Category Archives: Disinfection

Dye-enhanced solar disinfection

Ryberg EC, Chu C, Kim JH. Edible Dye-Enhanced Solar Disinfection with Safety Indication. Environ Sci Technol. 2018 Nov 20;52(22):13361-13369. doi: 10.1021/acs.est.8b03866.

The rural developing world faces disproportional inequity in drinking water access, where point-of-use water treatment technologies often fail to achieve adequate levels of pathogen removal, especially for viruses. Solar disinfection (SODIS) is practiced because of its universal applicability and low implementation cost, though the excessively long treatment time and lack of safety indication hinder wider implementation. This study presents an enhanced SODIS scheme that utilizes erythrosine-a common food dye-as a photosensitizer to produce singlet oxygen for virus inactivation and to indicate the completion of water disinfection through photobleaching color change. Experimental results and predictions based on global solar irradiance data suggest that over 99.99% inactivation could be achieved within 5 min in the majority of developing countries, reducing the time for SODIS by 2 orders of magnitude. Preserving the low cost of traditional SODIS, erythrosine embodies edible dye-enhanced SODIS, an efficient water disinfection method that could potentially be used by governments and non-governmental organizations to improve drinking water quality in rural developing communities.

The Henrys’ Law Constant of Monochloramine

Garcia MA, Anderson MA. The Henry’s constant of monochloramine. Chemosphere. 2017 Oct 30;192:244-249. doi: 10.1016/j.chemosphere.2017.10.157.

Monochloramine is a secondary disinfectant used in drinking water and is also formed in chlorinated wastewater. While known to hydrolyze over time and react with dissolved organic matter, its partitioning between the aqueous and gas phase has not been extensively studied. Preliminary experiments demonstrated that monochloramine concentrations in solutions open to the atmosphere or actively aerated decreased more rapidly than in sealed solutions, indicating significant losses to the atmosphere. For example, a monochloramine solution open to the atmosphere yielded a loss rate constant of 0.08 d-1, a value twice that for sealed samples without headspace (0.04 d-1) where loss occurs exclusively as a result of hydrolysis. A solution aerated at 10 mL s-1 had a loss rate constant nearly 10× greater than that for hydrolysis alone (0.35 d-1). To better understand partitioning of monochloramine to the gas phase and potential for volatilization, the dimensionless Henry’s law constants of monochloramine (KH) were determined using an equilibrium headspace technique at five different temperatures (11, 16, 21, 27, and 32 °C). The resulting values ranged from 8 × 10-3 to 4 × 10-2, indicating a semi-volatile compound, and were found to be consistent with quantitative structure activity relationship predictions. At 20 °C, monochloramine exhibits a dimensionless Henry’s constant of about 1.7 × 10-2 which is 35 times greater than ammonia but comparable to the Henry’s constant of inorganic semi-volatile compounds such sulfur dioxide. The Henry’s constant values for monochloramine suggests that volatilization could be a relevant loss process in open systems such as rivers receiving chlorinated wastewater effluent, swimming pools and cooling towers.

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.