Learning Objectives Understand why drinking water required sanitation. Know the three different types of water sanitation methods. Provide advantages and disadvantages of each type of sanitation method. Define the terms residual protection and disinfection byproducts. Chlorine-based methods Chlorination is the process of adding chlorine compounds to drinking water to disinfect it and kill germs. In 1908, New Jersey was the first state to utilize chlorinated compounds for sanitizing drinking water. This method is quite cheap for most countries and rids water of bacteria and most viruses. Regarding protozoa (Giardia and Cryptospordium), results can vary depending upon the type of chlorine product that it used and how long it is applied (refer to this CDC table). Chlorine does offer residual protection from treatment facility to consumer and is quite cheap. In the United States, chlorine (Cl 2 ) has been used to sanitize both drinking and waste waters since the early twentieth century. Gaseous chlorine (Cl 2 ) is known to be quite corrosive, poisonous, and explosive. Other chlorine-based sanitizing agents include chlorine dioxide (ClO 2 ), sodium hypochlorite (NaClO), calcium hypochlorite (Ca(ClO) 2 , and chloroamines (e.g., NH 2 Cl). The first of these, chlorine dioxide. is a gaseous compound that is capable of destroying viruses and bacteria in drinking water, but requires higher dosages to kill protozoa like Giardia. Sanitizing procedures involving chlorine dioxide require longer contact time at higher dosages than other using pure chlorine. Hypochlorite (ClO) - based compounds are effective at killing viruses and bacteria. Like chlorine dioxide, hypochlorites do not deactivate all protozoa. Deactivating Cryptosporidium can be challenging using chlorine based methods. In order to remove this protozoa, water must be flushed through a filtered which has a pore size of equal to or less than 1 micron (micrometer). Filters should be labeled as "absolute 1 micron." If reverse osmosis it used to purify water, Cryptosporidium and all other disease causing pathogens will be removed as well. Figure \(\PageIndex{1}\): Image of chlorine dioxide dissolved in water. (Copyright, https://commons.wikimedia.org/wiki/User:Iridos ) Chloroamines are a group of chemical compounds that contain chlorine (Cl 2 ) and ammonia (NH 3 ). The specific form of chloroamine used in drinking water disinfection is called monochloramine (NH 2 Cl). These sanitizers do not kill harmful organisms as fast as chlorine gas and can decompose when exposed to heat, light, and bacteria. Effective chloramine levels range from 1.0 to 4.0 ppm. These compounds provide long-lasting residual protection For this reason, monochlorinamine is often utilized as a secondary sanitizer in addition to chlorine or non-chlorine methods of sanitization. All forms of chlorination do alter smell and taste of drinking water. In addition, chlorine (most often responsible are the chloroamines compounds) can react with other chemicals in tap water to produce organochlorides. The EPA classifies these newly formed compounds as disinfectant byproducts and regulates them as primary drinking water contaminants. Ozone (O 3 ) Disinfection Ozone disinfection, or ozonation, is powerful oxidizing process which is toxic to most waterborne organisms. This method of disinfection is widely used in Europe. Ozone deactivates cyst formation of protozoa (like Giardia). In addition, this chemical effectively kills viruses and bacteria. Ozone machines were first constructed in the mid-1800's. New devices produce O 3 molecules by passing oxygen through ultraviolet light or a "cold" electrical discharge. To use ozone as a disinfectant, it must be created on-site and then added to the water by bubble contact. Unlike chlorine, the ozonation process does not alter the taste or smell of water. Video \(\PageIndex{2}\): Demonstration-Effects of Panasonic's "Ozone Water" Device (1.11 min). Unfortunately, ozone does not provide any residual protection once water has left the treatment facility. For water that must travel far distances to consumers, chlorine or chloramine should be added throughout a distribution system to remove any potential pathogens during the transportation process However, although fewer by-products are formed by ozonation, it has been discovered that ozone reacts with bromide ions in water to produce concentrations of a suspected carcinogen called bromate (BrO 3 ) 1- . Bromide (Br) - can be found in fresh water supplies in sufficient concentrations to produce (after ozonation) more than 10 parts per billion (ppb) of bromate — the maximum contaminant level established by the EPA. Other disadvantages to using ozonation methods are energy requirements and cost. Of the three types of sanitization processes (chlorination, ozonation, and UV irradiation), this technique is the most expensive. Ultraviolet Disinfection (UV) Ultraviolet radiation (namely UVC) can be used to eradicate viruses, bacteria, and parasites from drinking water. This method of sanitation does not produce byproducts or alter physical properties (taste or smell) of the water. Video \(\PageIndex{3}\): Understanding Ultraviolet UV Radiation and its Effects. (Copyright, Larson Electronics). (1:54 min). However, ionizing radiation has difficulty inactivating parasitic cysts in turbid (unclear) water. Like ozonation, UV irradiation offers no residual protection and is pricier than chlorination. Smaller ultraviolet units do supply over 2 million people in 28 developing countries clean water for drinking, eating, and cooking. Figure \(\PageIndex{2}\):Ultraviolet lamp sanitizing water. Image courtesy of: https://www.nab.usace.army.mil/Media/News-Stories/Article/946068/army-water-treatment-plant-brings-a-unique-first/ References 1) https://www.oxidationtech.com/ozone/history.html 2) 14.6: Making Water Fit to Drink - Chemistry LibreTexts 3) https://r.search.yahoo.com/_ylt=Awri...6JpE5SObYtIBc- 4) cdc.gov