Closed systems, mainly known as photobioreactors, can
address some of the problems associated with open pond
systems. The major advantages of the closed systems are as
follows: (a) minimization of water evaporation and (b) reduction
of the growth of competitive algal weeds, predators and pathogens
that may kill the desired microalgae. It is important to acknowledge
that although photobioreactors significantly reduce the
growth of competitive algal weeds, they cannot completely eliminate
the growth of contaminants [54]. A detailed comparison of
different closed photobioreactor systems and their biomass productivities
are reported in Table 3.