[photochemsyn]

For quite a few years I looked into similar processes based fundamentally on biological photosynthesis, for example algal pool farms and similar approaches to generating hydrocarbons from biomass.

At present, I think direct air capture of CO2 followed by reduction to methane and longer hydrocarbons using water-sourced H2 (all without going through the biological photosynthesis) is going to be the long-term winning technology. One main reason is control of the chemistry is a lot easier when you start with uniform small molecules (CO2 and H2) rather than trying to distill off and separate the products of pyrolysis of biomaterials (or even of crude fossil oil distillation and cracking, a similar process).

This isn't to say that if you have a completely renewable energy based power system, that converting agricultural byproducts to useful materials like biomethane, biooil and fertilizer (phosphorous recovery in particular) isn't going to be a plausible approach in specific situations, and the resulting products could have niche markets.

Now, if your goal is to remove CO2 permanently from the atmosphere, that's more difficult. Making materials like limestone (CaCO3) or perhaps carbon fiber is a better idea for that. Bricks of diamond would be even better, but that's a bit more sci-fi still - but possible. Air-captured diamonds would be a cool product.

[colechristensen]

I’ve thought a good target would be polluted lakes with algae problems or diverting part of rivers with agricultural runoff.

Pump oxygen and whatever bottleneck nutrient in and harvest algae. You’ll clean the excess nutrients out of the water and sink carbon at same time.

Do this in the Mississippi River delta for maximum effect, do a pilot in a Minnesota lake first.

[steve_adams_86]

There was an Oxygen and Nitrogen (I think) injection project here in BC which was attempting to burn out phosphorous from silt during seasonal turnover of the water columns. I recall that it never showed a positive effect on the body of water, though occasionally it was negative. Lots of fish died at one point. After several years the measurements of P in the silt were hardly any lower, but still too high.

I guess the trouble was only what to do with the algae. They expected it leave the lake, bringing the excess nutrients with it. How would you harvest it?

[GeekyBear]

A good way to get rid of excess nutrients is to pick a water plant with ridiculous growth rates (for example, duckweed), harvest and compost it for use in agriculture. Compost will certainly remain in agricultural fields longer than chemical fertilizers do.

[steve_adams_86]

Composted materials also help hold moisture in place!

The trouble is that distributing compost is extremely expensive and it doesn’t release into the soil quickly.

You can truck out tons of dry fertilizer and irrigate with it, getting immediate results through a system you already have on farms. Your nutrient to dollar ratio is far better (in the short term).

You might know this already. My main intent of mentioning that is that I suspect that way of thinking is actually totally misguided. The externalities seem to be far too severe, and damage to soils seems unsustainable as well. I have a feeling if we sucked up the cost of distribution and application of natural fertilizers, in the not-so-long term we might actually see major turn around on several issues related to crops and fertilizer run off.

There is plenty of evidence for it, but the scale of fertilizer needed is insane. No idea how we’d make that shift. Dry fertilizers are incredibly dense forms of nutrients, and they’re so easy to get from factory to plant.

US universities have published a lot of research showing natural fertilizers do yield good crops with better disease resistance, but any farm using them would need to put more money and time into fertilizing and could expect smaller yields. If everyone plays that game, okay… But if a farmer independently decides to, they need to find a market willing to pay more. That’s exceedingly rare.

We need to collectively value this investment, otherwise it’s very hard for farmers to afford the shift. At least, this is based on my limited hobby gardening/researching understanding. Someone in agriculture would know better.

[colechristensen]

Yup, my whole idea is to find a body of water already suffering from overgrowth of one of these organisms, do what you can to accelerate that growth, and continually harvest it.

[lostlogin]

Pretty much every river in New Zealand needs help. Thanks Fonterra.

[colechristensen]

I’m sure someone could come up with an efficient harvesting / filtering strategy. Pick a species that fit the requirements.

After harvesting do something similar to the process in the post. Dry it, pyrolyze, separate carbon goo from ash, bury one, use the other as fertilizer or another useful purpose.

[BizarroLand]

Even better, bubble CO2 rich air into freshwater vats of Wolffia.

Wolffia is the fastest growing plant on the planet and can double in size in a day. It's small, so it would work well as fuel for biomass reactors, the carbon char would be mostly derived from atmospheric carbon, resulting in a net negative, you can grow fish in the water underneath it, and it itself is edible and eaten already in many parts of the world where it grows naturally.

Further, it likes the slightly acidic water that bubbling CO2 into the water would create and it specifically oxygenates the water it floats in by stripping oxygen from CO2 during photosynthesis.

The downside is that no one has figured out the full process for continuously farming Wolffia yet, but if you solve that you can solve many other problems and create a multiple stream of income business out of taking carbon out of the air. (Biomass reactor fuel, plant food source for humans and animals, fish food source & selling carbon credits)

[bob29]

I believe you would pump in CO2 (and any missing nutrients), not Oxygen. Algae culture requires CO2 and produces Oxygen. It also requires light. https://en.wikipedia.org/wiki/Algaculture#Growing_algae

[lostlogin]

If you like plants in your fish tank, pumping in CO2 has an amazing effect on them. Far more growth than pumping in air.

There is some nice hardware for achieving it.

[colechristensen]

Are they actually CO2 concentrators or some variation of buying dry ice or compressed gas and injecting it?

[lostlogin]

I did it by running gas off fermentation (sugar and water) and it worked amazingly well.

I’d have to refuel about once a week.

Doing via CO2 bottle is the way I’d do it now and is how the impressive displays do it (for the ones I’ve seen).

[colechristensen]

I should have written air instead of oxygen, though plants still do respirate oxygen even though they’re net positive oxygen producers.

[bequanna]

So, this pilot would add more algae to a MN lake?

I don’t think you would ever get approval for something like this in a public lake. Maybe in some private, artificial pond?

[colechristensen]

The goal would be to farm and continually extract algae from the lake in just a section of it, presumably to increase the water quality in the rest of the lake.

And there are something like 14,000 lakes in MN though many of them one might be tempted to call ponds :) no need to build an artificial one though, there are plenty.