Thermal inactivation of water-borne pathogenic and indicator bacteria at sub-boiling temperatures

Evaluation of novel disinfection methods for the remediation of heavily contaminated thermostatic mixing valves and water systems with Pseudomonas aeruginosa biofilm: considerations for new and existing healthcare water systems

BACKGROUND

Pseudomonas aeruginosa is a leading cause of nosocomial Gram-negative bacteraemia. Water systems are a well-documented source of P. aeruginosa and established biofilms are difficult to remove.

AIM

To evaluate the efficacy of regular flushing, peracetic acid disinfection, in-tap thermal disinfection, and in-line thermal disinfection to eradicate P. aeruginosa biofilm in a colonized tap model.

METHODS

A simulated tap system was constructed and inoculated with a reference and an environmental strain of P. aeruginosa to form biofilm. Water samples were collected from the taps and P. aeruginosa levels enumerated following disinfection methods. To simulate regular flushing, taps were flushed for 5 min, five times per day with water tested daily. Peracetic acid (4000 ppm) was manually injected into the system and flushed through the system with a pump. Thermal flushing at 60 °C was performed in-line and with an in-tap bypass valve. Tests were conducted with cross-linked polyethylene (PEX) piping and repeated with copper piping.

FINDINGS

Regular flushing and peracetic acid applied with a pump did not reduce P. aeruginosa levels. A limited reduction was observed when manually injecting peracetic acid. In-tap thermal flushing eradicated P. aeruginosa in copper piping but not PEX. In-line thermal flushing was the most effective at reducing P. aeruginosa levels; however, it did not eradicate the biofilm.

CONCLUSION

In-line thermal flushing was the most effective method to remove P. aeruginosa biofilm. Results vary significantly with the strain of bacteria and the composition of the plumbing. Several methods used in combination may be necessary to remove established biofilm.

Assessment of biofilm, enzyme production and antibiotic susceptibility of bacteria from milk pre- and post-pasteurization pipelines in Algeria

Bacterial biofilm is a major concern of dairy industry due to its association with milk contamination and its derived products. Algerian pasteurized milk shelf-life does not exceed one day, which may reflect the high level of contamination of this product and presence of extracellular enzymes such as lipases and proteases. This work aimed to investigate the microbial biodiversity in milk-processing surfaces of a dairy plant in Algeria. Therefore, stainless steel cylinders were placed in piping system of the dairy system before and after pasteurization of the milk, being removed after 7 days, for biofilm maturation and microorganism isolation and identification by mass spectrometry. Fifty-nine Gram-positive isolates were identified, namely Bacillus altitudinis, Bacillus cereus, Bacillus pumilus, Bacillus subtilis, Bacillus weithenstephanensis, Enterococcus casseliflavus, Enterococcus faecium, and Staphylococcus epidermidis. In addition, twenty-four Gram-negative isolates were identified, namely Acinetobacter schindleri Enterobacter cloacae, Enterobacter xiangfangensis, Leclercia adecarboxylata, and Raoultella ornithinolytica. Bacterial isolates showed ability for production of extracellular enzymes, being 49 % capable of both proteolytic and lipolytic activities. Milk isolates were tested for the ability to form biofilms on stainless steel. The cell numbers recovered on plate count agar plates from stainless steel biofilms ranged from 3.52 to 6.92 log10 CFU/cm2, being the maximum number detected for Enterococcus casseliflavus. Bacterial isolates showed intermediate and/or resistant profiles to multiple antibiotics. Resistance to amoxicillin, cefoxitin and/or erythromycin was commonly found among the bacterial isolates.

The long-term effect of sub-boiling water on dental unit waterlines and its ability to control cross-contamination in dentistry

This study investigated the effect of water at high temperature on the physical and mechanical properties of polyurethane and on biofilm removal, aiming for its applicability in dental unit waterlines. The evaluations were carried out after simulating a 1-year period of daily immersion and measured changes in color, microhardness, surface roughness, and tensile strength before and after reproducing a disinfection protocol. For antibiofilm activity measurement, fragments of waterline were contaminated with Pseudomonas aeruginosa and submitted to the disinfection protocols. Relative to effects on the physical and mechanical properties, immersion in water at 60°C did not promote changes in color and tensile strength. However, lower values were observed for microhardness and increased values for surface roughness. Regarding antibiofilm action, water at 60°C significantly reduced the microbial load and promoted substantial changes in cells morphology. In conclusion, disinfection with water at 60°C demonstrated possible application in controlling cross-contamination in dentistry.

Nanophotonics triggered thermally enhanced solar water disinfection bottles for slum dwellers

Among several existing technologies, solar pasteurization is widely accepted as a reliable and cost-effective method for the removal of microbial pathogens from water. This work reports nanophotonics-triggered thermally enhanced solar water disinfection bottles (nano-SODIS) designed rationally by coating plasmonic carbon nanoparticles (CNP) on the outer surface for the targeted pathogen inactivation from water. The cost-effective CNP nanophotonic material used in this work has high efficiency in harvesting solar radiation and dissipating the heat locally. It has broad absorption efficiency to cover the entire solar spectrum; hence, it is capable to generate multiple scattering. It has also properties of boosting of photon absorption and focusing the light within a constrained spatial region, resulting in powerful and targeted heating that inactivates microorganisms in near proximity. These CNPs were used to coat the nano-SODIS water bottles that achieved the highest temperature of 65-70 °C within 90 min of exposure to solar radiation with a consequent six-log reduction. The disinfection period was reduced by a factor of 3 compared to the conventional solar disinfection system. The treated water was further assessed for 7 days, which confirmed the complete absence of bacteria and no sign of regeneration after storing for a longer period. The SODIS bottles coated with CNP thus overcome the problem of limited solar absorption by acquiring higher broadband absorption potential and thus achieving comparatively high disinfection efficiency. The broad band absorption of CNP was confirmed through UV-DRS absorption spectra. The nano-SODIS bottles designed and constructed in this work are simple, durable, and user friendly in nature and have been deployed in the rural and slums areas of Nagpur, Delhi, and Mumbai, India to provide pathogen-free potable water and to improve the health of local poor communities.

Numerical simulation of a solar water disinfection system based on a small-scale linear Fresnel reflector

This paper describes the details of the design of a solar water disinfection system based on a small-scale linear Fresnel reflector. The proposed system consists of a small-scale linear Fresnel reflector, a filtering system, two disinfection units, a heat exchanger, a compressed air system and the control system. A detailed mathematical model has been developed and solved through an iterative procedure. The system has been studied under different operating conditions, such as beam solar irradiance (the beam solar irradiance on a horizontal surface, corresponding to solar noon, varies from 325 to 798 W m^-2, for winter solstice and summer solstice, respectively), ambient temperature (the ambient temperature varies between 19 and 29 °C at the summer solstice and from 8 to 16 °C at the winter solstice), thermal fluid flow rate (2200 L h^-1, 2400 L h^-1, 2600 L h^-1, and 2800 L h^-1) and water temperature at the outlet of the filtered water tank (8 °C, 12 °C, 16 °C, and 20 °C). The performance of the system has been studied as a function of the temperature of the thermal fluid of the small-scale linear Fresnel reflector, the water temperature of the disinfection unit, the filling and emptying of inertia tanks, clean water productivity and the daily cumulative productivity of clean water. Numerical simulations reveal that the maximum values of cumulative daily productivity of clean water were 357.14 (L m^-2 day^-1) at 100 (°C) and 198.41 (L m^-2 day^-1) at 100 (°C) for summer solstice and winter solstice, respectively, in Almeria (Spain), for a thermal fluid flow rate of 2400 L h^-1. Values much higher than those obtained by other systems. The inclusion of a heat exchanger in this system significantly increases its productivity. Small-scale linear Fresnel reflector thermal fluid temperature, disinfection unit water temperature, clean water productivity and daily cumulative clean water productivity decreased with increasing thermal fluid flow rate above 2400 L h^-1. On the other hand, the water temperature at the outlet of the filtered water tank between 8 and 20 °C has a negligible influence on the small-scale linear Fresnel reflector thermal fluid temperature values, disinfection unit water temperature, clean water productivity and daily cumulative clean water productivity. It is concluded that the proposed solar system offers an energy efficient and environmentally friendly water treatment method.

Revisiting the effect of boiling on halogenated disinfection byproducts, total organic halogen, and cytotoxicity in simulated tap water

Boiling is a widely adopted household tap water treatment method because of its ability to inactivate chlorine-resistant pathogenic bacteria, and to reduce certain groups of disinfection byproducts (DBPs). From a more comprehensive point of view, this study revisited the effect of boiling on four groups of 17 aliphatic DBPs and six groups of 44 aromatic DBPs in both simulated chlorinated and chloraminated tap water samples, with a special focus on the changes of total organic halogen (TOX) and cytotoxicity. Results showed that the concentrations of aliphatic DBPs substantially decreased during boiling via volatilization (trihalomethanes and chloral hydrate) and hydrolysis (haloacetamides) in chlorinated and chloraminated tap water samples. The concentrations of aromatic DBPs during boiling generally followed an increasing trend due to decarboxylation of polycarboxylic precursors in chlorinated tap water samples, and showed a first increasing and then decreasing trend in chloraminated tap water samples. A sharp decreasing of TOX occurred in the heating process of tap water samples from room temperature to 100 °C, and a relatively gentle decreasing was kept in the prolonged boiling process till 5 min. The most abundant DBP group in the tap water samples without boiling was trihalomethanes, and was replaced by haloacetic acids with boiling for 5 min. Continuous boiling for 5 min substantially reduced the cytotoxicity of chlorinated and chloraminated water samples by 52.6% and 21.3%, respectively. Reduction of cytotoxicity matched well with the reduction of TOCl (r = 0.907, P < 0.01), TOBr (r = 0.885, P < 0.01) and TOX (r = 0.905, P < 0.01), suggesting that the cytotoxicity reduction during boiling was mainly ascribed to the reduction of halogenated DBPs. Therefore, boiling of tap water to 100 °C was strongly recommended to reduce the potential health risks induced by tap water ingestion.

Formation of halogenated disinfection byproducts in chlorinated real water during making hot beverage: Effect of sugar addition

Chlorine disinfection is widely applied in drinking water treatment plant to inactivate pathogens in drinking water, but it unintentionally reacts with organic matter present in source waters and generates halogenated disinfection byproducts (DBPs). Sugar is one of the most commonly used seasoning in our diet. The addition of sugar could significantly improve the taste of the beverages; however, the effects of sugar on DBP formation and transformation remain unknown. In this study, the effects of sugar type and dose on the halogenated DBP formation in chlorinated boiled real tap water were evaluated during making hot beverages. We found that sugar can react with chlorine residual in tap water and generate halogenated DBPs. As the most commonly used table sugar, the addition of sucrose in the water sample at 100 or 500 mg/L as C could increase the level of total organic halogen (TOX) by ∼35%, when compared with the boiled tap water sample without sugar addition. In addition, fifteen reported and new polar brominated and chlorinated DBPs were detected and proposed from the reaction between chlorine and sucrose; accordingly, the corresponding transformation pathways were also proposed. Moreover, the DBP formation in the chlorinated boiled real tap water samples with the addition of xylose, glucose, sucrose, maltose and lactose were also investigated. By comparing with the TOX levels in the water samples with different sugar addition and their calculated TOX risk indexes, it was suggested that applying xylose as a sweetener in beverages could not only obtain a relatively high sweetness but also minimize the adverse effect inducing by halogenated DBPs during making hot beverages.

Gold Nanorod-Incorporated Halloysite Nanotubes Functionalized with Antibody for Superior Antibacterial Photothermal Treatment

The global spread of antibiotic-resistant strains, and the need to protect the microflora from non-specific antibiotics require more effective and selective alternatives. In this work, we demonstrate for the first time a superior antibacterial photothermal effect of plasmonic gold nanorods (AuNRs) via their incorporation onto natural clay halloysite nanotubes (HNTs), which were functionalized with anti-E. coli antibodies (Ab-HNTs). AuNRs were incorporated onto the Ab-HNTs through a facile freeze-thaw cycle, and antibody integrity following the incorporation was confirmed via infrared spectroscopy and fluorescence immunolabeling. The incorporation efficiency was studied using UV-Vis absorption and transmission electron microscopy (TEM). Mixtures of E. coli and AuNR-Ab-HNTs hybrids or free AuNRs were irradiated with an 808 nm laser at 3-4 W cm^-2, and the resulting photothermal antibacterial activity was measured via plate count. The irradiated AuNR-Ab-HNTs hybrids exerted an 8-fold higher antibacterial effect compared to free AuNR under 3.5 W cm^-2; whereas the latter induced a 6 °C-higher temperature elevation. No significant antibacterial activity was observed for the AuNR-Ab-HNTs hybrid against non-target bacteria species (Serratia marcescens and Staphylococcus epidermidis). These findings are ascribed to the localization of the photothermal ablation due to the binding of the antibody-functionalized clay to its target bacteria, as supported through TEM imaging. In the future, the HNTs-based selective carriers presented herein could be tailored with other antibacterial nanoparticles or against another microorganism via the facile adjustment of the immobilized antibody.

Nanomaterial-enabled photothermal-based solar water disinfection processes: Fundamentals, recent advances, and mechanisms

The pathogenic microorganisms in water pose a great threat to human health. Photothermal and photothermocatalytic disinfection using nanomaterials (NPs) has offered a promising and effective strategy to address the challenges in solar water disinfection (SODIS), especially in the point-of-use operations. This review aims at providing comprehensive and state-of-the-art knowledge of photothermal-based disinfection by NPs. The fundamentals and principles of photothermal-based disinfection were first introduced. Then, recent advances in developing photothermal/photothermocatalytic catalysts were systematically summarized. The light-to-heat conversion and disinfection performance of a large variety of photothermal materials were presented. Given the complicated mechanisms of photothermal-based disinfection, the attacks from reactive oxygen species and heat, the destruction of bacterial cells, and the antibacterial effects of released metal ions were highlighted. Finally, future challenges and opportunities associated with the development of cost-effective photothermal/photothermocatalytic disinfection systems were outlined. This review will provide guidance in designing future NPs and inspire more research efforts from environmental nano-communities to move towards practical water disinfection operations.

Inactivation of antibiotic resistant bacteria and their resistance genes in sewage by applying pulsed electric fields

We evaluated the suitability of pulsed electric field (PEF) technology as a new disinfection option in the sewage treatment plants (STPs) that can inactivate antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). It was shown that PEF applied disinfection could inactivate not only vancomycin-resistant enterococci (VRE), but also vanA resistance gene. Cultivable VRE could be effectively inactivated by PEF applied disinfection, and were reduced to below the detection limit (log reduction value of VRE > 5 log). Although the vanA also showed a reduction of more than 4 log, it remained in the order of 10⁵ copies/mL, suggesting that ARGs are more difficult to be inactivated than ARB in PEF applied disinfection. Among parameters in each applying condition verified in this study, the initial voltage was found to be the most important for inactivation of ARB and ARGs. Furthermore, frequency was a parameter that affects the increase or decrease of the duration time, and it was suggested that the treatment time could be shortened by increasing the frequency. Our results strongly suggested that PEF applied disinfection may be a new disinfection technology option for STPs that contributes to the control of ARB and ARGs contamination in the aquatic environments.

Past and Future Trends in Medical Spas: A Co-Word Analysis

The present paper consists of a co-word analysis of the previous research in the medical spa field published in the Web Science Core Collection database. The study’s main purpose is to identify the past trends in the medical spa field from the tourist and medical perspectives and to anticipate the future research focuses in the field. In this regard, the article is based on four objectives that create a descriptive picture of the research in the medical spa area, such as (i) studying the current state of the art, (ii) analysing the most visible articles in the field, (iii) highlighting the leading research interests in medical spa research and (iv) anticipating new possible research trends that link cost-effective medical spa activity to COVID-19 post-recovery treatments. A total of 627 articles, published between 1997 and 2021 (March), were analysed, and the data were interpreted using the VOS Viewer software. The study results indicate that high interest in medical spas started to become observable in 2015, when the funding bodies became interested in this field and began supporting publishing and research regarding medical spas. The main subjects investigated in previous studies were related to the specific issues of the industry and tourism activity. They also considered the medical approach of the spa and the use of natural resources in treating different diseases. Except for these main interests, since 2020, it has started to become evident that another approach in the published studies may lead to a new trend in research. The study results show that researchers have begun to investigate the possibility of using medical spa resorts to aid post-COVID-19 recovery, which is considered a cost-efficient option for completing traditional treatment. This new focus in research proves that the medical spa field can rebrand itself as playing a supportive role in national healthcare systems in countries with a long tradition in balneotherapy, and gives a new developing trajectory to the medical spa industry.

Thermal disinfection at suboptimal temperature of Pseudomonas aeruginosa biofilm on copper pipe and shower hose materials

BACKGROUND

Hospital-acquired infections caused by Pseudomonas aeruginosa have been linked to contaminated shower systems in health care. Thermal disinfection, whereby colonized outlets are flushed with existing hot water supplies, is a commonly used method to disinfect contaminated systems. Temperatures of 60°C are recommended for inactivation of P. aeruginosa; however, this is often not achievable at outlets.

AIM

To investigate whether thermal disinfection at a suboptimal temperature (58°C) can effectively eradicate planktonic P. aeruginosa and biofilm adherent on copper piping and shower hoses. Exposure times of up to 60 min and efficacy of repeated cycles were evaluated.

METHODS

A type culture and an environmental strain of P. aeruginosa isolated from a hospital shower were tested. Planktonic bacteria and biofilm adhered to sections of copper pipe and shower hoses were exposed to water at 58°C for up to 60 min. Biofilms were tested with static water, flushing water and repeated cycles of disinfection. Remaining viable bacteria after disinfection were enumerated.

FINDINGS

Planktonic P. aeruginosa remained viable after up to 60 min of thermal disinfection. With static water, biofilm was removed from copper piping after 15 min, but remained viable in shower hoses for up to 60 min. With thermal flushing, biofilm was fully eradicated from copper piping after 2 min, but remained viable on shower hoses. Repeated cycles did not shorten thermal disinfection exposure times.

CONCLUSION

Thermal disinfection at 58°C was effective at eliminating biofilm on copper; however, biofilm on shower hoses remained viable after 60 min of exposure.

Solar disinfection of turbid hygiene waters in Lexington, KY, USA

Solar disinfection (SODIS) could be a key to providing a clean, hygiene water for birthing uses, but the recommended climate zone is limited, the microbial indicators are related to gastrointestinal illness and not wound infections. SODIS feasibility was investigated to remove Escherichia coli from turbid water at temperatures less than 50 °C in Lexington, KY. Increasing turbidity from 0 to 200 NTU decreased E. coli inactivation from 5 to 1 log. With the same experimental protocol, more than 4-log inactivation of Staphylococcus aureus and Staphylococcus epidermidis (common human-skin microorganisms related to serious post-partum infections of both mother and child) was achieved at different turbidity levels with a maximum, in-bottle temperature of 49.2 °C after 5.5 h. The thermal inactivation of the bacterial indicators was assessed without UV radiation and turbidity in water at 37 and 47 °C. Skin bacteria were inactivated completely after 9.5 h at 47 °C, but only 58% removal happened for thermo-tolerant E. coli. These results suggest that SODIS application may be expanded geographically to treat water for hygiene purposes. However, as E. coli is also capable of causing wound infections, UV with thermal inactivation may be required to produce safe hygiene water by SODIS outside of recommended latitudes.

Using the heat generated from electrically conductive concrete slabs to reduce antibiotic resistance in beef cattle manure

Proper treatment is necessary to reduce antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in livestock manure before land application. Conventional stockpiling suffers unreliable removal efficiency, while composting can be complicated and expensive. The objective of this study was to test the feasibility of a novel heat-based technology, i.e., stockpiling manure on conductive concrete slabs, to inactivate ARB and ARGs in beef cattle manure. In this study, two independent bench-scale trials were conducted. In both trials, samples were taken from manure piles on conductive concrete slabs and regular slabs (i.e., heated and unheated piles). In the heated pile of the first trial, 25.9% and 83.5% of the pile volume met the EPA Class A and Class B biosolids standards, respectively. For the heated pile of the second trial, the two values were 43.9% and 74.2%. In both trials, nearly all forms of the total and resistant Escherichia coli and enterococci were significantly lower in the heated piles than in the unheated piles. Besides, significant reduction of ARGs in heated piles was observed in the first trial. Through this proof-of-concept study, the new technology based on conductive concrete slabs offers an alternative manure storage method to conventional stockpiling and composting with respect to reduce ARB and ARGs in manure.

Influence of high power ultrasound on natural microflora, pathogen and lactic acid bacteria in a raw meat emulsion

Raw meat emulsions may have natural, spoilage and pathogenic microorganisms due to the origin and characteristics of this food matrix. All of these microorganisms must be minimized during industrial processing to make food consumption safe and meet quality regulations. Therefore, in this research, the effect of probe ultrasound on the inactivation of three kinds of microorganisms in a raw meat emulsion is evaluated. The microorganisms are: natural microflora NAM, Listeria monocytogenes LIS, and Lactobacillus delbrueckii LAC. A high-intensity probe ultrasound system was used, during 1.0, 2.5, 5.0, 7.5 and 10 min, with pulsed waves of 0.0, 10, 20 and 30 seg, and 200, 250, 300, 350 and 400 W of power. The interrelation between time, wave pulse cycle, and power factors was assessed. The results showed a positive linear independence effect in the treatments without wave pulse for each microorganism, and a quadratic interaction with the time and the ultrasound power for the inactivation of the three kinds of microorganisms. Besides, the desirability function for the inactivation reached up to 60% of the microbial population with the probe ultrasound treatment, with 10 min, a 7.56 s wave pulse and 400 W of power. Thus, these results could be useful to decide the incorporation of mild and emerging technologies in a meat industry line process.

Dynamic modelling of Legionella pneumophila thermal inactivation in water

A predictive mathematical model describing the effect of temperature on the inactivation of Legionella pneumophila in water was developed. Thermal inactivation of L. pneumophila was monitored under isothermal conditions (51 - 61°C). A primary log-linear model was fitted to the inactivation data and the estimated D values ranged from 0.23 to 25.31 min for water temperatures from 61 to 51°C, respectively. The effect of temperature on L. pneumophila inactivation was described using a secondary model, and the model parameters z value and D_ref (D-value at 55°C) were estimated at 5.54°C and 3.47 min, respectively. The developed model was further validated under dynamic temperature conditions mimicking various conditions of water thermal disinfection in plumbing systems. The results indicated that the model can satisfactorily predict thermal inactivation of the pathogen at dynamic temperature environments and effectively translate water temperature profiles to cell number reduction. The application of the model in combination with effective temperature monitoring could provide the basis of an integrated preventive approach for the effective control of L. pneumophila in plumbing systems.

Enrichment of Hydrogen Oxidizing Bacteria from High Temperature and Salinity Environments

There is an urgent need for sustainable protein supply routes with low environmental footprint. Recently, the use of hydrogen oxidizing bacteria (HOB) as a platform for high quality microbial protein (MP) production has regained interest. This study aims to investigate the added value of using conditions such as salt and temperature to steer HOB communities to lower diversities, while maintaining a high protein content and a high quality amino acid profile. Pressure drop and hydrogen consumption were measured for 56 days to evaluate autotrophy of a total of six communities in serum flasks. Of the six communities, four were enriched under saline (0.0, 0.25, 0.5 and 1.0 mol NaCl l^-1) and two under thermophilic conditions (65°C). Five communities enriched for HOB were subsequently cultivated in continuously stirred reactors under the same conditions to evaluate their potential as microbial protein producers. The protein percentages ranged from 41 to 80%. The highest protein content was obtained for the thermophilic enrichments. Amino acid profiles were comparable to protein sources commonly used for feed purposes. Members of the genus Achromobacter were found to dominate the saline enrichments while members of the genus Hydrogenibacillus were found to dominate the thermophilic enrichments. Here we show that enriching for HOB while steering the community toward low diversity and maintaining a high quality protein content can be successfully achieved, both in saline and thermophilic conditions.IMPORTANCE Alternative feed and food supply chains are required to decrease water and land use. HOB offer a promising substitute for traditional agricultural practice to produce microbial protein (MP) from residual materials and renewable energy. To safeguard product stability, the composition of the HOB community should be controlled. Defining strategies to maintain the stability of the communities is therefore key for optimization purposes. In this study, we use salt and temperature as independent conditions to stabilize the composition of the HOB communities. Based on the results presented, we conclude that HOB communities can be steered to have low diversity using the presented conditions while producing a desirable protein content with a valuable amino acid profile.

Is direct-drinking water safe for children? An analysis of direct-drinking water quality and its risk factors in Shanghai elementary and middle schools

BACKGROUND

Drinking water quality for children should be higher than adults due to both behavioral and physiological factors. Thus, to provide enough, safe, and easily accessible drinking water for children at schools, the Shanghai Municipal Government initiated a direct-drinking water project in 2013. However, there has been no study so far to assess the quality of direct-drinking water or to investigate its risk factors in Shanghai elementary and middle schools.

METHODS

In the present study, we selected direct-drinking water equipment from 183 elementary and middle schools (17% of total) in Shanghai to detect the colony-forming units (CFU), residual chlorine, chemical oxygen demand (COD), and turbidity of water samples, and analyzed the risk factors of its quality using both simple and multiple linear regression analysis.

RESULTS

Results showed that the CFU, residual chlorine, COD, and turbidity of direct-drinking water in Shanghai elementary and middle schools ranged from <LOD->300 cfu/mL, <LOD-0.670 mg/L, 0.090-2.710 mg/L, and 0.100-2.050 NTU, respectively. The results of simple linear regression analysis indicated that the CFU of direct-drinking water significantly increased when water temperature was between 25 and 60 °C (β = 19.862, p = 0.030), but it was decreased at 60-100 °C (β = - 16.387, p = 0.046). Additionally, the CFU was higher in elementary schools than middle schools, which was also affected by faucet type and water treatment technology (p = 0.006, 0.012 and 0.042, respectively). The residual chlorine in direct-drinking water significantly increased when there was no toilet within 10 m (β = 0.012, p = 0.045). The COD of direct-drinking water was significantly higher in rural areas and in warm water, compared to urban areas (p = 0.033) and room temperature water (p = 0.000), respectively. The turbidity of direct-drinking water was significantly higher in urban areas and water using UF/MF technology, compared to rural areas (p = 0.030) and RO technology (p = 0.009), respectively. The results of multiple linear regressions analysis drew the same conclusions.

CONCLUSIONS

In order to improve the quality of direct-drinking water, the equipment should be as far away from toilet as possible and direct-drinking water should be kept at room temperature or heated at high temperature (over 60 °C). Furthermore, sanitary standards of direct-drinking water quality and relevant laws and regulations should be established and implemented as soon as possible. Our study demonstrates that it is critical to improve direct-drinking water quality and ensure the safety of drinking water in elementary and middle schools in Shanghai.

Effects of ascorbate and carbonate on the conversion and developmental toxicity of halogenated disinfection byproducts during boiling of tap water

Chlorine disinfection inactivates pathogens in drinking water, but meanwhile it causes the formation of halogenated disinfection byproducts (DBPs), which may induce adverse health effects. Humans are unavoidably exposed to halogenated DBPs via tap water ingestion. Boiling of tap water has been found to significantly reduce the concentrations of halogenated DBPs. In this study, we found that compared with boiling only, adding ascorbate (vitamin C) or carbonate (baking soda) to tap water and then boiling the water further reduced the level of total organic halogen (a collective parameter for all halogenated DBPs) by up to 36% or 28%, respectively. Adding ascorbate removed the chlorine residual in tap water and thus prevented the formation of more halogenated DBPs in the boiling process. Adding carbonate elevated pH of tap water and consequently enhanced the hydrolysis (dehalogenation) of halogenated DBPs or led to the formation of more trihalomethanes that might volatilize to air during the boiling process. The comparative developmental toxicity of the DBP mixtures in the water samples was also evaluated. The results showed that adding a tiny amount of sodium ascorbate or carbonate (2.5-5.0 mg/L) to tap water followed by boiling for 5 min reduced the developmental toxicity of tap water to a substantially lower level than boiling only. The addition of sodium ascorbate or carbonate to tap water in household could be realized by preparing them in tiny pills. This study suggests simple and effective methods to reduce the adverse effects of halogenated DBPs on humans through tap water ingestion.

Treatment of Coral Wounds by Combining an Antiseptic Bilayer Film and an Injectable Antioxidant Biopolymer

Coral reefs are vital for the marine ecosystem and their potential disappearance can have unequivocal consequences on our environment. Aside from pollution-related threats (changes in water temperature, plastics, and acidity), corals can be injured by diseases, predators, humans and other invasive species. Diseases play an important role in this decline, but so far very few mitigation strategies have been proposed and developed to control this threat. In this work, we demonstrate that recently developed bi-layer human skin wound treatment patches containing antiseptics and natural antioxidants with controlled-release capacity can be adapted to treat scleractinian coral wounds effectively. A hydrophilic bilayer film based on polyvinylpyrrolidone (PVP) and hyaluronic acid was used to cover the open wounds while delivering the antiseptics for rapid action. Afterwards, the hydrophilic bi-layer covered wound was sealed with an antioxidant and hydrophobic ε-caprolactone-p-coumaric acid copolymer by melt injection at low temperatures. Treated coral injuries were monitored both in aquaria system and in natural environment in Maldives for over 4 months to reduce the number of entry points for organisms that could lead to diseases. The corals well-tolerated both biomaterials as well as the antiseptics incorporated in these materials. The treatments displayed self-adhering properties, tuneable dissolution time, and biocompatibility and stimulated regeneration properties within the coral wound. As such, this work demonstrates that certain human skin wound treatment materials can be successfully adapted to the curing of coral wounds and delivery of specific drugs to slow down, reduce or even stop the spread of diseases in scleractinian corals as well as in all other benthic organisms affected by uncontrolled pathologies.

Reverse QMRA as a Decision Support Tool: Setting Acceptable Concentration Limits for Pseudomonas aeruginosa and Naegleria fowleri

Opportunistic premise plumbing pathogens such as Pseudomonas aeruginosa and Naegleria fowleri are a growing concern in building water systems because of their potential risks to human health. The aim of this study was to determine the critical concentrations of P. aeruginosa and N. fowleri in water that are associated with meaningful public health risks. To determine these concentrations, a reverse quantitative microbial risk assessment (QMRA) was conducted. Environmental concentrations of P. aeruginosa and N. fowleri corresponding to the risk target of one micro-disability-adjusted life year (DALY) per person per year and 10−4 annual risks of illness were calculated for several applicable exposure scenarios. To calculate the concentration of P. aeruginosa, cleaning contact lenses with potentially contaminated tap water in the absence of an appropriate cleaning solution was considered. For N. fowleri, two exposure scenarios, recreational exposure (swimming) and nasal cleansing (via the use of a neti pot™ or similar device) were considered. The highest critical concentration for P. aeruginosa was found to be 33 CFU/L with a 95% confidence interval of (2.0, 118) for the drop exposure scenario using the 10−4 annual risk target. For N. fowleri, based on the DALY approach, critical concentrations were 0.000030 N. fowleri/L for swimming and 0.00000060 N. fowleri/L for neti pot™ use scenario. Considering heat inactivation, the critical concentration limits for P. aeruginosa using the DALY approach and the 10−4 annual risk target approach were found to be 0.55 CFU/L and 55 CFU/L, respectively. For N. fowleri, the 10−4 annual risk target approach resulted in 0.022 N. fowleri/L and the DALY approach resulted in 0.00000064 N. fowleri/L for the neti pot™ scenario. For P. aeruginosa, N50 (the median infective dose) and alpha (α) contributed the most and contact rates the least to the variability and uncertainty of the estimates for all the scenarios. For N. fowleri, N50 and contact rates contributed the most and α the least to the variability and uncertainty to calculate the concentrations for all the scenarios. The QMRA framework implemented in this research can be used to incorporate more information regarding opportunistic pathogens to inform management decisions, and to prioritize the best interventions regarding estimated reduction in infections caused by opportunistic pathogens.

Overview and comparison of Legionella regulations worldwide

BACKGROUND

Legionnaires disease occurs worldwide. Many authorities have guidelines and regulations to prevent and control Legionella in water systems. These regulations are based on often very limited field and laboratory observations and measurements. They are, therefore, very different from country to country. This article aims to map the existing regulatory framework of worldwide Legionella control to assess the feasibility of regulatory unification.

METHODS

This article gives an overview of the different standards, guidelines, and recommendations as well as how various authorities and/or countries deal with Legionella infection. A 3-step process is followed to identify current regulations.

RESULTS

Although Legionella is a global concern with a common scientific base, the regulatory framework is different from country to country. The current guidelines and standards are not the best possible. Despite different regulatory frameworks, there is still broad unification of underlying principles. Common principles across regulations are avoiding and monitoring critical spots, avoiding water stagnation, and maintaining sufficiently high temperature (above 60°C, below 25°C). Differences between regulations are target group and dangerous Legionella concentration levels.

CONCLUSIONS

The comparative analysis of the framework is a good starting point for reaching future regulatory unification based on common ground.

Structural and Functional Changes of Groundwater Bacterial Community During Temperature and pH Disturbances

In this study, we report the characteristics of a microbial community in sampled groundwater and elucidate the effects of temperature and pH disturbances on bacterial structure and nitrogen-cycling functions. The predominant phyla of candidate OD1, candidate OP3, and Proteobacteria represented more than half of the total bacteria, which clearly manifested as a "low nucleic acid content (LNA) bacteria majority" type via flow cytometric fingerprint. The results showed that LNA bacteria were more tolerant to rapid changes in temperature and pH, compared to high nucleic acid content (HNA) bacteria. A continuous temperature increase test demonstrated that the LNA bacterial group was less competitive than the HNA bacterial group in terms of maintaining their cell intactness and growth potential. In contrast, the percentage of intact LNA bacteria was maintained at nearly 70% with pH decrease, despite a 50% decrease in total intact cells. Next-generation sequencing results revealed strong resistance and growth potential of phylum Proteobacteria when the temperature increased or the pH decreased in groundwater, especially for subclasses α-, β-, and γ-Proteobacteria. In addition, relative abundance of nitrogen-related functional genes by qPCR showed no difference in nitrifiers or denitrifiers within 0.45 μm-captured and 0.45 μm-filterable bacteria due to phylogenetic diversity. One exception was the monophyletic anammox bacteria that belong to the phylum Planctomycetes, which were mostly captured on a 0.45-μm filter. Furthermore, we showed that both temperature increase and pH decrease could enhance the denitrification potential, whereas the nitrification and anammox potentials were weakened.

Nanoparticle Enhanced Interfacial Solar Photothermal Water Disinfection Demonstrated in 3-D Printed Flow-Through Reactors

Heat treatment, i.e., boiling or pasteurization, is the most widely recognized and practiced form of household water treatment. Considering recent advances in the development of light harvesting nanoparticles for solar-to-heat conversion, we envision that a nanomaterial enhanced water heating treatment system could obviate the need to use fuels or electricity to heat water by replacing the energy source with sunlight. In this study, we demonstrate that functional disinfection temperatures can be easily achieved with unconcentrated sunlight using a single layer interfacial photothermal film in direct contact with a tortuous flowing water channel. Photothermal films were fabricated by dispersing high concentrations of light harvesting nanoparticles, carbon black and Au nanorods, into a highly transparent curable polymer. Bench-scale 3-D printed reactors were employed to determine the effect of different parameters on reactor performance, such as channel height, retention time, flow rate, initial water temperature, and light intensity. Simulations demonstrate the scalability of the treatment system, predicting that a reactor footprint of 45 × 45 cm would be required for a photothermal treatment system that could produce 8 L of water per day with 8 h of sunlight at 1 Sun intensity.

Modeling the Reduction of Salmonella spp. on Chicken Breasts and Wingettes during Scalding for QMRA of the Poultry Supply Chain in China

The objective of this study was to develop predictive models for describing the inoculated Salmonella reductions on chicken during the scalding process in China. Salmonella reductions on chicken breasts at a 100 s treatment were 1.12 ± 0.07, 1.38 ± 0.01, and 2.17 ± 0.11 log CFU/g at scalding temperatures of 50, 60 and 70 °C, respectively. For chicken wingettes, 0.87 ± 0.02, 0.99 ± 0.14 and 1.11 ± 0.17 log CFU/g reductions were obtained at 50, 60 and 70 °C after the 100 s treatment, respectively. Greater bacterial reductions were observed on chicken breasts than on chicken wingettes (p < 0.05). A logistic (−1.12, 0.06) distribution could describe the bacterial reductions on chicken breasts at 50–60 °C. Weibull, exponential and log-linear models were compared for describing the bacterial reduction on chicken breasts at 70 °C and the Weibull model showed the best fit as indicated by the pseudo-R², root mean square error (RMSE) and standard error of prediction (SEP) values. For chicken wingettes, a logistic (−0.95, 0.07) distribution could be used to describe the bacterial reduction at 50–70 °C. The developed predictive models could provide parts of the input data for microbial risk assessment of the poultry supply chain in China.

Plasmonics driven engineered pasteurizers for solar water disinfection (SWADIS)

Rampant environmental pollution is the most ubiquitous concern of current world. A sustainable panacea to overarching contamination of water-borne pathogens demands cheap and eco-friendly oriented research. Solar energy is effortlessly accessible in most of the weather conditions and can be used for water decontamination. In this context, Solar Water Disinfection (SWADIS) appears to be feasible solution. Herein we are reporting newly developed Carbon nanoparticles (CNP) which shows absorption of light in broad region extending from Ultraviolet-Visible (UV) to Infrared Spectroscopy (IR). This CNP with pronounced photothermal effect has been used for SWADIS. Photothermal effect of plasmonic nanomaterials has massive potential and has exploited for disinfection of water. Moving towards practical device design we have developed an efficient CNP based Multipurpose Solar Pasteurizer (MSP) and Nano-Solar Pasteurizer (NSP) which can efficiently perform the SWADIS. Result shows that upon irradiation under natural solar radiation pasteurizers can thermally inactivate the bacteria. The system proves to be able to perform 100% bacterial inactivation in sunny days. We also conducted bacterial inactivation experiments by simulating 106 CFU mL^-1 concentration of E. coli in water to mimic field conditions. Results are evident that pasteurizers achieved 100% bacterial inactivation within period of ˜45 min under sunlight.

Household Contamination of Baby Bottles and Opportunities to Improve Bottle Hygiene in Peri-Urban Lima, Peru

Feeding of infant formula using contaminated bottles may be an important transmission pathway of enteric pathogens during early life. Determinants of suboptimal bottle hygiene and the feasibility and acceptability of intervention strategies have not been well assessed. We evaluated the extent of bottle contamination, its contributing factors, and options for promoting improved bottle hygiene in a Peruvian shantytown. During Phase 1, we sampled from bottles and caregiver hands (n = 48) and processed for enumeration of total coliform and Escherichia coli colony-forming units. A semi-structured questionnaire captured bottle use and hygiene practices. Phase 2 involved the identification of candidate practices to recommend to caregivers. Phase 3 consisted of a behavioral trial in which 14 caregivers were educated about improved practices for bottle disinfection and later reported on their experiences implementing them. Fecal bacteria were detected in 43.8% of bottles sampled during Phase 1 and in 21.7% of hands. Caregivers overall did not use effective methods for disinfecting bottles, displayed misunderstandings surrounding hygienic practices, and few had ever discussed bottle hygiene with a health provider. Findings from the behavioral trial indicated that the improved practice of brushing the bottle with dish detergent for 30 seconds after every use is preferable to boiling the bottle for several minutes daily as caregivers reported that the brush was simple to use, efficient, and practical. The promotion of a bottle brush and detergent is a feasible and acceptable intervention strategy in peri-urban settings, and future research should evaluate its long-term effectiveness for reducing bottle contamination.

A new automated solar disc for water disinfection by pasteurization

A new automated Solar Water Pasteurization Disc of double reflection of 3.8 and 1.3 m in diameter for the first and second reflectors has been erected and tested for performing microbiological disinfection of water in a simple, efficient, and continuous treatment in Brazil.

Particle attached and free floating pathogens survival kinetics under typical stream and thermal spring temperature conditions

Improved understanding of pathogen survival in the stream environment is needed to enhance existing predictive models of stream pathogen populations. Further, the increasing use of thermal springs for bathing necessitates additional studies focused on not only typical streams but also thermal spring conditions, where water temperature is relatively higher than typical streams. This study was conducted to assess the survival of E. coli O157:H7 and Salmonella Typhimurium in stream water under free floating and particle-attached conditions at a range of temperature. A series of microcosm studies were conducted to determine pathogen decay rates. In bench-scale experiments, water circulation and sediment resuspension mimicked natural stream and thermal spring conditions, with continuous air flow providing aeration, constant mixing and turbulent conditions, and improved water circulation. Data on E. coli O157:H7 and Salmonella survival were subsequently used to determine first-order decay equations for calculating the rate constant and decimal reduction time for the modeled experimental conditions. Results showed that at 40 °C, the survival of particle attached E. coli O157:H7 was longer than that of particle attached Salmonella. Under free floating condition, Salmonella survived longer than E. coli O157:H7. At 50 °C, survival of particle attached E. coli O157:H7 and Salmonella was longer than that of free floating E. coli and Salmonella. At 60 °C, survival of particle attached Salmonella was longer than that of free floating Salmonella. Similarly at 60 °C, the survival of E. coli O157:H7  under particle attached condition was longer than that of the free floating condition. The findings of this study suggest that the survival of E. coli O157:H7 differs than the survival of Salmonella in stream water and thermal spring conditions, and the assumption used in previous studies to estimate survival of bacteria in stream environment could result in over/underestimation if the impact of particle attachment on pathogen survival is not accounted for.

Solar Photothermal Disinfection using Broadband-Light Absorbing Gold Nanoparticles and Carbon Black

A simple heat treatment, perhaps the most globally recognized point-of-use water sterilization method, is seemingly effective against all major pathogens of concern, but bulk water boiling is not energy efficient or sustainable. Herein, we present the first application of solar-to-thermal converting nanomaterials for the direct inactivation of bacteria and viruses in drinking water through the application of Au nanorods, carbon black, and Au nanorod-carbon black composite materials as light absorbers. With broad absorption bands spanning the visible and near-infrared wavelengths, at sufficient concentrations, these nanoparticles induce multiple scattering events, increasing photon absorption probability and concentrating the light within a small spatial domain, leading to localized, intense heating that inactivates microorganisms in close proximity. Moving toward practical device design, we have developed a facile silane immobilization approach to fabricate films with densely packed layers of photothermal nanomaterials. Our results suggest that upon irraditaion with simulated solar light, these films can thermally inactivate bacteria and viruses, as demonstrated through the inactivation of surrogate organisms Escherichia coli K-12, and bacteriophages MS2 and PR772.

Effects of Boiling Drinking Water on Diarrhea and Pathogen-Specific Infections in Low- and Middle-Income Countries: A Systematic Review and Meta-Analysis

Globally, approximately 2 billion people lack microbiologically safe drinking water. Boiling is the most prevalent household water treatment method, yet evidence of its health impact is limited. To conduct this systematic review, we searched four online databases with no limitations on language or publication date. Studies were eligible if health outcomes were measured for participants who reported consuming boiled and untreated water. We used reported and calculated odds ratios (ORs) and random-effects meta-analysis to estimate pathogen-specific and pooled effects by organism group and nonspecific diarrhea. Heterogeneity and publication bias were assessed using I2, meta-regression, and funnel plots; study quality was also assessed. Of the 1,998 records identified, 27 met inclusion criteria and reported extractable data. We found evidence of a significant protective effect of boiling for Vibrio cholerae infections (OR = 0.31, 95% confidence interval [CI] = 0.13-0.79, N = 4 studies), Blastocystis (OR = 0.35, 95% CI = 0.17-0.69, N = 3), protozoal infections overall (pooled OR = 0.61, 95% CI = 0.43-0.86, N = 11), viral infections overall (pooled OR = 0.83, 95% CI = 0.7-0.98, N = 4), and nonspecific diarrheal outcomes (OR = 0.58, 95% CI = 0.45-0.77, N = 7). We found no evidence of a protective effect for helminthic infections. Although our study was limited by the use of self-reported boiling and non-experimental designs, the evidence suggests that boiling provides measureable health benefits for pathogens whose transmission routes are primarily water based. Consequently, we believe a randomized controlled trial of boiling adherence and health outcomes is needed.

Disinfection of water inoculated with Enterococcus faecalis using solar/Fe(III)EDDS-H2O2 or S2O82- process

In this study, the activation of H₂O₂ and persulfate ions induced by solar photolysis of Fe(III)EDDS complex were investigated in water disinfection, applying solar AOPs processes. The use of Fe(III)EDDS complex maintains iron in soluble form until slightly basic pH and so the photolysis is efficient in a large range of pH compatible with natural waters. Moreover, for the first time, the impact of photogenerated hydroxyl and sulfate radicals on the inactivation of Enterococcus faecalis in water was studied. E. faecalis was proposed as alternative model microorganism given its higher resistance than the commonly used E. coli. The reactivity of hydroxyl radicals seems to be more efficient for the inactivation of such strain than the reactivity of sulfate radicals. Moreover, experimental results show that the concentration of Fe(III)EDDS complex is a key parameter for the inactivation of microrganisms. For the direct application in natural waters, the efficiency of the process in the presence of ubiquitous inorganic compounds, such as carbonate (HCO₃^-/CO₃^2-) and chloride ions (Cl^-), was also investigated. Carbonates showed a strong reduction on the E. faecalis inactivation in all cases; meanwhile chloride ions enhanced the inactivation in the presence of persulfate as also shown by using a complementary kinetic modeling approach. A dual role of Fe(III)EDDS complex was established and discussed; essential for the generation of radical species but a trap for the reactivity of these same radicals.

Investigation on microbial inactivation and urea decomposition in human urine during thermal storage

The World Health Organization suggests storing human urine for at least 6 months at 20°C prior to application as fertilizer to reduce the potential health risks from pathogenic organisms. Such a storage condition for human urine,however,not only requires along period of time and large space but also ignores the risk of nitrogen losses. In this study, human urine underwent thermal treatment during storage to improve disinfection and to inhibit urea hydrolysis. Microbial indicators such as Escherichia coli and fecal coliforms and the concentration of ammonia/ammonium were investigated in urine samples that were stored at 60°C and 70°C. Both the inactivation of indicators and decomposition of urea improved under storage temperatures of 60°C and 70°C compared with storage under ambient temperature. Therefore, human urine is recommended to be stored at 70°C for 7 days for hygienic and stabilization purposes. Under this storage condition, pH is maintained below 8.0 and ammonia/ammonium content is maintained at approximately 800 mg/L.

Potential effects of rainwater-borne hydrogen peroxide on pollutants in stagnant water environments

Microcosm experiments were conducted to examine the effects of rainwater-borne H₂O₂ on inactivation of water-borne coliforms, oxidation of ammonia and nitrite, and degradation of organic pollutants in canal and urban lake water. The results show that the soluble iron in the investigated water samples was sufficiently effective for reaction with H₂O₂ in the simulated rainwater-affected stagnant water to produce OH (Fenton reaction), which inactivated coliform bacteria even at a H₂O₂ dose as low as 5 μM within just 1 min of contact time. Coliform inhibition could last for at least 1 h and repeated input of H₂O₂ at a 30 min interval allowed maintenance of microbial inhibition for at least 3 h. Nitrification was also impeded by the Fenton process. The resulting inhibition of ammonia-oxidizing microbes reduced the removal rate of NH₄⁺ and the emission of gaseous N species. In the presence of H₂O₂ at a dose of 20 μM, Fenton-driven chemical oxidation appeared to outplay the impediment of biodegradation caused by inhibited microbial activities in terms of removing total polycyclic aromatic hydrocarbons from the water column. The findings point to a potential research direction that may help to explain the dynamics of water-borne pollutants in ambient water environments.

Seasonal Assessment of Opportunistic Premise Plumbing Pathogens in Roof-Harvested Rainwater Tanks

A seasonal study on the occurrence of six opportunistic premise plumbing pathogens (OPPPs) in 24 roof-harvested rainwater (RHRW) tanks repeatedly sampled over six monthly sampling events (n = 144) from August 2015 to March 2016 was conducted using quantitative qPCR. Fecal indicator bacteria (FIB) Escherichia coli (E. coli) and Enterococcus spp. were enumerated using culture-based methods. All tank water samples over the six events were positive for at least one OPPP (Legionella spp., Legionella pneumophila, Mycobacterium avium, Mycobacterium intracellulare, Pseudmonas aeruginosa, or Acanthamoeba spp.) during the entire course of the study. FIB were positively but weakly correlated with P. aeruginosa (E. coli vs P. aeruginosa τ = 0.090, p = 0.027; Enterococcus spp. vs P. aeruginosa τ = 0.126, p = 0.002), but not the other OPPPs. FIBs were more prevalent during the wet season than the dry season, and L. pneumophila was only observed during the wet season. However, concentrations of Legionella spp., M. intracellulare, Acanthamoeba spp., and M. avium peaked during the dry season. Correlations were assessed between FIB and OPPPs with meteorological variables, and it was determined that P. aeruginosa was the only OPPP positively associated with an increased antecedent dry period, suggesting stagnation time may play a role for the occurrence of this OPPP in tank water. Infection risks may exceed commonly cited benchmarks for uses reported in the rainwater usage survey such as pool top-up, and warrant further exploration through quantitative microbial risk assessment (QMRA).

Comparative analysis of solar pasteurization versus solar disinfection for the treatment of harvested rainwater

Background

Numerous pathogens and opportunistic pathogens have been detected in harvested rainwater. Developing countries, in particular, require time- and cost-effective treatment strategies to improve the quality of this water source. The primary aim of the current study was thus to compare solar pasteurization (SOPAS; 70 to 79 °C; 80 to 89 °C; and ≥90 °C) to solar disinfection (SODIS; 6 and 8 hrs) for their efficiency in reducing the level of microbial contamination in harvested rainwater. The chemical quality (anions and cations) of the SOPAS and SODIS treated and untreated rainwater samples were also monitored.

Results

While the anion concentrations in all the samples were within drinking water guidelines, the concentrations of lead (Pb) and nickel (Ni) exceeded the guidelines in all the SOPAS samples. Additionally, the iron (Fe) concentrations in both the SODIS 6 and 8 hr samples were above the drinking water guidelines. A >99% reduction in Escherichia coli and heterotrophic bacteria counts was then obtained in the SOPAS and SODIS samples. Ethidium monoazide bromide quantitative polymerase chain reaction (EMA-qPCR) analysis revealed a 94.70% reduction in viable Legionella copy numbers in the SOPAS samples, while SODIS after 6 and 8 hrs yielded a 50.60% and 75.22% decrease, respectively. Similarly, a 99.61% reduction in viable Pseudomonas copy numbers was observed after SOPAS treatment, while SODIS after 6 and 8 hrs yielded a 47.27% and 58.31% decrease, respectively.

Conclusion

While both the SOPAS and SODIS systems reduced the indicator counts to below the detection limit, EMA-qPCR analysis indicated that SOPAS treatment yielded a 2- and 3-log reduction in viable Legionella and Pseudomonas copy numbers, respectively. Additionally, SODIS after 8 hrs yielded a 2-log and 1-log reduction in Legionella and Pseudomonas copy numbers, respectively and could be considered as an alternative, cost-effective treatment method for harvested rainwater.

Bacteria Inactivation during the Drying of Struvite Fertilizers Produced from Stored Urine

Human urine can be processed into market-attractive fertilizers like struvite; however, concerns regarding the microbial safety of such products remain. The present study evaluated the inactivation of in situ heterotrophs, total bacteria as observed by flow cytometry, and inoculated Enterococcus spp. and Salmonella typhimurium during the drying of struvite under controlled temperature (from 5 to 35 °C) and relative humidity (approximately 40 and 80%) as well as dynamic field conditions. Bacteria accumulated in the struvite cake during struvite filtration. Despite the use of sublethal temperatures, all bacteria types were subsequently inactivated to some degree during struvite drying, and the inactivation typically increased with increasing drying temperature for a given relative humidity. Heterotrophic bacteria inactivation mirrored the trend in total bacteria during struvite drying. A linear relationship was observed between inactivation and sample moisture content. However, bacteria survivor curves were typically nonlinear when struvite was dried at low relative humidity, indicating bacterial persistence. Weibull model survivor curve fits indicated that a shift in the mechanism of inactivation may occur with changing humidity. For increased efficiency of bacterial inactivation during the production of struvite, initial heating under moist conditions is recommended followed by desiccation.

Bactericidal and virucidal mechanisms in the alkaline disinfection of compost using calcium lime and ash

In the present study, the bactericidal and virucidal mechanisms in the alkaline disinfection of compost with calcium lime and ash were investigated. Two indicator microorganisms, Escherichia coli and MS2 coliphage, were used as surrogates for enteric pathogens. The alkaline-treated compost with calcium oxide (CaO) or ash resulted primarily in damage to the outer membrane and enzyme activities of E. coli. The alkaline treatment of compost also led to the infectivity loss of the coliphage because of the partial capsid damage and RNA exteriorization due to a raised pH, which is proportional to the amount of alkaline agents added. These results indicate that the alkaline treatment of compost using calcium oxide and ash is effective and can contribute to the safe usage of compost from a mixing type dry toilet.

Predictive modeling for hot water inactivation of planktonic and biofilm-associated Sphingomonas parapaucimobilis to support hot water sanitization programs

Hot water sanitization is a common means to maintain microbial control in process equipment for industries where microorganisms can degrade product or cause safety issues. This study compared the hot water inactivation kinetics of planktonic and biofilm-associated Sphingomonas parapaucimobilis at temperatures relevant to sanitization processes used in the pharmaceutical industry, viz. 65, 70, 75, and 80°C. Biofilms exhibited greater resistance to hot water than the planktonic cells. Both linear and nonlinear statistical models were developed to predict the log reduction as a function of temperature and time. Nonlinear Michaelis-Menten modeling provided the best fit for the inactivation data. Using the model, predictions were calculated to determine the times at which specific log reductions are achieved. While ≥80°C is the most commonly cited temperature for hot water sanitization, the predictive modeling suggests that temperatures ≥75°C are also effective at inactivating planktonic and biofilm bacteria in timeframes appropriate for the pharmaceutical industry.

EMA-qPCR to monitor the efficiency of a closed-coupled solar pasteurization system in reducing Legionella contamination of roof-harvested rainwater

Solar pasteurization is effective in reducing the level of indicator organisms in stored rainwater to within drinking water standards. However, Legionella spp. were detected at temperatures exceeding the recommended pasteurization temperatures using polymerase chain reaction assays. The aim of the current study was thus to apply EMA quantitative polymerase chain reaction (EMA-qPCR) to determine whether the Legionella spp. detected were intact cells and therefore possibly viable at pasteurization temperatures >70°C. The BacTiter-Glo™ Microbial Cell Viability Assay was also used to detect the presence of ATP in the tested samples, as ATP indicates the presence of metabolically active cells. Chemical analysis also indicated that all anions and cations were within the respective drinking water guidelines, with the exception of iron (mean: 186.76 μg/L) and aluminium (mean: 188.13 μg/L), which were detected in the pasteurized tank water samples at levels exceeding recommended guidelines. The BacTiter-Glo™ Microbial Cell Viability Assay indicated the presence of viable cells for all pasteurized temperatures tested, with the percentage of ATP (in the form of relative light units) decreasing with increasing temperature [70-79°C (96.7%); 80- 89°C (99.2%); 90-95°C (99.7%)]. EMA-qPCR then indicated that while solar pasteurization significantly reduced (p<0.05) the genomic copy numbers of intact Legionella cells in the pasteurized tank water (~99%), no significant difference (p>0.05) in the mean copy numbers was detected with an increase in the pasteurization temperature, with 6 × 10(3) genomic copies/mL DNA sample obtained at 95°C. As intact Legionella cells were detected in the pasteurized tank water samples, quantitative microbial risk assessment studies need to be conducted to determine the potential health risk associated with using the water for domestic purposes.

Multiplex PMA-qPCR Assay with Internal Amplification Control for Simultaneous Detection of Viable Legionella pneumophila, Salmonella typhimurium, and Staphylococcus aureus in Environmental Waters

Pathogenic microorganisms are responsible for many infectious diseases, and pathogen monitoring is important and necessary for water quality control. This study for the first time explored a multiplex quantitative real-time PCR (qPCR) technique combined with propidium monoazide (PMA) to simultaneously detect viable Legionella pneumophila, Salmonella typhimurium, and Staphylococcus aureus in one reaction from water samples. Sodium lauroyl sarcosinate (sarkosyl) was applied to enhance the dead bacterial permeability of PMA. The sensitivity of the multiplex PMA-qPCR assay achieved two colony-forming units (CFU) per reaction for L. pneumophila and three CFU per reaction for S. typhimurium and S. aureus. No PCR products were amplified from all nontarget control samples. Significantly, with comparable specificity and sensitivity, this newly invented multiplex PMA-qPCR assay took a much shorter time than did conventional culture assays when testing water samples with spiked bacteria and simulated environmental water treatment. The viable multiplex PMA-qPCR assay was further successfully applied to pathogen detection from rivers, canals, and tap water samples after simple water pretreatment.

Impact of electronic faucets and water quality on the occurrence of Pseudomonas aeruginosa in water: a multi-hospital study

OBJECTIVE

To compare Pseudomonas aeruginosa prevalence in electronic and manual faucets and assess the influence of connecting pipes and water quality.

SETTING

Faucets in 4 healthcare centers in Quebec, Canada.

METHODS

Water samples from 105 electronic, 90 manual, and 14 foot-operated faucets were analyzed for P. aeruginosa by culture and enzymatic detection, and swab samples from drains and aerators were analyzed by culture. Copper and residual chlorine concentrations, temperature, and flow rate were measured. P. aeruginosa concentrations were analyzed in 4 consecutive volumes of cold water and a laboratory study was conducted on copper pipes and flexible hoses.

RESULTS

P. aeruginosa contamination was found in drains more frequently (51%) than in aerators (1%) or water (culture: 4%, enzyme detection: 16%). Prevalence in water samples was comparable between manual (14%) and 2 types of electronic faucets (16%) while higher for foot-operated faucets (29%). However, type 2 electronic faucets were more often contaminated (31%) than type 1 (14%), suggesting that faucet architecture and mitigated volume (30 mL vs 10 mL) influence P. aeruginosa growth. Concentrations were 100 times higher in the first 250 mL than after flushing. Flexible hoses were more favorable to P. aeruginosa growth than copper and a temperature of 40°C led to higher counts.

CONCLUSIONS

The types of faucets and connecting pipes, flow rate, and water quality are important parameters influencing the prevalence and the concentrations of P. aeruginosa in faucets. High concentrations of P. aeruginosa in the first 250 mL suggest increased risk of exposure when using the first flush.

Microbiological Evaluation of Household Drinking Water Treatment in Rural China Shows Benefits of Electric Kettles: A Cross-Sectional Study

Background

In rural China ~607 million people drink boiled water, yet little is known about prevailing household water treatment (HWT) methods or their effectiveness. Boiling, the most common HWT method globally, is microbiologically effective, but household air pollution (HAP) from burning solid fuels causes cardiovascular and respiratory disease, and black carbon emissions exacerbate climate change. Boiled water is also easily re-contaminated. Our study was designed to identify the HWT methods used in rural China and to evaluate their effectiveness.

Methods

We used a geographically stratified cross-sectional design in rural Guangxi Province to collect survey data from 450 households in the summer of 2013. Household drinking water samples were collected and assayed for Thermotolerant Coliforms (TTC), and physicochemical analyses were conducted for village drinking water sources. In the winter of 2013–2104, we surveyed 120 additional households and used remote sensors to corroborate self-reported boiling data.

Findings

Our HWT prevalence estimates were: 27.1% boiling with electric kettles, 20.3% boiling with pots, 34.4% purchasing bottled water, and 18.2% drinking untreated water (for these analyses we treated bottled water as a HWT method). Households using electric kettles had the lowest concentrations of TTC (73% lower than households drinking untreated water). Multilevel mixed-effects regression analyses showed that electric kettles were associated with the largest Log₁₀TTC reduction (-0.60, p<0.001), followed by bottled water (-0.45, p<0.001) and pots (-0.44, p<0.01). Compared to households drinking untreated water, electric kettle users also had the lowest risk of having TTC detected in their drinking water (risk ratio, RR = 0.49, 0.34–0.70, p<0.001), followed by bottled water users (RR = 0.70, 0.53–0.93, p<0.05) and households boiling with pots (RR = 0.74, 0.54–1.02, p = 0.06).

Conclusion

As far as we are aware, this is the first HWT-focused study in China, and the first to quantify the comparative advantage of boiling with electric kettles over pots. Our results suggest that electric kettles could be used to rapidly expand safe drinking water access and reduce HAP exposure in rural China.