What is a bioreactor? It sounds complicated, but it’s really a two dollar word for something that pumps air through algae. There’s a few designs on YouTube, this is my home brew variation of those.

On a large scale, bioreactors can help scrub CO2 and some pollutants from the air and return oxygen and a whole lot of algae for food, fertilizer of biofuels.

The air is pumped via a compressor, through a solution containing water, algae and nutrients. The algae takes the CO2 and uses it for growth and in return, gives off oxygen which is released back into the surrounding air.

We have ours connected to our solar setup so the power to run it is free.

I made one recently, a very simple proof of concept and thought I’d share it here in case you want to try your own.

How to make your own bioreactor

You will need:

• transparent container or two
• aquarium hose (and connections if you want more than one tank
• iron or steel weight
• aquarium air pump
• algae
• aater
• soluble nutrients

That’s it. Pretty simple. Here’s how it goes together:

The water and algae go into the transparent container. I used two 11 litre plastic spring water containers.

Attach one end of the aquarium hose to the weight and lower it into the water so the weight is at the bottom of the container. This holds the hose at the bottom of the tank. Also, as it rusts, the weight releases small amounts of iron into the water to feed the algae.

Attach the other end of the hose to the pump, turn on the power and watch the bubbles!

Add a little of your favourite soluble fertiliser. For ours here, pretty well anything works – urine, seaweed liquid, Osmocote

That’s it, you’ve got a bioreactor!

Of course, it can get as complicated as you like. You can:

• make a loop of hose at the bottom of the tank to distribute the air more evenly
• experiment with different air-stones
• play around with the airflow
• vary the shape of the containers to increase the time the air is kept in the solution
• experiment with different types of algae
• bounce light onto the container, or use powered lighting
• use multiple containers, like you see in ours

If anyone can suggest a way to measure the amounts of CO2 going in and O2 coming out using home brew technology, I’d love to learn from you. Maybe I’ll investigate if it is possible to do with an Arduino

Bioreactors…fun for all the family!