Growing microalgae in a building’s walls

AS demand for microalgae grows, so too does the need for space to grow them, and researchers in France have proposed a novel idea of growing algae in vertical panels on the facades of buildings.

Algae have a high oil content, meaning that they are in demand for biofuels, as well as for some natural-based… cosmetic products. They also have high vitamin and mineral levels, so can be used in nutritional products. Their nitrate content makes them useful for fertilisers. However, the large open ponds and raceways often used to grow algae have low productivity and take up large areas of land and volumes of water. Photobioreactors are a more productive alternative.

Jeremy Pruvost and his team at the University of Nantes say that integrating vertical photobioreactors into industrial and commercial buildings would not have the same acceptability issues as it might on domestic buildings. They have worked with architects to realise their design ideas and are currently building a prototype model on an industrial building in Nantes.

The photobioreactors will have what Pruvost describes as a “symbiotic relationship” with the building to which they are attached. The reactors could also make use of a building’s COemissions, and in winter, they will be able to benefit from the building’s heating, while in summer, they will benefit from cooling systems. Excess heat is a common problem in closed photobioreactors, as 85% of the light which hits the surface is converted into heat and cannot dissipate, causing the algae to die. Additionally, the photobioreactors could act as insulation on the buildings.

CO2 and nutrients will be bubbled through the photobioreactors using an airlift system. Oxygen and other waste products are removed through the same system.

Pruvost and the team conducted computer modelling which took into account changing seasonal light levels in France, photosynthetic growth models and mass balances. They compared the vertical photobioreactors with other growth methods, including 45° angle bioreactors and traditional raceways.

Even with the reduced light level caused by the 90° angle, they showed that algae productivity was comparable to that of other methods, and higher than that of raceways, due to the mixing and better distribution of nutrients and CO2. The energy requirements are higher, but of course the vertical photobioreactors will benefit from energy from the buildings to which they are attached.

“The integration of photobioreactors into buildings is a very specific application of the technology, but it is interesting because it can decrease the cost of the process. We have to manage specific problems related to productivity but we also induce more constant production throughout the year. CO2 feeding and thermal regulation are the two parameters to manage,” said Pruvost.

The research was presented at the 21st International Congress of Chemical and Process Engineering (CHISA) in Prague in the Czech Republic, held from 23–27 August 2014.

 

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