Uso de jardim filtrante com sistema de aeração por gravidade para manutenção da qualidade da água de piscicultura

Abstract

The constructed wetland (or Filter Garden) is a technology for treating domestic effluents that has been increasingly explored, with the advantage of low cost of maintenance, implementation and operation, as well as the possibility of reusing treated water for various uses. However, in a treatment system with recirculation of water directed at fish production, the evaluation and understanding of the efficiency of the aeration system used is essential to guarantee the quality of life of the fish and, consequently, a high production. Thus, the present study had as main objectives: to analyze the performance of a subsurface vertical flow filtering garden in the treatment of an effluent from a fish farming tank with water recirculation, in São Carlos, SP; and to evaluate the efficiency of the gravity aeration system established downstream of the filter garden. The analyzed filter garden has two subsystems: P (filter garden) and C (aeration cascades), where four and seven points were collected during nine days, respectively. The parameters analyzed were: pH, Temperature, Chlorophyll A, Electrical Conductivity (EC), Turbidity and Dissolved Oxygen (DO). The methodology for analyzing the limnological parameters of the filter garden consisted of comparing the data collected with the literature and performing the non-parametric tests by Friedman and Wilcoxon, with a 95% confidence level. As main results, it was observed that the effluent water returns to the fish farming tank with the appropriate temperature, turbidity, pH and DO for the fish farming according to CONAMA resolution nº 357/05 and the literature. The results of the non-parametric tests showed a significant difference in the subsystem P of the variables EC and turbidity; and in subsystem C, the variables pH, temperature and DO. Regarding the evaluation of the efficiency of the aeration system by gravity, the applied methodology consisted of the estimation of the saturation concentration (Cs), of the reaeration coefficient (Kla) and of the efficiency coefficient (K). The results obtained were compared with the specialized literature. As main results, it is noteworthy that the Cs presented the percentage of saturation recommended by the literature for fish culture. The value of the reaeration coefficient (Kla) varied between 0.03 and 0.2/min for any temperature of the effluent, framing the performance of the aeration system as superior to what is found in rapids and falls in natural waters. Finally, when comparing the results obtained from the efficiency coefficient K with the models described in the literature, it was observed that, according to the model by Barret, Gameson and Ogden, from the fifth collection on, the effluent was classified as "clean water". Following the Pomeroy model, the effluent was classified as "clean water" after the second collection. The results were satisfactory and proved the potential of the filter garden and the gravity aeration system. This work is linked to a project prepared, financed and executed by Embrapa and co-financed by BNDES, for improvement of the Brazilian aquaculture production