I just skimmed the article, but given that you already willing to make suck huge investment in capital and space, I just got a feeling it’s easier if you just have a grow room or an algae bio-reactor running at night. the immediate benefit would be the hardware are available in consumer form and most of the design parts have been attempted.
This way the on going cost would only be marginally higher [back of envelope calculation] and you would reap other benefit beside. [food or algae oil]
Back of the envelope: a person exhales about as much carbon as they eat, and a plant removes carbon from the air only by increasing its size, so to remove one person’s CO2 exhalations, you would need to grow as much plant matter as they ate. That’s not impossible, but at that point you’re looking at something more like a greenhouse than like a grow room.
yeah, I dropped the ball on that one, the grow box is out but I got a feeling a grow room is still possible but this is splitting hair.
I am wondering if I also dropped the ball on the algae claim
[EDIT: I see numbers as high as 4 g/L/day quoted for algae growth rates, I updated the reasoning accordingly]
The numbers don’t quite add up on an algae bioreactor for personal use. The stated growth rate for chlorella algae is 0.6 g/L/day, and there are about 4 liters in a gallon, so 100 gallons of algae solution is 400 liters is 240 g of algae grown per day, and since about 2/3ds of new biomass comes from CO2 via the 6CO2+6H2O->C6H12O6 reaction, that’s 160 g of CO2 locked up per day, or… about 1⁄6 of a person worth of CO2 in a 24 hour period. [EDIT: 1 person worth of CO2 in a 24 hour period, looks more plausible]
Plants are inefficient at locking up CO2 relative to chemical reactions!
Also you wouldn’t be able to just have the algae as a giant vat, because light has to penetrate in, so the resulting reactor to lock up 1⁄6 [EDIT: 1] of a person worth of CO2 would be substantially larger than the footprint of 2 55-gallon drums.
Also, a paper on extremely high-density algal photobioreactors quotes algal concentration by volume as being as high as 6% under optimal conditions. The dry mass is about 1⁄8 of the wet mass of algae, so that’s 0.75% concentration by weight percent. If the algal inventory in your reactor is 9 kg dry mass (you’d need to waste about 3 kg/day of dry weight or 24 kg/day of wet weight, to keep up with 2 people worth of CO2, or a third of the algae each day), that’s 1200 kg of water in your reactor. Since a gallon is about 4 kg of water, that’s… 300 gallons, or 6 55-gallon drums, footprint 4 ft x 6 ft x 4 ft high, at a bare minimum (probably 3x that volume in practice), so we get the same general sort of result from a different direction.
I’d be quite surprised if you could do that in under a thousand dollars.
I vaguely remember the 4 g/L/day but on further inspection, I now realise that we can’t ever reach that efficiency. If we use the 1 g/L/day but human use 1kg/day (they use less in sleep don’t they?) divided by 2⁄3 it would be about 1.5 m3 (still quite big) and we have to account for the actual foot print which would be much higher (2x higher? 3 m3?).
I am tempted to argue that we don’t have to match the CO2 production rate so perfectly since the CO2 should naturally diffuse a bit, but let’s leave some margin of error on our side.
for the total volume, can’t we just continuously filter out the algae to retain the optimal condition while barely increasing total volume? and since we only use it at night, the total volume need would be less. If we automatically drain it to a hidden larger tank or press it straigth to oil in the basement we maybe saving effort here but increasing volume.