The Science and Technology of Microalgae cultivation

Just like all plants, each species of microalgae grows best under certain conditions. There is an ideal combination of temperature, nutrient mix, pH and other factors for each species.

Most microbes grow well in water. Microbes such as bacteria and fungi, which are grown commercially, are produced in water-filled, controlled bioreactors, otherwise known as fermenters. The ability to grow bacteria and fungi in fermenters at large scale has existed for centuries. In order to produce a product that is free of contamination and with consistent quality, the fermenter is closed, allowing a high degree of control over the growing environment. However, none of the organisms successfully cultivated via fermentation has been photosynthetic, i.e., dependent on light to grow. As a result, it is necessary only to ensure that the proper mix of nutrients is present in the medium with the culture promote growth. Large volume fermenters are feasible because it is not necessary to deliver light throughout the culture medium. Huge industries in fine chemicals and pharmaceuticals rely on the fermentation process to make the products that they sell.

However, microalgae are photosynthetic. Standard fermenters will not work for them. Even if grow lights are placed inside the fermenter, only the top layer of algae will “see” the light and grow. As they do they will actually shade the plants below them, preventing them from growing. A pine forest, in which the canopy of branches above prevents plants from growing beneath, is a very good example of that “shading” effect.

Avoiding shading is relatively easy in a small (ten-gallon) container, since the depth is shallow enough to eliminate the shading. However, commercial production must be done on a very large scale, where the medium is several feet deep, otherwise it is too expensive. Industrial fermenters usually hold thousands of gallons. It was necessary for a commercial scale photobioreactor to achieve a similar size before commercial scale cultivation of microalgae could be feasible.

That is exactly what the MGM has accomplished. It is a closed, controlled system that admits through its transparent walls the light that plants need to grow. The depth of the nutrient medium is great enough to cause shading, but the entire volume of the water/nutrient mixture in which the microalgae grow is kept in constant circulation. As a result, all of the organisms are exposed to enough light to grow at an optimal rate. This innovative, patented system has enabled Mera Pharmaceuticals to open the door to commercial production of 30,000 species of microalgae, creating access to the valuable and beneficial compounds that they produce for the first time.

Traditional microalgae production methods

Microalgae have long been grown under controlled conditions in the laboratory, where temperature, pH and other important variables can be well controlled, usually with large amounts of researcher and technician time spent doing it. However, these systems are too small – just a few gallons – and the amount of time and effort needed to keep them optimized is too costly, for them to be suitable for commercial use.

The first attempts to produce microalgae on a very large scale were done in “open ponds.” The broad, shallow channels in the open ponds minimized the shading effect and could be affordably built at a substantial scale. However, the tradeoff for achieving an acceptable commercial scale was the loss of control over the growing environment. Since ponds are open to the atmosphere, many variables, like temperature, cannot be effectively controlled without great expense. Contaminants that can completely destroy the commercial value of an entire crop can easily invade these open systems.

Only a few microalgae have ever been grown successfully in open ponds. These are generally species that can thrive in harsh environments that are hostile to competing species, such as high salinity or extreme pH. Such atypical growth habits reduce the potential for contamination by other undesirable aquatic organisms, but the number of species that can be pond-grown is very few, and they are not necessarily the ones that offer the most valuable products. Thousands of microalgae have been grown at small scale in the laboratory, proving that with proper controls they can also be grown at large scale. The obvious solution was a large-scale photobioreactor, but the way to design and operate such a system was not nearly as apparent.

The global race to develop photobioreactors

Photobioreactors are a brand new platform technology. Fermentation technology is used to commercialize tens of thousands of microbe species that do not require light to grow. Photobioreactor technology will permit Mera Pharmaceuticals to exploit tens of thousands of photosynthetic species. The combination of control and large scale is the key to success, and Mera has found a way to achieve it. The scale of our photobioreactor – the “Mera Growth Module” (MGM) – is comparable to that of industrial fermenters.

Our initial growth module had a capacity of a few thousand liters. We more than doubled its size successfully in 1997. We successfully increased capacity by a factor of 5 in 1998. Mera Growth Modules are now the largest scale photobioreactors in existence. We believe the MGM is the foundation of a new, large industry that uses our commercial scale photobioreactors to develop valuable products from the untapped resource of microalgae.

The Mera Growth Module (MGM) – our platform technology

The MGM is a closed, controlled, large-scale photobioreactor. It incorporates proprietary methods for controlling pH, temperature and nutrient levels to optimize growth rates. It also rests on a broad patent for the use of turbulence that provides a consistent mixing of the nutrient medium and eliminates the shading effect that had previously limited the scale of closed photobioreactors.

Laboratory-scale photobioreactors have been used to grow thousands of species successfully at small scale, since a favorable environment can be maintained, often manually. The value of the MGM is that it allows for complete control over all growth parameters, but at a scale that is thousands of times larger than a standard laboratory photobioreactor. It also permits this control to be achieved with computerized controls, which maximizes effectiveness and minimizes cost.

The MGM permits continuous growth and harvesting of microalgae over a number of months. This minimizes down time for the system, which contributes to its efficiency. We have successfully cultivated many microalgal species in the MGM that have never been produced in open pond systems. The Mera Growth Module opens the door to commercial exploitation of thousands of species of microalgae.

Mera has chosen AstaFactor®, its astaxanthin nutritional supplement, as its first commercial product. Astaxanthin is known to have a number of beneficial effects, yet it is extremely difficult to produce using standard commercial methods. As a result, it has a very high value (greater than $100,000 per kilogram at retail). That high value is supported by the numerous desirable properties of astaxanthin as a nutritional supplement.

Fermenter Open Pond MGM
Volume (liters) 5,000 – 500,000 5,000 – 500,000 5,000 – 20,000
Nutrient Control Yes Yes Yes
Temperature Control Yes No Yes
Turbulence Control Yes No Yes
Light Control N/A No Yes
Gas Exchange Control Yes No Yes
Organisms Grown bacteria, fungi microalgae microalgae
No. of Species >10,000 3 >10,000