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Greenhouses often use burners for CO2 enrichment, which requires a source of liquid propane or natural gas.

The yeast fermentation process can also be used to create CO2 for a greenhouse by supplying water, sugar and yeast. The fermentation process creates ethanol and CO2. Continuously burning off the ethanol that is produced by the yeast would produce even more CO2 and also water, and would allow for continuous operation without getting the yeast too drunk.

How can this be done safely and inexpensively, in practice? Any pointers to papers, system designs, or products would be appreciated.

Transistor
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Sebastian Goodman
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    Search "continuous fermentation", "vacuum fermentation". A quick search shows that alternative ethanol extraction methods have been explored for this purpose -- https://www.mdpi.com/2227-9717/7/7/458/pdf-vor -- and in theory at least, you'd get your CO2 at the same time. – Pete W Sep 11 '21 at 17:03
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    What papers have you found already, so we don't waste time repeating things? – Solar Mike Sep 11 '21 at 17:07
  • This site is not a free design service. Please do some research and/or get started yourself and come back with specific questions. – Drew Sep 11 '21 at 23:15
  • I didn't know any of the terms to research this, just the basic chemical reactions. I didn't even know basic terms like "bioreactor" and "fermentor". Pete's answer was exactly what I needed. The fact that this is an active research field showed me that this isn't even a practical thing to attempt, which explains why there aren't any widely available products or well known names for systems matching my description. Thanks, Pete. – Sebastian Goodman Sep 12 '21 at 02:38
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    @Sebastian - glad you found it helpful. If it's an area that is being actively explored, that could be viewed as an opportunity. Believe it or not, what you're describing has a meaningful chance of getting grant funding in NY state, under initiatives to develop eco-friendly agriculture. The fancier fermentation/distillation setups also do have niche uses when the substance being produced by the yeasts and extracted or distilled is something more valuable than just ethanol. – Pete W Sep 12 '21 at 15:36
  • Thanks, Pete. That's really cool that NY might support that kind of research. This idea originally came up after I saw how much propane was being burned in commercial greenhouses to produce CO2. Not only is it supporting the fossil fuel industry but there is plenty of sugar in the form of agricultural waste that could be used instead. Plus in a greenhouse context the CO2 from burning ethanol actually serves two useful purposes, heating and feeding, rather than being dumped into the atmosphere. I don't have the bandwidth to pursue it right now but I hope someone else does! – Sebastian Goodman Sep 13 '21 at 16:53

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Continuous fermentation is an ongoing field of research (see Pete's comment above), so there isn't really a system matching my description yet

After following up on some papers and products, I'll answer with the most practical solution I've come up with:

By breaking the system into three batch stages, it's possible to accomplish the same overall effect by using well known and widely used technologies, albeit with higher labor cost:

  1. Batch fermentation - converts water, sugar, and oxygen into CO2 and ethanol
  2. Batch distillation - separates ethanol from the fermentation broth created by step 1
  3. Ethanol burning - for heat and/or CO2 and/or electricity (see consumer grade ethanol fireplaces, though they likely could be redesigned for a greenhouse application)

The additional labor cost comes in with having to move the broth to the distiller, refill the fermentor, refill the burner, clean everything, etc. Ideally the system would be more automated and self contained.

Sebastian Goodman
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