What we did
We started growing the spirulina in 3 liter jars (from ajvar and chili) in order to start in smaller scale. We heated it in a water bath in a 30 liters aquarium.
Our light source was a lamp on the top of the aquarium.
We used pre-mixed nutritions for the medium
We aimed to have the water in the jars at 30 degrees celsius. Since we the light also added some heat, we set the thermostat to 28 degrees.
The light cycle was: on for 12 hours, off for 12 hours. Controlled by an Arduino 220V AC timer made by MrAlvin
We regularly measured the pH. It stayed around 9.6 +/- 0.2 without adding soda continually.
We had to regularly add water (1-2 times a week) due to evaporation. We managed to reduce the evaporation by covering the jars with hard plastic that we drilled holes for the tubes in.
We started using demineralized water, but eventually we changed to tap water for convenience. It worked fine, but it should also be noted that Copenhagen tap water does not contain chlorine.
We made a secchi disk to measure the density of the culture. This worked fine.
After a month we transferred the content of the jars (the arthrospira and their medium) to the aquarium and added new medium containing water and plant fertilizer. Unfortunately the athrospira gradually died during the next two weeks. In retrospect we assume this was due to a too large concentration of ammonia in the fertilizer. According to Ak: “Because Spirulina cells are easily damaged in high ammonia concentrations, nitrogen source is a limiting factor for organic fertilizers and more than 3 ppm of ammonia would be toxic to Spirulina (Shimamatsu 2004)” (Ak 2011:419)
For more see our lab journal
Encountered challenges and derived recommendations
To get the right medium. We wanted to have a cost-effective and ideally organic medium, well-fit for the spirulina. We found several recipes online, but with very varying instructions. We ended up trying a plant fertiliser, however with negative results. We suspect the reason to be a too high ammonia-nitrate ratio, inspired by the reference above and calculations showing the total N-concentration to not be high, and thus we recommend future projects to have this in consideration.
To prevent the lights from breaking due to evaporating water. We experienced twice that the lights on the top of the aquarium broke because water got into the containing box. A possible solution could be to have a light source on the side of the aquarium instead. Or to use a better isolated light source on top.
Mentions of the project elsewhere
Júlia, who's a design student from Umeå University in Sweden visited us on a research trip related to her masters project 'Food for Tomorrow' and wrote about it on her blog.
"A few years ago, the DIYBio movement has reached Labitat, a makerspace in Copenhagen: Biologigaragen is a well-kept secret backdoor to a room full of biotech equipment used for simple science experiments. To make these experiments relatable and exciting for people who have no background in biology, often they involve (planned-to-become) edible organisms – like Arthrospira platensis, protein-rich green algae known as Spirulina. Once the culture has reached adequate growth, it can be harvested, dried and consumed.
So why bother growing Spirulina for months instead of picking it off the shelf at a health food store? Apart from the intrinsic interest in biology and biotechnology, Biologigaragen’s hackers find such experiments a way to think about alternative food sources, decentralised food systems, just in case of emergency. The plan is to get through the first trials and errors, then share the learnings with other members who are interested in growing Spirulina at home."