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Growth and harvesting

Partly due to their simple structures, algae are highly efficient converters of solar energy, fixing five times more solar energy to chemical energy than most terrestrial plants. As a result they can achieve high growth rates; some microalgae species can double their biomass in only a few hours. The principle requirements for growth are light (sunlight or artificial), carbon dioxide, nutrients and trace elements.

The algae cultures used by the EnAlgae project all begin life in test tubes in a controlled environment. Culture volume is gradually increased to meet demand and provide inoculum for our larger sized production systems.

EnAlgae uses freshwater or seawater, depending on the species, and provide additional nutrients and CO2 to promote growth.

Macroalgae (seaweed) farming

Although seaweed can be collected simply from the shore, efforts to increase productivity through farming have taken place in the Far East and Europe since the 17th Century. Commonly used substrates on which to grow the algae include ropes (called longlines), rings or nets employed in a variety of configurations. These are first ‘seeded’ with young seaweed gamaphytes grown in on-shore hatcheries and then deployed off-shore, supported by networks or stakes or suspended beneath floats. Depending on the species, the seaweed is left to grow for months to a year, before it is harvested manually or by using specially modified barges.

Emma Gorman from Queen's University Belfast explains the growth and harvesting process used at their long line site in Strangford Lough near Belfast.

Cultivation and harvesting of microalgae

Microalgae have been cultivated on an industrial scale for decades, most typically grown in open ponds or raceways for human and animal nutrition. With the desire to produce more specific products, closed photobioreactor (PBR) systems have become increasingly common.

What is photobioreactor?

These systems are flexible in design and could be transparent tubes, panels, bags in a range of configurations. They can be intricately engineered or very simple. Cultivation in closed PBRs enables greater environmental control resulting in predictable and reproducible growths of high density microalgal cultures.

Harvesting

Once optimum concentrations of microalgae are reached, the PBR is drained and the algae are separated from the liquid media until a thicker algal paste is obtained. Dewatering techniques include settling or flocculation, centrifugation and micro-filtration.