Difference Between Excess Chlorine and Residual Chlorine?

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12 Answers

1. The sole reliance on free chlorine is NOT good practice. As Marco pointed out that although the concept of free chlorine is simple, there are many factors which could lead to erroneous readings e.g. insufficient contact time, uneven distribution of dosed chlorine (short-circuiting), poor quality DPD tablets, water chemistry, etc. It is nice to understanding the theory of chlorine dosage - however, the challenges lie in its physical application, measurement and control. All factors must be considered including the quality of the measurement instruments, etc.

2. Very simple:

   After dosing the exact amount of Chlorine (no excess) you may still find residual chlorine, which did not react for some reasons, typically:

   -  insufficient contact time

   - unevenly distribution of th dosed chlorine in the maa of the treated water

   1 Comment

   1. Hello dear

       

      Could u tell me the suitable contact time ?

       

      Thanks in advance.

3. It is a little complicated. Are you treating drinking water?If you add enough chlorine to exceed the chlorine demand you will have some excess remaining for a time. If there is ammonia or amines in the water you can add enough chlorine to go to breakpoint where the ammonia is converted to nitrous oxide and nitrogen, anything after that will leave free chlorine in solution. The complete reactions with excess chlorine and organic carbon would continue slowly until all of the TOC has been converted to organochlorine or mixed halogen compounds if some bromide was in the water.

   With wastewater the chlorine demand is so high (so much ammonia nitrogen) that  wastewater is seldom taken to breakpoint. That means that wastewater is usually marginally disinfected, and has residual chloramines that are weak and slow disinfectants.

4. In the U.S. we use the term residual chlorine, which includes all remaining after contact time, both free HOCl, OCl- and combined, monochloramine, if used.  Free + combined = Total. Please lets stick to one term and not use 'excess.' U.S. limits the residual to 4.0 mg/L and anything in excess of that would indeed be excessive.

5. Why still using chlorine?  There is a perfect 100% biodegradable solution. use only 8% of the amount of chlorine, Easier logistics, less dangerous. contact me for availability in your region.

   2 Comments

   1. Tell me more please.

   2.  let me know sir about 100% biodegradable solution...

6. As an aside, for industrial water treatment, always feed an approved biodispersant 1/2 hour prior to dosing Cl2 and always shut off the blowdown. Always calculate the Half Time Index so that you will know when Cl2 is depleted for you to work out the next dose. Cl2 works best at pH less than 7.5. If there are humus and organic matter in the water, Trihalomethanes will form. You must be careful in your testing to take account of that.

7. they are same. any chlorine that remains after having met the chlorine demand is excess/residual chlorine

8. Residual Chlorine (also called Free Available Chlorine - FAC) is the ppm that remains in the water to prevent bacterial issues. Depending on the microbiological load within the water, you would dose in an amount of chlorine to kill off the bacteria or pathogens.

   Example: you have to dose in 5 ppm to obtain a Residual of 1 ppm, therefore you have used 4 ppm to kill off the microbiological load. 

   If this was a potable water application the dosing would allow a residual range of 0.2 to 5 ppm.

   In respect of excess chlorine surely this would be an amount that is higher than the Residual you require for your application?

   Are you dosing manually or using an ORP or Free Available Chlorine Controller and sensors?

9. They must be the same 

10. Excess chlorine is surplus in relation to the demand (eg for disinfection).  Residual chlorine is the chlorine remaining after chlorination, required in the water transported by the water supply network, but in a limited concentration, dependence on the regulations of the water quality (eg. drinking water).

11. Effectively they're the same thing. 'Excess chlorine' refers to the chlorine added after break point has been achieved, where all of the chlorine is in the form of dissociated HOCl, as does residual chlorine. The difference being that the chlorine residual is an analysed value whereas whereas excess chlorine would be a calculated mass value.  

     

    Its a little convoluted but you get the gist...

12. Excess is over of Chlorine and Res is 2 ppm for tap water in  Thailand 

    1 Comment

    1. If dosing at Pumping Station be over 2%, the nearest Taps will have over 2% however the most further ends could have 2% or less. is it correct?  How do adjust.