Development and performance evaluation of a UV-C coupled recirculation system for enhancing cistern water microbiological qualityABSTRACT
In semi-arid regions, the lack of adequate water treatment for human consumption frequently gives rise to intestinal disorders and, in more severe cases, severe microbial infections. In this context, many households depend on cistern water for their potable needs. This project aimed to develop and use a system composed of an ultraviolet C radiation-emitting lamp coupled to a water recirculation pump to ensure the bacteriological safety of cistern water. The recirculation system was operated for 6, 12, and 24 h, and tests were conducted using environmental samples or with E. coli ATCC 25922. The results demonstrated that the system could achieve 100% inhibition of the growth of total coliforms and thermotolerant coliforms after 6 h of operation. The low-cost system can potentially be a social technology, thereby ensuring water security in semi-arid regions that do not have public water distribution systems.
Keywords
potable water; semiarid; public policies; environmental sanitation; sustainable development goals
RESUMO
Nas regiões semiáridas, a ausência de tratamento adequado da água para consumo humano frequentemente dá origem a distúrbios intestinais e, em casos mais graves, a infecções microbianas severas. Nesse contexto, muitas famílias dependem da água de cisterna para suprir suas necessidades de água potável. Este projeto teve como objetivo desenvolver um sistema composto de uma lâmpada emissora de radiação UV-C acoplada a uma bomba de recirculação de água, a fim de garantir a segurança bacteriológica da água de cisternas. O sistema de recirculação foi operado por 6, 12 e 24 horas, e os testes foram realizados com amostras ambientais ou com Escherichia coli ATCC 25922. Os resultados demonstraram que o sistema foi capaz de alcançar 100% de inibição do crescimento de coliformes totais e coliformes termotolerantes após 6 horas de operação. O sistema de baixo custo apresenta potencial para atuar como uma tecnologia social, garantindo a segurança hídrica em regiões semiáridas onde não há sistema público de distribuição de água.
Palavras-chave
água potável; semiárido; políticas públicas; saneamento ambiental; objetivos de desenvolvimento sustentável
INTRODUCTION
Rainwater harvesting is common in many parts of the world (Alim et al., 2020). One way to store rainwater is through the use of cisterns, which provide water to families with no access to public supply systems (Iliopoulou et al., 2022; Cardoso Castro et al., 2024). Although it is considered a sustainable alternative to ensure water security, the consumption of cistern water can pose health risks to the population that consumes it (Hamilton et al., 2019).
Cisterns are usually low-cost structures built close to houses, where rainwater that falls on the roof is channeled and directed into the reservoir (Nogueira, 2017). The conditions for collecting and storing water can favor the growth of pathogenic microorganisms (Khan; AlMadani, 2017), and health control and education are needed to prevent diseases caused by the microbiological contamination of cistern water. Diarrhea is one of the diseases caused by microorganisms found in water not properly treated. It is estimated that diarrhea caused 1.17 million deaths worldwide in 2021 (GBD 2021 Diarrhoeal Diseases Collaborators, 2025), making it one of the leading causes of death among people of all ages. Taking into account estimates for children under five years of age, diarrhea is the fifth leading cause of death worldwide, with 446,000 deaths in 2016 (GBD 2016 Diarrhoeal Disease Collaborators, 2018).
Bacteria, protozoa, and viruses, represented by Escherichia coli, Giardia spp., and Rotavirus A, respectively, are microorganisms that cause infections (Lima et al., 2019; Pankov et al., 2019; Santos et al., 2019) leading to diarrhea in children in the Brazilian semi-arid region. Research by Hamilton et al. (2019) shows that rainwater collected from roofs and stored in tanks is contaminated with E. coli in 24 to 92% of samples. The use of chemical compounds to disinfect water is common, but their potential risks to human health are known.
Ultraviolet C (UV-C) radiation has a known antimicrobial effect when used to reduce the density of microorganisms in water (Makuei; Peleato, 2025) and air (Eisenlöffel et al., 2019). UV radiation emitted by low-power lamps has a low potential to form harmful by-products (Claus, 2021). UV-C radiation with a spectrum between 200 and 280 nm inactivates microorganisms by damaging their nucleic acids. The wavelength range of 250–270 nm is strongly absorbed by nucleic acids, making it highly effective for inducing cellular lethality or viral inactivation (Devitt et al., 2024). This is due to the peak absorption by DNA occurring near 260 nm (Wang et al., 2025). Most of the lethal effects of UV radiation on biological systems are attributed to photochemical changes in pyrimidine residues (Kittler; Löber, 1977; Fraikin et al., 2024).
There are several studies in the literature demonstrating the success of using UV-C radiation to control microbial growth on surfaces (Górny et al., 2024), in air (Reed, 2010; Guimera et al., 2018; Freire et al., 2024), and in water (Nelson et al., 2013; Kim et al., 2023). In terms of water disinfection, UV-C radiation is effective against several pathogenic species, including E. coli (Gross et al., 2015; Matsumoto et al., 2019; Sousa et al., 2024).
The use of UV-C radiation devices can reduce microbial density and consequently improve the quality of cistern water, making it potable from a microbiological point of view. The present study aimed to assemble a water recirculation system consisting of a water pump coupled to a device containing a UV-C lamp and to evaluate its efficiency in inactivating total and thermotolerant coliforms, including E. coli, in cistern water.
This study proposes a novel methodology by integrating a low-cost UV-C irradiation filter with a continuous water recirculation unit specifically designed for household cistern systems in semi-arid regions. In contrast to conventional UV treatment units, this prototype minimizes energy consumption, ensures uniform exposure of water to UV-C, and can be deployed in remote settings with no centralized treatment. This design constitutes a novel contribution to point-of-use water disinfection technologies, tailored to vulnerable communities.
MATERIALS AND METHODS
Structure and operation of the water recirculation system
Each recirculation unit was assembled to contain a 20-litre PVC barrel, a submersible water recirculation pump with a capacity of 150 L h-1, and a device including a 15W Osram® UVC tubular fluorescent lamp with peak emission at 254 nm and 7.800 cd of light intensity. Water flows unidirectionally between the surface of the lamp and a PVC tube into which it is inserted, with a maximum distance of 1 cm from the lamp when it enters the device, with enough volume for 180 mL of water. The recirculation pump located inside the drum was connected to the device containing the UV-C lamp through a silicone tube, with the other end of the device containing another tube that supplied water directly to the barrel (Figure 1).
Water recirculation system with type C ultraviolet radiation-emitting device in (a) front view and (b) front section, with indications of the constituent parts. 1. Barrel; 2. Silicone hose for water outlet; 3. Silicone hose for water return; 4. Device containing UV-C radiation-emitting lamp; 5. Water to be recirculated; 6. Recirculation pump; 7. PVC pipe; 8. UV-C radiation-emitting lamp; 9. Lamp ballast; 10. Water inlet hose connector; 11. Water outlet hose connector.
Study site and sampling
Water samples were collected from concrete cisterns used to store rainwater at five sites in the interior of the states of Ceará and Piauí, Brazil (Figure 2). Approximately 45 liters of water were collected at each sampling time and immediately sent for experimental setup and physicochemical analysis.
Geographical localization of (a) Ceará, Brazil; and (b) geographical distribution of cistern sampling sites.
Physicochemical analysis
The collected samples were analyzed for pH, chloride concentration, electrical conductivity, turbidity, total hardness, total alkalinity, and calcium content. pH, electrical conductivity, and turbidity were determined using a LUCA-210 pH meter (Lucadema), an AT-255 microprocessor-based conductivity meter (Alfakit), and a 2020we portable turbidity meter (LaMotte), respectively. The remaining parameters were quantified according to the methods described in the Standard Methods for the Examination of Water and Wastewater (APHA, 2023).
Carrying out experiments with recirculation
Before the experiments, the entire system was disinfected with 0.1% (v/v) sodium hypochlorite. For each experiment, a set of four tanks was used, including a “control” tank in which the water was recirculated but without activation of the UV-C lamp (No UV treatment) and three others in which UV radiation was kept on to obtain samples after 6, 12, and 24 h of continuous operation (UV treatments). Each barrel received 10 L of water from the same cistern, and the water was circulated at 150 L h-1. The barrels were kept closed, and the laboratory was dark throughout the experiment. After each interval, water samples were taken in triplicate and then subjected to microbiological analysis.
Microbiological analysis
Cultivable heterotrophic bacteria
Aliquots of 1.0 mL were used to perform the pour plate technique on R2A agar (Himedia®) containing 0.64% fluconazole (to inhibit fungal colony growth). Cultures were performed in triplicate using samples from three of the five cisterns evaluated. Plates were incubated at 30°C for 48 h, and the colonies obtained were counted.
Total and thermotolerant coliforms
Total and thermotolerant coliforms were determined according to the method described by the American Public Health Association (APHA, 2023). Presumptive tests were performed using tubes containing lactose broth (Himedia®). Confirmatory tests were performed using tubes containing Brilliant Green broth 2% (Himedia®) and EC broth (Himedia®) to detect total and thermotolerant coliforms, respectively. Analyses were performed using the most probable number method (MPN.100 mL-1) with Durham tubes inverted in the medium to detect gas production. As a control (time 0 h), microbiological analyses were performed on the water from the cisterns as soon as it arrived at the laboratory.
Typical Escherichia coli cells
Aliquots of 100 mL of water were vacuum-filtered through 0.45 μm pore filter membranes designed to retain bacterial cells. The membranes were transferred to Petri dishes containing eosin-methylene blue agar (Himedia®). Plates were incubated at 37°C for 24 h, followed by colony counting. Analyses were performed in triplicate for each time the system was irradiated with UV-C radiation.
Assays with Escherichia coli ATCC 25922
Determination of the growth curve for E. coli ATCC 25922
First, E. coli ATCC 25922 was activated in TSA medium (Himedia®) with incubation at 37°C for 24 h. After obtaining isolated colonies, one was inoculated into 50 mL of nutrient broth (Himedia®) in a 125 mL Erlenmeyer flask to obtain a pre-inoculum. The incubation was carried out with shaking at 37°C for 24 h. The absorbance was measured in a spectrophotometer at 600 nm, and the pre-inoculum was added to an Erlenmeyer flask containing 400 mL of nutrient broth (Himedia®) in a volume sufficient to obtain an OD600 of 0.05. Incubation was carried out at 37°C with shaking for 24 h. Every two hours, a 3 mL aliquot of the culture was taken to determine the absorbance at 600 nm and measure the bacterial growth curve.
Preparation of mesocosms with Escherichia coli ATCC 25922
After preparation and sterilization of 40 L of 0.1% peptone water, each barrel received 10 L. At the same time, E. coli ATCC 25922 cells were grown as described in 2.3.1 to log phase, then washed and centrifuged at 6,000 rpm for 5 min. The supernatant was discarded, and the sedimented cells were resuspended in sterile 0.9% saline using a vortex mixer. This procedure was repeated two more times. The resuspended contents were assayed for absorbance at 600 nm, and 1 mL of the saline solution containing cells with an OD600 of 0.05 was added to each tube. The experiment was carried out according to the methodology described in point 2.2.2. To obtain the representative sample at time 0h (control), the system was left to run for 10 min without UV-C irradiation to allow for cell homogenization. Aliquots were then taken for analysis.
Microbiological analysis
Thermotolerant coliforms
The most probable number (MPN) was determined following the procedures outlined in section 2.2.3.2, with E. coli cells serving as the sole representatives of thermotolerant coliforms in the experiment.
Prokaryotic density
Samples were fixed in 2% neutral buffered formaldehyde and stored for later filtration through 0.22 μm polycarbonate membrane filters. Although paraformaldehyde is commonly used, formaldehyde fixation has been demonstrated to be suitable for fluorescence in situ hybridization (FISH) analysis in similar environmental samples (Roller et al., 1994). FISH was used to quantify E. coli ATCC 25922 cells using the ENT183 probe (Friedrich et al., 2003). The hybridization procedure was performed according to Del’Duca et al. (2013), using 20% formamide and NaCl concentrations for hybridization and washing, respectively. A generic probe was used as a negative control. The probes were labeled with Cy3 fluorochrome. Prokaryotic density was determined by evaluating ten random fields using an Olympus BX60 epifluorescence microscope (Olympus, Japan) equipped with Chroma U-N41007, U-MWU2, and U-MWG2 filters. Total prokaryotic density was determined by staining with 4’,6-diamidino-2-phenylindole — DAPI (Hobbie et al., 1977), following the methodology described by Porter and Feig (1980).
Statistical analysis
Statistical analyses were conducted using SigmaPlot 12.0 software. Data distribution was assessed for normality using the Shapiro-Wilk test. Subsequently, comparisons were performed using Dunnett’s test or t-test at a significance level of 5%.
RESULTS AND DISCUSSION
Physicochemical parameters
The analysis of the physicochemical data revealed that only one of the water samples did not have the basic pH value, with an average value of 8.3 ± 0.86 (Table 1). Concerning the conductivity data, a variation was observed from 15.5 to 159.8 μS cm-1. The turbidity values ranged from 0.2 to 1.16 NTU, while the chlorides occurred at an average of 9.6 ± 4.17 mg L-1. The alkalinity and hardness data indicate that the water stored in the evaluated cisterns is primarily influenced by calcium-containing compounds (Natalli et al., 2021), which act as alkaline agents, increasing the pH of the water. This effect likely results from the gradual leaching of calcium from the cement used to build the cisterns.
Physicochemical parameters evaluated in the water from the cisterns used in the present study.
During the evaluation process, the Guideline for Drinking Water Quality (WHO, 2017) was utilized to establish limits for conductivity, chlorides, and turbidity, with maximum values of 2,000 μS cm-1, 250 mg L-1, and 5.0 NTU, respectively, and a pH range between 6.5 and 8.5. Accordingly, the World Health Organization (2017) asserts that cistern water has good physical-chemical quality for human consumption.
When considering UV-C radiation for water disinfection, turbidity is recognized in the literature as one of the physical-chemical parameters that cause the most significant interference. Research has demonstrated that elevated turbidity levels can substantially compromise the efficacy of UV disinfection systems. Nourmoradi et al. (2012) performed experiments using a UV reactor and observed that increasing turbidity from 1 to 5 NTU resulted in a 0.2 to 0.5 log reduction in microbial inactivation. Wu and Doan (2005) observed a similar decline in disinfection efficiency as turbidity increased within the same range.
Evaluating cistern water system effectiveness
After evaluating the density of heterotrophic bacteria, the average values showed a significant variation between the system operating when UV radiation was applied and when compared to the control (system operating without UV radiation) (Figure 3). Considering the density of heterotrophic bacteria found in the water immediately after sampling, according to the Dunnett’s test at 5% probability, only the 6-h treatment in the recirculation system promoted a significant reduction in the density of these microorganisms, causing an average reduction of 99.6%, considering the average data of the water from the cisterns evaluated (Figure 3a). When the system is operated without UV radiation, bacterial density tends to increase. This is probably due to the movement of the water, which increases the availability of oxygen and promotes metabolic activity and population growth of heterotrophic bacterial groups (Chen et al., 2024).
Density of total heterotrophic bacteria considering the (a) mean value of the densities evaluated for water from three cisterns, whose statistical analyses demonstrated that for all the time points assessed, they were statistically different, comparing the treatments with (UV) and without exposure (NoUV) to UV radiation. Considering each cistern as an experimental unit, the density values were statistically different for (b) cistern 1, (c) cistern 2, and (d) cistern 3 at the same time point, considering the UV and NoUV treatments.
The experiments were conducted under dark conditions to prevent photoreactivation, a process that has been demonstrated to reverse specific types of UV damage (Wozniak; Simmons, 2022). However, it is important to note that bacterial DNA damage repair mechanisms function through various pathways that do not depend on light. These mechanisms are crucial for maintaining genomic integrity in response to diverse DNA lesions caused by environmental factors. Key repair pathways include direct reversal, base excision repair, nucleotide excision repair, and double-strand break repair, each employing distinct proteins and processes to address specific types of damage (Rastogi et al., 2010; Svanishvili, 2024). This may provide a rationale for the increase in the number of heterotrophic bacteria quantified after 12 h and 24 h of system operation.
The data for total and thermotolerant coliforms show that the recirculation system combined with UV radiation was effective across all the exposure times tested (Table 2). In all treatments, for all cisterns, no bacterial growth was observed at any dilution level tested using the multiple-tube technique. Despite the lack of a consensus microorganism that can be universally established as an indicator of microbiological water quality, certain microbial groups are widely used for this purpose, with total coliforms and fecal coliforms being the most commonly used (AWWA, 1998; Wen et al., 2020). In the present study, a significant reduction in the concentration of the microorganisms analyzed was observed in all the time intervals evaluated, demonstrating that even in the shortest time of exposure to the equipment (6h), the water showed satisfactory microbiological quality, according to the Guideline for Drinking Water Quality (WHO, 2017)
Density of total coliforms and thermotolerant coliforms (MPN.mL-1) in aliquots of water obtained from cisterns at 0h (Control) and after 6, 12, and 24 h. The same water kept in a closed recirculation system coupled to a type C ultraviolet radiation emitting system.
Adhikari et al. (2020) indicate that turbidity can interfere with the effectiveness of UV radiation in inactivating E. coli in water. According to the results obtained in the present study, the range between 0.2 and 1.17 NTU was not large enough to interfere with the effectiveness of the radiation applied to reduce total and thermotolerant coliforms. This is evidenced by the fact that the results are the same for all system recirculation times, regardless of the turbidity level of the samples.
Concerning the analysis of typical E. coli cells performed employing the filter membrane technique, the results demonstrated system effectiveness in inactivating the cells at all the time points evaluated (Table 3).
Density of typical E. coli cells (cells.100 mL-1) estimated from the membrane technique in aliquots of water obtained from cisterns at 0h (Control), and after 6h, 12h, and 24h from the same water kept in a closed recirculation system coupled to a type C UV radiation-emitting system.
Although the system demonstrated high disinfection efficiency at 6 h, the increase in heterotrophic bacteria observed after 12 and 24 h indicates that prolonged recirculation may stimulate microbial metabolism due to increased oxygen availability or allow recovery through dark repair mechanisms. This represents a limitation regarding long-term operation. Future studies should therefore investigate system performance in environments with longer water residence times and explore design improvements, such as increasing UV dose, adding multiple irradiation chambers, or reducing lamp–water distance, to optimize disinfection under extended operation.
Preliminary cost analysis indicates that building a UV-C recirculation system would require approximately R$ 300 (US$ 55). The operational energy consumption of the system is 6 W for the water pump and 15 W for the UVC fluorescent lamp per treatment cycle, amounting to 0.126 kWh. This renders the system economically viable for low-income households. Furthermore, the use of UV-C disinfection precludes the generation of chemical residues and by-products concomitant with chlorination (Claus, 2021; Wang et al., 2024), thus offering an option that is more environmentally safe.
System evaluation with Escherichia coli ATCC 25922
After contaminating 0.1% peptone water with E. coli ATCC 25922 and introducing it into the recirculation systems—both with and without UV-C radiation—the initial quantification of thermotolerant coliforms was conducted by measuring the E. coli density, which was found to be 2.4 × 103 MPN mL-1 (Figure 4). Following the initiation of system operation, a statistically significant variation was observed between the treatments containing or not UV radiation (UV × NoUV). During the 6-h operating period of the system with UV radiation, no positive tubes for thermotolerant coliform growth were detected. In contrast, the quantification of thermotolerant coliforms reached 7.5 × 104 MPN mL-1 when the system operated without UV radiation. A similar outcome was observed in the 12-h UV treatment, while the 12-h NoUV treatment resulted in data points exceeding 1.1 × 106 MPN.mL-1. After 24 h of operation, the NoUV system maintained a thermotolerant coliform density above 1.1 x 10⁶ MPN.mL-1, whereas the UV system effectively controlled these coliforms, with a quantified density of 83.6 MPN mL-1.
Densities of thermotolerant coliforms determined in water recirculation systems with (UV) and without UV radiation (NoUV) at different operating times after contamination with E. coli ATCC 25922. The values at each point on the graph refer to the density data (MPN.mL-1) of thermotolerant coliforms.
The lack of microbial growth in the tests conducted after 6 h and 12 h confirms the system’s effectiveness in inactivating total and thermotolerant coliforms, using E. coli as the indicator microorganism. After 12 h of system operation without UV-C radiation, an increase in the density of thermotolerant coliforms (represented by E. coli) was observed, although the exact magnitude of this increase could not be accurately quantified. This finding suggests that UV-C radiation may have been the factor responsible for regulating the population under study. The quantification of 83.6 MPN.mL-1 of thermotolerant coliforms after 24 h of UV-C treatment may be attributable to the heightened sensitivity of E. coli population to radiation during the exponential growth phase. However, after repeated exposure cycles, genomic adaptation can lead to increased resistance to UV radiation (Selveshwari et al., 2021). Moreover, Maghsoodi et al. (2022) demonstrated that E. coli strains can repair DNA damage even in the absence of light, independent of photoreactivation, enabling some cells to remain viable post-repair despite dark conditions. Furthermore, Recacha et al. (2024) identified several light-independent repair genes in the genome of strain ATCC 25922, including recA, recB, lexA, uvrA and uvrB. The expression of these and other genes involved in the response to UV-C-induced damage explains the detection of cells 48 h after treatment in the recirculation system.
By direct counting using DAPI, the average density of prokaryotic cells was initially quantified at 0.34 × 106 cells.mL-1. Similarly, by FISH using the ENT183 probe, which allows the quantification of members of the Enterobacteriaceae family, we attempted to quantify the population of E. coli ATCC 25922 cells introduced into the system, resulting in an initial density of 0.14 × 106 cells.mL-1. As shown in Figure 5, during the first 6 h of system operation, there is a significant difference in the density of both prokaryotic cells and Enterobacteriaceae representatives, according to the t-test at 5% probability. Only for prokaryotic cells, the difference does not occur for the 12-h period. The direct counting data, both for total prokaryotic cells and for Enterobacteriaceae, confirm the effectiveness of the system.
Density of (a) prokaryotic cells and (b) Enterobacteriaceae cells in the experiments conducted in the presence (UV) and absence (NoUV) of ultraviolet radiation. Asterisks indicate a significant difference for the same time point according to the t-test at 5% probability.
The efficacy is even more evident if we look specifically at the initial time (0 h) of the 6-h UV treatment (Figure 6). In this case, a significant reduction is observed for both prokaryotic cells and representatives of Enterobacteriaceae. After 6 h of operation of the recirculation system with UV-C, there is a reduction of prokaryotic cells and Enterobacteriaceae to 0.13 × 106 and 0.03 × 106 cells.mL-1, respectively. This represents 60.77% for prokaryotic cells and 76.21% for Enterobacteriaceae. Considering that the system was disinfected and E. coli ATCC 25922 cells were added as a representative of Enterobacteriaceae, a 76.21% reduction in E. coli density is indicated in the system after 6 h of recirculation.
Density of prokaryotic and Enterobacteriaceae cells at the beginning of the experiment (0 h) and after 6 h of recirculation with ultraviolet radiation. There is a statistically significant difference according to the t-test at 5% probability in cell densities between the two time points for both prokaryotic cells and Enterobacteriaceae cells.
Comparing the quantification of thermotolerant coliforms with that of prokaryotic cells and Enterobacteriaceae under UV irradiation, a variation in the magnitude of the data is observed. While for thermotolerant coliforms there is an increase only during the 24 h treatment, and even then with a most probable number of 83.6 cells.mL-1, the microbial density by direct count indicates a greater growth over time. With 12-h recirculation, even with the presence of UV radiation, there was an increase in the total number of prokaryotic cells from 0.34 to 2.16 × 106 cells.mL-1, an increase of 6.35x. Considering the 24-h period, the increase was 19-fold, as the density increased to 6.47 × 106 cells.mL-1. The same occurred for Enterobacteriaceae cells, which increased 2.85x (0.4 × 106 cells.mL-1) and 47.85x (6.7 × 106 cells.mL-1) for the 12 and 24 h times, respectively.
These variations indicate that although the system is functional for a recirculation time of 6 h, times longer than this do not contribute to improved microbiological quality of the water, but rather result in an increase in both cultivable and non-cultivable microbial populations. The differences between cultivation data and direct microbial enumeration data (Figure 7) indicate that the abiotic conditions of the recirculation system maintain a large proportion of cells in VBNC state.
Density of cultivable and non-cultivable microbial cells after contamination with E. coli ATCC 25922 cells at the initial time and different treatment times in the water recirculation system exposed to UV-C radiation, quantified using three different methods.
Considering the reductions in microbial densities observed between the initial time point and after 6 h of exposure to UV-C radiation in the recirculation system, which demonstrated higher disinfection efficiency, several notable trends were identified. A 2.5-fold decrease was detected in the total prokaryotic cell density, as determined by DAPI staining. The density of Enterobacteriaceae, represented by E. coli ATCC 25922 cells introduced as contaminants, showed a 4.2-fold reduction based on the FISH method using the Ent183 probe. Additionally, there was at least an 800-fold decrease in the density of thermotolerant coliforms, also represented by ATCC 25922, as quantification yielded values below 3.0 MPN.mL-1. After 24 h, the reappearance of coliforms detected by the Most Probable Number (MPN) method indicated that a portion of the bacterial population either survived UV-C exposure or repaired DNA damage. This suggests that some cells remained in a VBNC state. The observed discrepancy between the reduction in cultivable cells and the total cell counts, which include non-culturable cells, under identical experimental conditions supports this hypothesis, indicating a potential induction of the VBNC state by the recirculation system.
The discrepancy between cultivation-based and direct cell counting methods may lead to an underestimation of microbiological risk in water samples intended for human consumption (Hammes; Egli, 2005; Angelescu et al., 2024). Moreover, the use of specific probes in the FISH technique — such as ENT183, employed in this study to quantify E. coli — enhances the accuracy of detecting target groups, even when these bacteria are unable to form colonies on culture media (Del’Duca et al., 2013). As demonstrated by Oliver (2010), exclusive reliance on cultivation-independent methods may overlook the persistence of microorganisms in the VBNC state. Therefore, the integration of multiple analytical approaches is essential for accurately evaluating the true effectiveness of disinfection systems, such as the one examined in this study.
UV radiation induces a VBNC state in E. coli, characterized by a loss of culturability while retaining metabolic activity (Zhang et al., 2018; Xiao et al., 2025). Recently, the use of UV radiation for water disinfection has been reported as a contributing factor in maintaining E. coli in the VBNC state (Zhu et al., 2022). The presence of VBNC E. coli in treated water can lead to an underestimation of health risks associated with drinking water (Gehr, 2015), as these cells are capable of producing toxins while in the VBNC state. Some lineages, however, remain avirulent during this state but can regain virulence upon resuscitation (Pienaar et al., 2016).
The present findings contribute to advancing point-of-use UV-C disinfection technologies by providing empirical evidence of efficacy under real cistern water conditions. This is highly relevant for public health, particularly in low-income semi-arid regions where water insecurity and diarrheal disease burdens remain elevated. Beyond academic contributions, the system has strong potential for deployment in rural communities, schools, and emergency contexts.
Future studies should evaluate long-term operational stability, assess performance in large-volume cisterns with extended residence times, integrate renewable-energy sources such as solar panels, and conduct field validation in communities with chronic water scarcity.
CONCLUSIONS
Based on these findings, a 6-h recirculation time is the most advantageous option for water disinfection. It reduces time and energy consumption, effectively controls heterotrophic bacteria, total and thermotolerant coliforms, and lowers the risk of UV-C-resistant mutant development, as well as the growth of culturable and viable but non-culturable (VBNC) cells. The disinfection technology developed and presented in this study offers a practical solution for ensuring microbiologically safe access to cistern water, directly enhancing community health autonomy and water security. This initiative aligns with multiple Sustainable Development Goals, particularly SDG 6 — Clean Water and Sanitation, and SDG 3 — Good Health and Well-being, by promoting resilient and sustainable access to safe water in conditions of environmental vulnerability.
ACKNOWLEDGMENTS
We thank Cassiano Ricardo de Souza for providing the georeferenced map. We also thank Manoel Paiva de Araújo Neto for providing E. coli ATCC 25922.
DATA AVAILABILITY STATEMENT
Data will be made available on request.
REFERENCES
-
ADHIKARI, Achyut; PARRAGA ESTRADA, Katheryn J.; CHHETRI, Vijay S.; JANES, Marlene; FONTENOT, Kathryn; BEAULIEU, John C. Evaluation of ultraviolet (UV-C) light treatment for microbial inactivation in agricultural waters with different levels of turbidity. Food Science & Nutrition, v. 8, n. 2, p. 1237-1243, 2020. https://doi.org/10.1002/fsn3.1412
» https://doi.org/10.1002/fsn3.1412 -
ALIM, Mohammad A.; RAHMAN, Ataur; TAO, Zhong; SAMALI, Bijan; KHAN, Muhammad M.; SHIRIN, Shafiq. Suitability of roof harvested rainwater for potential potable water production: A scoping review. Journal of Cleaner Production, v. 248, 119226, 2020. https://doi.org/10.1016/j.jclepro.2019.119226
» https://doi.org/10.1016/j.jclepro.2019.119226 - AMERICAN PUBLIC HEALTH ASSOCIATION (APHA). Standard Methods for the Examination of Water and Wastewater 24. ed. Washington, D.C.: APHA, 2023.
- AMERICAN WATER WORKS ASSOCIATION (AWWA). Using reclaimed water to augment potable water resources New York: American Water Works Association, 1998.
-
ANGELESCU, Dan E.; ABI-SAAB, David; GANAYE, Raphael; WANLESS, David; WONG, Joyce. Addressing underestimation of waterborne disease risks due to fecal indicator bacteria bound in aggregates. Journal of Applied Microbiology, v. 135, n. 11, lxae280, 2024. https://doi.org/10.1093/jambio/lxae280
» https://doi.org/10.1093/jambio/lxae280 -
CARDOSO CASTRO, Pedro Pablo; VACHKOVA, Maya; RAVENA, Nirvia; VELOSO, Nircele. The One Million Cisterns Programme—a viability assessment of community rainwater management in Brazil. Frontiers in Sustainability, v. 5, 1401440, 2024. https://doi.org/10.3389/frsus.2024.1401440
» https://doi.org/10.3389/frsus.2024.1401440 -
CHEN, Fan; HUANG, Tinglin; WEN, Gang; LI, Kai. Impact of artificial mixing and oxygenation on bacteria in a water transfer reservoir: Community succession and the role in water quality improvement. Science of The Total Environment, v. 908, 168581, 2024. https://doi.org/10.1016/j.scitotenv.2023.168581
» https://doi.org/10.1016/j.scitotenv.2023.168581 -
CLAUS, Holger. Ozone generation by ultraviolet lamps. Photochemistry and Photobiology, v. 97, n. 3, p. 471-476, 2021. https://doi.org/10.1111/php.13391
» https://doi.org/10.1111/php.13391 -
DEL’DUCA, Alessandro; EVANGELISTA CESAR, Dionéia; GALUPPO DINIZ, Cláudio; ABREU, Paulo César. Evaluation of the presence and efficiency of potential probiotic bacteria in the gut of tilapia (Oreochromis niloticus) using the fluorescent in situ hybridization technique. Aquaculture, v. 388-391, p. 115-121, 2013. https://doi.org/10.1016/j.aquaculture.2013.01.019
» https://doi.org/10.1016/j.aquaculture.2013.01.019 -
DEVITT, George; JOHNSON, Peter B.; HANRAHAN, Niall; LANE, Simon I. R.; VIDALE, Magdalena C.; SHETH, Bhavwanti; ALLEN, Joel D.; HUMBERT, Maria V.; SPALLUTO, Cosma M.; HERVÉ, Rodolphe C.; STAPLES, Karl; WEST, Jonathan J.; FORSTER, Robert; DIVECHA, Nullin; MCCORMICK, Christopher J.; CRISPIN, Max; HEMPLER, Nils; MALCOLM, Graeme P. A.; MAHAJAN, Sumeet. Mechanisms of SARS-CoV-2 Inactivation Using UVC Laser Radiation. ACS Photonics, v. 11, n. 1, p. 42-52, 2024. https://doi.org/10.1021/acsphotonics.3c00828
» https://doi.org/10.1021/acsphotonics.3c00828 -
EISENLÖFFEL, Lisa; REUTTER, Tobias; HORN, Matthias; SCHLEGEL, Simon; TRUYEN, Uwe; SPECK, Stephanie. Impact of UVC-sustained recirculating air filtration on airborne bacteria and dust in a pig facility. PLoS One, v. 14, n. 11, e0225047, 2019. https://doi.org/10.1371/journal.pone.0225047
» https://doi.org/10.1371/journal.pone.0225047 -
FRAIKIN, G. Ya.; BELENIKINA, N. S.; RUBIN, A. B. Photochemical processes to cellular DNA damage by UV radiation of different wavelengths: biological consequences. Молекулярная биология, v. 58, n. 1, p. 3-21, 2024. https://doi.org/10.31857/S0026898424010019
» https://doi.org/10.31857/S0026898424010019 -
FREIRE, Joana de Oliveira Pantoja; PAES, Graciele Oroski; GONZALEZ, Christiany Moçali; BARREIROS, Maria da Gloria Carvalho; FERREIRA, Adriana Lucia Pires. UVC light as a strategy for disinfection of hospital air and surfaces. Acta Paulista de Enfermagem, v. 37, eAPE002191, 2024. https://doi.org/10.37689/acta-ape/2024AO000121911
» https://doi.org/10.37689/acta-ape/2024AO000121911 -
FRIEDRICH, Udo; VAN LANGENHOVE, Herman; ALTENDORF, Karlheinz; LIPSKI, André. Microbial community and physicochemical analysis of an industrial waste gas biofilter and design of 16S rRNA-targeting oligonucleotide probes. Environmental Microbiology, v. 5, n. 3, p. 183-201, 2003. https://doi.org/10.1046/j.1462-2920.2003.00397.x
» https://doi.org/10.1046/j.1462-2920.2003.00397.x -
GBD 2016 DIARRHOEAL DISEASE COLLABORATORS. Estimates of the global, regional, and national morbidity, mortality, and aetiologies of diarrhoea in 195 countries: a systematic analysis for the Global Burden of Disease Study 2016. The Lancet Infectious Diseases, v. 18, n. 11, p. 1211-1228, 2018. https://doi.org/10.1016/s1473-3099(18)30362-1
» https://doi.org/10.1016/s1473-3099(18)30362-1 -
GBD 2021 DIARRHOEAL DISEASES COLLABORATORS. Global, regional, and national age-sex-specific burden of diarrhoeal diseases, their risk factors, and aetiologies, 1990–2021, for 204 countries and territories: a systematic analysis for the Global Burden of Disease Study 2021. The Lancet Infectious Diseases, v. 25, n. 5, p. 519-536, 2025. https://doi.org/10.1016/S1473-3099(24)00691-1
» https://doi.org/10.1016/S1473-3099(24)00691-1 -
GEHR, Ronald. Comment on “UV disinfection induces a Vbnc state in Escherichia coli and Pseudomonas aeruginosa”. Environmental Science & Technology, v. 49, n. 17, p. 10750-10751, 2015. https://doi.org/10.1021/acs.est.5b02534
» https://doi.org/10.1021/acs.est.5b02534 -
GÓRNY, Rafał L.; GOŁOFIT-SZYMCZAK, Małgorzata; PAWLAK, Andrzej; ŁAWNICZEK-WAŁCZYK, Anna; CYPROWSKI, Marcin; STOBNICKA, Agata; PŁOCIŃSKA, Magdalena; KOWALSKA, Joanna. Effectiveness of UV-C radiation in inactivation of microorganisms on materials with different surface structures. Annals of Agricultural and Environmental Medicine, v. 31, n. 2, p. 287-293, 2024. https://doi.org/10.26444/aaem/189695
» https://doi.org/10.26444/aaem/189695 -
GROSS, Andrej; STANGL, Felix; HOENES, Katharina; SIFT, Michael; HESSLING, Martin. Improved drinking water disinfection with UVC-LEDs for Escherichia coli and Bacillus subtilis utilizing quartz tubes as light guide. Water, v. 7, n. 9, p. 4605-4621, 2015. https://doi.org/10.3390/w7094605
» https://doi.org/10.3390/w7094605 -
GUIMERA, Don; TRZIL, Jean; JOYNER, Joy; HYSMITH, Nicholas D. Effectiveness of a shielded ultraviolet C air disinfection system in an inpatient pharmacy of a tertiary care children’s hospital. American Journal of Infection Control, v. 46, n. 2, p. 223-225, 2018. https://doi.org/10.1016/j.ajic.2017.07.026
» https://doi.org/10.1016/j.ajic.2017.07.026 -
HAMILTON, Kerry; REYNEKE, Brandon; WASO, Monique; CLEMENTS, Tanya; NDLOVU, Thando; KHAN, Wesaal; DIGIOVANNI, Kimberly; RAKESTRAW, Emma; MONTALTO, Franco; HAAS, Charles N.; AHMED, Warish. A global review of the microbiological quality and potential health risks associated with roof-harvested rainwater tanks. npj Clean Water, v. 2, p. 7, 2019. https://doi.org/10.1038/s41545-019-0030-5
» https://doi.org/10.1038/s41545-019-0030-5 -
HAMMES, Frederik A.; EGLI, Thomas. New method for assimilable organic carbon determination using flow-cytometric enumeration and a natural microbial consortium as inoculum. Environmental Science & Technology, v. 39, n. 9, p. 3289-3294, 2005. https://doi.org/10.1021/es048277c
» https://doi.org/10.1021/es048277c -
HOBBIE, John E.; DALEY, Ryan J.; JASPER, Smitha. Use of nuclepore filters for counting bacteria by fluorescence microscopy. Applied and Environmental Microbiology, v. 33, n. 5, p. 1225-1228, 1977. https://doi.org/10.1128/aem.33.5.1225-1228.1977
» https://doi.org/10.1128/aem.33.5.1225-1228.1977 -
ILIOPOULOU, Theano; DIMITRIADIS, Panayiotis; SIGANOU, Aimilia; MARKANTONIS, David; MORAITI, Konstantina; NIKOLINAKOU, Maria; MELETOPOULOS, Ilias Taygetos; MAMASSIS, Nikos; KOUTSOYIANNIS, Demetris; SARGENTIS, G.-Fivos. Modern use of traditional rainwater harvesting practices: an assessment of cisterns’ water supply potential in West Mani, Greece. Heritage, v. 5, n. 4, p. 2944-2954, 2022. https://doi.org/10.3390/heritage5040152
» https://doi.org/10.3390/heritage5040152 -
KHAN, Munawwar Ali; ALMADANI, Asma Mohammad Abdulrahman Ahmad. Assessment of microbial quality in household water tanks in Dubai, United Arab Emirates. Environmental Engineering Research, v. 22, n. 1, p. 55-60, 2017. https://doi.org/10.4491/eer.2016.051
» https://doi.org/10.4491/eer.2016.051 -
KIM, Hyun-Joong; YOON, Hee-Won; LEE, Min-A; KIM, Young-Hoon; LEE, Chang Joo. Impact of UV-C irradiation on bacterial disinfection in a drinking water purification system. Journal of Microbiology and Biotechnology, v. 33, n. 1, p. 106-113, 2023. https://doi.org/10.4014/jmb.2211.11027
» https://doi.org/10.4014/jmb.2211.11027 - KITTLER, Leonhard; LÖBER, Günter. Photochemistry of the nucleic acids. In: SMITH, Kendric C. (org.). Photochemical and photobiological reviews Boston: Springer US, 1977, p. 39-131.
-
LIMA, Aldo A. M.; OLIVEIRA, Domingos B.; QUETZ, Josiane S.; HAVT, Alexandre; PRATA, Mara M. G.; LIMA, Ila F. N.; SOARES, Alberto M.; FILHO, José Q.; LIMA, Noélia L.; MEDEIROS, Pedro H. Q. S.; SANTOS, Ana K. S.; VERAS, Herlice N.; GONDIM, Rafhaella N. D. G.; PANKOV, Rafaela C.; BONA, Mariana D.; RODRIGUES, Francisco A. P.; MOREIRA, Renato A.; MOREIRA, Ana C. O. M.; BERTOLINI, Marcelo; BERTOLINI, Luciana R.; FREITAS, Vicente J. F.; HOUPT, Eric R.; GUERRANT, Richard L. Etiology and severity of diarrheal diseases in infants at the semiarid region of Brazil: A case-control study. PLoS Neglected Tropical Diseases, v. 13, n. 2, e0007154, 2019. https://doi.org/10.1371/journal.pntd.0007154
» https://doi.org/10.1371/journal.pntd.0007154 -
MAGHSOODI, Mostafa; LOWRY, Grace L.; SMITH, Ian M.; SNOW, Samuel D. Evaluation of parameters governing dark and photo-repair in UVC-irradiated Escherichia coli Environmental Science: Water Research & Technology, v. 8, n. 2, p. 407-418, 2022. https://doi.org/10.1039/D1EW00644D
» https://doi.org/10.1039/D1EW00644D -
MAKUEI, Mehrnaz Soleimanpour; PELEATO, Nicolas. Manipulation of particle microorganism association for improved UV disinfection of surface waters. Scientific Reports, v. 15, n. 1, 17798, 2025. https://doi.org/10.1038/s41598-025-01101-3
» https://doi.org/10.1038/s41598-025-01101-3 -
MATSUMOTO, Takahiro; TATSUNO, Ichiro; HASEGAWA, Tadao. Instantaneous water purification by deep ultraviolet light in water waveguide: Escherichia coli bacteria disinfection. Water, v. 11, n. 5, p. 968, 2019. https://doi.org/10.3390/w11050968
» https://doi.org/10.3390/w11050968 -
NATALLI, Juliana Fadini; THOMAZ, Eduardo Christo Silveira; MENDES, Júlia Castro; PEIXOTO, Ricardo André Fiorotti. A review on the evolution of Portland cement and chemical admixtures in Brazil. Revista IBRACON de Estruturas e Materiais, v. 14, n. 6, e14603, 2021. https://doi.org/10.1590/S1983-41952021000600003
» https://doi.org/10.1590/S1983-41952021000600003 -
NELSON, Kristina Y.; MCMARTIN, Dena W.; YOST, Christopher K.; RUNTZ, Ken J.; ONO, Takaya. Point-of-use water disinfection using UV light-emitting diodes to reduce bacterial contamination. Environmental Science and Pollution Research, v. 20, n. 8, p. 5441-5448, 2013. https://doi.org/10.1007/s11356-013-1564-6
» https://doi.org/10.1007/s11356-013-1564-6 -
NOGUEIRA, Daniela. Segurança hídrica, adaptação e gênero. Sustentabilidade em Debate, v. 8, n. 3, p. 22-36, 2017. https://doi.org/10.18472/SustDeb.v8n3.2017.26544
» https://doi.org/10.18472/SustDeb.v8n3.2017.26544 -
NOURMORADI, Heshmatollah; NIKAEEN, Mahnaz; STENSVOLD, Christen R.; MIRHENDI, Hossein. Ultraviolet irradiation: An effective inactivation method of Aspergillus spp. in water for the control of waterborne nosocomial aspergillosis. Water Research, v. 46, n. 18, p. 5935-5940, 2012. https://doi.org/10.1016/j.watres.2012.08.015
» https://doi.org/10.1016/j.watres.2012.08.015 -
OLIVER, James D. Recent findings on the viable but nonculturable state in pathogenic bacteria. FEMS Microbiology Reviews, v. 34, n. 4, p. 415-425, 2010. https://doi.org/10.1111/j.1574-6976.2009.00200.x
» https://doi.org/10.1111/j.1574-6976.2009.00200.x -
PANKOV, Rafaela C.; GONDIM, Rafhaella N. D. G.; PRATA, Mara M. G.; MEDEIROS, Pedro H. Q. S.; VERAS, Herlice N.; SANTOS, Ana K. S.; HAVT, Alexandre; SILVA, Marcelle F. M. da; FUMIAN, Tulio M.; MIAGOSTOVICH, Marize P.; LEITE, José P. G.; LIMA, Aldo A. M. Rotavirus A infections in community childhood diarrhea in the Brazilian semiarid region during postvaccination era. Journal of Pediatric Gastroenterology and Nutrition, v. 69, n. 4, p. e91-e98, 2019. https://doi.org/10.1097/mpg.0000000000002416
» https://doi.org/10.1097/mpg.0000000000002416 -
PIENAAR, Jennifer A.; SINGH, Atheesha; BARNARD, Tobias G. The viable but non-culturable state in pathogenic Escherichia coli: A general review. African Journal of Laboratory Medicine, v. 5, n. 1, p. 368, 2016. https://doi.org/10.4102/ajlm.v5i1.368
» https://doi.org/10.4102/ajlm.v5i1.368 -
PORTER, Karen G.; FEIG, Yvette S. The use of DAPI for identifying and counting aquatic microflora1. Limnology and Oceanography, v. 25, n. 5, p. 943-948, 1980. https://doi.org/10.4319/lo.1980.25.5.0943
» https://doi.org/10.4319/lo.1980.25.5.0943 -
RASTOGI, Rajesh P.; RICHA; KUMAR, Ashok; TYAGI, Madhu B.; SINHA, Rajeshwar P. Molecular mechanisms of ultraviolet radiation-induced DNA damage and repair. Journal of Nucleic Acids, v. 2010, n. 1, p. 592980, 2010. https://doi.org/10.4061/2010/592980
» https://doi.org/10.4061/2010/592980 -
RECACHA, Esther; KUROPKA, Benno; DÍAZ-DÍAZ, Sara; GARCÍA-MONTANER, Andrea; GONZÁLEZ-TORTUERO, Enrique; DOCOBO-PÉREZ, Fernando; RODRÍGUEZ-ROJAS, Alexandro; RODRÍGUEZ-MARTÍNEZ, Jose Manuel. Impact of suppression of the SOS response on protein expression in clinical isolates of Escherichia coli under antimicrobial pressure of ciprofloxacin. Frontiers in Microbiology, v. 15, 1379534, 2024. https://doi.org/10.3389/fmicb.2024.1379534
» https://doi.org/10.3389/fmicb.2024.1379534 -
REED, Nicholas G. The history of ultraviolet germicidal irradiation for air disinfection. Public Health Reports, v. 125, n. 1, p. 15-27, 2010. https://doi.org/10.1177/003335491012500105
» https://doi.org/10.1177/003335491012500105 -
ROLLER, Carsten; WAGNER, Michael; AMANN, R.; LUDWIG, W.; SCHLEIFER, Karl H. In situ probing of Gram-positive bacteria with high DNA G + C content using 23S rRNA-targeted oligonucleotides. Microbiology, v. 140, part 10, p. 2849-2858, 1994. https://doi.org/10.1099/00221287-140-10-2849
» https://doi.org/10.1099/00221287-140-10-2849 -
SANTOS, Ana Karolina S.; MEDEIROS, Pedro Henrique Q. S. de; BONA, Mariana D.; PRATA, Mara M. G.; AMARAL, Marília S. M. G.; VERAS, Herlice N.; PANKOV, Rafaela C.; RIBEIRO, Samilly A.; CAVALCANTE, Paloma A.; FREITAS, Thiago M.; GONDIM, Rafhaella D. G.; OLIVEIRA, Daniel M. N. de; MELO, Natália K. F. M.; HAVT, Alexandre; LIMA, Aldo A. M. Virulence-related genes and coenteropathogens associated with clinical outcomes of enteropathogenic Escherichia coli Infections in children from the Brazilian semiarid region: a case-control study of diarrhea. Journal of Clinical Microbiology, v. 57, n. 4, e01777, 2019. https://doi.org/10.1128/jcm.01777-18
» https://doi.org/10.1128/jcm.01777-18 -
SELVESHWARI, S; LELE, Kasturi; DEY, Sutirth. Genomic signatures of UV resistance evolution in Escherichia coli depend on the growth phase during exposure. Journal of Evolutionary Biology, v. 34, n. 6, p. 953-967, 2021. https://doi.org/10.1111/jeb.13764
» https://doi.org/10.1111/jeb.13764 -
SOUSA, Mariana; OLIVEIRA, Isabel M.; CORREIA, Liliana; GOMES, Inês B.; SOUSA, Cátia A.; BRAGA, Daniel F. O.; SIMÕES, Manuel. Far-UV-C irradiation promotes synergistic bactericidal action against adhered cells of Escherichia coli and Staphylococcus epidermidis. Science of the Total Environment, v. 917, 170352, 2024. https://doi.org/10.1016/j.scitotenv.2024.170352
» https://doi.org/10.1016/j.scitotenv.2024.170352 - SVANISHVILI, Giorgi. Stopping DNA damage: a newly discovered protein-enhancing DNA repair mechanisms. Premier Journal of Science, v. 4, 100040, 2024.
-
WANG, Di; REN, Anran; YAO, Mingchen; HU, Bin; VAN DER MEER, Walter; LIU, Gang. Bio-safe drinking water with or without chlorine: a review. Blue-Green Systems, v. 6, n. 1, p. 169-183, 2024. https://doi.org/10.2166/bgs.2024.008
» https://doi.org/10.2166/bgs.2024.008 -
WANG, Wenting; YANG, Guangcan; WANG, Yanwei. Single molecular investigation of influence of silver ions on double-stranded and single-stranded DNA. Journal of Physical Chemistry B, v. 129, n. 9, p. 2426-2432, 2025. https://doi.org/10.1021/acs.jpcb.4c08212
» https://doi.org/10.1021/acs.jpcb.4c08212 -
WEN, Xiaotong; CHEN, Feiyu; LIN, Yixiang; ZHU, Hui; YUAN, Fang; KUANG, Duyi; JIA, Zhihui; YUAN, Zhaokang. Microbial indicators and their use for monitoring drinking water quality—a review. Sustainability, v. 12, n. 6, p. 2249, 2020. https://doi.org/10.3390/su12062249
» https://doi.org/10.3390/su12062249 - WORLD HEALTH ORGANIZATION (WHO). Guideline for drinking water quality 4. ed. Geneva: World Health Organization, 2017.
-
WOZNIAK, Katherine J.; SIMMONS, Lyle A. Bacterial DNA excision repair pathways. Nature Reviews Microbiology, v. 20, n. 8, p. 465-477, 2022. https://doi.org/10.1038/s41579-022-00694-0
» https://doi.org/10.1038/s41579-022-00694-0 -
WU, Jiangning; DOAN, Huu. Disinfection of recycled red-meat-processing wastewater by ozone. Journal of Chemical Technology & Biotechnology, v. 80, n. 7, p. 828-833, 2005. https://doi.org/10.1002/jctb.1324
» https://doi.org/10.1002/jctb.1324 -
XIAO, Yang; WANG, Jiayang; SUN, Pengdong; DING, Ting; LI, Jingyuan; DENG, Yang. Formation and resuscitation of viable but non-culturable (VBNC) yeast in the food industry: A review. International Journal of Food Microbiology, v. 426, 110901, 2025. https://doi.org/10.1016/j.ijfoodmicro.2024.110901
» https://doi.org/10.1016/j.ijfoodmicro.2024.110901 -
ZHANG, Shenghua; GUO, Lizheng; YANG, Kai; ZHANG, Yin; YE, Chengsong; CHEN, Sheng; YU, Xin; HUANG, Wei E.; CUI, Li. Induction of Escherichia coli into a VBNC state by continuous-flow UVC and subsequent changes in metabolic activity at the single-cell level. Frontiers in Microbiology, v. 9, p. 2243, 2018. https://doi.org/10.3389/fmicb.2018.02243
» https://doi.org/10.3389/fmicb.2018.02243 -
ZHU, Lin; SHUAI, Xinyi; XU, Like; SUN, Yujie; LIN, Zejun; ZHOU, Zhenchao; MENG, Lingxuan; CHEN, Hong. Mechanisms underlying the effect of chlorination and UV disinfection on VBNC state Escherichia coli isolated from hospital wastewater. Journal of Hazardous Materials, v. 423, part B, 127228, 2022. https://doi.org/10.1016/j.jhazmat.2021.127228
» https://doi.org/10.1016/j.jhazmat.2021.127228
Edited by
-
Editor:
Caroline Maria Bezerra de Araujo, Centro de Química, Universidade do Minho (Portugal). https://orcid.org/0000-0002-5336-1390
Source: Elaborated by the authors.
Source: Elaborated by the authors.
Source: Elaborated by the authors.
Source: Elaborated by the authors.
Source: Elaborated by the authors.
Source: Elaborated by the authors.
Source: Elaborated by the authors.