Category Archives: Disinfection

Geonotoxicity of Drinking Water Treated with Disinfectants; China

Nie X, Liu W, Zhang L, Liu Q. Genotoxicity of drinking water treated with different disinfectants and effects of disinfection conditions detected by umu-test. Journal of environmental sciences (China). 2017 Jun;56:36-44. doi: 10.1016/j.jes.2016.07.016.

The genotoxicity of drinking water treated with 6 disinfection methods and the effects of disinfection conditions were investigated using the umu-test. The pretreatment procedure of samples for the umu-test was optimized for drinking water analysis. The results of the umu-test were in good correlation with those of the Ames-test. The genotoxicity and production of haloacetic acids (HAAs) were the highest for chlorinated samples. UV+chloramination is the safest disinfection method from the aspects of genotoxicity, HAA production and inactivation effects. For chloramination, the effects of the mass ratio of Cl2 to N of chloramine on genotoxicity were also studied. The changes of genotoxicity were different from those of HAA production, which implied that HAA production cannot represent the genotoxic potential of water. The genotoxicity per chlorine decay of chlorination and chloramination had similar trends, indicating that the reaction of organic matters and chlorine made a great contribution to the genotoxicity. The results of this study are of engineering significance for optimizing the operation of waterworks.

Monochloramie Loss Mechanisms in Tap Water

Zhang Evan G R Davies James Bolton Yang Liu Q. Monochloramine loss mechanisms in tap water. Water Environ Res. 2017 Mar 1. doi: 10.2175/106143017X14902968254421.

Chloramination has been widely applied for drinking water disinfection, with monochloramine (NH₂Cl) the dominant chloramine species. However, under neutral pH, NH₂Cl can autodecompose and react with chemical components in drinking water, thus decreasing disinfection efficiency. In tap water, the NH₂Cl loss rate can be influenced by temperature, pH, Cl/N molar ratio, the initial NH₂Cl concentration and the natural organic matter (NOM) concentration. A good prediction of NH2Cl loss can assist in the operation of drinking water treatment plants. In this research, a kinetic rate constant (k_docr=(3.57 ± 0.54)×〖10〗^6 〖 M〗^(-1) h^(-1)) and a reactive site fraction (S = 0.43 ± 0.06) for the reaction between free chlorine released from NH₂Cl autodecoposition and tap water NOM were derived from a kinetic model to predict the NH₂Cl loss under various conditions. A temperature-dependent model was also developed. The model predictions match well with the experimental results, which demonstrates the validity of the model and provides a convenient and accurate method for NH₂Cl loss calculations.

Intracellular mechanisms of solar water disinfection

Castro-Alférez M, Polo-López MI, Fernández-Ibáñez P. Intracellular mechanisms of solar water disinfection. Science Reports. 2016 Dec 2;6:38145. doi: 10.1038/srep38145.

Solar water disinfection (SODIS) is a zero-cost intervention measure to disinfect drinking water in areas of poor access to improved water sources, used by more than 6 million people in the world. The bactericidal action of solar radiation in water has been widely proven, nevertheless the causes for this remain still unclear. Scientific literature points out that generation of reactive oxygen species (ROS) inside microorganisms promoted by solar light absorption is the main reason. For the first time, this work reports on the experimental measurement of accumulated intracellular ROS in E. coli during solar irradiation. For this experimental achievement, a modified protocol based on the fluorescent probe dichlorodihydrofluorescein diacetate (DCFH-DA), widely used for oxidative stress in eukaryotic cells, has been tested and validated for E. coli. Our results demonstrate that ROS and their accumulated oxidative damages at intracellular level are key in solar water disinfection.

Solar Disinfection Applications for Drinking Water and Wastewater

A very comprehensive review. But what happened to Part 1?

Stefanos Giannakis, Marıa Inmaculada Polo Lopez, Dorothee Spuhler, Jose Antonio Sanchez Perez, Pilar Fernandez Ibanezbc, Cesar Pulgarin, Solar disinfection is an augmentable, in situ-generated photo-Fenton reaction—Part 2: A review of the applications for drinking water and wastewater disinfection, Applied Catalysis B, Environmental

This is the second part of a comprehensive review article about photo-Fenton reaction at near-neutral pH used for water and wastewater disinfection. In this part, a critical revision of the fundamental physical, chemical and biological parameters affecting the photo-catalytic process efficiency are discussed. The effects of the chemical aspects, considered either as facilitators or competitors of photoFenton are deeply analyzed, with special focus on organic matter and its effect over bacterial inactivation. The role of solubilized iron and the biological nature of different pathogens are deeply assessed according to reported experimental data. Water temperature, turbidity, and radiation parameters like solar UV energy, ligh scattering and absorption during photo-Fenton are pictured in terms of treatment efficiency and suitable reactor design. Recent unconventional photo-Fenton strategies using iron chelates, iron oxides (including zero valent iron) and iron-based materials are also highlighted as new approaches to this process. Finally, the existing pilot scale studies in real conditions using photo-Fenton at near-neutral pH are revised, while alternative options and further research for real implementation are proposed.

Evaluation of a Handheld UV Disinfection Unit

Timmermann LF, Ritter K, Hillebrandt D, Küpper T. Drinking water treatment with ultraviolet light for travelers – Evaluation of a mobile lightweight systemTravel Medicine and Infectious Disease. 2015 Nov 6. pii: S1477-8939(15)00174-X. doi: 10.1016/j.tmaid.2015.10.005.

BACKGROUND: The SteriPEN® is a handheld device for disinfecting water with ultraviolet (UV) radiation. The manufacturer claims a reduction of at least 99.9% of bacteria, viruses, and protozoa. The present study intends to verify the general effectiveness of the device. Furthermore, the influence of bottle geometry and water movement is examined and the issue of user safety with regard to UV-C radiation is addressed.

METHODS: The device was applied on water containing a known number of microorganisms (Escherichia coli, Staphylococcus aureus, and the spore of Geobacillusstearothermophilus) and the survival rate was examined. Three different types of bottles commonly used among travelers served as test containers. All tests were conducted with and without agitating the water during irradiation. Furthermore, a spectral analysis was performed on the light of the device.

RESULTS: The SteriPEN® reached a mean reduction of more than 99.99% of bacteria and 99.57% of the spores when applied correctly. However, the results of the trials without agitating the water only yielded a 94.98% germ reduction. The device’s maximal radiation intensity lies at 254 nm which is the wavelength most efficient in inactivating bacteria. The UV-C fraction is filtered out completely by common bottle materials. However, when applied in larger containers a portion of the UV-C rays exits the water surface.

CONCLUSIONS: If applied according to the instructions the device manages a satisfactory inactivation of bacteria. However, it bears the danger of user errors relevant to health. Therefore, education on the risks of incorrect application should be included in the travel medical consultation. Also there are still aspects that need to be subject to further independent research.

Household Water Treatment Technologies Equally Effective for Thermotolerant Coliform Bacteria

Mohamed H, Clasen T, Njee RM, Malebo HM, Mbuligwe S, Brown J. Microbiological Effectiveness of Household Water Treatment Technologies under Field Use Conditions in Rural Tanzania. Tropical Medicine and International Health 2015 Oct 27. doi: 10.1111/tmi.12628.

OBJECTIVES: To assess the microbiological effectiveness of several household water treatment and safe storage (HWTS) options in situ in Tanzania, before consideration for national scale-up of HWTS.

METHODS: Participating households received supplies and instructions for practicing six HWTS methods on a rotating five-week basis. We analysed 1202 paired samples (source and treated) of drinking water from 390 households, across all technologies. Samples were analysed for thermotolerant (TTC) coliforms, an indicator of faecal contamination, to measure effectiveness of treatment in situ.

RESULTS: All HWTS methods improved microbial water quality, with reductions in TTC of 99.3% for boiling, 99.4% for Waterguard brand sodium hypochlorite solution, 99.5% for a ceramic pot filter, 99.5% for Aquatab® sodium dichloroisocyanurate (NaDCC) tablets, 99.6% for P&G Purifier of Water flocculent/ disinfectant sachets, and 99.7% for a ceramic siphon filter. Microbiological performance was relatively high compared with other field studies and differences in microbial reductions between technologies were not statistically significant.

CONCLUSIONS: Given that microbiological performance across technologies was comparable, decisions regarding scale-up should be based on other factors, including uptake in the target population and correct, consistent, and sustained use over time.

Microbiological Evaluation of Electric Kettles; Rural China

Cohen A, Tao Y, Luo Q, Zhong G, Romm J, Colford JM Jr, Ray I. Microbiological Evaluation of Household Drinking Water Treatment in Rural China Shows Benefits of Electric Kettles: A Cross-Sectional Study. PloS one. 2015 Sep 30;10(9):e0138451. doi: 10.1371/journal.pone.0138451. 

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.