Cultivation of marine microalgae Nannochloropsis oculata in effluent from shrimp production in BFT system
The massive production of microalgae is limited by several technical aspects, among which the need for cheaper means of cultivation stands out. Effluents from aquaculture, which contain high concentrations of nutrients, can be a more economical alternative to conventional farming media. The objective of this study was to use the effluent from shrimp production in a biofloc environment (BFT system - Biofloc Technology System) as a culture medium for the marine microalgae Nannochloropsis oculata. In a first experiment, laboratory tests showed the growth of microalgae in different concentrations of the integral effluent (25, 50, 75 and 100%). In the second experiment carried out in an agricultural greenhouse, in a volume of 5L, under environmental conditions the microalgae was grown in the integral effluent and compared with the f/2 media and one with chemical fertilizers. Both experiments were carried out in triplicate and the data were analyzed for statistical differences by the ANOVA test (one way) and the Tukey test (p <0.05). The results of the first experiment demonstrated that the greatest cell growth occurred in the treatments with 75% (219 ± 34.4 cells. X 106 mL-1) and 100% (192.4 ± 27.7 cells. X 106 mL-1) . These were significantly larger than the other treatments, but similar to each other. In the second experiment, the maximum cell abundance was recorded in the treatment with BFT medium (T-BFT: 25.57 ± 0.17 cells. X 106 mL-1), but there was no statistical difference from the others.The highest percentage of lipids was registered in the treatment with bioflocs (34.76 ± 5.8%), but in the same way this result did not differ statistically from the other treatments. Differences in the fatty acid profile were detected between the BFT and fertilizer treatments, with higher percentages of the C18: 1t, C18: 1c and C18: 2 fatty acids in the BFT treatment, possibly due to the different sources of nitrogen in the media. N. oculata removed 27.95 mg L-1 of nitrate and 4.78 mg L-1 of phosphate in twelve days of the experiment. The reduction of ammoniacal nitrogen at the end of the crop seems to have resulted mainly from the action of nitrifying bacteria present in the BFT treatment. Conclude that the pure BFT effluent can be used as a medium for the massive cultivation of N. oculata, producing the same biomasses ,amounts of lipids and fatty acid composition than other means normally used. In addition, the growth I saw of this microalgae in this medium has removed a large amount of nutrients that can cause eutrophication of the receiving water body and the biofloc aquaculture system itself, demonstrating the great effluent clearance capacity of N. oculata.