chlorine-resistant bacteria in drinking water

The wide application of chlorine disinfectant for drinking water treatment has led to the appearance of chlorine-resistant bacteria, which pose a severe threat to public health. This study was performed to explore the physiological-biochemical characteristics and environmental influence (pH, temperature, and turbidity) of seven strains of chlorine-resistant bacteria isolated from drinking water. Ozone disinfection was used to investigate the inactivation effect of bacteria and spores. The DNA concentration and cell surface structure variations of typical chlorine-resistant spores (Bacillus cereus spores) were also analysed by real-time qPCR, flow cytometry, and scanning electron microscopy to determine their inactivation mechanisms. The ozone resistance of bacteria (Aeromonas jandaei < Vogesella perlucida < Pelomonas < Bacillus cereus < Aeromonas sobria) was lower than that of spores (Bacillus alvei < Lysinibacillus fusiformis < Bacillus cereus) at an ozone concentration of 1.5 mg/L. More than 99.9% of Bacillus cereus spores were inactivated by increasing ozone concentration and treatment duration. Moreover, the DNA content of Bacillus cereus spores decreased sharply, but approximately 1/4 of the target genes remained. The spore structure exhibited shrinkage and folding after ozone treatment. Both cell structures and gene fragments were damaged by ozone disinfection. These results showed that ozone disinfection is a promising method for inactivating chlorine-resistant bacteria and spores in drinking water.

Prevalence and public health implications of mycotoxigenic fungi in treated drinking water systems

Insufficient potable water resources and poorly treated drinking water quality are the world's number one cause for preventable morbidity and mortality from water-related pathogenic microorganisms. Pathogenic microorganisms, including mycotoxigenic fungi, have been identified in treated drinking water. This paper presents a review of mycotoxigenic fungi as a health risk to the public as these fungi are responsible for allergies, cancers and opportunistic infections mainly to immunocompromised patients. The exacerbating factors contributing to fungal presence in water distribution systems, factors that lead to fungi being resistant to water treatment and treated drinking water quality legislations are also discussed. This paper provides a review on the prevalence of mycotoxigenic fungi and their implications to public health in treated drinking water, and the need for inclusion in treated drinking water quality regulations.

Remediation efficiency of different methods for rapid-response of microbiological and/or organic matter contaminated beach sand: A laboratory study

In this article we compare the efficiency of different methods of rapid-response remediation of beach sand contaminated with microbiological and/or organic matter. Contaminated beach sands were treated in laboratory by different treatment methods (i.e., oxidation, UV-photoexposure, or thermal methods) and the efficiency of disinfection and breakdown of organic matter were evaluated. Contaminants in raw and treated beach sands were measured by membrane filtration method, and by chemical and biochemical oxygen demand, and chromatographic analysis. All the methods tested were efficient for disinfecting beach sand with microbiological contamination, except for the UV-photoexposure method, which showed only moderate disinfection potential. Chemical degradation efficiency of beach sand contaminated by crude petroleum was higher with Fenton and Photo-Fenton (associated with the use of surfactant and ultrasound) methods. Photo-Fenton method improvement can increase the efficiency of contaminated beach sand treatment, and can also help beach managers when selecting which method to adopt for remedial actions.