Hydrogen sulfide (H2S) is sometimes found in ground
water. It has the odor of rotten eggs
and has a threshold of 0.0011 mg/l. It
can also cause water to have characteristic and unpleasant tastes. While aeration can be used to strip some of
the hydrogen sulfide from the water, this converts a water problem to an air
pollution problem if further treatment is not applied.
Hydrogen sulfide is easily and rapidly oxidized by ozone,
ultimately to form sulfate. The initial oxidation is to form elemental sulfur
which is seen as a light colored colloidal suspension. Further oxidation dissolves the elemental
sulfur to sulfite and continued oxidation produces sulfate. As a result, more
ozone is required to produce sulfate from hydrogen sulfide than is required to
produce sulfur.
The theoretical dose to oxidize ozone to sulfate is 3:1, but
in practice the ratio is 4:1. This will leave a small ozone residual in the
water, 0.2-0.3 ppm. This residual can be used to ensure that the hydrogen
sulfide is fully removed. In the case of variable hydrogen sulfide
concentration, following the residual will allow for adjustment in the ozone
dosage rate to maintain complete removal of the ozone. A dissolved ozone monitor with PID controller
integrated with ozone generator power control can be used for this purpose.
Off gas from the ozonation process can strip hydrogen
sulfide from water. Ozone in the off gas is often removed using an ozone
destruct catalyst. If H2S is present in
the off gas the ozone destruct catalyst can be poisoned. This means that the way the off gas is
handled needs to take this issue into consideration.
Ozone has been used by the City of Orlando to remove H2S
from their ground water for a number of years.
Commercial beverage companies using similar water sources have also
adopted ozone for controlling this problem.
Integrated ozone water treatment systems are relatively easy to install,
operate and maintain for this application.
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