Hi Daniel, Thank you for your answer, Yes, it is a batch process and I will know test it as you said. Another question: Do you have experience with disinfection time of sodium hypochlorite? The producer suggests 30 minutes, but also after 1-2 hours the FRC keeps on decreasing indicating that the disinfection is still happening.   Thank you. Donato

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Hi Daniel,

Thank you for your answer, Yes, it is a batch process and I will know test it as you said.

Another question: Do you have experience with disinfection time of sodium hypochlorite? The producer suggests 30 minutes, but also after 1-2 hours the FRC keeps on decreasing indicating that the disinfection is still happening.

 

Thank you.

Donato

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Hi Donato,

Yes I do have experience with disinfection ​time of sodium ​hypochlorite!

I'm not sure where/in which country your application is based, however,  the WHO recommends maintaining a free chlorine residual of 0.5 mg/L for 30 minutes within the tank.

If you suspect cholera might be present you should increase this to 1.0 mg/L for 30 minutes.

You might want to trial this in a beaker (using the water) before you do it at full scale to get an idea of what your initial chlorine concentration will need to be in order to still have at least 0.5 mg/L after 30 minutes (i.e. a chlorine decay test).

Dose the tank and monitor the free chlorine within the tank over the 30 minute period. Try to measure relatively frequently (every 5 or 10 minutes) to make sure the free chlorine in the tank doesn't drop below 0.5 mg/L at any stage over the 30 minute period. If need be you can top up the chlorine during the process if it looks like it might drop below 0.5 mg/L.

Note that the free chlorine will continue to decrease over time. This is not necessarily due to it killing harmful bugs (disinfecting) but is often due to it reacting with harmless organic matter present in the water. In addition chlorine will simply break down over time due to decomposition, particularly in the presence of light. But as long as you have maintained at least 0.5 mg/L of free chlorine in the tank for 30 minutes, that should be sufficient for disinfection purposes.

Also let me know if the pH of your water is above 8.0. Sodium ​hypochlorite is less effective as a disinfectant in waters with pH greater than 8.0.

Regards,

Daniel

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