C FACTOR
Disinfection: Part One Kenneth Enlow
President, FWPCOA
G
reetings everyone. Here we are at midyear already. July brings hot weather, resulting in warmer water. This is the time of year when we face some of our most difficult disinfection challenges. For July’s C Factor I am starting a two-part series on disinfection. This month’s column will take a look at the history and methods of disinfection.
would limit the spread of infection. From this erroneous belief, the disinfection of both water and sanitary wastes evolved. Rational of Disinfection Water disinfection involves specialized treatment for the destruction of harmful and otherwise objectionable organisms, primarily disease-producing (pathogenic) organisms and particularly bacteria of intestinal origin.
The History of Disinfection
Efficiency of Disinfection The major factors influencing the efficiency of disinfection are as follows: S Kind and concentration of organisms to be destroyed S Kind and concentration of disinfectant S Contact time provided S Chemical character and temperature of the water to be treated
The Origin of Disinfection The disinfection of water probably has been practiced for millennia, but obviously with little or no understanding at first of the principals involved in its improvement of water quality. Records show that the boiling of water was practiced as early as 500 B.C. Until the germ theory of disease was established in the mid-1880s, odors were believed to be the transmitter of diseases. It was commonly believed that the control of odor
The resistiveness of the same and different kinds of organisms to a specific disinfectant varies considerably. Nonspore-forming bacteria are less resistant than spore-forming types. Cysts and viruses are sometimes quite resistant and may require treatment in degree or kind different than that for less-resistive organisms. Organisms within the same species can have varying degrees of resistance. The concentration of organisms in high numbers can cause clumping that forms a barrier against disinfection processes.
42 July 2021 • Florida Water Resources Journal
It’s very important to note that the kill of a species of organisms by a particular disinfectant, other factors being constant (pH, temperature, etc.), is proportional to the concentration of the disinfectant and the reaction time. Means of Disinfection There are several means of accomplishing disinfection, excluding the water treatment process, that result in the partial removal of potentially infective and objectionable organisms, such as sedimentation, coagulation, filtration, etc. They are: Ph ysical treatment - such as the application of heat or other physical agents. Irradiation - such as by ultraviolet light. Metal ions - such as copper and silver. Al kalis and acids - such as contact with alkaline or acid waters related with pH adjustment and corrosion control, lime softening, etc. Sur face-active chemicals - such as quaternary ammonium compounds (any of a group of compounds in which organic radicals replace hydrogen atoms of the ammonia radical used as solvents, antiseptics, and emulsifying agents). Ox idants - such as halogens, ozone, and other inorganic or organic material. The criteria for determining the suitability of various potential water disinfectants are: S The ability of the disinfectant to destroy
