Yesterday we were asked a good question in a comment on a blog post from back in March about disinfecting water with hydrogen peroxide. Erik asked, “What would the recommended dosage of H2O2 be per volume unit of water?”
The dosage of H2O2 required depends on the concentration of contaminants in water, not so much the volume of water in your system. Of course, contaminants are measured in parts per million (ppm), so any measurement of their concentration already accounts for the total volume of water present.
Hydrogen peroxide is injected in parts per million, which is the same as saying milligrams per liter (mg/L). The amount of hydrogen peroxide needed depends on the “hydrogen peroxide demand” of the water. Hydrogen peroxide demand is the amount of various contaminants in the water that combine with the hydrogen peroxide after it has been injected and sufficient contact time has occurred.
After the hydrogen peroxide has combined with the various contaminants such as bacteria, iron, manganese, and odor, some level of uncombined or “free” hydrogen peroxide will remain. The goal is to have some small amount of free peroxide, usually around 0.2 to 0.4 ppm of peroxide, up to a maximum of 1.0 ppm of hydrogen peroxide, present before filtration.
For bacteria you’ll want to inject 1 – 2 pp,m of hydrogen peroxide with approximately 5 to 10 minutes of contact time depending on your water’s temperature and turbidity (cloudiness). If the water is colder than 50° F (10° C) and/or the pH is higher than 7.5, you may need longer contact time or a higher dosage.
You should generally inject 1.0 ppm of hydrogen peroxide for each part per million of iron or manganese, and 1-2 ppm of H2O2 for each 1.0 ppm of hydrogen sulfide gas (the cause of rotten egg smell in water).