Only 22% of the nitrogen introduced into the system is converted into biomass , much of which is discarded into the environment (Silva et al. 2003 ). As a way of treating effluent , macroalgae can be added to take advantage of the nutrients and produce biomass. Howe ver, different types of biofloc can affect the organism’s performance. The aim of this study was to evaluate the growth and absorption of nutrients by the macroalga Ulva lactuca in two biofloc systems: chemoautotrophic and mixed/mature.
The experiment was carried out in an agricultural greenhouse with constant aeration and lasted 15 days . After 56 days of cultivation in an integrated system, the animals were harvested and the effluent from the cultivation was directed into 6 tanks with a useful volume of 3.5 m3 . The macroalgae were stocked in each tank at a density of 1g m3 and an initial weight of 3.52±0.15 kg. Two biofloc strategies were used , the chemoautotrophic system presented 25.0±0.0, 2.43±0.21 and 131.7±79.7 mg L-1 at the end of cultivation . And the mature/mixed system showed 32.3±2.0, 2.17±0.35 and 346.7±115.6 mg L-1 at the end of cultivation, resulting in two treatments (Chemoautotrophic and Mixed ) with three replicates each. The macroalgae was kept in the tank using a rectangular structure measuring 1x1x0.3 (length x width x depth ). At the end of the 15 days , the macroalgae were weighed after removing excess moisture . Nutrients were analyzed three times a week and total suspended solids were analyzed at the end of the experiment.
As a result , the nitrate removal rate was significantly different (p ≤ 0.05) between the treatments , showing that in the mixed treatment there was greater absorption of nitrate by the macroalgae. And in total suspended solids there was a higher concentration in the mixed treatment (Table 1).
The greater absorption of nitrate in the mixed treatment is probably due to the N:P ratio which was closer to the ideal for macroalgae in this treatment , 30:1 being the ideal ratio according to Duke et al (1995 ). The increase in phosphate concentration in both treatments is due to the decomposition of the floc and the release of phosphorus (Silva et al. 2013 ). The absence of an organism to move the flake led to a decrease in the concentration of solids in the experiment, even with aeration , and thus to its decomposition .
Growing the macroalgae in a mixed biofloc system as an effluent treatment resulted in greater nitrate absorption , as well as biomass production.