How Is Spirulina Farmed?
From Green Goop To A Highly Nutritious Powder
If you take a breath right now, 50% of the oxygen you just breathed in comes from algae. 🤯
If algae did not exist, we humans or any living creatures wouldn’t be alive! Around 3.5 billion years ago, cyanobacteria (aka blue-green algae) came to be when oxygen was absent on earth. It released oxygen into the atmosphere because of its process of photosynthesis.
Although algae have existed even before us, only recently are we starting to experiment on how something so tiny can combat one of the biggest problems we are facing; climate change
In this article, you’ll learn how we can replicate spirulina (cyanobacteria) grown in open bodies of water to be grown in bioreactors.
If you want a more surface-level article to learn about in general, check out my previous article to learn the basics + why spirulina and other types of algae are good for us in the first place!
🌊 Natural growing environments
Let’s start by learning about how algae grows on its own to understand what we want to replicate in a controlled environment.
Cyanobacteria can live in any body of water, salt water, oceans, lakes, rivers and ponds. Like any other plant, it goes through photosynthesis needing 🌬️ oxygen, 💡 light, and 🚰 water, and it also needs nutrients like nitrogen and phosphorus. Although cyanobacteria can live in many conditions, that’s different in the areas where it thrives the most.
It prefers “brackish” water more, meaning it’s more of a combination of fresh and saltwater. Cyanobacteria make their food from the sunlight as well. It usually thrives and has a more rapid growth in warm and nutrient-rich waters (meaning it’s high in phosphorus and nitrogen).
They thrive especially in shallow, slow and warm water, which is most common during the summer and fall. In these conditions, it tends to multiply quickly, creating blooms.
Usually, cyanobacteria don’t grow as quickly because of a lack of sunlight or minerals. When algae tend to grow bigger and bigger, especially in a smaller area, a lot of the time, not all of the organisms get equal access to the sunlight, so the top row stays healthy. In contrast, the bottom algae start to die off, sometimes producing toxins and creating a really high pH environment causing the rest of the healthy parts to die off.
🤔 Can’t we just harvest it straight from the ocean?
When I started to look into algae, I wondered why can’t we farm spirulina straight from the ocean since there seemed to be too much in some regions?
Technically, you can eat specific types of algae grown in a safe area, and then after purifying, harvesting either into paste or powder, it can be edible. But there are a few things to consider.
(note: I am talking about algae for human consumption, not for other uses like bio products)
If you are trying to actively farm that algae directly in the sea, you can’t control it as much as the different factors like temperature, other creatures/microorganisms, and pH, leading to bad harvests or the batch going bad.
You can think of this as just farming in the wild as opposed to farming on a properly taken care of farm. There are many exterior things you can’t control on an open farm in the wild.
Another thing you would need to consider is that different algae blooms can be very toxic for humans and animals.
Microsystins are a class of toxins released by cyanobacteria (a type of algae) that can be lethal to living creatures. For humans, it directly affects the liver, and the damage varies on how much of the toxins are consumed.
Well, now you’re probably confused… I just said you can and can’t eat algae from the ocean, but one is toxic!?
The harmful algae are in toxic blooms, producing toxins because when algae are together in large amounts (which is considered a bloom), the algae starts to degrade or decay. So when there’s a lot of algae in a space with limited oxygen, it creates hypoxic conditions. Hypoxia means low levels of oxygen within a body of water. When there is an overgrowth, it leads to oxygen depletion, making them die and sink to the bottom.
Here’s where the toxic part comes in; when there are no sustainable conditions for the cyanobacteria, like light or nutrients, the cyanobacteria start to produce toxic secondary metabolites known as cyanotoxins. The metabolites try to make energy for themselves to stay alive.
Still, the cyanotoxins, which are the type of secondary metabolites they produce, are toxic and lethal for the organisms around them. (note: only certain cyanobacteria do this, that’s why not all algae blooms are toxic)
If you didn’t understand any of that…
tl;dr — you can eat certain algae from the ocean after it’s processed, but harmful algal blooms are toxic for you, so don’t eat them. the reason why they are toxic is that they release a particular toxin to stay alive
🌱 How can we replicate how spirulina grows naturally, in a controlled space?
For any situation, you need to have a starter culture to start with taken from another farm/bioreactor. Even from that considerably smaller batch taken from another farm, it can multiply very quickly with the right conditions. Apart from the starter culture, it needs water, nutrients/minerals, a form of light, agitation and most importantly, a place to grow.
🚰 Water
For spirulina, you can use just regular filtered water or even saltwater. If you don’t use salt water and filtered water, you would have to add sodium chloride (which is just salt) to the culture medium you create after.
A big thing to be aware of when using water is that you cannot have chlorine in the water; that’s why you must use filtered water. Chlorine is used to kill algae, and that’s why you have it in pools, so nothing starts to grow there! Another thing to be aware of is that the water shouldn’t contain any heavy metals since spirulina can absorb them, and that will harm the batch :(
🧪 Culture medium
You can create multiple types of culture mediums for growing spirulina for different results (for nutritional value or functionality). Usually, all fertilizer recipes are variations of the Zarrouk Medium, which was made in 1966 for spirulina farms that experimented with culture mediums.
Here are the components of the medium:
- Sodium Bicarbonate (naHCO3) — basically any drinking soda powder
- Potassium Nitrate (KNO3) — there are a few substitutes to this, you can use any fertilizer that contains nitrogen, but you would have to add potassium sulfate.
- Sodium Chloride (NaCI) — salt.
- Potassium Dihydrogen Phosphate (KH2PO4)
- Magnesium Sulfate MgSO4 — pentahydrate
- Iron Sulfate (FeSO4) — Pentahydrate but not the type that’s used for lawns
If you are growing your spirulina farm, there are ready-made mediums that you can buy as well, so you don’t have to go through the process of getting everything individually.
For spirulina to thrive, you need to have to monitor the pH of the medium itself. The recommended pH is between 8 and 11, but it’s at its best at 10.5–11. Unlike spirulina, parasites, viruses, and germs can’t survive in an alkaline environment. Alkaline (aka basic) means having a pH greater than 7.
☀️ Light
Like any other plant, spirulina needs some form of light to grow, artificial or natural, just from the sun. Spirulina needs light for about 16 hours daily, and it’s best not to have it in light constantly.Direct sunlight can harm it in the early stages of growth.
Depending on your location when you grow spirulina, natural light is best since it is also 100. times brighter than artificial light. Artificial light works too but having it on a cycle of 16 hours helps to prevent overstressing the algae and maybe even harming it.
🪝 Agitation
Spirulina usually tends to gather on top of the culture where the sun is most exposed. It’s almost similar to how sunflowers (or any other plant) turn towards where they get the most sun since they need that to grow. BUT when there is a buildup at the top, the spirulina near the bottom doesn’t get enough sunlight and starts to die off.
To prevent that, the water must be agitated so all spirulina filaments are equally exposed to sunlight. Large-scale farms use paddle wheels to mix the algae since it requires less energy.
A crucial thing to consider is that if the flow speed is too high (above 30cm/s), it can harm the algae differently. The right speed for flow speeds results in more effective photosynthesis as well. If you have a smaller scale area to grow algae, something like an aquarium pump or some sort of paddle works too!
🗺️ How do you exactly grow spirulina?
Now you know what you need to grow it, where and how you grow the spirulina? There are three broad categories of how to grow- spirulina, open, closed and hybrid bioreactors. Spirulina bioreactors are usually between the size of 1,00 to 5,00m2 in volume.
Open bioreactors
This method has more of a resemblance to a pond or the ocean. It’s almost like a large swimming pool in a controlled environment where the spirulina can grow.
The most common type of open bioreactor is the raceway, an ovular-shaped pond that looks like a race track.
It is around 0.2–0.4m deep and is either built with super thin glass fibers or plastic that is safe for the spirulina to grow. It can also just be built directly on the ground, and the area is just lined with plastic. You must use suitable plastic. It can be a greenhouse tarp or HDPE (high-density polyethylene. Polyethylene plastics don’t have any health hazards and can affect microorganisms.
It also has rotating blades to help agitate the medium, and its connection has an electric motor. Some of the pros of this bioreactor are that it has less contribution and operational costs. Building a 100,000m2 raceway is about USD 725k (including all other parts like lining, outlet, and blades). For the production, on the other hand, the spirulina would be around $1.8-$2.9 per kg.
They also have direct access to sunlight and a low accumulation of oxygen. An open bioreactor is easier to clean; a good analogy is comparing a bowl to a water bottle to clean (open bioreactor being the bowl and closed being the water bottle)!
Some of the problems with this method are that it depends more on the climate itself. If there is rain, it can dilute the growing culture as well as alter the pH levels. Sand and dust can also make the spirulina heavier, causing it to sink into the bottom and die off because it won’t have access. Another significant issue is that the batches can get contained more easily by insects and flies.
Closed bioreactor
A closed bioreactor helps have a more controlled environment, enabling higher pH and better temperature control. It also has a higher biomass production, and the photosynthesis process is much more efficient. A study showed that a photobioreactor (a version of a closed bioreactor) had almost a 90% increase in biomass harvest than an open version.
The cost for closed, tube-shaped photobioreactor costs around 10.3$-11.4 $ per kg, which is considerably higher than the open bioreactor due to other costs of maintaining and constructing the structure itself
Since it is closed and doesn’t rely on much of the exterior conditions, the water evaporation and Co2 loss in the atmosphere can be controlled/minimized. Unlike the open bioreactor, the risk of contamination from external organisms is also much less.
As a closed bioreactor has many benefits, it has more significant construction and operation costs, making it much harder to scale. There have to be certain constraints when you take into factors like how light will be able to reach the microalgae. Unlike the open bioreactor, if the closed bioreactor is confused with a transparent material, the sunlight can reach all of the figments from any direction, not only the top.
Hybrid
This model is just a mix of both, compensating for the other two options’ downsides. One type of hybrid is just placing a cover on the pool to give some closure and not have it entirely shut in.
The second is almost like an open bioreactor in a greenhouse with just a roof over it. In whatever case you are growing the spirulina, what you’re optimizing for, and what your condition is, you can choose either or combine using the hybrid method.
It’s just taking what’s good in one and good in the other, combining them without having their negatives. A downside with this method, though, is that it costs more than the open bioreactor, but something like just a cover costs less than the closed option but more than the open one.
🥳 Harvesting the Culture!
Now, after the growing period (the time depends on how big your batch is, the first step in harvesting is to reduce the amount of water in the spirulina to a concentration of about 10–20% of solids by weight (this is called dewatering)
After the cultures have grown, you need to filter them to remove the solid from the liquid. You can do this by pouring the medium through a semipermeable barrier, a filter. You can use a screen printing cloth or butter muslin.
Once we have extracted the solid, we need to dry it out. There are many methods for biomass drying, like spray drying and drum drying. The spray dryer is powerful, but the drum drying method uses less energy. You can also freeze dry it, which does not affect the intrusion of the spirulina, but it’s much more expensive.
After it’s all dry and ready to go, it can be made into a powder, nibs, pills for supplements, or combined with other foods! You can incorporate spirulina in almost anything as well. You can skip the drying process to harvest the spirulina as a paste after it’s refined.
There are a lot of applications for spirulina and other types of algae, but we still need to overcome challenges. One of the biggest hurdles is scalability; the process cost of the cultivation is relatively high, and if we can lower it, that will help scale farming algae. The goal is to create algae farming as common as farming any other crop. Although this organism is tiny, it can have a much bigger impact on our future.
I will also be releasing more content on this topic very soon, so make sure to follow up to stay updated!
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