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?”
You should generally inject 1.0 ppm of hydrogen peroxide for each part per million of iron or manganese, and 2 ppm of H2O2 for each 1.0 ppm of hydrogen sulfide gas (the cause of rotten egg smell in water).
The dosage of H2O2 required depends on the concentration of contaminants in water. 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. Adding peroxide to water creates dissolved oxygen in the water, as well as bubbles that are not dissolved.
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.
Often peroxide injection is followed by a backwash filter containing catalytic activated carbon, a type of carbon that works as a catalyst when dissolved oxygen is present in the water.
Peroxide is not a good disinfectant in water, compared with chlorine. If you have bacteria present, you might want to use chlorine instead of peroxide, or use the peroxide to oxidize iron and sulfur odors, and install a UV sterilizer or bacteria filter as a final stage.