Floating aquatic macrophytes for the treatment of aquaculture effluents

Aquaculture is an activity with economic and social importance since it generates food, employment, and income. However, like other human activities, it negatively impacts the environment, in this respect mainly due to the production of effluents rich in sedimentable solids, organic matter, phosphorus, and nitrogen. These last two are responsible for the eutrophication of water courses, causing changes in the aquatic biota. Hence, there is a need to adopt strategies to improve the efficiency of wastewater reuse. In this sense, the objective of this work was to evaluate the efficiency of using the floating aquatic macrophytes Eichhornia crassipes, Pistia stratiotes, and Salvinia molesta for the treatment of aquaculture effluents. The experiment was conducted in a completely randomized design, with seven treatments and three repetitions; the treatments were the following: T1, without plant, treated only with sedimentation; T2, Eichhornia crassipes; T3, Pistia stratiotes; T4, Salvinia molesta; T5, Eichhornia crassipes and Pistia stratiotes; T6, Eichhornia crassipes and Salvinia molesta; and T7, Pistia stratiotes and Salvinia molesta. The treatments were evaluated for a period of 168 h: the first collection of effluent allowed analysis of the raw effluent; the second occurred 24 h after the first collection and the others, on alternate days with 72, 120, and 168 h, totaling five collections in each experimental unit. The effluent used came from breeding tanks of Nile Tilapia (Oreochromis niloticus). The quality of the effluent was evaluated by the rate of removal of nutrients N-total, N-nitrite, N-nitrate, N-ammoniacal and Ptotal, temperature, pH, turbidity, dissolved oxygen, electrical conductivity, total alkalinity, BDO, and CDO. After the effluent was treated, the values of the parameters were compared with the maximum admissible values (MAVs), as specified by Brazil's National Environmental Council (CONAMA) in Resolutions 430/2011 and 357/2005. With the use of floating aquatic macrophytes, the concentrations of all evaluated limnology parameters improved significantly. There was also an improvement in the physical aspect of the effluent (transparency and turbidity). Thus, it can be concluded that the use of the macrophytes Eichhornia crassipes, Pistia stratiotes, and Salvinia molesta is effective in the treatment of effluents from fish farming.