Dear Syazwan,

Maybe you may use urea solution that the feeding is based on concentration (g/L).

-H. Kamilah- 

Dear Syazwan:

according to my experience to use total Kjeldahl nitrogen (TKN) for adjusting C:P:N ratio in waste is not feasible. The main reason is, that the absolute value of TKN contains also some forms of nitrogen in waste which are not bioavailable to microorganisms. So that TKN value overestimate biologicaly evailable nitrogen. According to my experience the sum of ammonium nitrogen + nitrate nitrogen + nitrite nitrogen works much better. In many wastes the nitrite nitrogen concentration is very low, so it could be omitted from analysis.

Concerning sources of nitrogen for microorganisms: it depends on type of microorganisms mostly. But for microorganisms responsible for anaerobic digestion the most suitable form of nitrogen is ammonium nitrogen (supplied as ammonium sulfate).

Best regards    Vit  

Hello. What is your main substrate and type and scale of digester ?

For an optimal digestion, your C:N ratio should be lower, more like 25-32:1. I can't recall the exact reference,

I would be concerned about the potentially high presence of nitrate and nitrite in your feed. They can severely inhibit methanogenesis, even at low concentration. There are many references in the literature about it, I just dig one as an example:

Biodegradation. 2009 Nov;20(6):801-12. doi: 10.1007/s10532-009-9268-9. Epub 2009 May 18.Banihani Q1, Sierra-Alvarez R, Field JA.

Nitrate and nitrite inhibition of methanogenesis during denitrification in granular biofilms and digested domestic sludges.

Most of the substrates we work with are lacking carbon, not nitrogen. However, I support the idea mentioned above of adding urea as a nitrogen source if necessary. If you are working with solids, you could even add a a nitrogen-rich co-substrate, like manure.

Thank you so much for all the responsive and brilliant answers. I really appreciate it.

Suitable form of nitrogen for bacterial growth is nitrate forms. It's also a preferred terminal electron acceptor for microbial decomposition process. But C:N ratio play very important role and the most desired C:N ratio ranges between 25:1 to 30:1.