Dear. Bhavik

1.- Bod is consumed in nitrification or denitrification?

The nitrification is a microbiological process in which the ammonium is oxidized by autotrophic bacteria in presence of oxygen and carbon inoganic, in this process does not eliminate BOD. on the other hand DENITRIFICATION uses the nitrate generated in nitrification to generate nitrogen molecular, in this process (denitrification) takes place in the absence of oxygen and at this stage the bacteria remove organic matter quantified as BOD or COD.

2.- why in definition of BOD, it is stated that amount of oxygen required to degrade organic substances???

Biochemical Oxygen Demand (BOD) is the amount of dissolved oxygen needed (i.e. demanded) by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over 5 days.

Your confusion is that you are taking a textual definition, and BOD is an indirect parameter that allows you to measure the amount of biodegradable organic matter present in the wastewater based on the amount of oxygen required to oxidize it. That is, it is the amount of oxygen that you need biologically speaking to oxidize the organic matter present, a concept very similar to the COD. The difference is that here all the organic matter is oxidized by chemical reactions (degradable and non-biodegradable).

3.- In real life, anoxic bacteria (denitrfiers) are consuming BOD

Yes, in real life, these bacteria consume the organic matter measured as BOD or COD as a carbon source to transform nitrate into molecular nitrogen.

4. I have to design biological system for BOD removal but I do not have nitrogen source (NH3) in my feed. Do I have to provide nitrogen source like urea for bacteria to work or there are certain bacteria which do not need any nitrogen source.

If you do not have a source nitrogen, because you want to use a nitrification / denitrification process, this biological process is used when your wastewater is rich in nitrogen, based on your coments, I recommend you use another type of treatment, for example using a anaerobic bioreactor such as a uasb, egsb or anaerobic filter. If you give me more information related to your water type, not only your dbo could help you decide which bioreactor to use to eliminate that BOD.

dbo, dqo, nitrogen, sulfates and ph.

All the bacteria used in wastewater treatments need nitrogen since without this they can not synthesize new cells or their genetic information, so there is a C / N relationship as a rule of thumb which must be met depending on the biological process.

If my wastewater does not have the minimum requirements of nitrogen, it is necessary to add it

5. is worth it to go for biological treatment with high soluble BOD upto 6000 ppm? Is there any other way to reduce soluble BOD?

yes, but I need more information to suggest you what process yuo need use.

Best regards

Abumalé

The question about nitrification should be examined as a separate group of organisms that grow relatively slowly and convert ammonia nitrogen, where one group of organisms convert ammonia to nitrites and a second group of organisms concert nitrite to nitrate. The carbon source is from bicarbonate alkalinity that may be from carbonate generate in organic carbon biological conversion. If this source is not adequate, carbonate alkalinity must be added.

Conversion of one milligram of ammonia nitrogen to nitrate nitrogen requires 7.14 mg of bicarbonate alkalinity. No organic carbon (BOD) is involved.

Dear Abumalé Cruz-Salomón,

Thank you for the detailed explanation. Actually, I am confused because as you said amount of oxygen required to biologically degrade organic compound but in real life BOD is consumed by denitrifying bacteria which do not require oxygen. So, I am not getting that BOD is consumed by the bacteria that do not need oxygen and in definition it says amount of oxygen required to oxidize the compound. Isn't it contradictory?