Efficiently cultivate microalgae in PLEXIGLAS® tubes

Microalgae harbor enormous potential – not only in food production and pharmaceutical products, but also as raw materials in energy production. Thanks to their excellent transparency, bioreactors made from PLEXIGLAS® contribute to creating the optimal environment for cultivating the minuscule all-rounders.

Microalgae are microscopic fauna. Depending on their type, they can grow up to 30 times faster than terrestrial plants and can generate up to five times more biomass per area than plants traditionally used for energy. Microalgae also do not compete for available arable land, as in algae farms they also grow strongest where there is no fertile ground. The fauna also use CO2 as a source of carbon and contribute to binding this greenhouse gas.

Raw material of the future

For these reasons, many different sectors are interested in microalgae. Algae extracts are already used in food supplements and concentrated feeds, for example, as well as cosmetic and pharmaceutical products. Microalgae are also currently being researched for their potential use as an alternative energy source when producing biogas. And they may become even more important as a food source to ensure global food supplies in the future.

According to the United Nations, the global population is estimated to grow to 9.7 billion people by the year 2050. At the same time, the amount of fertile, arable land is shrinking. This means that even less space will be available per person for cultivating crops in the future. As a result, new concepts for producing food are needed.

Microalgae could play an important role here, as they contain many valuable nutrients and are rich in proteins. Species such as Chlorella and Spirulina, for example, contain more protein than meat, fish or soy, and algae extracts are therefore already included in food supplements today. In years to come, this content may increase further – and algae may also be seen increasingly on our plates.

Industrial production still in its infancy

Microalgae grow in oceans and lakes, or on stone surfaces. As harvesting algae which occur naturally is a laborious process, these algae are not considered feasible raw material suppliers for mass production. However, the industrial production of microalgae offers an alternative solution. Algae cultivators use different systems to this end: either open pools or closed bioreactors comprising sheets or tubes which are installed outdoors or in greenhouses – and sometimes even on the facades of houses. In these systems, microalgae are supplied with everything they need to grow rapidly: light, CO2 and nutrients.

Despite the numerous promising application areas, the industrial-scale cultivation of microalgae is still in its infancy. According to Fachgruppe Algenbiotechnologie (Specialized Group for Algae Technology) at DECHEMA (the Society for Chemical Engineering and Biotechnology), there are still significant problems when it comes to producing high-quality algae biomass on an industrial scale, both in terms of cost-effectiveness and above all in an energy-neutral manner.

Benefits of bioreactors

Companies and research institutes around the world are currently working on developing more efficient methods to cultivate algae. However, cultivating microalgae is not that simple. When selecting a suitable system, the respective type of algae and its requirements, the local environment and the intended application all play a role. For example, more stringent requirements must be met when cultivating algae for food production than for energy generation.

For stricter requirements in particular, many experts believe that closed systems have two decisive benefits compared to open pools: Compared to the exposed surfaces of the open pools, bioreactors are less susceptible to contamination. For example, the closed systems do not allow wind and dust to transport pesticides or other pollutants into the system. Bioreactors also allow light to reach the algae from multiple sides, not just from above. To benefit from this, the transparent shell of the bioreactor must be large when compared to the volume and permanently enable as much light as possible to reach the algae. This is the case for the bioreactors made from PLEXIGLAS®, which are currently being used for the cultivation of microalgae in various projects around the world.

92 percent transparency

PLEXIGLAS® can be manufactured to be UV-permeable across the entire spectrum of sun rays and, with its transparency of up to 92 percent, provides ideal conditions for the microalgae to grow. Along with nutrients, water and carbon dioxide from the air, they primarily require plenty of even light for growing. PLEXIGLAS® is one of the most transparent materials available, absorbing almost no visible light.

And the transmittance level of the tubes remains unchanged for decades: The UV stability inherent to the material prevents yellowing and thus the loss of transparency in virtually all colorless, transparent versions of the brand acrylic glass – guaranteed for 30 years. Furthermore, PLEXIGLAS® is lighter than glass sheets of comparable size and is suitable for contact with both fresh water and salt water. Many PLEXIGLAS® products are also approved for contact with foods.

At the same time, PLEXIGLAS® is extremely easy to process and can be manufactured in different shapes. Currently, PLEXIGLAS® XT tubes are primarily used in algae cultivation. Other shapes may also be suitable, such as PLEXIGLAS® multi-skin sheets with their hollow chambers. It is also conceivable that special PLEXIGLAS® shapes may be manufactured for algae cultivation in order to build bioreactors that suit the respective requirements of the microalgae.

Easy to clean

Thanks to these properties, the microalgae grow in PLEXIGLAS® bioreactors under virtually natural conditions and can be harvested efficiently. The cultivation process can then begin again from the start, meaning that the bioreactors also need to be cleaned and refilled. The smooth, non-porous surface of PLEXIGLAS® ensures that no putrid bacteria or microorganisms remain stuck to the walls. Bioreactors made from PLEXIGLAS® remain clean for long periods and are also resistant to many cleaning agents. As such, they contribute to the efficient and sustainable production of biomass.

Practical examples of PLEXIGLAS® in algae cultivation

Algicel – algae cultivator on the Azores

Built: 2019

The facts:

  • Industrial-scale, indoor and outdoor cultivation of Haematococcus pluvialis microalgae
  • More than 1,000 two-meter tall PLEXIGLAS® XT tubes
  • UV-permeable, 92 percent transparency
  • Tubes are durable and easy to clean

Read the entire story here.

© Algicel


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