The purpose of this study was to explore efficient
methods of harvesting the microalga Phaeodactylum
tricornutum. Natural sedimentation experiments, performed
at different light and temperature conditions, did not yield
significant improvements in efficiency even after 1 week.
When alkalinity-induced flocculation was performed, both
the flocculation efficiency and the concentration factor
dramatically improved at pH=9.75 (0.5–0.7 units over the
original pH of the culture) after 10 min settling time.
Sedimentation rates are documented at pH ranging between
pH 9.75 and 11.0. The results of the application of two
conventional flocculants used in wastewater treatment,
polyaluminium chloride and aluminium sulphate, are also
presented. Chitosan was also used as a natural flocculating
agent to improve possible contamination problems in the
downstream process. pH was adjusted in order to determine
optimum flocculation efficiency of chitosan in combination
with a high concentration factor. Satisfactory results were
found with chitosan at an adjusted pH of 9.9 using
concentrations as low as 20 mg L−1, after testing a
flocculant range of 5–200 mg L−1.