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I have been developing LED grow lights for a year or so and one of the things I am trying to do is to build a grow chamber where I can control temperature, humidity, light intensity and quality and levels of $\ce{CO2}$ and $\ce{O2}$. I don't have any problems with most of the variables except the gases. I can inject $\ce{CO2}$ and monitor the gas, but as the chamber is hermetically sealed, how do I get rid of excess oxygen produced by the plants? Is there something similar to the $\ce{CO2}$ scrubbers used in aquariums? As a matter of fact, plants also need oxygen for their metabolic processes occurring during darkness, but they produce oxygen in excess of this requirement during the day. It is the excess of oxygen the one I want to extract, and not the whole amount of oxygen in the air of the chamber.

The whole idea is that through the chamber, I can adjust light conditions to each crop based on performance. Gas exchange is an important proxy for Chlorophyll fluorescence and has shown a good correlation with performance.

Any ideas?

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    $\begingroup$ A basic problem is that metabolic (life) processes require oxygen. You could flow CO2 through the chamber to eliminate oxygen, but the plant will die. On the other hand, you could seal the chamber with a known composition (e.g., normal air) and then analyze the gas contents some time later. So, it seems to me that you need to have some kind of gas analyzer (and this seems to be a non-trivial problem). $\endgroup$
    – user24965
    Feb 22 '21 at 3:07
  • $\begingroup$ Hi Jim. Yes, plants also need oxygen, particularly during dark periods of time, but they produce oxygen in excess of their metabolic needs. I will edit the question to reflect this. $\endgroup$ Feb 22 '21 at 8:53
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Absolutely, this is actually looking more as an engineering problem rather than a biology one.

In any case, I think I have found a satisfactory answer on a paper from the 1997 Proceedings of the Sixth European Symposium on Space Environmental Control Systems. The article is called: Oxygen Scrubbing and Sensing in Plant Growth Chambers using Solid Oxide Electrolyzers.

Basically, a disk of non-porous yttria stabilised zirconia (YSZ) is sandwiched between platinum electrodes and inserted in the chamber half-way, with the other half enclosed in whatever will store the extracted oxygen. The electrodes must be porous to allow gas diffusion. The only problem is, that sort of electrolysis cell needs to be maintained at an elevated temperature (800 to 1000 Celsius) in order to work.

By means of electrocatalysis and thermal dissociation the oxygen molecule dissociates to form two oxygen atoms, these in turn pick up two electrons from the cathode and become ions. The ion is then transported by the electrolyte (YSZ) by means of electron vacancies located in the crystal lattice (basically a similar process to that of a N-doped semiconductor whereby impurities create electron holes).

I think I am satisfied with the above explanation. Doable at home? No way, but it does answer the core question.

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It's going to be tricky to strictly regulate CO2 and oxygen in a chamber.

We use a palladium catalyst to maintain an anaerobic environment for microbiology purposes, but this requires a source of hydrogen to work, and it doesn't work well for fine adjustments, but rather for maintaining extremely low oxygen conditions. We also have a hypoxic chamber that regulates O2 concentrations with good precision (0.1%), but it's expensive to maintain, and requires sensors for oxygen, CO2, and nitrogen, and an automatic gas injection system for each component.

A simpler design would probably be to have some gas exchange with the room your chamber is in, using a tyvek membrane to minimize water loss (and HEPA filters if you're worried about pathogen contamination). My friend who farms oyster mushrooms did something similar, and also rigged up a humidity sensor to a humidifier using a RaspberryPi to manage the moisture loss.

However, if you're dead set on having a strictly regulated atmosphere for you grow chamber, you might want to consider consulting with Coy Labs. When we needed a chamber with the ability to tightly regulate oxygen levels for microbiology research, they came to the lab and worked with us on our specific needs and together we develop their first working model nearly from scratch (we modified one of their existing anaerobic chambers). But it worked so well that they now sell hypoxic chambers as part of their standard line of products. As far as I know, they haven't done any work with plant grow chambers, but they're a small company with a lot of experience building contained atmospheric control systems. Pretty much every order is custom built, so they're used to answering a lot of questions and tailoring their products to the specific needs of a customer, and they're very helpful and responsive with maintenance and upkeep. Just know that they're products aren't cheap.

https://coylab.com/

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  • $\begingroup$ Hi @MikeyC, good stuff on your above answer! There are plenty of clues on what direction to take, even more so after checking the company's site you've recommended. I'll leave it open though as it does not necessarily answers the question of how to extract the extra concentration of O2 from within the chamber. $\endgroup$ Mar 7 '21 at 10:44
  • $\begingroup$ Fair point. The system I'm describing is additive, not subtractive. Essentially, the gas injectors would add other gasses (either Nitrigen or CO2) to keep the O2 below a set concentration. To avoid over pressurizing the chamber, it would need a vacuum pump to purge some atmosphere after injection, or maybe even a simple water-filled airlock system like beer-brewers might use. It's starting to sound like your problem is one of engineering, rather than biology. Maybe try an engineering forum. $\endgroup$
    – MikeyC
    Mar 8 '21 at 15:15

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