Comparison of different microalgae cultivation systems.

There are a number of different cultivation systems for microalgae. Traditionally, microalgae are cultivated in open basins (open ponds), especially in the Asian region. This inexpensive system has the disadvantage of very low densities (and therewith little productivity). Apart from that, process control is restricted since no sterile and closed circuitries exist. Also, freshwater evaporation is very high.

Here photobioreactors present several fundamental advantages. Closed systems in form of tubes, plates or columns allow accurate process control (light availability, nutrient, CO2 and O2 concentrations, temperature, mixing etc.), high degree of protection against contamination and high volumetric productivity. Due to the high surface to volume ratio in comparison with open ponds more light can penetrate into the system. With respect to terrestrial crops a multiple of biomass can be generated and CO2 bound per area for this reason.

Subitec has notably refined this technology with the Flat Panel Airlift (FPA) reactor. Features and efficiencies of conventional reactors are outperformed by the construction of patented static mixers. Using the FPA system algal biomass can be produced environmentally compatible, continuously and at a reasonable price. Compared to currently common shallow pond systems space-time-yield is ten times higher. In Subitec's FPA significant higher cell concentrations are reached with less energy input required allowing the production of algal biomass with net-energy-yield.

Despite all advantages of closed systems open pond technology does have its rights to exist due to its little capital expenditures. Both systems can also be combined advantageously in one plant e.g. when biomass cultivated in a controlled environment using FPA technology is stimulated to accumulate specific substances in open systems. Hereby, precise process control is of secondary importance.