In case you run the AnMBR with the objective of Biogas production, you would maintain minimum DO level as possible.

In Anaerobic process, bacteria grow by using electron acceptor sources other than molecular oxygen (DO measured the molecular oxygen in water). Hence, theoretically AnMBR does not require DO. However, initial phase manning zero DO is not easy due to system conditions (such as influent and efficiency of microorganisms etc.).

Similar discussion 6 years ago in RG.

https://www.researchgate.net/post/Dissolved_oxygen_in_anaerobic_wastewater_treatment2

this is our work few years ago with AnMBRs.

Article Effect of organic loading rate on VFA production, organic ma...

Article Developments and future potentials of anaerobic membrane bio...

Article Effect of polyvinyl alcohol hydrogel as a biocarrier on vola...

It's a little difficult to answer this question without knowing the exact purposes of the anaerobic bioreactor and whether it is a continuous or batch setup.

That being said, oxygen requirements for facultative anaerobes can vary widely in terms of growth especially depending on what you feed into the reactor and whether other microbes are present that can potentially help support their metabolism.

If we assume that you want the cells to eventually recover some aerobic growth capacity and that the machinery is still expressed at a low level, microaerophilic growth can generally be maintained at [O2] of ~1 to 5 mg/L. It's unlikely they would completely lose the capacity to use an electron acceptor that would allow them to yield more energy compared to alternative molecules, however it does run the risk of cells running into oxidative stress if conditions switch between anoxia, low oxygen and high oxygen.

I've read a recent paper where a contaminant degrading aerobe was subject to anoxic conditions and the authors verified how long anoxic conditions could be maintained before cells lost their function that I think may be of interest to you:

Article A Mixed Microbial Community for the Biodegradation of Chlori...

I hope this helps, if you come back with some more detail I'd be happy to try and help some more!

For wastewater treatment it should be minimum of 4 mg/L

Atun Roychoudhury , what you mentioned is for aerobic wastewater treatment. This questions is about Anaerobic process. Minimum 4 mg/L DO level will not support Anaerobic wastewater treatment. It is completely contradict with the requirements.

Yeah, sorry I haven't seen that anaerobic part. Then it should be exactly opposite of my previous answer. It should be below 4 mg/L

Daniel Gregoire and Amila Abeynayaka , thank you so much for your kind suggestions and reference data.

Dear Daniel Gregoire , the AnMBR system under question is a continuous flow.

Hi Syed,

One thing to keep in mind under continuous flow if the water is going through the membrane is you need to make sure you oxygen stripping rate is high enough to meet the demands of how much water is flowing through the membrane and that your pumping mechanism limits the introduction of oxygen.

One way to do this is to bubble your water upstream of the treatment with N2 or argon so it goes in anoxic. Alternatively, I found that using peristaltic pumps (even cheap ones) worked well in conjunction with an aquarium stone used as a diffuser. We were able to do this at laboratory scale in a 10L bioreactor with a free floating culture of obligate anaerobes and all oxygen was stripped in under an hour with a flow of N2 at 0.5 L min-1 (although I wager you could go lower). We were able to then drop the flow and maintain bubbling for a long period of time (~2-3 weeks) off of a single gas cylinder.

Another thing to keep in mind you need to make sure that your flow doesn't result in back pressure building in the line regardless of the pumping mechanism employed or your ability to send water through the membrane may suffer.

Let me know if this helped and if you would like to brainstorm further

Hello Syed,

Let's not forget (1) that oxygen is toxic/inhibitive for methanogenic archae/bacteria which are strictly anaerobes and (2) that facultative bacteria providing most of the substrate for the methanogens by definition (facultative) operate well in both oxic and anoxic/anaerobic conditions.

This implies that the dissolved oxygen levels in your AnMBR shall best be 0 ppm as to prevent decoupling and full acidification. In this respect don't forget to include automatic master-slave pH control from the AnMBR outlet to its inlet.

It is not clear why are you interesting in dissolved oxygen concentration in an anaerobic membrane reactor.When it is intended for wastewater treatment under anaerobic conditions, there no dissolved oxygen is needed. I fully agree with opinion of BRUNO PEETERS. No dissolved oxygen is needed in your case.

Even if there could be some oxygen in the inlet of substrate, it is nearly immediately consumed by facultative bacteria, so no dissolved oxygen is present.

Best regards

Vit

Your system is anaerobic hence it should be completely deficient of oxygen. You can bleed your reactor with Nitrogen gas to achieve that.

Interesting pro-ecological technology, congratulations!

When it is planned for anaerobic conditions, It should be 0 ppm no dissolved oxygen is needed.