Development
of an efficient biomass-harvesting technology for microalgae
would achieve cost and energy savings in large-scale microalgae biomass
cultivation. Cationic surfactants could improve biomass harvesting,
but determining the optimal type and dose of surfactant requires mechanistic
understanding. In this study, we evaluated how the alkyl-chain length
and dose of three cationic surfactantshexadecyltrimethylammonium
bromide (CTAB), myristyltrimethylammonium bromide (MTAB), and dodecyltrimethylammonium
bromide (DTAB)affected biomass harvesting of Synechocystis. Flow cytometry (FC) with the nucleic-acid
(NA) stain SYTOX Green (SG) was used to differentiate the release
of extracellular polymeric substances (EPS) from cell lysis. All selected
cationic surfactants dramatically improved the biomass-harvesting
efficiency, and harvesting kinetics were represented well with a first-order
kinetic model. The efficiency of biomass harvesting correlated positively
with the alkyl-chain length; i.e., CTAB > MTAB > DTAB. A longer
alkyl
chain increased EPS release, which made it easier to achieve a less-negative
zeta potential but without cell lysis. For CTAB, the largest cationic
surfactant tested, a dose of 4.5 mM and treatment for 60 min achieved
the maximum harvesting efficiency of ∼91%. This work lays the
foundation for optimizing surfactant species and dose for biomass
harvesting.