UV and Chloramines

[holden94]

UV systems have been by all accounts, a very effective means for treating chloramines ( along with proper ventilation, filtration, etc) in indoor pools. Commercial outdoor pools typically have very low levels of chloramines. With air circulation being a non-issue, how much can the Sun's UV rays account for the destruction of chloramines in outdoor pools? Probably impossible to quantified that. If chloramines are found to be elevated in an outdoor pool, could it be suggested that the sun is treatment itself?

 

[chem geek]

For a residential pool that is typically low bather-load, the UV in sunlight along with outdoor air circulation is sufficient to make chloramines a non-issue. However, in a high bather-load pool, the UV in sunlight may not be enough to control chloramines. The UV in sunlight is not in the strongest absorbing region for chloramines. This graph shows that the molar absorptivity for dichloramine extends beyond 300 nm wavelength where the UV in sunlight cuts off (sun irradiance peaks at around 1.5 W/m²/nm in the 500-600 nm range, but drops to 0.5 at 350 nm and to 0.15 at 320 nm, 0.03 at 310 nm, 0.002 at 300 nm and 0.000003 at 290 nm).

Since dichloramine is an intermediate towards nitrogen trichloride in the chlorine oxidation of ammonia, the sunlight helps, but it doesn't compare to a UV system which is better suited to high bather-load situations and indoor pools.

Note that UV in chlorinated swimming pools may be a mixed bag as noted in this paper where some chloramines may be reduced, but some other byproducts such as cyanogen chloride may be increased. It is not a panacea.