Turning carbon dioxide into fish food

With 7.2 billion people on Earth, and rising, the carbon footprint of the human population runs to tens of billions of tonnes of CO₂ every year. Now a company called Deep Branch, spawned by entrepreneurs who studied at the University of Nottingham, think they’ve got a way to harness the CO₂ chucked out of the chimneys of cement factories. By feeding it to a special population of bacteria, they can turn it into fish food! Adam Murphy heard how from one of the brains behind the operation, Pete Rowe...

Pete - So it's a microbial process called gas fermentation. We can take CO₂ directly from industrial sources, let's say a cement plant or a power plant that has a large CO₂ output, we combine that with hydrogen, we bubble it through a liquid medium -  just kind of like brewing beer but rather than producing ethanol we produce protein -  and that protein is used as an animal feed.

Adam - And where do you get the raw materials to do that with?

Pete - The CO₂ we get directly from an industrial partner. So at the moment we're at kind of like a pilot stage so we've built a shipping container where we've installed a scaled-down version of our equipment, put that on-site at a cement plant and installed the CO₂ pipe directly from their chimney. We provide some hydrogen from a cylinder in this instance and then all we need is a bit of water, some salts, some nitrogen and that's it.

Adam - And what are the bacteria doing - the microbes sorry, what are the microbes doing?

Pete - So the microbes they are bacteria. They're thought to be the oldest evolved thing known to man. So they're really the start of life, and what they do is they use the CO₂ as a carbon source and they use the hydrogen as an energy source. So if you think about a conventional fermentation process that might use sugar, let's say you were making wine, you'd be using grapes that have got a lot of sugar in them, and the yeast in that process uses the sugar as energy to grow. And it has carbon in there and they need a carbon source to build the molecules of life.

Now we have a more stripped down version with our bacteria from ancient times when sugars weren't really available so instead they used the CO₂ as a carbon source, as this molecular building block for life, and they use the hydrogen which is very energy rich as an energy source.

Adam - What is the protein, is it the ground up bacteria or what is the protein which you make?

Pete - The product is a biomass. So the same way in which you think about soya bean being a good protein source, it's about 30% protein in a soya bean, but what you're feeding to people or to animals in a soya meal is just a ground up version of the soya bean. So with us it's a biomass as well, it's the bacterial cells that form a pulp and within that we have 60% or 70% protein, so the protein yield is really good. And, of course, if you think about how much water, how much fertiliser it takes to make soya beans, or in the instance of fishmeal how much fish you have to catch to feed animals, with us it's a lot less resource intensive and, of course, if we’re capturing the carbon it's got a sustainability angle on there as well.

Adam - And the protein, are you feeding it to people or what's your approach to use it?

Pete - I mention fishmeal, this is a real problem in aquaculture so fish farming. Soy meal isn't really appropriate there because the fish can't digest soya very well so instead fishmeal is used and this is fish that's caught from the sea. Of course, there's a finite amount of fish there. People want to eat the fish, fish farms want to use it as a feedstock and fish stocks are dwindling, prices are going up so the aquaculture sector is actively looking for other protein sources. So they're looking at insects for instance, but they're quite hard to scale; whereas our technology is only limited by the amount of CO₂, and if you think about a cement plant that's not far off a million tons of CO₂ per year, so there's plenty of that going around.

Adam - It sounds like a "two birds with one stone" kind of job, taking concrete and turning it into fish food?

Pete - Precisely, yeah. So sustainability on two sides, yeah.

Adam - And what stage you are at now and what you looking to do?

Pete - Yeah. So now we have full lab-scale validation and I spoke a bit earlier about this mobile production unit that were going to deploy with our partner who is a cement manufacturer. Once we get full validation that it works with industrial gases rather than just CO₂ in a lab, we are then looking to scale up to a pilot plant that will produce tonnes and at that stage we can start getting full validation that it works as a fish feed in this instance. And then within three or four years we hope to reach full commercial scale, whereby you'll be able to buy aquaculture products, so fish on the supermarket shelf, that are fed with our protein.

Adam - Have you fed any fish with it yet?

Pete - We've done a few tests in the fish tank, but not any commercially relevant species because our production volumes aren't enough to get good data back on that yet.

Adam - Well do your fish tank fish seem to like it?

Pete - Yeah, they love it!