Integrated system for bioremediation of Nile tilapia rearing effluent and astaxanthin production by Haematococcus pluvialis

Haematococcus pluvialis is a microalga that can reduce the levels of inorganic and organic components in effluents, in addition to production of the high-value carotenoid astaxanthin. The present study proposed an integrated system for the simultaneous treatment of effluent from a Nile tilapia recirculation system and astaxanthin production using the microalga H. pluvialis. Cultures were developed in 2 L bottles, with freshwater previously treated and enriched with a modified Bold’s Basal Medium (BBM). The experiment was carried out on a laboratory scale using a completely randomized experimental design with five treatments: control (100% BBM), E25 (25% Nile tilapia effluent + 75% BBM), E50 (50% Nile tilapia effluent + 50% BBM), E75 (75% Nile tilapia effluent + 25% BBM), E100 (100% Nile tilapia effluent), with three replicates for each condition. H. pluvialis could grow in all proportions of effluent from Nile tilapia cultivation. The use of effluent as culture medium (E100), despite having lower cell density and biomass, resulted in biomass with high astaxanthin content (10 mg g⁻¹) and antioxidant activity (89% inhibition of DPPH radicals). Meanwhile, this integrated system significantly contributed to the effluent remediation (98% N and 91% P removal). H. pluvialis can be used for cost-effective treatment of aquaculture effluent with simultaneous production of astaxanthin, with potential application as aquafeed, in a holistic bioeconomy approach.