The cultivation of blue-green algae using the tilapia RAS effluent

The recirculating aquaculture system (RAS) is one of the important technologies to support the sustainable aquaculture because it allows for higher density cultivation, minimizes reliance on water resources, and reduces waste discharged to the environment. However, wastewater form RAS still contains nitrate and phosphate which are both required for the growth of microalgae. Thus, this work aims to utilize RAS effluent to generate value-added algae biomass. The blue-green algae, Arthrospira platensis and Oscillatoria okeni were chosen for utilizing tilapia RAS effluent since they are easily harvested and contain high protein, essential fatty acids, and phycocyanin, which have a potential for feed supplement.

The results from batch culture showed that O. okeni could be grown in the tilapia RAS effluent without adding any nutrients, whereas an addition of sodium bicarbonate 4 g L-1 was required for A. platensis. However, the productivity of A. platensis was approximately 3-fold higher than that of O. okeni. Moreover, the phycocyanin content in A. platensis biomass (13.1% dry wt.) was also significantly higher than that of O. okeni (9.9% dry wt.). These results indicated that the tilapia RAS effluent can be used to grow algae and obtain the biomass as animal nutritional supplements.