Why does COD increase over time when external carbon sources are added in the denitrification process in waste water?
After 1 hour, the concentration increased from 30mg/l to 40mg/l after 20 hours.
carbon source : ethanol
Hyunjun Song , chemical oxygen demand indicates the amount of matter that will react with oxygen. Your result generally means that there is more matter available to react with oxygen. It sounds like despite of your denitrification process, that the addition of ethanol has a greater effect and therefore COD increases.
Dear Hyunjun Song
Ethanol has its own COD, i.e. it can be chemically oxidized by oxygen. So you must observe a temporary COD increase in the denitrification system.
Regards
Dear Hyunjun Song
It is clear the observed COD increase over time from 1 hour to 20 hours after adding ethanol is NOT due to the ethanol itself which is readily biodegradable (fast COD/BOD) but to the previously slowly biodegradable COD adsorbed and absorbed by the bacteria which is enzymatically broken down and released in anoxic and anaerobic conditions. That's why we apply the far more efficient simultaneous bio-N-removal process via partial nitritation (NO2-) and anammox. This process does not need the addition of external carbon sources.
Bruno Peeters if you allow how the amount of external carbon source to be added for successful denitrification can be calculated.
Khadija Zaki as stated in the last part of my reply (click "Read more") there is no need to add an external carbon source when applying simultaneous bio-N-removal process via partial nitritation (NO2-) and anammox.
Bruno Peeters Yes exactly, I want to know how the external carbon is calculated. In fact, I am working on two reactors for leachate treatment, the first using external carbon for denitrification, and the second using the nitritation and anammox process.
In the 2nd reactor, how can we detect the presence of anammox bacteria and that the elimination of ammonium is due to anammox and not to denitritation.
Thank you very much for your help.
Khadija Zaki
Using the inefficient sequential full nitrification (NO3-) and denitrification process (your 1st case) requiring the addition of organic carbon is obsolete for us since 1991 when we developed and applied the simultaneous bio-N-removal process via partial nitritation (NO2-) and anammox (your 2nd case) at full scale.
In the obsolete 1st case we controlled the addition of organic carbon by online monitoring the residual nitrate/nitrite (NOx-).
In the 2nd case, anammox removes ammonium (NH4+) by stoechiometric amounts of nitrite (NO2-) resulting in denitritation (NO2- > N2 gas). That's why 50% of the ammonium (moles) needs to be oxidized to nitrite. This is confirmed by plenty of scientific literature on anammox. We monitor and control this balance on line via ORP measurement backed by NOx- analysis of samples.
Bruno Peeters , This is very interesting, thank you very much for your clarification
Bruno Peeters I have the same problem in the denitrification batch reactor. How long does it take to remove this COD and start new a batch? It is not feasible that we omit external carbon addition and look for COD from hydrolysis to increase rbCOD.
One of the solutions is decreasing biomass concentration to reduce the hydrolysis rate.
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