Comparison of Anolyte and Chlorine Dioxide for a Continuous Hot Water Disinfection in Nursing Home: A Two Years Legionnaires’ Disease Prevention

Worldwide epidemiological reports assert that drinking water is a source for infections and Legionella control represents a critical issue in healthcare settings. Chemical disinfections of water networks are control measures that need to be fine-tuned to obtain satisfactory results in large buildings over prolonged time periods. Aim of study is the evaluation of the effect of anolyte and chlorine dioxide, applied in two different hot water networks of a nursing home to manage Legionella risk. Nursing home has two buildings (A and B), with the same point of aqueduct water entrance. From June 2016, following a shock chlorination, the continuous disinfections with chlorine dioxide and anolyte were applied in hot networks of building A and B, respectively. Hot water was sampled at the central heating system and at two points of use for Legionella research, while chemical tests of manganese (Mn), iron (Fe), zinc (Zn) and trihalomethanes compounds (THM) were implemented to evaluate the disinfection by-products presence. Before chlorination Legionella pneumophila sg1 was recovered with a mean count of 2.4 × 104 CFU/L, while chemical compounds concentrations were within the law limits (Directive 98/83/EC). Then the disinfections Legionella was not recovered in both hot water plants. After the disinfection with chlorine dioxide (from June 2016 to May 2018), a statistically significant increase of iron, zinc and THM concentrations was detected in building A (p = 0.012;p = 0.004;p = 0.008). Both disinfectants appear effective against Legionella spp. growth in water network, but anolyte ensures a lower disinfection by-products release.

Growth and Repair Potential of Three Species of Bacteria in Reclaimed Wastewater after UV Disinfection

Objective The growth and repair potential of three typical microorganisms in reclaimed water after UV disinfection was investigated to assess the effects of photo-reactivation and dark repair of microorganisms,and the microbial safety of reclaimed water following this procedure.Methods The growth and repair potential of Escherichia coli,a fecal coliform strain and Bacillus subtilis in the effluent of a biological wastewater treatment plant disinfected by a low-pressure UV lamp were investigated.Results Any increase in bacterial numbers in the effluent after UV disinfection was due to damage repair.Exposure to photo-reactivating light for 8-10 h after UV irradiation with a dose of 5 mJ/cm 2,the highest percentage of photo-reactivation observed for E.coli and the fecal coliform strain was 29% and 15% respectively.B.subtilis showed little photo-reactivation under these conditions.The percentage of photo-reactivation was related to the UV dose and the photo-reactivating time,and a function was developed to forecast the final concentrations of E.coli and the fecal coliform strain after UV disinfection with possible photo-reactivation.Conclusion Different species of bacteria displayed different responses to UV light and different repair potentials.The repair of indigenous bacteria in wastewater needs to be investigated in future work.

Simultaneous Control of Microorganisms and Disinfection By-products by Sequential Chlorination

Objective To introduce a new sequential chlorination disinfection process in which short-term free chlorine and chloramine are sequentially added. Methods Pilot tests of this sequential chlorination were carried out in a drinking water plant. Results The sequential chlorination disinfection process had the same or better efficiency on microbe （including virus） inactivation compared with the free chlorine disinfection process. There seemed to be some synergetic disinfection effect between free chlorine and monochloramine because they attacked different targets. The sequential chlorination disinfection process resulted in 35.7%-77.0% TTHM formation and 36.6%-54.8% THAA5 formation less than the free chlorination process. The poorer the water quality was, the more advantage the sequential chlorination disinfection had over the free chlorination. Conclusion This process takes advantages of free chlorine＇s quick inactivation of microorganisms and chloramine＇s low disinfection by-product （DBP） yield and long-term residual effect, allowing simultaneous control of microbes and DBPs in an effective and economic way.

Preparation and Evaluation of Novel Solid Chlorine Dioxide-based Disinfectant Powder in Single-pack

Objective To prepare and evaluate novel chlorine dioxide-based disinfectant powder in single-pack that is more convenient for use and transportation. Methods Orthogonal experiment was performed to determine the recipe of the disinfectant powder. Stability test, suspension quantitative bactericidal test, simulation field triM, and animal toxicity test were carded out to observe its bactericidal and toxicological effects. Results The orthogonal experiment showed that the type of water solution had no effect on the disinfectant powder and the best ratio of sodium chlorite to solid acid was 1：3. Ten grams of the disinfectant powder was fully dissolved in 20 mL water for 2 min, and diluted to 500 mL in water. After 5-10 min, the concentration of chlorine dioxide （CIO2） solution was 266 mg/L to 276 mg/L. After stored at 54℃ for 14 d, the average concentration of CIO2 was decreased by 5.03%. Suspension quantitative bactericidal test showed that the average killing logarithm （KL） value for both Staphylococcus aureus and Escherichia coli in 100 mg/L CIO2 solution for 2 min was over 5.00. In simulation field triM, the average descending KL value for Escherichia coli in the solution containing 100 mg/L CIO2 for 5 min was over 3.00. The mouse acute LD50 in the solution 5 times exceeded 5000 mg/kg. The disinfectant powder was not toxic and irritative to rabbit skin and had no mutagenic effect on mouse marrow polychromatic erythrocytes （PCE）. Conclusion The stability and bactericidal efficacy of solid chlorine dioxide-based disinfectant powder in single-pack are good. The solution containing 100 mg/L CIO2 can kill vegetative forms of bacteria. The concentration of CIO2 on the disinfecting surface of objects is 100 mg/L. The disinfectant powder is not toxic and irritative.

Formation potentials of typical disinfection byproducts and changes of genotoxicity for chlorinated tertiary effluent pretreated by ozone

The effects of ozonation on the formation potential of typical disinfection byproducts （DBPs） and the changes of genotoxicity during post chlorination of tertiary effluent from a sewage treatment plant were investigated. Ozonation enhanced the yields of all detected chlorine DBPs except CHCI3. At a chlorine dose of 5 mg/L, the three brominated THMs and five HAAs increased, while chloroform decreased with the increase of ozone dose from 0 to 10 mg/L （ozone dose in consumption base）. At a chlorine dose of 10 mg/L, the two mixed bromochloro species THMs and two dominant HAAs （DCAA and TCAA） increased firstly and then decreased with the increase of ozone dose, with the turning point approximately occurring at an ozone dose of 5 mg/L. The genotoxicity detected using umu test, on the other hand, was removed from 7 Ixg 4-NQO/L to a negligible level by ozonation under an ozone dose of 5 mg/L. Chlorination could further remove the genotoxicity to some extent. It was found that SUVA （UV absorbance divided by DOC concentration） might be used as an indicative parameter for monitoring the removal of genotoxicity during the oxidation.

Prescreening teratogenic potential of chlorinated drinking water disinfection by-products by using Hydra regeneration assay

Practicability of method for the Hydra regeneration assay on the prescreening teratogenic potential of chlorinated drinking water disinfection by products was studied through both the assays of toxicity of adult Hydra (T) and inhibition of the growth of regeneration Hydra (I) by using chloroform, dichloromethane and chloroacetic acid. The results showed that T 50 / I 50 ratios of chloroform and chloroacetic acid were 2 77 and 6 16 respectively, with teratogenic potential. T 50 / I 50 ratio of dichloromethane was 1.69, with weaker teratogenic potential. These experimental results indicated preliminarily that the Hydra regeneration assay has certainly applied value as a prescreening assay for developmental toxicity.

Chlorine poisoning caused by improper mixing of household disinfectants during the COVID-19 pandemic:Case series

BACKGROUND Misuse of disinfectants during the coronavirus disease 2019 pandemic has led to several poisoning incidents.However,there are few clinical case reports on poisoning caused by improper mixing of household disinfectants.AIM To summarize the clinical characteristics and treatment effects of chlorine poisoning caused by improper mixing of hypochlorite bleach with acidic cleaning agents.METHODS We retrospectively analyzed baseline and clinical data,clinical symptoms,and treatment methods of seven patients with chlorine poisoning who were admitted to the National Army Poisoning Treatment Center.RESULTS Among the seven patients,the average poisoning time(exposure to admission)was 57 h(4-240 h).All patients were involved in cleaning bathrooms.Chest computed tomography scans revealed bilateral lung effusions or inflammatory changes in five patients.The partial pressure of oxygen decreased in six patients,and respiratory failure occurred in one.Five patients had different degrees of increase in white blood cell count.Humidified oxygen therapy,non-invasive mechanical ventilation,anti-inflammatory corticosteroids,antioxidants,and antibiotics were administered for treatment.The average length of hospital stay was 7 d(4-9 d).All seven patients recovered and were discharged.CONCLUSION Improper mixing of household disinfectants may cause damage to the respiratory system due to chlorine poisoning.Corticosteroids may improve lung exudation in severe cases,and symptomatic supportive treatment should be performed early.

Disinfection of Primary Municipal Wastewater Effluents Using Continuous UV and Ozone Treatment

UV radiation and ozonation were investigated as disinfection alternatives for the wastewater treatment plant. The inactivation of total and fecal coliforms using ozone and ultraviolet radiation as separate treatments was evaluated. Different ozone concentrations (3 to 40 mg O3/L) were applied and UV fluencies ranging from 8.5 to 12 mJ/cm2 at different pH values (from 5 to 9) were tested. Best results were obtained for ozone doses near 20 mg/min with removals of 72% and 78% of fecal and total coliforms, respectively. The ozone also was capable of oxidizing organic matter in the effluent measured as COD (the highest removal obtained was 36% for 20 mg O3/min). Maximum bacterial resistance was observed at pH 7 in both cases. The UV light offered a high bacterial inactivation (over 80%) and the lowest bacterial inactivation was observed at pH 7. Finally, we obtained the electric energy per order (EEO, kWh/m3/order), defined as the electric energy (kW-h) required to degrade a contaminant by one order of magnitude in a unit volume of contaminated water, being noteworthy that EEO values for the UV process resulted were lower than those determined for the process with ozone in all the water flow tested.

UV-LED表面消毒辐射场的数学模拟体系的建立及试验验证

为了实现紫外发光二极管(Ultraviolet Light-Emitting Diodes,UV-LED)表面消毒器设计的优化、高效、智能化目的,研究建立了UV-LED表面消毒辐射场的数学模型,并进行了试验验证。根据该数学模型,编写了VBA(Visual Basic for Applications)程序,对辐射场进行了模拟和分析。结果显示,辐射模型的计算值与实测值接近,试验验证了辐射模型的可行性。试验进行了应用举例,当照射距离与灯间距的比值为0.4时,选择最大发光角90°的UV-LED可使辐射场最优化;当照射距离与灯间距的比值为0.8和1.6时,对应的最优选择分别是45°和30°的UV-LED。数学模型和相关计算方法为优化设计紫外线表面消毒设施提供了模拟、优化的有效工具。

Characterization of dissolved organic matter fractions and its relationship with the disinfection by-product formation

Dissolved organic matter （DOM） has been identified as precursor for disinfection by-products （DBPs） formation during chlorination. Recently, it has been demonstrated that the characteristics of DOM influence the DBPs formation mechanism. A study was, therefore, initiated to investigate the effects of DOM fractions on DBPs formation mechanism. In the chlorination process, organic acids are dominant precursors of total thihalomethanes （TTHM） because of the vc-o and unsaturated structures. Furthermore, the TTHM formation of organic acids was affected by pH more greatly. Based on the fluorescence spectroscopy analysis, DOM fractions contained several fluorescence substances. During chlorination, humic acid-like substances were found to exhibit high chlorine reactivity and hydrophobic organics decomposed to smaller molecules faster than hydrophilic organics even at lower chlorine dosages. Unlike hydrophobic fractions, hydrophilic organics showed no toxicity following chlorination, suggesting that the toxic structures in hydrophihc organics showed high chlorine reactivity during chlorination.

Waste Water Disinfection During SARS Epidemic for Microbiological and Toxicological Control

Objective To evaluate the disinfection of wastewater in China. Methods During the SARS epidemic occurred in Beijing, a study of different disinfection methods used in the main local wastewater plants including means of chlorine, chlorine dioxide, ozone, and ultraviolet was carried out in our laboratory. The residual coliform, bacteria and trihalomethanes, haloacetic acids were determined after disinfection. Results Chlorine had fairly better efficiency on microorganism inactivation than chlorine dioxide with the same dosage. Formation of THMs and HAAs does not exceed the drinking water standard. UV irradiation had good efficiency on microorganism inactivation and good future of application in China. Organic material and ammonia nitrogen was found to be significant on inactivation and DBPs formation. Conclusion Chlorine disinfection seems to be the best available technology for coliform and bacteria inactivation. And it is of fairly low toxicological hazard due to the transformation of monochloramine.

Removal effect on Mesocyclops leukarti and mutagenicity with chlorine dioxide

Mesocyclops leukarti of zooplankton propagates excessively in eutrophic water body and it cannot be effectively inactivated by the conventional drinking water treatment process. In order to tackle this problem, a study of removal effect on Mesocylops leukarti with chlorine dioxide in a waterworks was performed. The results showed that Mesocyclops leukarti could be effectively removed from water by 1.0 mg/L chlorine dioxide prcoxidation combined with the conventional drinking water treatment process. Higher oxidizability and molecular state of chlorine dioxide in water is the key to the inactivation of Mesocyclops leukarti. The chlorite, disinfection by-products （DBPs） of chlorine dioxide, was stable at 0.45 mg/L, which is lower than that critical value of the USEPA. GC-MS examination showed that the quantity of organic substance in the water treated by chlorine dioxide obviously decreased. Ames test further revealed that the mutagenicity was reduced by chlorine dioxide with respect to prechlorine. The propagation ofMesocyclops leukorti can be inactivated effectively and safely by chlorine dioxide pre-oxidation.

pH effect on the formation of THM and HAA disinfection byproducts and potential control strategies for food processing

Chlorine-based sanitizers have seen wide spread use in food sanitation. The reaction of chlorine species with organic matter is a concern for two reasons. Available chlorine can be “used up” by organic compounds resulting in a lower amount of chlorine available for disinfection. Another concern is that some forms of chlorine can react with some organic compounds to form toxic halogenated disinfection byproducts（DBPs）. Many studies have been conducted to evaluate the role of hypochlorous acid（HOCl） and hypochlorite ion（OCl–） in the production of DBPs with a particular interest in the production of trihalomethanes（THMs） and haloacetic acids（HAAs）. Since most of the chlorine reactions are pH dependent, pH is found to have a significant effect on the formation of chlorine DBPs. In many cases, the concentration of THMs decreases and HAAs increases as pH decreases. pH also plays an important role in the determination of the type and amount of DBPs formed, with lower, more acidic, pHs resulting in the formation of less chloroform. This review summarizes the information from the literature on the role of chlorine-based sanitizers as affected by pH in the formation of different types of DBPs. Alternative novel strategies to minimize the formation of DBPs are also discussed.

Levels of Norovirus and <i>E. coli</i>in Untreated, Biologically Treated and UV-Disinfected Sewage Effluent Discharged to a Shellfish Water

The efficacy of an activated sludge (modified Ludzack-Ettinger (MLE)) UV disinfection processes in removing human noroviruses and E. coli from sewage were compared with the prevalence of these microorganisms in a settled storm discharge from the same sewage treatment works. Both discharges impacted a designated oyster production area. The treatment process delivered average NoV and E. coli reductions of 2.9log10 and 5.2log10, respectively. Most E. coli reductions occurred during the UV disinfection process whereas the MLE process was comparatively more important in reducing NoV levels. A positive relationship was found between NoV removal and measured applied UV dose. The average levels of total NoV in the settled storm tank were of the same order of magnitude of those in screened raw influent at the works. These results highlight the importance of measures to reduce the impact of stormwater discharges to minimise the risk of NoV gastroenteritis associated with the consumption of oysters.

The Disinfection of Drinking Water in Trunk Water Mains

This study aimed to explore the disinfection of drinking water in trunk water mains, based on published conditions denoted within the Irish Republic. The variables within the study were consumer draw-off rates, trunk main length, pipe diameter, and water temperature. All these factors are known to impact the free chlorine residual in operational supply networks. Based on published conditions obtained within the literature review, 60 hypothetical trunk mains were generated for this study. Of primary concern were the variables that affect the chlorine decay rate;total amount of chlorine decay;available amount of chlorine in the periphery of the trunk main;and the costs associated with effective chlorine disinfection of trunk mains. Based on the analysis performed, the following were the salient observations: 1) Low consumer draw-off rates and increased trunk main length and diameter increased the risk of the free chlorine residual in the periphery of the trunk mains not complying with the Environmental Protection Agency’s (EPA) minimum recommended residual value of 0.1 mg/l (EPA Drinking Water Audit Report, 2014). 2) Increasing the diameter of the trunk main from 125 mm to 180 mm had a negligible effect on the chlorine decay rate. However, increasing the trunk main diameter from 125 mm to 180 mm was shown to have a major impact on the total amount of chlorine decay and free chlorine residual available in the periphery of the main. The key parameters that affected disinfection costs associated with trunk mains include length, diameter and the need for chlorine boosting.

UV-LED辐射模式对表面消毒辐射场均匀度的影响

在使用紫外发光二极管(Ultraviolet light-emitting diodes,UV-LED)进行表面消毒时,物体表面会出现部分区域消毒剂量超出必要,部分区域消毒剂量不足的现象。理想的辐射场是物体表面各点的辐射照度相同。为了优化辐射场,建立了辐射场的通用公式,编写VBA程序,实现了对辐射场的数学模拟、分析和优化。对9种UV-LED辐射模式的辐射场进行了实际模拟分析。结果显示:对于由多颗UV-LED组成的光源板,辐射距离与UV-LED间距的比以及UV-LED的辐射模式是辐射场均匀性的决定因素。由于边缘效应,在光源板正下方投影的边长的80%范围内才有可能实现辐射场均匀。当辐射距离和UV-LED间距之比在3~15的范围内时,均匀性良好(最小和最大值的比≥81.8%)。较小的最大发光角的辐射模式在照射距离和UV-LED间距比例偏大的情况下更为适用,反之亦然。

Suspended particle effects on ClO_2/ultraviolet light combined disinfection of effluent

The concentration of suspended solids of effluent often varies in a wide range, therefore the dose of ultraviolet light （UV） in disinfection process needs to be adjusted to meet the disinfection criterion at a high frequency, and the desired disinfection effect is difficult to be ensured. The particles size and particle-associated fecal coliform （F.C.） contribution, and their influence on UV disinfection were investigated when ClO2 and UV combined disinfection process was used. The results showed that suspended solids content had a major impact on UV disinfection efficiency, especially the large particle size fraction. Particles （D〉10μm） associated F. C. were difficult to be disinfected and were the main part of the railings of F.C. inactivation curve. Pre-ClO2 oxidation could reduce the number of particles in effluent, and make large particles decrease to small ones. Therefore, the influence of particles on UV disinfection could be reduced after pre-ClO2 oxidation, and the resistance ability to particle loadings of combined process was enhanced. Moreover, the combined process has a lot of advantages, such as low toxicity, low operational/maintenance costs; it is also convenient to be established in the existing wastewater plant or the new planned one.

在UV_(365)和太阳光辐照下EfOM生成DBPs及其毒性的变化

为了探究污水厂出水中溶解性有机物(EfOM)经氯化消毒处理后生成的消毒副产物(DBPs)暴露在太阳光下的变化规律,探究了单一及混合DBPs在UV_(365)和太阳光辐照下的光解和水解特性,从而揭示氯化EfOM过程生成的DBPs的增衰规律以及伴随的两种生物毒性的变化.结果表明,氯化EfOM生成的6种DBPs中,一氯二溴甲烷和1,1,1-三氯丙酮在UV_(365)和太阳光辐照下均可降解,在UV_(365)辐照下的光解速率分别为0.0072和0.0523h~(-1),而在太阳光下光解速率分别为0.0293和0.1551h^(-1),其在太阳光下的光解速率大于UV_(365).混合DBPs体系中,在UV_(365)或者太阳光的辐照下,共存的DBPs之间可产生促进/抑制降解现象.在UV_(365)辐照下,Ef OM生成的DBPs(除了三氯甲烷)基本随着时间的延长而增加了16.5%~231.1%,并且氯化EfOM溶液的急性毒性和遗传毒性分别升高了17.0%和降低了5.6%.但是,在太阳光辐照下,三氯乙酸和1,1,1-三氯丙酮则下降了36.2%和82.2%,其它DBPs基本保持稳定,且氯化EfOM溶液的急性毒性和遗传毒性降低了35.8%和37.7%.这将为污水厂尾水排放到开放性水体受太阳光辐照后的生态安全保障提供了一定的依据.

Impact of Suspended Particles and Enhancement Techniques on Ultraviolet Disinfection of a Secondary Effluent

The concentration of suspended solids in the secondary effluent often varies widely, leading to frequent adjustment of the UV dosage to meet the disinfection criterion. In addition, a desired disinfection rate is difficult to achieve sometimes. The authors studied the particle size distribution, contribution of particle-associated Fecal Coliform (F.C.), and their influences on UV disinfection. A combined disinfection process (chlorination with a subsequent UV disinfection) was tested to improve the disinfection effect. The results indicated that the content of suspended solids, especially that of large particles, has a strong impact on UV disinfection efficiency; D>10 μm particles associated F.C. are difficult to be disinfected and are the main part of the tailings of F.C. inactivation curves. Pre-chlorination could decrease the number of particles in the secondary effluent and transform the large particles into small ones, reducing the influence of particles on UV disinfection and enhancing the resistance ability of the combined process to particle loading.

Disinfection Water Wells and Sterilization

Disinfection is an important step in ensuring that water is safe to drink. Well disinfection is used to inactivate or control bacteria populations in a well and the distribution system. Disinfection is the inactivation or destruction of pathogenic organisms through the disruption of the organisms’ normal life processes. The objective of this work is to clean and/or disinfect entire borehole to prepare wells for pump installation. The last water sample was collected after the well disinfec-tion on that time. The results of water chemical analysis are presented in Tables 2-4, and there was nothing found against the specification requirements. After a reaction time of approximately 12 h, the well was cleaned from the sterilization solution by airlifting until chlorine concentration in the water reached 0 mg/l. Then through analyzing the test for samples of water after disinfection and sterilization the wells showed the Iron Bacteria were not seen and the Bacteria Species/Anaerobic Bacteria were absent.