Evaluation of growth and bioremediation potential of Arthrospira sp. (Sitzenberger ex Gomont, 1892) in the treatment of intensive production effluents of marine shrimp
With the increase in aquaculture, the negative impacts on the environment tend to intensify. The biggest environmental problem in aquaculture is related to effluents with great potential for pollution of natural waters. One of the goals of aquaculture should be to produce more products without significantly increasing the use of water and soil resources. The biofloc aquaculture system (Biofloc Technology - BTF) meets this expectation, however there is still release of effluents with high concentrations of nutrients and organic matter, especially during harvesting. Several studies demonstrate the efficiency of using microalgae in removing nutrients from crop effluents, however, for a microalgae to meet the requirements to be used in wastewater treatment systems,it needs to present some characteristics such as having cells that are easily removable by simple filtration, easy to carry out massive cultivation, tolerance to a wide range of salinity and generation of value-added by-products. The cyanobacterium Arthrospira sp. is a promising species for the treatment of effluents from marine shrimp farming. Thus, the present work aims to evaluate the efficiency of a low-cost cultivation medium, composed of agricultural fertilizers and sodium bicarbonate, for large-scale production of Arthrospira sp., In addition to evaluating the costs for producing this new medium cultivation, as well as testing the feasibility of treating marine shrimp production effluents in a biofloc environment (BFT System), using this microalgae.Four experiments were carried out and presented here in two chapters of this Dissertation. In the first chapter, cyanobacteria was grown in f/2 and Fertilizer media, where it showed a higher cell yield in this last culture medium. A second experiment aimed to increase the Fertilizer medium by testing the addition of different concentrations of sodium bicarbonate. The treatment where 15 gL-1 of sodium bicarbonate was added showed cell growth similar to the standard Zarrouk medium for cultivation of Arthrospira sp. In the second chapter, two experiments were carried out. An experiment aimed to evaluate which concentration of effluent from the BFT system would be better for the growth of Arthrospira sp. Cyanobacteria showed greater cell growth in 100% of the effluent from the decanted BFT system,when compared to growth in Fertilizer (Control) medium. vii A second experiment aimed to determine the possibility of cyanobacteria growth in the effluent of the BFT system without any previous treatment, as well as to measure the absorption of nutrients from this effluent by the microalgae. Cell growth was the same in the two treatments EFLU (effluent without previous treatment) and EFLU DEC (decanted effluent), and there was an important remediation of phosphate in the effluent, thus realizing that the cultivation of Arthrospira sp. in the effluent of cultivation of marine shrimp in BFT system, as well as the removal of much of the phosphate from that system.