I am working on a biogas plant, digester volume 3000 liter, right now pH condition is acidic at 4.00 my requirement is to maintain pH to 6.50 to 7.20 what should I do? some suggestions are there like, add NaOH or CaCo3 but I am confused about the how much amount should I add to increase pH

  • $\begingroup$ There has to be information on web about biogas digesters. What kind of gunk are you even digesting? // Off the top of my head I'd think adding anything willy nilly to the digester would be tedious at best. Seems like you need to take a sample, treat that, and then use sample size to scale up additions. // Part of the problem here is $\ce{Na+}$. I'd suspect that microbes aren't going to like high $\ce{Na+}$ concentrations from NaOH or NaHCO3. So you need a biofriendly base. $\endgroup$ – MaxW Aug 2 '18 at 14:01

Add a base (whichever is suitable for your application) and then use pH paper (eg. https://www.coleparmer.in/i/hach-ph-strips-ph-paper-test-strips-0-to-14-ph-range-100-strips-pk/0554642) to test the pH in a sample of a specific volume of the mixture. Keep adding base (keeping track of the total amount added) and measuring the pH using pH paper until you are in the desired pH range. Just be careful not to add too much base and end up at higher pH than you need. Also make sure to give enough time to the solution to stir after each base addition before testing the pH. Once done, scale the amount of base used to the total volume in the digester. Ideally i would use an inline pH meter to continuously monitor the pH if possible (could contact mettler toledo who has really good quality products but wont be cheap, eg https://www.mt.com/int/en/home/products/Process-Analytics/pH-probe.html).

It seems that here: https://www.biogasworld.com/biogas-plant-monitoring/ a procedure is described that addresses your question where the ratio of volatile organic acids to alkaline buffer capacity is determined and therefore the risk of acidification of a biogas plant.

| improve this answer | |
  • $\begingroup$ Down voted - Doubt NaOH is good for a biodigester. Need to take a sample and scale up. It doesn't seem that pH paper strips would work. Not sure if there are any specialty strips that would let you measure pH to 6.50 to 7.20 accurately. $\endgroup$ – MaxW Aug 2 '18 at 14:10
  • $\begingroup$ @MaxW The question was to maintain the pH in the specified (broad) range and how to monitor the pH, not which base to add (actually NaOH was the OP suggestion and i used it as an example of a base, hence said 'say NaOH'). I assume it is obvious that he needs to sample and scale up (it is 3000 L after all). Here are the strips: coleparmer.in/i/…, they measure within 1 unit. Alternatively a simple pH meter can also be used. Also, 6.50 to 7.20 is not accurate, it is a range. Thank you for the comment i ll edit. $\endgroup$ – AMM Aug 2 '18 at 14:25

Not the answer you're looking for? Browse other questions tagged or ask your own question.