Due to zero water exchange and microbial community growth , biofloc technology (BFT) is characterized by high nutrient loads and total suspended solids (TSS). As a result , the introduction of different species is focused on waste recovery . However, the distinct characteristics of the biofloc system can become a challenge when introducing a photosynthetic organism into the environment . Therefore , the adoption of different management practices may be essential for greater biomass production and nutrient absorption.
Three experiments were conducted in an agricultural greenhouse , with constant aeration and tanks with constant recirculation between the shrimp , fish, and macroalgae tanks . The first experiment evaluated different depths of structure for macroalgae, one shallow (5 to 10 cm deep ) and one deep (25 to 30 cm deep ). The second experiment evaluated the influence of a clear water system, starting a biofloc from the beginning (T0) and using a mature biofloc inoculum with 250 mg L−1 of SST (T250). The third experiment evaluated the use of a biofloc system with inorganic fertilization (Chemoautotrophic ) and a mature biofloc inoculum with organic fertilization (Heterotrophic ). In all experiments , water quality analyses , weekly weighing of macroalgae, and evaluation of organism performance were performed.
As a result , a higher growth rate was found in the shallow treatment (0.14 ± 0.14 % day −1) , due to greater proximity to light in an environment with high organic load (Table 1) . However, there was a loss of biomass in some weeks caused by low temperature (15 ºC ) and the structure’s limited support capacity . A higher growth rate was also found in the chemoautotrophic treatment , with an average of 3.12 % day−1, due to lower organic load , compared to an average of 2.09 % day−1 in the heterotrophic treatment . However, in terms of nutrient absorption , the heterotrophic treatment showed greater phosphate removal due to the better nitrogen:phosphorus balance in the system. The availability of nutrients from bioflocs also showed that in the T250 treatment , a nitrate and phosphate removal rate was found compared to T0, in addition to an increase in protein content in the macroalgae tissue (Table 1).
As a conclusion , macroalgae production with the adoption of management strategies such as a shallow structure (5 to 10 cm deep ), with an average of 250 mg L−1 of suspended solids in a biofloc system with a high nutrient load , proved to be viable in bioremediation , biomass growth , and sustainability.