Coagulation consists of neutralizing negative surface charges of colloidal
particles (in this case microalgae),while flocculation is the aggregation
of neutralized particles followed by floc formation. Coagulants
that have been traditionally used in water and wastewater treatment
are salts of aluminumor iron. However, these substances have a limited
application inmicroalgal systems because they can contaminate downstream
products restricting biomass valorization [3,8]. This drawback
may be overcome by using natural organic coagulants like tannin
based polymers or modified starch which are being increasingly used
since the 80s [9]. These types of coagulants (also referred to “flocculants”,
as from now in the text) are becoming very popular in the field
of water treatment as substitutes for polyacrylamide based flocculants
due to health concerns [2]. Previous studies on microalgae coagulation–
flocculation and sedimentation with different types of organic
polymers have shown promising results in terms of separation efficiency
(Table 1).