I was wondering if you could help point me in the right direction as my experience with Chlorine dosing is rusty at best. I just want to run some thinking by you to see if I have the wrong end of the stick.
I’ve been challenged on the suitability of using recycled water as a contingency at Christmas for washing produce (not drinking) and the products we would use it on are ready to cook not ready to eat and rinsed after washing using potable water. However during testing of the recycled water, we’ve seen higher than expected TVC results. The water is currently exposed to UV and dosed with chlorine at an effluent plant and using a titration testing kit at the outlet we have measured the available chlorine in the recycled water between 100ppm and 700ppm (0.01% and 0.07%). Although I need to be sure I’m using the testing kit correctly as when I add the drops to turn the solution clear it I don’t know whether I should swill the water (takes 1 drop) or leave it (6/7 drops).
Looking at the drinking water directive I think the legal limit for chlorine is: 0.05 mg Cl/l which I think accounts to 50ppm which is double the amount of free chlorine in the water, however this level of chlorine is still not adequate to reduce the TVC levels
Using an additional doser on site we ran tests for adding sodium hypochlorite at 0.5% and 1.5% However when we dose using a 0.5% solution we do not achieve the log reduction required to make the water safe and our TVC are still above reporting levels even with a 24hr dwell time.
Using quick math if we were to dose at 1.5% we’d be adding chlorine at 1500ppm (our hypochlorite is 10% concentration)
10% (Hypochlorite concentration) of 1.5% (Dosing Concentration) = 0.15% = 15000ppm even a 1% additional dose would be 1000ppm way above the drinking water directive.
- Firstly is my math sounding right.
- Should i swill the water when addid the drops.
- Do we need to get washing water to drinking water quality when we have spray bars, as in my head I think it’s likely the free chlorine on the finished product would be marginal once the produce has been rinsed. Its also not apparent how much of the recycled water would still be on the surface of the produce prior to the rinse.
- In other business do they use similar dosages
- Would a longer dwell time help.
- If there is free chlorine in the water why are TVC levels so high?
