What could be the possible reasons for that? Could it be that, the bacteria may use polyhydroxyalkanoets as alternate carbon source. Because the bacterial staining shows PHB accumulation.
The reasons can be:
The anammox process,
The autotrophic denitrification,
The use of internal source of carbon e.g. PHB.
Do you measure soluble COD in order to calculate organics removal? Is there a possibility that the “somehow less COD removal” occurs due to interference of particulate organics? I also have seen small but not negligible differences in soluble COD measurements when using 45μm membrane filters or fiber-glass filters.
Thank you Georgios. Yes We measure soluble COD in order to calculate organics removal. And we also use 45μm fiber-glass filters to filtrate the sample. But as we are following the APHA method in which we are countering the interference.
Thank you Georgios. Yes We measure soluble COD in order to calculate organics removal. And we also use 45μm fiber-glass filters to filtrate the sample. But as we are following the APHA method in which we are countering the interference.
Thank you Korneliusz.. Can Autotrophic denitrification and heterotrophic denitrification co-exist in a system?
Jyotsna, I agree with Korneliusz except for Anammox which does not consume/reduce nitrate but instead produces nitrate as side product.
Most likely the denitrication is heterotrophic using some of the internally stored organics as to complement the readily biodegradable fraction of the soluble COD in the bulk liquid.
Autotrophic denitrification can co-exist with heterotrophic one in the same system depending on operating conditions including level and type of e-acceptors.
Jyotsna, I agree with Korneliusz except for Anammox which does not consume/reduce nitrate but instead produces nitrate as side product.
Most likely the denitrication is heterotrophic using some of the internally stored organics as to complement the readily biodegradable fraction of the soluble COD in the bulk liquid.
Autotrophic denitrification can co-exist with heterotrophic one in the same system depending on operating conditions including level and type of e-acceptors.
Besides the previous answers (and particularly eventual errors in samples or in laboratorial measurements?), my considerations are quite simple. It is assumed comparable values of aeration time, time of settling, composition/quantity of the wastewater and/or sludge, and quantity or age of sludge? The composition (characteristics) of the wastewater is very important (domestic, industrial or mix?) both in terms of organic matter, chemical characteristics and biologic cultures. Industrial contributions in domestic wastewater without pretreatment may introduce uncontrolled/unexpected variations. Topic includes “Industrial wastewater treatment”?
Maybe You should measure soluble BOD, in order to evit solids interference!
Jena,
1) how much solids are removed after filtration? Have you tried to make COD on solids? and calculate total COD of filtrate + solids & and compare with N-balance
That might be quite big source of organics for denitrification stored in solids?
2) How much ammonia is present in the system? If not much - then you need to consider utilisation of N-nitrate for biomass synthesis. it could be sometimes quite substantial.
Best, Alexander.
Dear Alexander Sir
Thank you for your valuable suggestion. I ll evaluate the COD on solid.
Yes we have very negligible ammonia in the system. So naturally some nitrate must be utilized for biomass formation.But how can I get the exact/approx amount that has been utilized for biomass synthesis? Please do suggest.
Thank you so much.
Regards
Jyotsna
Dear Jyotsna,
If you perform your experiment under strict anoxic conditions, then, you need to estimate (perhaps, approximately) electron & nitrogen balance. You also need to estimate biomass formation, perhaps, via protein measurement. For bacteria it is assumed 1) that protein is ~ 50 % of dry biomass; 2) there is also average bacterial biomass formula in the literature where N is also included. From 1) and 2) you may estimate amount of nitrate that was used for assimilation. You may also estimate how many electrons were used for assimilatory nitrate reduction. When you know & caclulate all estimations - then you may see total processes. With best wishes and apologies for the late answer due to the lack of time, Alexander.
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