Disinfection: A Beginners Need To Know

Disinfection is the removal or inactivation of pathogenic organisms in water. In simpler terms it is the stopping of disease causing organisms in water through removal/killing/blocking the bacteria’s ability to reproduce.

Disinfection is not the killing of all organisms in the water; that is sterilization. Disinfection is also not the removal of all contaminants. It only refers to the living contaminants (bacteria, virus, cysts, oocysts, protoza, etc).

There are two stages of disinfection. Primary disinfection and secondary. Primary disinfection is the procedure to make the water safe to drink, and secondary disinfection is done to keep water safe for storage or distribution.

Secondary disinfection is necessary because over time water can become recontaminated with bacteria that survived primary disinfection and some usually do. Secondary disinfection keeps bacteria growth minimal/nonexistent.

Primary and secondary disinfection are not always separate steps. As the disinfectant is added, it is used up. This is called the demand. As the demand is met, some of the disinfectant remains as a residual. This residual is your secondary disinfection. I will point out here that not all disinfectants leave a residual. I will talk more about the different methods of disinfection in another article. This article I am focusing on the basics of disinfection. Monitoring the disinfectant residual with the appropriate kit is absolutely essential. It is the easiest way to know when to refresh your water.

I will say it many times, it is ALWAYS best to settle and filter your water first. Pathogens can hide in and on suspended particles and be shielded from the disinfectant. It is like a little bacteria bunker, and they are waiting till the coast is clear to emerge again. Except this time it will be inside you. Another reason to filter first is that the dirtier the water the higher the disinfectant demand and more disinfectant will be needed to do the same thing. This will be very important for two reasons. First, your supplies will be depleted significantly sooner. I have seen the disinfectant demand go up over seven times normal levels when there is a small increase in turbidity (cloudiness due to suspended particles). The disinfectant demand is one of the critical monitoring points at my water treatment plant (and most others) not just because the water needs to be disinfected before it can be delivered to the customer, but it lets me know that something is not working properly in my facility.

There are many recipes available for how to disinfect water. So many drops and for so many minutes. I will never give you a statement like that because there are cases where that may not be true. Water disinfection is determined by a calculation. Concentration times Time CT value. For each source of water there is a CT value that must be met for it to be disinfected. This is not a fixed number.

I hope to help my readers get to a point where they can choose their source water in such a way that treatment is easiest and with the right tools, disinfect their water EVERY time. I will be writing about some of the common methods for disinfecting water. Each one requires different procedure and thought/decision process (read here: MORE articles!)

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6 thoughts on “Disinfection: A Beginners Need To Know

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