Water tools

Trihalomethane and haloacetic acid formation potential

Chlorine reacts with natural organic matter to form trihalomethanes and haloacetic acids. The absorbing fraction of the organic matter and the bromide present set an upper limit you can screen from three measurements.

UV254 absorbance1/cm

Dissolved organic carbonmg/L

Bromidemg/L

THM4 formation potential

172µg/L

HAA9 formation potential

182µg/L

Specific UV absorbance

2.50L/mg·m

Above about 4 the organic matter is hydrophobic and humic, with a high by-product yield; below 2 it is largely non-humic.

Formation potential tests hold time, temperature and chlorine dose constant and run high; distribution-system values are usually lower. Regressions on average water quality are a general guide, not a site prediction.

How it works

T H M F P_{4} = 1147 U V_{254}^{0.83} (B r + 1)^{0.27}

(1)

H A A F P_{9} = 1151 D O C^{0.17} U V_{254}^{0.89} (B r + 1)^{- 0.60}

(2)

where

$T H M F P_{4}$: formation potential of the four trihalomethanes, µg/L
$H A A F P_{9}$: formation potential of the nine haloacetic acids, µg/L
$U V_{254}$: absorbance at 254 nm, 1/cm
$D O C$: dissolved organic carbon, mg/L
$B r$: bromide, mg/L

UV absorbance in per cm, carbon and bromide in mg/L, results in µg/L. Bromide raises the trihalomethane potential (brominated species) and lowers the haloacetic acid potential. Enhanced coagulation, activated carbon and moving the chlorination point downstream of organic removal are the levers; chlorine dioxide and ozone form different by-products.

Trihalomethane and haloacetic acid formation potential

How it works

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