Water Treatment Disinfection Research Articles

Households’ Willingness to Use Water from a Solar Water Disinfection Treatment System for Household Purposes

The consumption of contaminated water contributes to the global burden of diarrhea and other water-borne diseases, especially among young children. While decentralized solar water disinfection treatment systems (hereafter SODIS) remain a viable option to have safe drinking water, our understanding of the effects of household water treatment before use on willingness to accept and adopt a SODIS is limited. In this study, a complementary log-log regression analysis of the compositional and contextual factors that systematically vary with willingness to accept and adopt a SODIS in the Sawla-Tuna-Kalba (STK) district of Ghana was carried out. Based on our findings, a greater proportion of households (97%) are willing to accept and adopt a SODIS. Compositional and contextual factors such as age, marital status, education, religion, and geographical location significantly contribute to households’ willingness to accept and adopt a SODIS in the STK district of Ghana. Households that treat their water before use (66%, p < 0.05) are more likely to accept and adopt a SODIS compared to those that do not treat their water before use. The findings, therefore, suggest that scaling up SODIS in the STK district is sacrosanct and highlight the necessity to analyse compositional and contextual factors influencing willingness to accept and adopt SODIS. Our findings will inform policies and programs aimed at implementing SODIS in the study area to improve the health of communities that rely on poor-quality drinking water sources.

Real-time water quality monitoring using AI-enabled sensors: Detection of contaminants and UV disinfection analysis in smart urban water systems

This study introduces a novel method for assessing water quality, employing a cutting-edge sensor system integrated with artificial intelligence (AI) technologies. Addressing the global challenge of water scarcity and pollution, the research focuses on the innovative use of spectroscopic analysis for real-time water quality monitoring. The study evaluates the effectiveness of this system in distinguishing between clean, contaminated, and UV-disinfected water samples, highlighting its precision in detecting variations in water quality. Central to the research is the deployment of advanced machine learning algorithms, including Random Forest, Support Vector Machines (SVM), and Neural Networks, to process and classify spectral data. These models demonstrate remarkable accuracy in real-time classification, underscoring the synergy between AI and environmental science in addressing critical public health issues. Significantly, the study showcases the potential of UV disinfection in water treatment, as evidenced by the spectral changes observed in disinfected water samples. This aspect of the research emphasizes the role of spectral analysis in verifying the efficacy of water treatment processes. Overall, this study paves the way for more sophisticated and accessible water quality monitoring systems, offering a promising solution to one of the most pressing environmental challenges. The integration of AI and spectral analysis in this research offers a breakthrough in ensuring a safe water supply and effective water resource management. This study utilizes advanced machine learning algorithms, including Random Forest, Support Vector Machines (SVM), and Neural Networks, for water quality assessment. These models process and classify spectral data with high precision, highlighting variations in water quality.

Pre-exposure to peracetic acid followed by UV treatment for deactivating vancomycin-resistant Enterococcus faecalis through intracellular attack

Antimicrobial resistance (AMR) poses a global health threat to aquatic environments and its propagation is a hot topic. Therefore, deactivating antibiotic-resistant bacteria (ARB) and removing antibiotic resistance genes (ARGs) from water is crucial for controlling AMR transmission. Peracetic acid (PAA), which is known for its potent oxidizing properties and limited by-product formation, is emerging as a favorable disinfectant for water treatment. In this study, we aimed to assess the efficacy of pre-exposure to PAA followed by UV treatment (PAA-UV/PAA) compared with the simultaneous application of UV and PAA (UV/PAA). The focus was on deactivating vancomycin-resistant Enterococcus faecalis (VREfs), a typical ARB in water. Pre-exposure to PAA significantly enhanced the efficacy of subsequent UV/PAA treatment. At a UV fluence of 7.2 mJ cm−2, the PAA-UV/PAA method achieved a 6.21 log reduction in VREfs, surpassing the 1.29 log reduction observed with UV/PAA. Moreover, compared to UV/PAA, PAA-UV/PAA showed increased efficacy with longer pre-exposure times and higher PAA concentrations, maintaining superior performance across a broad pH range and in the presence of humic acid. Flow cytometry analysis indicated minimal cellular membrane damage using both methods. However, the assessments of superoxide dismutase (SOD) activity and adenosine triphosphate content revealed that PAA-UV/PAA induced greater oxidative stress under similar UV irradiation conditions, leading to slower bacterial regrowth. Specifically, SOD activity in PAA-UV/PAA surged to 3.06 times its baseline, exceeding the 1.73-fold increase under UV/PAA conditions. Additionally, pre-exposure to PAA amplified ARGs degradation and reduced resistance gene leakage, effectively mitigating the spread of AMR. Pre-exposure to 200 μM PAA for 10 and 20 min enhanced vanB gene removal efficiency by 0.14 log and 1.29 log, respectively. Our study provides a feasible approach for optimizing UV/PAA disinfection for efficient removal of ARB and ARGs.

Analisis Pengaruh Sisa Klor Terhadap Air Distribusi PDAM Surya Sembada IPAM Karang Pilang 3 Kota Surabaya

The provision of drinking water for the community must meet quality standards that include physical, chemical and bacteriological aspects. The use of chlorine gas as a disinfectant can affect the quality of drinking water in an installation. One method to reduce bacteria in the water treatment process is to use disinfectants, among which chlorine is often used. The use of chlorine as a disinfectant in water treatment plays an important role in eliminating bacteria in water. This research aims to evaluate the quality of water treated by PDAM Surya Sembada, with the hope of providing an understanding to the public about the impact of residual chlorine on distributed water

Photochemical Transformation of Monochloramine Induced by Triplet State Dissolved Organic Matter

The photoexcited dissolved organic matter (DOM) could produce reactive intermediates, affecting chemical oxidant transformation in UV based advanced oxidation processes (AOPs). This study confirmed the critical role of triplet state DOM (3DOM*), generated from DOM photoexcitation, in the transformation of monochloramine (NH2Cl), a commonly used chemical oxidant and disinfectant in water treatment. NH2Cl (42.25 μM, as Cl2) was decayed by 17.4–73.4 % within 60 min, primarily due to 3DOM* , in DOM (2–30 mgC L−1) solutions irradiated by 365 nm, where NH2Cl has no absorption. The second-order quenching rate constants of triplet state model photosensitizers by NH2Cl were determined to be 0.95(± 0.04)–4.49(± 0.04)× 108 M−1 s−1 by using laser flash photolysis. As a reductant, 3DOM* reacted with NH2Cl through one-transfer mechanism, leading to amino radical (NH2•) generation, which then transferred to ammonia (NH4+, pKa 9.25) through H-abstraction by the phenolic moieties in DOM. Additionally, the intermediate product of 3DOM* oxidized by NH2Cl or those triplet state quinones can hydrolyze to form phenolic moieties, elevating NH4+ yield to higher than 99% upon 365 nm irradiation. These findings suggest that the widespread DOM can be applied to convert NH2Cl via 3DOM* with minimal toxic risks.

Assessing passive thermosyphon solar water heater as low-cost, sustainable water disinfection technology: Leveraging the Germicidal effect of copper and thermal convection loops

This study investigated the passive thermosyphon solar water heater (TSWH) as a domestic size point-of-use water disinfection treatment system for inactivating bacteria by utilizing both the germicidal properties of copper in heat exchanger and the heat generated in thermal convection loops. Additionally, life cycle analysis and manufacturing cost analysis were conducted to reveal its environmental and economic benefits. Initially, the germicidal capacity of copper tube against E. coli and total coliform in rapidly flowing polluted water was tested in laboratory settings with contact times ranging from 1.5 to 94 min. Without any additional heat, the copper tubes achieved 99.9% (log 3.01) removal of E. coli, and 99.24% (log 2.12) removal of total coliform after 94 min of contact. In the presence of heat (50–80 ºC), complete removal of the bacteria was achieved after only 1.5 mins of contact time at 50ºC. A domestic-sized passive TSWH with a copper tube heat exchanger was evaluated for disinfecting 20 L/day of microbiologically polluted tap water and synthetic groundwater in a field study. The average contact time of polluted water in copper tube heat exchanger was 5.58±1.2 min in the morning (with an outlet water temperature of 87.3 ºC), and 11.83±1.41 min in the afternoon (with an outlet water temperature of 78±5.1 ºC). These contact times and temperatures, achieved throughout the year, were sufficient to meet the required minimum for complete bacterial removal in the synthetic groundwater. Importantly, the system achieved complete inactivation of pathogens at pasteurization temperatures below 75 ºC, relying solely on the combined effect of copper and thermal convection loops, without pumps or electricity. Compared to an active TSWH using circulating pumps and controls, the passive system generated 62.2% less green house gas, had 55.5% lower cumulative energy demand and cost 323.3 $ compared to 544.64 $. Highlighting significant economic and environmental benefits, the passive TSWH offers a promising solution for disinfecting water in low-income areas with limited access to safe water.

Chlorine Photolysis: A Step Forward in Inactivating Acanthamoeba and Their Endosymbiont Bacteria

Chlorine and solar disinfection are widely used disinfectants in water treatment. However, certain potential pathogens can resist these methods, posing a public health risk. One such case is Acanthamoeba, a resistant free-living amoeba that protects pathogens inside from disinfection, thus endangering the health of water users. This work is the first evaluation of the inactivation efficiency achieved by combining NaClO (Cl2) and solar radiation (SR) against two Acanthamoeba strains from different sources (freshwater and pool water) and their endosymbiont bacteria (EB). Amoebae were exposed to different Cl2 doses (0–500 mg/L), SR wavelength ranges (280–800 nm and 320–800 nm), used as gold standards, and their combinations. The EB exhibited resistance to conventional Cl2 and SR treatments, requiring up to 20 times higher disinfectant doses than those needed to inactivate their protective Acanthamoeba. The pool strain and its EB demonstrated greater resistance to all treatments compared to the freshwater strain. Treatments with Cl2 (5 mg/L)/SR280–800nm completely inactivated both Acanthamoeba and EB of the freshwater strain, reducing up to 100 times the necessary Cl2 doses, suggesting that chlorine photolysis is an attractive treatment for disinfecting freshwater and preventing waterborne diseases associated with Acanthamoebae and its EB.

Peracetic acid as an alternative disinfectant for micropollutants degradation and disinfection byproducts control in outdoor swimming pools

Peracetic acid (PAA) has garnered significant interest as a novel alternative to chlorine-based disinfectants for water treatment due to its broad-spectrum antimicrobial activity and its ability of reactive species generation when exposed to UV light. However, limited studies have investigated micropollutant degradation in the presence of PAA under solar irradiation. This is the first study to comprehensively investigate the photodegradation of caffeine (CAF) and 4-methylbenzylidene camphor (4-MBC) and the removal of disinfection byproducts (DBPs) in the presence of PAA under simulated solar light. The study revealed that the photodegradation of CAF and 4-MBC was significantly enhanced in the presence of PAA, following pseudo-first-order kinetics (R2 > 0.98) with reaction rates (kobs) of 0.220 and 0.111 h-1, respectively. In addition, substantial reduction of 21 DBPs, including trihalomethanes, haloacetic acids and haloacetonitriles, and no DBPs formation were observed in the presence of PAA and simulated solar irradiation. The proportion of coexisting H2O2 in the PAA solution considerably influenced target compounds degradation. CAF and 4-MBC were degraded faster under acidic conditions than under alkaline conditions. Hydroxyl radicals (·OH) dominated the degradation of CAF at different pH values, while direct photolysis and other reactive species played a major role in the degradation of 4-MBC.

The temperature-dependent kinetics and bacteria regrowth by performic acid and sodium hypochlorite disinfection.

Sodium hypochlorite (NaOCl) has been widely used as a disinfectant in water and wastewater treatment, because of its high efficiency and low cost, whereas the bio-toxicity of its disinfection byproducts (DBPs) raised great concern. Performic acid (PFA) produces less DBPs and shows strong oxidation abilities. In this study, the effect of temperature on NaOCl and PFA disinfection as well as bacteria regrowth were evaluated. First, the inactivation of Escherichia coli, Staphylococcus aureus, and Bacillus subtilis by NaOCl and PFA at 4 and 20 °C, detected by cell cultured-based plate counting were fitted to kinetic models, and the predicted CTs were calculated. The results showed that NaOCl was more effective than PFA for E. coli and S. aureus inactivation, and the temperature was positively correlated to disinfection. Second, bacteria regrowth was evaluated at different temperatures (4 and 20 °C) of disinfection and storage. The results showed that the bacteria inactivated by NaOCl regrew prominently, especially for those inactivated at 4 and stored at 4 °C, probably through the mechanism of reactivation of viable but non-culturable (VBNC) bacteria. PFA was superior in suppressing bacteria regrowth, and it may be used as an alternate disinfectant in water treatment in cold environment.

Microbiological hazards associated with the use of water in the post-harvest handling and processing operations of fresh and frozen fruits, vegetables and herbs (ffFVHs). Part1 (outbreak data analysis, literature review and stakeholder questionnaire).

The contamination of water used in post-harvest handling and processing operations of fresh and frozen fruit, vegetables and herbs (ffFVHs) is a global concern. The most relevant microbial hazards associated with this water are: Listeria monocytogenes, Salmonella spp., human pathogenic Escherichia coli and enteric viruses, which have been linked to multiple outbreaks associated with ffFVHs in the European Union (EU). Contamination (i.e. the accumulation of microbiological hazards) of the process water during post-harvest handling and processing operations is affected by several factors including: the type and contamination of the FVHs being processed, duration of the operation and transfer of microorganisms from the product to the water and vice versa, etc. For food business operators (FBOp), it is important to maintain the microbiological quality of the process water to assure the safety of ffFVHs. Good manufacturing practices (GMP) and good hygienic practices (GHP) related to a water management plan and the implementation of a water management system are critical to maintain the microbiological quality of the process water. Identified hygienic practices include technical maintenance of infrastructure, training of staff and cooling of post-harvest process water. Intervention strategies (e.g. use of water disinfection treatments and water replenishment) have been suggested to maintain the microbiological quality of process water. Chlorine-based disinfectants and peroxyacetic acid have been reported as common water disinfection treatments. However, given current practices in the EU, evidence of their efficacy under industrial conditions is only available for chlorine-based disinfectants. The use of water disinfection treatments must be undertaken following an appropriate water management strategy including validation, operational monitoring and verification. During operational monitoring, real-time information on process parameters related to the process and product, as well as the water and water disinfection treatment(s) are necessary. More specific guidance for FBOp on the validation, operational monitoring and verification is needed.

Exposure to irregular microplastic shed from baby bottles activates the ROS/NLRP3/Caspase-1 signaling pathway, causing intestinal inflammation

Irregularly shaped microplastics (MPs) released from infant feeding bottles (PP-IFBs) may exhibit increased cytotoxicity, in contrast to the commonly studied spherical MPs. This study presents an initial analysis of the thermal-oxidative aging process of plastic shedding from feeding bottles, and investigates the inflammatory response induced by these atypical MPs in human intestinal cells (Caco-2). The PP-IFBs' surface displayed non-uniform white patches and increased roughness, revealing substantial structural alteration and shedding, especially during actions such as shaking, boiling water disinfection, and microwave heating. FT-IR and 2D-COS analyses revealed that oxygen targeted the C–H and C–C bonds of polypropylene molecular chain, producing RO· and ·OH, thereby hastening polypropylene degradation. When human intestinal cells were exposed to MPs from PP-IFBs, oxidative stress was triggered, resulting in lowered glutathione levels, augmented reactive oxygen species (ROS), and heightened lipid peroxidation. Elevated levels of pro-inflammatory cytokines (IL-6 and TNFα) signified an active inflammatory process. The inflammatory response was notably more intense when exposed to MPs released through boiling water disinfection and microwave heating treatments, primarily due to the larger quantity of MPs released and their higher proportion of smaller particles. Furthermore, the NLRP3 inflammasome was identified as critical in initiating this inflammatory chain reaction due to the mitochondrial ROS surge caused by MPs exposure. This was further validated by inhibitor studies, emphasizing the role of the ROS/NLRP3/Caspase-1/IL-1β signaling pathway in in promoting intestinal inflammation. Therefore, swift actions are recommended to protect infants against the potential health effects of MPs exposure.

Advantages of ozone disinfection method for water purification over chlorine disinfection

The improvement of various advancements for water sanitization is a significant issue. Among numerous elective drinking water treatment advances, the well-known disinfectant techniques are ozonation and chlorination to treat drinking water. All through the ozonation procedure, it produces biodegradable organic by-products while in the chlorination process, some risky by-products (trihalomethanes and haloacetic acids) are generated. Because of the possible danger of these results, several water purification methods have been reported, such as ozonation, chlorination, UV, etc. During ozonation, exceptionally reactive hydroxyl radicals are produced, which has a crucial effect on purifying water. In this paper, we have discussed the wide use of ozone disinfectants for water treatment with an emphasis on radical chemistry of ozonization as well as advanced oxidation processes instead of the chlorination process, low-cost ozone generation processes, the impact of ozone and chlorine disinfectants on cryptosporidium oocysts, and the removal of seven strains microbes from drinking water. The favorable circumstances, hindrances of the utilization of ozone and chlorine in wastewater treatment, and their confinements in water treatment innovation just as the elective advances, for example, ozone-based oxidation process, catalytic ozonation, photocatalytic oxidation, and so on are additionally clarified in this paper.

UV disinfection in water treatment: when, where, and who was the first?

UV disinfection in water treatment: when, where, and who was the first?

Porous pillararene-based polymer as adsorbent and solid disinfectant for water treatment

Pillararene polymers have been widely used as excellent adsorbents for water treatment, but pillararene polymers with ultra-high specific surface area and versatility are still rarely reported. Herein, a quaternary ammonium salt modified pillar [5] arene polymer, QPBP [5], with specific surface area of 1844 m2 g−1 was successfully synthesized. Since QPBP [5] has abundant different adsorption sites, it exhibits excellent performance for the simultaneously removal of organic pollutants with different charges from water. The selected three model pollutants, Rhodamine B (RhB, positively charged), Sulfamethazine (SMT, electrically neutral) and Fulvic acid (FA, negatively charged), could be rapidly and efficiently removed from water by QPBP [5] within 10 min, which are much faster than them by most of the reported adsorbents. RhB and SMT are mainly adsorbed through hydrophobic interactions with the QPBP [5] surface, while FA is mainly removed through ion exchange. In addition, QPBP [5] also showed excellent reusability and adsorption performance for the environmentally relevant concentration of pollutants. Furthermore, the quaternary ammonium groups on QPBP [5] makes it a solid disinfectant with excellent antibacterial properties. In conclusion, QPBP [5] is a promising multifunctional adsorbent for the treatment of complex pollutants in water.

Byproduct Formation of Chlorination and Chlorine Dioxide Oxidation in Drinking Water Treatment

Increasing water scarcity caused by population growth, climate change, pollution from natural and anthropogenic sources, etc. is likely to impact the occurrence of water-associated infectious diseases. Nowadays, access to clean and safe water is a growing concern worldwide. Therefore, disinfection of drinking water is a vital step in public treatment systems as it ensures the removal of various contaminants, including pathogenic microorganisms (protozoa, viruses, bacteria, and intestinal parasites) that give rise to waterborne diseases. Nevertheless, undesirable disinfection byproducts (DBPs) are formed during disinfection as a result of reactions between chemical disinfectants and natural organic matter (NOM), and/or anthropogenic contaminants, and/or bromide/iodide that are present in the raw water. The chemical complexity and heterogeneity of matters in the raw water makes the characterization and the mechanism of DBPs formation quite difficult and ambiguous regardless of the previous hundreds of studies on DBPs generation. As chlorination is still the most economic and most often used disinfection method, and beside chlorination, the application of chlorine dioxide is becoming more widespread, this paper investigates the possible DBPs generated using chlorine and chlorine dioxide with highlighting their adverse health effects. It overviews the reactions of those disinfectants with inorganic and organic compounds. It is important to note that in order to better understand the performance of disinfectants in water treatment, further investigations on the mechanisms of them with inorganic and organic compounds found in water are critically needed.

Efficacy of solar water disinfection treatment system in improving rural and peri-urban household drinking water quality and reducing waterborne diarrhoeal diseases

Abstract Consumption of untreated microbiologically contaminated water, prevalent in many developing countries, exposes the vulnerable population to inordinate health risks including most life-threatening diarrhoeal diseases like cholera and other illnesses. In response, innovative techniques for treating water at the household level, known as household water treatment (HWT), have emerged as practical and cost-effective solutions. Solar water disinfection (SODIS) has gained recognition as one such method that utilizes sunlight to inactivate harmful micro-organisms in water. This review examines the effectiveness of SODIS as an HWT technique by analysing scientifically robust evidence documenting its microbiological efficacy and the positive health gains among SODIS users. It explores the challenges and limitations that impact its inactivation efficiency and sustainability. Its novelty lies in its expanded exploration of the available strategies and techniques for enhancing the effectiveness of SODIS to address its associated limitations and challenges. By providing a comprehensive analysis of the scientific evidence, this review presents compelling reasons for the implementation and scalability of SODIS in the developing world. This novel perspective contributes to the existing literature on improving access to safe drinking water in underserved communities, offering valuable insights into the advancement of SODIS as a practical and sustainable HWT solution.

The Effect of UV Irradiation on Rearing Water Quality, Growth, and Survival of European Lobster (Homarus gammarus, L.) Larvae

The successful establishment of European lobster (Homarus gammarus) land-based production is hampered by the high mortality rate during larval development, which can be partially explained by the proliferation of pathogens in the communal tanks commonly used for larval rearing. Therefore, disinfection water treatment could improve the low survival rates frequently recorded in H. gammarus farming. In this study, we evaluated the effect of UV irradiation on the microbial abundance and physicochemical quality of the culture water, as well as on H. gammarus larvae growth and survival reared on a flow-through system for a period of 15 days. Results showed that UV treatment significantly decreased the microbial abundance and reduced the variation in water parameters but did not improve physicochemical water quality (turbidity, ultraviolet transmission, nitrogenous compounds, biochemical, and chemical oxygen demand). Moreover, contrary to the expectations, UV irradiation did not improve but slowed down larvae growth. We initially hypothesized that UV disinfection would enhance the rearing water quality by inactivating bacteria, including potential pathogens, and hence, benefit larvae growth and survival. Our findings suggest that UV disinfection can stabilize the rearing environment but does not benefit H. gammarus larvae rearing, at least in a flow-through system set-up. This could be due to UV disinfection eliminating not only potential harmful pathogens but also other microbial groups important for the establishment of a healthy gut microbiota supporting lobster larvae growth.

Impact of drinking water treatment processes on the residues of plant protection products for consumer and aquatic risk assessment: theoretical and experimental studies.

Pesticides residues can occur in ground and surface waters, and potentially react with chemicals used for water disinfection treatments, such as chlorine. This can lead to the formation of unknown reaction products, which can be more toxic and/or persistent than the active substances themselves, and therefore become a potential risk for human health and environment. Thus, in the framework of the EU Regulation 1107/2009, the identification of these by-products and their potential risk should be assessed. Within the European Food Risk Assessment (EU-FORA) Fellowship Programme, the fellow studied the behaviour of herbicides belonging to the families of imidazolinones and sulfonylureas in waters treated with chlorine disinfectants. Due to their physicochemical properties, these herbicides are susceptible of reaching natural waters. In fact, some of them have been detected in water monitoring programmes. During the experimental part of the present work programme, reactions between the active substances and the most used chlorine disinfecting reactants (hypochlorite and chloramines) were performed. Degradation kinetic parameters such as half-lives and degradation constants were calculated. Results showed that herbicide degradation was both pH and chlorine/chloramines concentration dependent. In order to identify the degradation by-products, high-resolution mass spectrometry experiments were performed, and a possible route of formation of these compounds was proposed. Finally, their risk assessment was carried out by using tox/ecotoxicological properties determined by QSAR methodology and FOCUS modelling for hazard and exposure assessment, respectively. These results will contribute to the definition of a risk assessment scheme for pesticides by-products potentially occurring in drinking water.

PCN-222/Ag2O-Ag p-n heterojunction modified fabric as recyclable photocatalytic platform for boosting bacteria inactivation and organic pollutant degradation

Organic chemical and pathogenic bacterial contaminations in wastewater posed great risks towards human health and ecological balance. In this work, amino-modified PCN-222/Ag2O-Ag heterojunction were immobilized on polydopamine (PDA) decorated woven cotton fabric (WCF) by catechol-amine reaction to construct a stable photocatalytic fabric (WCF@PCN-222/Ag2O-Ag), which was applied as a recyclable photocatalytic platform for bacteria inactivation and organic pollutant degradation. The as-fabricated photocatalytic fabric has the capability to effectively inactivate typical Gram-bacteria Escherichia coli and Staphylococcus aureus (6 log units) in water under visible light. Besides, the photocatalytic fabric recovered from bacterial inactivation can also be used to purify organic dye polluted water with high degradation efficiency. The WCF@PCN-222/Ag2O-Ag exhibited high photocatalytic activity due to that the p-n heterojunction built by the interface contact of PCN-222 and Ag2O can improve the separation of photogenerated charge carriers, and the SPR-excitation of Ag enhanced visible light adsorption as well as showed a certain photothermal effect. In addition, the photocatalytic fabric exhibited good stability, reusability and biocompatibility. The present research demonstrated that PCN-222/Ag2O-Ag based photocatalytic platform has great potential for the applications in water disinfection and organic wastewater treatment.

Cross-contamination of Escherichia coli O157:H7 and Listeria monocytogenes in the viable but non-culturable (VBNC) state during washing of leafy greens and the revival during shelf-life

Some water disinfection treatments, such as chlorine and chlorine dioxide, used in the fresh-cut industry to maintain the microbiological quality of process water (PW), inactivate bacterial cells in the water but they also lead to the induction of an intermediate state between viable and non-viable known as viable but non-culturable (VBNC) state. Viable cells can participate in cross-contamination events but the significance of VBNC cells in PW, transfer to the product and potential resuscitation capacity during storage is unclear. The present study aims to determine first, if VBNC cells present in PW can cross-contaminate leafy greens during washing and secondly its potential revival during shelf-life. Process water characterized by a high chemical oxygen demand, due to the presence of high levels of organic matter, was inoculated with Listeria monocytogenes or Escherichia coli O157:H7. Inoculated PW was then treated for 1 min with chlorine dioxide (3 mg/L) or chlorine (5 mg/L) to generate VBNC cells. Absence of culturable cells was confirmed by plate count and VBNC cells by viability quantitative polymerase chain reaction (v-qPCR) complemented with two dyes, ethidium (EMA) and propidium (PMAxx) monoazide. Cross-contamination of shredded lettuce was demonstrated by monitoring the VBNC cells after washing the product for 1 min in the contaminated PW and during shelf life (15 days at 7 °C). In the case of L. monocytogenes, considering the total concentration of L. monocytogenes VBNC cells present in the PW, only a low proportion of cells were able to cross-contaminate the product during washing. VBNC L. monocytogenes cells were able to resuscitate on the product during shelf life, although levels of cultivable bacteria, close to the limit if detection (0.7 ± 0.0 log CFU/g), were only detected at the end of storage. On the other hand, VBNC cells of E. coli O157:H7 present in PW were not able to cross-contaminate shredded lettuce during washing. Moreover, when shredded lettuce was artificially inoculated with VBNC E. coli O157:H7, resuscitation of the VBNC cells during storage (15 days at 7 °C) was not observed. Based on the results obtained, injured L. monocytogenes cells present in the PW are able to be transferred to the product during washing. If VBNC L. monocytogenes cells present in leafy greens (shredded lettuce and baby spinach), they can resuscitate, although cultivable numbers remained very low. Taking all the results together, it could be concluded that under industrial conditions, VBNC cells can be transferred from water to product during washing, but their capacity to resuscitate in the leafy greens during storage is low.