Non-chemical Methods for Chlorine Dissipation

The chlorine concentration in stored water gradually decreases with time due to aeration, reaction with sunlight, and reaction with surfaces of holding tanks. A number of utilities store filter backwash water and main disinfection water in holding tanks to allow for residual chlorine decay. On some occasions the chlorine demand of the water is reduced by retention in a holding tank for some time, prior to dechlorination using chemicals. 

Combined chlorine is more stable than free chlorine in the environment. Hence, decay of combined chlorine in holding tanks will require much longer retention times than those of free chlorine. 

Organic and inorganic impurities in soil and pavements exert a significant amount of chlorine demand and rapidly neutralize chlorine in waters. Hence, spraying chlorinated waters onto soils or pavements can be a very effective method for disposing of chlorine-containing waters. The presence of impurities in the soil typically increases decay rates compared with those observed in holding tanks. 

Discharging Through Hay Bales and Other Natural Obstructions 

The availability of a sanitary sewer near the point of chlorinated water release, and the capacities of the sanitary sewer and the wastewater treatment plant to handle the additional load, are the primary limitations in this method. Potential upset of treatment plant operations due to chlorinated water release must also be evaluated. A back-flow prevention device or an air gap method must he used to prevent cross-connection problems. 

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