Water Disinfection systems generally fall under two categories, the type that uses chemicals like Chlorine (Sodium Hypochlorite), Hydrogen Peroxide, Bromine, Ionisation, to name a few and other types include Ozone and Ultra Violet.
Pathogens can be greatly reduced with filtration and flocculation but water disinfection systems are generally the last thing in the system before its put to use.
How chemicals are dosed into a line is a calculation based on how clean the water is to begin with, the flow rate and how much residual chemical is required to be left over. In chlorine this is measured as FAC or Free Available Chlorine. Most municipal water disinfection system incorporate chlorine into the water lines as it’s a contact disinfectant – as the name suggests it disinfects with whatever it comes into contact with. As the chemical is passed down the line it generally starts to lose its effectiveness due to the chemical reacting with organics or the atmosphere.
Most home water disinfection systems on un treated water supplies use Ultra Violet Light as it’s highly effective and doesn’t leave any taste in the water. Many commercial and industrial disinfection systems like breweries and water bottling plants incorporate many types of disinfection systems as a belt and braces precaution. Just like chlorine, specifying UV and Ozone is a calculation dependant on the water quality and flow rate. A water supply that has to meet New Zealand Drinking Water Standards for certain supplies may require to have a validated UV. This is a UV system that’s validated by a third party to a NSF 55 standard. This means that the water that is being supplied to the UV must also meet the criteria specified by the manufacturer.
Some disinfection systems don’t necessarily have to come into direct contact with the water as an in-tank UV system can be fitted to the tops of tanks to sterilise the airspace as when the tank is emptying and there is a vacuum inside the tank, contaminated air may be drawn in from the outside into the tank. A lot of tanks have their own tank vent filters to help with this.
Water Disinfection systems are designed around the application and the regulations that may be required.