Cultivation of the red seaweed Kappaphycus alvarezii using biofloc effluent

Abstract

The aim of this work was to evaluate the use of effluent from a Biofloc System (BFT) as a fertilizer for the red seaweed Kappaphycus alvarezii cultivated in tanks and analyze its influence on carrageenan yield and quality. Firstly, the optimum effluent concentration and period for enrichment were determined by an in vitro study. The seedlings were then cultivated for 7 days in two different culture media: 50% von Stosch solution (V) and 25% BFT (B), both diluted in sterilized seawater. Seaweeds cultivated only in sterilized seawater were used as a control (C). After this period, all plants were grown in only sterilized seawater for a further 28 days. Seedlings from V (1.05 ± 0.02% day −1 ) and B (1.13 ± 0.01% day −1 ) showed no significant differences in growth rates, being both higher than the control (0.91 ± 0.06% day −1 ). Seedlings from V and B also removed a greater quantity of nitrate (58.39% and 22.97%, respectively). Seedlings from V removed 100% phosphate, while those from B removed 83.58%. The tissue nitrogen content was higher only in the V. Although no significant differences were observed among treatments in the carrageenan yield, significantly higher gel strength and viscosity were observed in B (248.85 g cm −2 and 19.89 mPa s, respectively). According to the results, BFT effluent can be used to replace von Stosch solution to grow K. alvarezii in tanks. At the same time, the seaweed, together with bacteria and microalgae from the effluent, can be an effective biofilter in IMTA systems using bioflocs.