VIABILIDADE ECONÔMICA DE SISTEMA AQUAPÔNICO CULTIVADO COM ALFACE SOB EFEITO DA DENSIDADE DE JUVENIS DE TILÁPIA E VOLUME DE MATERIAL FILTRANTE

Abstract

In agriculture, aquaponics emerges as an alternative to reduce the environmental impact in food production and can be implemented in the countryside and in the city. Aquaponics is an integrated activity that unites aquaculture and hydroponics. This technique is considered sustainable, as aquaculture water is used by plants, taking advantage of available nutrients, reducing the amount of waste released into the environment. This system has a biofilter colonized by nitrifying bacteria that convert ammonia to nitrite and subsequently to nitrate. One of the main advantages of aquaponic compared to conventional systems is the lower water volume used, as it is carried out through total recirculation. This system can be applied on a small and large scale, with low implementation costs, allowing the diversification of food production of animal and plant origin. Several factors can affect production in aquaponics, among them are the fish stocking density and the biofilter volume. The greater the number of fish, the greater the amount of waste generated and nutrients available to plants, however lower densities promote greater fish growth, but may not be enough to nourish the plants. The biofilter volume is extremely important for the nitrogen cycle in the aquatic environment, the greater the biofilter volume, the better the water quality. However, oversized volumes can make it economically unfeasible. The economic viability study is extremely important to evaluate the business applicability and for market projection, being a way to have greater security in the aquaponic system implementation for producers and companies. The present work aimed to evaluate the economic viability and aquaponic system cultivated with lettuce under different densities of tilapia and filter material volume. The densities of 30, 60 and 90 juveniles of tilapia/m3 and the volumes of 50 and 70 liters of expanded clay were evaluated, with three replications per treatment. The NFT consisted of a 1,000 liter box for fish cultivation, a 200 liter decanter, a 200 liter bifilter, six hydroponic troughs with 9 plants per trough spaced 20 centimeters apart and a pump model SB270 brand Sarlo Better. The implementation costs and working capital were raised after growing a lettuce cycle and analyzed economic indicators such as cash flow, Net Present Value (NPV), Internal Rate of Return (IRR) and Payback, considering a rate of attractiveness of 15% per year in the five-year scenario. It was found that there was no effect of stocking density and ilter material volume on the juvenile tilapia final weight, with the same market value for all treatments. As for lettuces, it was found that the selling price, those that were grown in a lower density of fish had a lower market value than the others, with no effect of the filter material volume. These results had a direct impact on the economic indices, and it was verified that the densities of 60 to 90 juveniles/m3 presented positive NPV, IRR greater than the minimum rate of attractiveness of 15% with return on capital invested in the third year of cultivation. On the other hand, treatments with lower fish densities were not viable with negative NPV and IRR. The results show that aquaponics is an economically viable activity when using adequate fish density, and may be an alternative for urban agriculture production.