Residual Chlorine Information 1

[Njeckebr]

I have to treat a system that needs to maintain a chlorine concentration of roughly 100ppm.

once the bacteria is killed, how long will the residual free chlorine remain in the water?

Until more bacteria is formed?

Evaporation is not a factor.

Thank you

 

[bimr]

100 mg/L is a very large dose.

The length of time the dose remains depend on the size of the piping and the fluid contents. If the system is completely closed, the residual may taper off over a few weeks times.

 

[Njeckebr]

The system is not closed. The water is sprayed at about 500 gal/min, drained off, and then recirculated through the system again.

 

[bimr]

Not sure what you are doing. Cooling towers usually have a much lower chlorine residual.

For a cooling tower, chlorine can be fed either continuously (typically 1-3 ppm), or as a shock dosage (typically 3-5 ppm) at regular intervals. On a shock basis, sufficient chlorine may be fed to provide a total residual chlorine (TRC) level up to 1 mg/l, measured downstream of water cooling systems, for one hour, two or three times daily. If the cooling system is operating at an alkaline pH (8-9 pH), continuous low dosage chlorination may be preferred. In this case, chlorine is fed to maintain a TRC of approximately 0.2 to 0.5 mg/l throughout the system.

The amount of chlorine needed to destroy the biofouling organisms in the water and oxidize organic and inorganic matter is called the chlorine demand of the system. The chlorine feed rate depends upon the degree of biofouling expected under worst conditions, the non-biological chlorine demand in the water, the holding time in the system, and the discharge limitations. Chlorination equipment should be sized to provide a chlorine dosage several times the final TRC level allowed. This provides chlorinator capacity to meet the demand in the system, and losses of chlorine through aeration in the cooling towers.

You will have some chlorine loss because of aeration of the water and pickup of microbials from the air.

 

[EdStainless]

And even the oxidation of non-microbial organics will consume free Cl.
There is no function of free chlorine above 0.5ppm for any significant period, except to destroy the system that contains it.
If you have a system (pumps, piping, and so on) have you considered what damage 100ppm Cl will do?

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P.E. Metallurgy, Plymouth Tube