Dimensionamento, implementação e operação de um sistema aquapônico em escala comercial no município de Maranguape - CE

Abstract

This study aimed at the design, implementation, and operation of a commercial-scale aquaponic system in the municipality of Maranguape – CE, detailing the development of an integrated system that combines Nile tilapia (Oreochromis niloticus) farming with lettuce (Lactuca sativa) cultivation. The system was designed to operate commercially, with a monthly production capacity of 2,000 kg of fish and 1,600 vegetable seedlings. As a sustainable technique, aquaponics enables efficient water reuse and the integration of aquaculture and hydroponics. The developed system consists of fish production tanks, water treatment units (settler, mechanical filtration, biological reactor, and equalizer), an aeration system, pumping, and hydroponic units. Water continuously circulates between the fish tanks and treatment units, where fish waste is converted into nutrients for the plants. In return, the plants filter the water, returning it clean to the tanks. The system was designed based on precise calculations, considering factors such as fish biomass, daily feed quantity, ammonia production, dissolved oxygen requirements, and biological treatment capacity. The system was designed for continuous operation, with a 24-week production cycle divided into two phases: nursery and grow-out. Lettuce production was staggered to allow for weekly harvests of 256 heads, with a growth cycle of 42 days. The results demonstrated the system's feasibility, with fish survival rates ranging from 60.9% to 99.7% throughout different cultivation phases. Tilapia production nearly reached the target of 2,000 kg per month, with a feed conversion ratio (FCR) ranging from 0.949 to 1.716, indicating satisfactory feed efficiency. Water quality parameters remained within optimal limits for aquaponics for most of the experiment. The pH ranged from 6.5 to 7.2, within the ideal range for tilapia and plant development. Total ammonia levels remained below 3 mg/L, while nitrite levels did not exceed 1 mg/L, ensuring a safe environment for aquatic organisms. Nitrate concentration remained stable, favoring plant growth. However, dissolved oxygen levels decreased along the length of the hydroponic tank, reaching values close to 0.0 mg/L after 25 to 35 days of cultivation, negatively impacting lettuce production. Due to this issue, lettuce production was temporarily suspended after several transplant attempts, highlighting the need for a bottom aeration system in the hydroponic tanks. The water treatment system proved efficient in removing solids and converting ammonia into nitrate, using a biological reactor with fluidized media and filter brushes. The aeration system was designed to maintain adequate dissolved oxygen levels, essential for both fish and nitrifying bacteria. Additionally, a backup system, consisting of an electric generator and an automatic transfer switch, ensured the continuous operation of the system, even in the event of power supply failures.