It was a recommendation from Donovan to test if denitrification is happening. However, after finding his post he suggested 30 min. I would use his recommendation of 30 min instead of 15min.Could you explain to me the 15min check after dosing carbon? In my DND it takes 3.5-4hrs for inlet water to exit the DND. I am auto dosing 2.5ml every 3hrs. My DND is working fine but curious about your 15min rule.
A few recommendations:-
1) Your outlet pipe is too big, allowing air to enter the second chamber. We want air tight chamber here as denitrification happens at low oxygen
2) To test whether denitrification do happens, test the effluent output after 30 minutes vodka being dosed. If it is lower, test one more time after few hours and compare the differences.
3) If no NO3 reduction at item 2, reduce the flow to 25ml/10 seconds and repeat test no 2
* Please make the outlet hose smaller first