Water disinfection with UVC and or chemical inactivation. Mechanistic differences, implications and consequences.

FLORES MARINA; BRANDI RODOLFO; CASSANO ALBERTO; LABAS MARISOL

Sustainable Energy Developments.

Jochen Bundschuh. ENGINEERING, WATER & EARTH SCIENCES. CRC Press. Balkema

Lugar: Londres; Año: 2014; p. 253 - 279

Human society requires water for drinking, sanitation, cleaning, production of food and energy, and support of commercial and industrial activities. Water in nature can contain a variety of contaminants such as minerals, salts, heavy metals, organic compounds, radioactive residues and living materials, for example parasites, fungi, and bacteria (US EPA, 2003). In rural and urban areas of low-income countries, millions of the most vulnerable people lack access to improved water, sanitation and hygiene (WASH) services. Unsafe water from all sources contributes significantly to the global burden of disease, principally through the waterborne transmission of gastrointestinal infections such as cholera, typhoid, hepatitis, and a wide range of agents that cause diarrhea and even death. Thus, cheap and effective water treatment systems that can be used at different scales, from single-point water sources to small-community water supplies, can make a valuable contribution to reducing the burden of disease by improving access to safe water (Ahmed et al., 2011). Microbiological contamination is a widespread problem and water is one of the most important vehicles for disseminating this type of pollution, contributing to the dispersion of bacteria, yeasts, fungi, spores, etc. Part of this contamination is the product of an uncontrolled discharge of biological wastes or the usage of domestic sewage systems without the corresponding treatment. Typically, these problems are very often solved with chlorine (or its derivatives) disinfection, an old, low cost water treatment technology that is very efficient and has an extensive use. Alongside these advantages, it is well-known the existence of an important drawback resulting from the toxicity of some of the chlorine disinfection by-products (DBPs) produced by the interaction of chlorine and chlorine derivatives with organic substances either naturally existing in water, or resulting from improperly treated industrial or sanitary wastes (McDonnel and Russell, 1999). Some of these DBPs have been already included in the existing lists of substances having mutagenic or carcinogenic properties. During the last years, organizations of different origin have insisted in the need for a gradual substitution of chlorine for water disinfection and requested for more research efforts aimed at developing efficient alternatives having reasonable costs (Ahmed et al., 2010). Global reduction of chemical deposition into the environment is necessary. Addressing these problems calls out for a tremendous amount of research to be conducted to identify robust new methods of purifying water at lower cost and with less energy, while at the same time minimizing the use of chemicals and impact on the environment. In the latest advances in water purification and disinfection, mainly in the oxidation of toxic organic compounds, persistent and cumulative, are used the new technologies of Advanced Oxidation Process (APOs), which are methods that involved chemical or photochemical generation and use of species transitional powerful as the hydroxyl radical (OH˙). This work contains a comprehensive, albeit reduced, report on some of the processes in use, the kinetic modeling that accompany several of them and the theories behind those proposals, especially when they have been developed by us, in relation to technologies for water disinfection. Five disinfection methods were compared: (i) UV disinfection, (ii) Hydrogen peroxide disinfection, (iii) Peracetic acid disinfection (iv) Peracetic acid + UV disinfection and (v) Hydrogen peroxide + UV disinfection. The main target of the study was try to understand and interpret the differences that exist between the different procedures. In addition, we were searching for quantitative information in order to get an idea, as approximate as possible, about operating conditions and final results, with the aim of being able to distinguish among them, which might be the most efficient, economical and environmentally friendly method. Disinfection is the process used to reduce the number of pathogenic microbes in the water (US EPA, 2003). The most common and widespread health risk associated with drinking water is contamination, either directly or indirectly, by human or animal excreta and the microorganisms contained in feces. Drinking such contaminated water or using it in food preparation may cause new cases of infection. Pathogenic (disease-causing) organisms of concern include bacteria, viruses and protozoa. The disinfection process has been routinely carried out since the dawn of the 20th century to eradicate and inactivate the pathogens from water used for drinking purpose. Disinfectants in addition to removing pathogens from drinking water, serve as oxidants in water treatment. They are also used for (a) removing taste and color; (b) oxidizing iron and manganese; (c) improving coagulation and filtration efficiency; (d) preventing algal growth in sedimentation basins and filters, and (e) preventing biological regrowth in the water distribution system (US EPA, 1989). Disinfection may be chemical, physical or a combination of both. Many disinfectants are used alone or in combinations (e.g. hydrogen peroxide and peracetic acid) in the health-care setting. These include alcohols, chlorine and chlorine compounds, formaldehyde, glutaraldehyde, ortho-phthalaldehyde, hydrogen peroxide, iodophors, peracetic acid, phenolics, and quaternary ammonium compounds. A viable alternative could be the use of chemical agents plus UV radiation to avoid revival of microorganisms. Disinfection kinetic models are the basis for assessing the disinfection performance and the design of contactor systems (Trussell and Chao, 1977). Over the years, a number of kinetic models have been proposed for the formulation of disinfection design criteria. Model adequacy is dependent upon the robustness of the underlying inactivation rate law. If the model accounts for the disappearance, the most cited are: Chick (1908); Watson (1909); Gard (1957); Cerf (1977); Selleck et al., (1978); Hom (1972), Hass (1999); Severin et al., (1983) among others.