What Causes Low PH in Chlorine Dioxide Treated Water?
Low PH levels in treated water can render it undrinkable and unusable for its intended purpose. Fortunately, low PH levels in chlorine dioxide treated water are usually caused by simple mistakes or equipment failures related to the process of adding the chemicals which combine to form chlorine dioxide. A step by step analysis of this process can usually reveal the problem.
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Where the acid which causes low PH originates
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Low PH in chlorine dioxide treated water most commonly arises when the chlorine dioxide has been produced by combining sodium chlorite and hydrolchloric acid. Sodium chlorite and hydrolchloric acid are added to the untreated water where they combine to form water, sodium chloride and chlorine dioxide. However, an excess of acid is used to push the reaction to its completion. As a result not all of the acid will be converted by the reaction into less acidic products. As a result, there will be left over acid in the water, lowering its PH.
Normal procedures for dealing with left over acid
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The left over acid and the resulting low PH of the water must obviously be treated. This is usually done by adding higher PH, alkaline products to the water to neutralize it before it leaves the treatment plant. For a number of reasons this treatment can fail to neutralize the unreacted acid left over from the first reaction.
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Failures in PH monitoring and neutralization.
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In many water treatment processes the PH is measured and the quantity of alkaline added to the water is regulated automatically, ensuring that the water is entirely neutralised before it is released. However, a failure in the PH monitoring equipment can result in water which is still excessively acidic being released. Additionally, water may be checked once for PH, an appropriate quantity of alkaline added and the water released without a secondary check on its PH. If the alkaline substance has gotten wet or been otherwise contaminated with something acidic prior to use, its neutralising properties may have been reduced so that they fail to neutralise the water as expected.
Failure in the dosing procedure.
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If the entire process is regulated according to the quantities of chemicals added to the water, without checking the PH of the outgoing water, one or more of the systems delivering the chemicals to the water may be faulty and failing to correctly measure the quantity added to the water. If an excess of hydrochloric acid or a deficiency of sodium chlorite or neutralising chemical have been added then the reaction will remain imbalanced and excess acid will be added to, and remain in, the water.
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- Photo Credit Water treatment plant image by Andrei Merkulov from Fotolia.com
