Hi everyone~

I’m working on selecting microorganisms that degrade lignin present in pulp and paper wastewater. I am trying various methods to quantify lignin according to the references, but I’m having difficulties with reproducibility and unexpected results.

[Exp. Condition]

• In order to check whether there are microorganisms that selectively decompose only lignin, a medium mixed with M9 medium and Lignin alkali (CAS 8068-05-1) 3~7g/L was prepared. However, a precipitate was formed immediately after the medium was prepared (adjust as pH 7.5). Approximately 40-50% of the input weight is measured as VSS (1.2um pore filter paper).
• Seeding Microorganisms: Microorganisms taken from on-site aeration tanks also contain a lot of solids and lignin
• In the future, I plan to apply the same lignin quantifying method to the wastewater of the pulp and paper plant.
• Due to the small amount of microbial culture sampling, it was impossible to use only solids by drying a large amount of wastewater. (maximum 10ml for lignin measurement)

[The methods and problems that have been tried so far are as follows]

• In Trial-1, high weight was measured up to 200-800% of the input lignin, and the measurement result was not constant. (During filtration, the black liquid sometimes flows down and sometimes a transparent solution is obtained.)
• I suspected that carbonization occurs by reacting with sulfuric acid during digestion, or salt generation during drying can cause some problems. So I modified the method more (trial-2)
• In Trial-2, 10% lower lignin concentration was measured in the experimental group, and it looks like I got the reproducible (constant) result.
• Unbelievably, M9 medium without lignin also shows 'containing lignin results'…. M9 media with seed (1% V/V) shows the same or more lignin content than M9+seed+7g lignin Exp. Group.
• Results what I got is: M9 only >= M9+seed (1%) >= M9+7g lignin+ seed (1%) > M9 + 3g lignin + seed (1%)

[Questions]

* The acetyl bromide method in Ref 4. is difficult to use due to the limitations of laboratory equipment.

[Ref.]

Thank you for your interest and advice

Best regards - Sang Hyeok