C FACTOR
Disinfection: Part Two • Salmonella • Bacillus • Cholera
Kenneth Enlow
President, FWPCOA
S Viruses • Norovirus • Polio • Hepatitis
G
reetings everyone. August brings us the oppressive heat and humidity we are accustomed to, as well as our hurricane season. Keeping our utilities operating efficiently and safely is always job one. July’s C Factor focused on the history of disinfection. This month’s column is going to review disinfection and the disinfection methods that we practice today.
What is Disinfection? Disinfection Versus Sterilization Disinfection is the process designed to kill or inactivate most microorganisms, including all pathogenic (disease-causing) bacteria. Sterilization is the complete destruction of all organisms, but it is not necessary and would be rather difficult for water utilities to perform. When done properly, disinfection is sufficient to ensure that the water provided to your customers is safe to drink, which is what the term potable means. We also want to provide a product to our customers that’s palatable, meaning it smells good, taste good, and looks good. So, what are examples of some of the pathogenic organisms transmitted by water that are targeted when disinfecting? S Bacteria • Legionella
S Intestinal Parasites • Giardia lamblia • Cryptosporidium Disinfection Standards The treatment of water for the inactivation of pathogens is defined by the U.S. Environmental Protection Agency (EPA), which is responsible for setting and enforcing drinking water standards. The Safe Drinking Water Act (SDWA) is responsible for: S Setting standards for primary and secondary contaminants. S Defining what to do if a maximum contaminant level (MCL) is exceeded. S Defining standards based on raw water source and treatment methods. S Setting standards for disinfection byproducts. Effective and proper disinfection is a balance between providing the best protection against pathogens and control of disinfection byproducts. Florida Administrative Code (FAC) 62-550, Disinfection Byproducts, uses the EPA Federal Register Subpart L, 40 CFR Part 141, as guidance for MCLs for disinfection byproducts. Organics from source water combine with chlorine compounds to form byproducts, specifically, trihalomethanes (THMs) and haloacetic acids (HAA5). There are four specific
Cell lysing.
12 August 2021 • Florida Water Resources Journal
THMs compounds and five defined HAA5, but the EPA standard for MCL regulates them on a combined total. The MCLs for total trihalomethanes (TTHMs) and HAA5 are: S TTHMs - 0.08 mg/L or 80 parts per billion (ppb) S H AA5 - 0.06 mg/L or 60 ppb The THMs and HAA5 are suspected of causing liver, kidney, and reproductive system damage; cancer in humans; and other health issues. These standards apply to all community water systems that disinfect their water. Other disinfectant byproducts that are regulated are bromate and chlorite. Bromate can form when using ozone as a disinfectant. With the presence of bromide, ozone will combine with it to produce bromate. The pH has a significant effect on the formation of bromate above a pH value of 6.5. The MCL for bromate is: S B romate - 0.010 mg/L Chlorite byproducts are usually a result of disinfection with chlorine dioxide or with hypochlorite. The MCL for chlorite is: S C hlorite - 1 mg/L Factors Influencing Disinfection There are many factors that can influence the effectiveness of disinfection: S pH – Generally, the lower the pH, the faster the disinfectants work. S Temperature – The higher the temperature of the water, the more efficient it can be treated. Lower temperatures require longer contact time. S Turbidity – High turbidity greatly reduces disinfectant efficiency and can create a higher demand for chlorine. S Organic Matter – Consumes disinfectant while forming byproducts, such as THMs and HAA5. S Inorganic Matter – Free ammonia in the water can combine with oxidizing chemicals, like chlorine, causing a partial loss of disinfection power. Silt and other debris can create demand as well. S Reducing Agents – Iron, hydrogen sulfide, manganese, and nitrite can react with the chlorine, causing greater demand, as well as produce solids during the oxidation process. S Microorganisms – The higher the number of microorganisms, the greater the demand for disinfectant. Resistance varies greatly with different microorganisms.
