at such pH of the solution, dissolving of CO2 in the solution and decreasing the pressure of the gas. 

First it is necessary to ensure anaerobiosis

Secondly, what is the type of inoculum

Thirdly in what temperature range you work

Dear Kurniawan,

You know four basic stages in anaerobic digestion: hydrolizis, acidogenesis, acetogenesis and methanogenesis. At the last stages, methanogens converts the organic products to methane and CO2. Fate of treatment depend on this stage. Methanogens can not growth easily and quickly in reactors. May be your reactor is in the acidogenic stage and  you can not get methane and CO2 much in this stage. First of all you should be sure that your reactor is really full anaerobic. Even mikroaerofilic conditions will inhibit the methanogens. Temperature will not be under 35 C for normal generation. Please supply sludge from locally available working anaerobic treatment systems. Finally you should be patient because methanogens can grow slowly. May be you should wait more than 2 months.

Dear Professor Olcayto Keskinkan, you quoted that the mikroaerofilic conditions will inhibit the methanogens.

I think there are novelties about this subject

I read an article entitled "Effect of micro-aeration and inoculum type on the biodegradation of lignocellulosic substrate" DOI: 10.1016/j.biortech.2016.11.081

In the case of our dear colleague Allen Kurniawan I think there is a macro aeratio, or one of the other causes that you have quoted (acidification may be)

Hi Mr. Mohammed,

Thank you for the link you sent. I have read the article on this link. It's obviously that the work you pointed out, has very interesting results. However, if we focus on the result part, it is understood that the application was made in very short time (3 days). These short durations may not have provided oxygenation of methanogens in a reactor(because they supplied very very little oxygen). In addition to these, there are too many facultative anaerobic bacteria in their reactor(not full anaerobic). They also says that increased micro-oxygen concentration inhibits methane production. So it is not a very contradictory result to what I am saying.

As a result, Mr. Kurniawan should check whether oxygen entered or not in the anaerobic reactor.

you are right Dear Professor Olcayto Keskinkan , I agree with you, there was no contraduction between the article and what you said. Yes, exactly, methanogenic bacteria are strict anerobic, oxygen input may cause asphyxia for this type of bacteria.

I say that there is not only a microaeration but there is perhaps a macroaeration.

For which I insisted that there is a macro aeration because the increase of the concentration of micro-oxygen = macroaeration, on the one hand,

Also the microaration in the article is controlled and in the current case is arbitrary, So it will enlarge with time

Therefore as you explained when there is an intake of oxygen there is a failure in anarobic digestion. It is quite normal.

My goal was to draw your attention to this point only (microaeration) in future.

I did not mean that there is a contradiction betwen that you say and the article.

I apologize.

thank you dear professor

Dear Dr. Mohammed,

There is no situation to apologize. I was very happy to get some ideas from you. The article you pointed out to me emphasizes a fact that I did not know much before. So, thank you again very much. It has emerged that it is necessary to work on this issue. 

Warm Regards

Dear Dr. Djaafri Mohammed,

Thank you for your kindly comments. According to your comments,

-  I have to consider for your first comment

- For the inoculum, I use the sludge from the effluent of anaerobic digestion plan. Additionally, I feed synthetic wastewater of 300 mL/day which contains mainly glucose, yeast extract, and ammonium bicarbonate as the influent of my reactor. Because of batch reactor, then I put the wastewater out also of 300 mL/day because I have to maintain the HRT of 20 days. 

- I use the standard temperature of AD, 35-45 C. My reactor temperature has a stable operating at 40 C.

Dear Prof. Olcayto Keskinkan,

Thank you for your kindly responding. I will check it out for the anaerobic condition inside my reactor. As your mention, my reactor was predicted in the acidogenic stage, but I am still wondering what happened. If my reactor is acidogenic/acetogenesis stage, the VFA will increase and increase and pH will decrease down. However, the VFAs remain stable at the concentration below 150 mg/L as acetic acids using GC analysis and the ratio of VFA/Alk. is small (0.02). I am going to analysis the microbiologies parameter like ATP, lypid and carbohydrate to see the viability of the cell later. 

Please kindly note that my reactor had been produced gas, but on the other days (the 23-32th and 44-52th day (now)) suddenly there was no gas production. When I measured the gas components (when it had gas) at the 15th and 36 days, the concentration of CH4 and CO2 was 55%, and 28%, respectively. In my opinion, the main problem is the decreased down biomass from 7500 mgMLSS/L to 3000 mgMLSS/L because I only use synthetic wastewater without any adding biomass. Then I'm considering to add the fresh biomass for increasing up the MLSS or MLVSS to 8,000-10,000 mg/L. However I have to be careful about the possibility of this option. Let me know your another consideration. Thank you.

Thank you Dear Professor Olcayto Keskinkan.

Dear Dr. Allen Kurniawan, check the concentration of Ammonia.

According to Michael H. Gerardi et al in the book "The Microbiology of Anaerobic Digesters" cited that :

"The ammonia concentrations> 1500mg / l at high pH may result in digester failure"

"Concentrations above 3000 mg / l, free ammonia becomes toxic enough to cause Digester failure. "

Hi Mr. Kurniawan,

I wonder, were you using domestic-industrial waste water before synthetic wastewater? If so, an adaptation process may have occurred. As a result, pH balance may be impaired. In any case, it is a more rational idea that the result is a decrease in the total amount of biomass. Prof. As Mohammed said, ammonia concentrations are very important. High ammonia concentrations may increase the pH value and inhibit growth. In addition to these, denitrification may be occur in your reactor and pH values may be increase due to hydroxyles come from denitrification process.

Dear Dr. Mohammed,

I also measure NH3 almost everyday The trend of ammonia concentration slightly increases from 500 mg/L to 700 mg/L. However, it is still far from the ammonia threshold of 1500 mg/L.  

Dear Dr. Allen Where are the other answers?. I can not find them.

Dear Prof. Keskinkan,

I did not use domestic or industrial wastewater for my reactor. I only use synthetic wastewater as a feed and AD sludge as an inoculum. I will note your idea about denitrification process. In fact, does the denitrification indicate the decrease of nitrate? In my reactor, nitrate has not shown any decrease in the concentration.

Dear Kurniawan,

Yes it does. The denitrification process reduces nitrate concentrations. So if nitrate concentrations do not change in your tank, we can not logically say that denitrification exist in your tank. I'll think the other possibilities that to be reason of increasing pH.

I will back to you if I find a solution for your problem.

Thank you for kindly respons Prof. Keskinkan, Dr. Mohammed, and Dr. Aziz. I appreciated your attention.

Correction and additional comment: 

Dear Kurniawan,

I mentioned before that denitrification increase the pH due to release of OH ions. I should correct this information because the factor of increasing pH is increasing carbonates in denitrification processes. If you added carbonates for buffer the reactor before you should decrease this buffer. Because denitrification may produce carbonates. The other think that I would like to say you is to check your pH meter whether it has calibration or not. 

You can consult this:

How Does Anaerobic Digestion Work? | US EPA

https://www.epa.gov › agstar › how-does-anaerobic-dig...