You can bubble your reactor with inert gas like Nitrogen keeping positive pressure in the reactor to keep the system anaerobic.

Dear Sujala Sultana, 

Thank you so much for your information. I can do that ,but it will effect on purity produced hydrogen gas in MEC. are there any chemicals can maintain anaerobic condition?

Chemical reducing agents may be added to your media but you will still need to exclude oxygen from the headspace of your reactor to maintain anaerobic conditions.

It is best to flush the headspace of your reactor with inert gas such as nitrogen. Once the oxygen is removed from your reactor's headspace, there is no need to continually add nitrogen. So, you could flush the headspace once with nitrogen when the MEC is set up. Then, the hydrogen that is produced will only be diluted by the initial amount of nitrogen in the headspace. To improve your hydrogen purity, you can make your headspace volume small and use a liquid displacement system to capture the gas produced.

Dear Christine Dykstra,

Thank you so much for your suggestion.

 I am going to use Geobacter sulfurreducens PCA strain for my project.Geobacter sulfurreducens, generally considered to be a strict anaerobe. Atmosphere: Anaerobic gas mixture,  80% N2 and 20% CO2 

In my case should i need to flush the headspace of my reactor with mixture of 80% and N2 20% CO2 ?

Why some microorganism need a anaerobic condition that include mixture of gases?

Yes, it is a good idea to flush the headspace with the N2 and CO2 mixture. Microorganisms that are autotrophic require inorganic sources of carbon (CO2) for biomass production. In this case, you need to supply enough CO2 to meet their carbon needs, so that is why the mixture of gases is used.

G. sulfurreducens cannot grow autotrophically with CO2 and needs organic carbon for cell growth. For this reason, carbon-containing electron donors are, in principle, necessary to support the growth of Geobacter sulfurreducens PCA strain in Microbial Electrolysis Cell (MEC). do you have any idea about hydrogen production in Microbial Electrolysis Cell (MEC)? how about Electrochemically Active Bacteria (EAB)?

thank you.

Yes, you are correct. If you are only using G. sulfurreducens, which is not autotrophic, the CO2 is not necessary for a carbon source.

With G. sulfurreducens, I believe the N2/CO2 mix is used because CO2 in solution positively affects the MEC performance. A recent paper is: Soussan et al., 2013. Electrochemical reduction of CO2 catalysed by Geobacter sulfurreducens grown on

polarized stainless steel cathodes. Electrochemistry Communications, 28, p 27-30. DOI: 10.1016/j.elecom.2012.11.033   

I am working with MECs but not in the area of hydrogen production. Best of luck to you in your research!

Dear Christine Dykstra,

Thank you so much again.

May i know which area of MECs are you working on? if you wish we may work together.exchange ideas.....

CO2 in solution positively affects the MEC performance.

Geobacter medium contains sodium bicarbonate as buffer and CO2 works as its buffer conjugate to maintain the pH.

Dear Sujala Sultana,

Thank you so much for your information. Do you have any idea about growth profile of Geobacter sulfurreducens PCA strain? 

Abudukeremu Kadier may i ask how do you sparge the MEC with nitrogen? Will the biofilm in the anode chamber retain its anaerobic condition while sparging? i am working on MEC research specifically to determine the inoculation of the mixed culture onto the anode electrode material using the OLR from the simulation to determine the hydrogen yield