Sulphur Denitrate effluent dosing rate

rpgraff · Sunday at 9:13 AM

I have been using a sulphur denitrate reactor for about 3 months now, have reached my target levels of NO3 at 5.0ppm and PO4 0.15ppm (+/- 5%). I am controlling phosphate with lanthanum.

Everything I have read and recommendations from others indicate that the effluent dosing rate should be a slow drip. However in my case in order to read any nitrate in the effluent (Hanna HR Checker), I have to dose the effluent at about 125ml per minute, more like a steady stream.

I have tried dosing at a much less rate, more like a steady drip of 3-4 drops per second and the effluent nitrate will drop to zero on the HR checker and the lowest the ORP probe gets is +300 ORP. It has been suggested to me that when monitoring ORP it shouldn’t drop below -300orp. Should I expect a much lower orp than I am experiencing?

Are there any inherent issues with running the reactor at a higher flow rate? Or should I remove some sulphur media?

I am using a Deltec NF90, their smallest reactor that is about half filled with sulfur beads and an inch of reborn media. The system is about 150gallons to total water volume less rock and corals.

Randy Holmes-Farley · Sunday at 9:23 AM

My concern with a higher flow rate is that you may still reduction in nitrate from aerobic oxidation of the sulfur, which will lower nitrate and alkalinity. If you do not see that effect, its not a concern.

rpgraff · Monday at 3:47 AM

Randy Holmes-Farley said:
My concern with a higher flow rate is that you may still reduction in nitrate from aerobic oxidation of the sulfur, which will lower nitrate and alkalinity. If you do not see that effect, its not a concern.

Should I assume that anaerobic reduction of nitrate does not oxidize the sulphur and consume alkalinity?

Other than the reduction of alkalinity is there any adverse issues with oxidation of the sulfur?

Randy Holmes-Farley · Monday at 11:50 AM

rpgraff said:
Should I assume that anaerobic reduction of nitrate does not oxidize the sulphur and consume alkalinity?

Other than the reduction of alkalinity is there any adverse issues with oxidation of the sulfur?

It does, but only when nitrate is consumed. Aerobic oxidation would use O2 and not nitrate. Too much O2 in the reactor will prevent nitrate from being consumed.