Did you know that chlorine does not sanitize until the oxidant demand has been destroyed? According to (http://dnr.wi.gov/regulations/labcert...), that's one of the fundamental pieces in the science of chlorination. This video explains breakpoint chlorination, hyperchlorination and more. Breakpoint
Did you know that chlorine does not sanitize until the oxidant demand has been destroyed? According to (http://dnr.wi.gov/regulations/labcert...), that's one of the fundamental pieces in the science of chlorination. This video explains breakpoint chlorination, hyperchlorination and more.
Breakpoint chlorination is the point where chlorine levels exceed the oxidant demand, and the water begins to build a residual of free available chlorine (FAC). Theoretically, exceeding the "breakpoint" prevents increased levels of disinfectant byproducts (like chloramines).
The chemical reaction that creates Monochloramine (NH2Cl) looks like this:
2NH3 + 2HOCl → 2NH2Cl + 2H2O
Ammonia + Hypochlorous Acid yields Monochloramine + Water
Further chlorination of monochloramine creates Dichloramine (NHCl2):
2NH2Cl + 2HOCl → 2NHCl2 + 2H2O
Monochloramine + Hypochlorous Acid yields Dichloramine + Water
And of course, even further chlorination yields the most noxious of chloramines that off-gasses from pools, Nitrogen Trichloride, aka Trichloramine (NCl3):
NHCl2 + 3HOCl → NCl3 + 3H2O
Dichloramine + Hypochlorous Acid yields Trichloramine + Water
All of these reactions depend on pH and temperature.
As noted before, chloramines are disinfectants-which is why they are referred to as disinfectant byproducts (DBPs). In fact, many water treatment plants add chloramines to their water as a secondary disinfectant. Albeit weak and slow, chloramines first contribute to the total chlorine levels because they help with disinfection. This, however, reaches a threshold where chlorine turns on chloramines, indicated at point (B). In other words, chlorine oxidizes all contaminants, which includes chloramines after point (B) on the graph. That's why the total chlorine level drops with the addition of more free chlorine (the X axis on the graph).
The downward trend on the graph shows chlorine starting to "win the fight" against contaminants until it oxidizes all but the combined chlorine residual. This level of chlorine residual is shown on the graph at point (C). If chlorine cannot overcome the oxidant demand, your water's chlorine demand rises, and the ORP drops. This would look like a more prolonged downward trend toward breakpoint, because breakpoint would be at a much higher dose of chlorine. When the chlorine can meet the oxidant demand, the water has reached breakpoint chlorination.