Aquaculture effluent: adequacy to environmental legislation through the implantation of Artificial Floating Islands (AFIs)

Abstract

Brazil reached the 14th place among the world's largest aquaculture producers in 2014 and grew by 123% between 2005 and 2015. That growth promotes social and economic improvements; however, it can lead to serious environmental damage due to the characteristics of the activity. In this sense, the Brazilian States have intensified the monitoring and control of water quality, which has led to the adjustment of legal requirements, among which is compliance with the standards established by CONAMA Resolution 357/2005 and its amendments. Fish farming ponds generate organic matter (OM) derived mainly from excessive feeding and excretion of fishes. This OM is mainly composed of nitrogen (N) and phosphorus (P) which are commonly released by the effluent from the ponds to the receiving water body without previous treatment. To comply with environmental legislation, aquaculture effluents should not have concentrations of N and P above 0.27 mg L-1 and 0.03 mg L-1 (lentic environments), respectively. Currently, complying with the standards established by current legislation has been an obstacle to environmental adequacy, especially for small producers, since conventional treatments can economically cripple the production due to high costs. Constructed wetlands (CWs) are alternatives of lower cost, simple operation and maintenance, and present great efficiency in the removal of OM from aquaculture effluents. However, studies show the need to use at least 10% of the production area for WCs implantation, a fact that can also make production unviable economically. Therefore, the implantation of Artificial Floating Islands (AFIs) systems colonized with aquatic macrophytes within the ponds can be an alternative to improve the water quality of the aquaculture effluent. The hypothesis of the present study is that the AFIs implanted within the ponds will be as or more efficient in the removal of nutrients than the CWs. Thus, the objective of this study will be to test the efficiency in the removal of nutrients from tilapia production ponds through the implantation of AFIs within tilapia production ponds with a view to the adequacy of the aquaculture effluent to the current environmental legislation. To test our hypothesis, two semi-intensive commercial production systems of Nile tilapia (Oreochromis niloticus) with three replicates each will be evaluated; 1) Floating islands colonized with Eichhornia crassipes, arranged within the tilapias production ponds; 2) without AFIs system. Water samples will be collected in the water supply, center and effluent of the ponds. The following physical and chemical variables of the water will be evaluated: water temperature, dissolved oxygen, pH and electrical conductivity (multiparameter probe); in addition, the nutrients: total nitrogen, nitrate-N, nitrite-N, ammoniacal-N, total phosphorus, orthophosphate; and the suspended particulate matter (analytical methods). Univariate and multivariate statistical tests will be used to evaluate the difference between the two treatments. (AU)