Hi Mr. Wahiduzzman ,

I think I would do a few tests to verify or rule out the presence of other non-ammonium nitrogen species and how they could affect my results in the water samples you are working with. If your wastewater comes from an agroindustrial activity, it might be advisable to do a certain degree of fractionation depending on what you are looking for. Now, if you need the total N content present as you state in your question, you absolutely need to do the digestion process. If you only need ammonium-N, not necessary. Take also into account that there might also be very labile organic compounds such as urea that can easily transform into ammonium ions by a rapid hydrolysis.

Good luck with your research

I think if you just want ammonium-N no digestion is necessary. When determining ammonium-N on soil extracts, we usually just add MgO to the sample to convert the ammonium-N to ammonia-N, which is then trapped in boric acid. Perhaps you may have to filter the sample prior to analyzing it. Digestions with strong acids are done when determining Total Kjeldahl N (TKN) to convert organic N in the sample to ammonium-N so that is can be quantified by steam distillation, In this case, a stronger alkali (e.g. 5N NaOH) is used to raise the pH of the digest so that the ammonium-N is converted to ammonia-N. Bear in mind that I am speaking from the perspective of a soil scientist. However, the same principles may apply. I hope this helps

Thank you Dr De Shorn Edmund Bramble for his attractive answer. Just like soil, in waste water also, the nitrogen remains in various forms, like organically bound (largely), Nitrate and Nitrite as partially oxidised form, and as Ammonia, a product during anaerobic degradation. If anybody wants for available nitrogen, then he has to measure all these forms (NO3, NO2,NH3) spectrophotometrically. Without digestion, distillation by adding alkali will give you only the amount of available ammonia.But if total nitrogen content in organic matter is needed, the digestion must be done to produce ammonium salt which is distilled by adding alkali solution and trapping in boric acid just like soil. This will give you the amount of nitrogen coming from organic matter and free ammonia. So Organic nitrogen equals to total nitrogen after distillation minus available ammonia in water.

Phani Bhusan Ghosh , you're most welcome. Thanks for the further clarification.

Hi Mr. Wahiduzzman ,

I think I would do a few tests to verify or rule out the presence of other non-ammonium nitrogen species and how they could affect my results in the water samples you are working with. If your wastewater comes from an agroindustrial activity, it might be advisable to do a certain degree of fractionation depending on what you are looking for. Now, if you need the total N content present as you state in your question, you absolutely need to do the digestion process. If you only need ammonium-N, not necessary. Take also into account that there might also be very labile organic compounds such as urea that can easily transform into ammonium ions by a rapid hydrolysis.

Good luck with your research

The question is quite clear:

Do i need to digest waste-water sample with acid for Nitrogen (ammonium-N) analysis?

The answer is simple, too: For determination of ammonium-N the mineralization with acids is not necessary.

Best regards

Vit