Industrial reactors for algal culture are at present. There are open
ponds, photobioreactors and closed systems. Photobioreactors are
different types of tanks or closed systems in which algae are cultivated.
Open pond systems are shallow ponds in which algae are cultivated.
Nutrients can be provided through runoff water from nearby
land areas or by channelling the water from sewage/water treatment
plants. Technical and biological limitations of these open systems
have given rise to the development of enclosed photoreactors. Microalgae
cultivation using sunlight energy can be carried out in open
or covered ponds or closed photobioreactors, based on tubular, flat
plate or other designs. A few open systems are presented for which
particularly reliable results are available. Emphasis is then put on
closed systems, which have been considered as capital intensive
and are justified only when a fine chemical is to be produced. Microalgae
production in closed photobioreactors is highly expensive.
Closed systems are much more expensive than ponds. However,
the closed systems require much less light and agricultural land to
grow the algae. High oil species of microalgae cultured in growth
optimized conditions of photobioreactors have the potential to yield
19,000–57,000 l of microalgal oil per acre per year. The yield of oil
from algae is over 200 times the yield from the best-performing
plant/vegetable oils [14].