The effect of phosphate addition with different concentration on the capability of Nannochloropsis oculata as a bioremediation agent of medium heavy metal (Cd2+)

Nannochloropsis oculata is a unicellular marine microalgae that has a role as an important food source and additive for marine organisms. Nannochloropsis oculata contains high levels of carbohydrate, protein, and chlorophyll so it has the potential as a bioremediation agent. In its growth, it needs an important component of nutrients as a growth medium, one of which is a source of phosphate. Phosphate itself acts as a constituent of protein compounds to bind metal ions in cells. This research aims to determine the effect of the addition of KH2PO4 as a phosphate source on the growth of Nannochloropsis oculata as a bioremediation agent to reduce levels of heavy metal pollution (Cd2+). This research was conducted from June to August 2019 in the Laboratory of Microbiology and Molecular Biotechnology of FIP-UNIDA, Bogor, West Java. Nannochloropsis oculata microalgae were obtained from UGO Plankton Shop, Purwodadi, Central Java. The research method used is a Completely Randomized Design (CRD) with 4 treatments and two replications. The Cd2+ concentration used is 2 ppm in this research. The addition of KH2PO4 as a phosphate source is 0 ppm (control), 3, 4, and 5 ppm. The results of this research showed that the highest growth peak of Nannochloropsis oculata was achieved at 4 ppm treatment on the 9th day with cell density reaching 17.8 × 106 cells/mL, while the highest absorption of cadmium (Cd2+) was found in the 4 ppm phosphate treatment with the absorption efficiency reaching 39.23%.