The removal of phytoplankton cells from aquaculture systems generally results in the reduction of
nitrogenous waste and improves water quality. With this study, the effects of chitosan concentration,
environmental condition and pH adjustment on flocculation of phytoplankton in marine shrimp
(Litopenaeus vannamei) culture tanks were investigated. The remaining phytoplankton and suspended
solids in the system were indicators for evaluating the efficiency of chitosan on flocculation. The results
indicate that the flocculation efficiency of chitosan was highest (>85%) and remained fairly constant at a
chitosan concentration of 40–80 mg L1 and a pH range of 7–9 after chitosan addition. With this novel
technique including 40 mg L1 chitosan addition, pH adjustment to 6.5 and then to 8.5, high efficiency
and consistency of flocculation were achieved. This technique could also be applied with various water
alkalinity up to 400 mg CaCO3 L1
. The experiment for phytoplankton removal by chitosan flocculation
in the recirculating aquaculture system showed that flocculation efficiency remained constant even
though flocculation was repeated several times.