I find opposite and contradictory range for ORP which reported by various researchers who worked on denitrification. I need to reliable reference for ORP range in aerobic, anoxic and anaerobic metabolic conditions. thanks for your contribution
It should not be an exact value, but approximate, -100mv to 20mv for denitrification.
Dear Dr.Daniel and Zhiping
thanks a lot for your answer
can you introduce any reliable reference?
Dear Mahdi,
I am working with autohydrogenotrophic bacteria for denitrification. I observed that the ORP value is always lower than -250 mV. You can see the attached file (Pg.25) for more details. Hope that it is useful for you. In other situations, the ORP value range for denitrification is mentioned at from - 50 mV to 50 mV.
Best Regards
Phu
Dear Phu
Thank you very much for your answer. The attached file is so useful for me
The reason why there is such a large range in ORP is its imprecise nature (oxidants/reactants). I would say -150 to +50 mV. If you measure ORP and track nitrate concentrations during denitrification in activated sludge systems you will see what is characteristically identified as the nitrate knee which is when nitrate disappears. Even ORP probes from the same manufacturer will give different OPRs for the same reactor. The only effect that can be reliably measured by ORP is dC/dt effects. I hope this helps.
Dear Angus
your comment was helpful for me
thanks a lot for your contribution
I agree completely with the advise of Angus. In addition, it may be useful to look at oxygen levels (if you are not already) as the heterotrophic organisms responsible for denitrification will typically only use nitrate as electron acceptors once the oxygen is expended. As you are probably already aware, although oxygen levels have a profound effect on Eh, are many other elements that also have an influence.
Dear Dr. Pamela J Welz
I have used gas tight reactor and dissolved oxygen concentration was kept blow 0.5 mg/L and ORP variation was between +50 to -50 mV.
Thanks for your comment.
Many people throw the variation at which you find denitrification on the probes. I think a lot has to do with correct measurements, and the understanding of the variabililty of natural systems.
In soils it is crucial to know how the vertical profile reacts and what the redox potential profile is in there.
@ Tran Ngoc Phu Nguyen: your values seem very low. Did you add the reference value to the measured potential, in order to get Eh?
Perhaps another aspect to consider is GHG emissions, it's a balance between one environmental benefit at the expense of another. Eg Hou et al 2000 found that "significant CH4 emission occurred only at soil redox potential lower than approximately −100 mV, while the emission of N2O was not significant below +200 mV."
Hou, A. X. et al. (2000) ‘Methane and Nitrous Oxide Emissions from a Rice Field in Relation to Soil Redox and Microbiological Processes’, Soil Science Society of America Journal, 64(6), pp. 2180–2186. doi: 10.2136/sssaj2000.6462180x.
There is not an accurate value of redox conditions for biological denitrification. The reason is that redox potential depends among others on groundwater chemistry and the measured value ios influenced by chemicaůl processes in water. This is the reason why the correct answer in my opinion is redox potential in the range - 100 mV to + 100 mV is suitable for denitrification.
Regards
Vit
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