Aquaponics water use and nutrient cycling in a seawater-cooled controlled environment agriculture system

To demonstrate the water use efficiency and nutrient cycling of an aquaponics system in combination with a seawater based evaporative cooling system, a pilot-scale aquaponics unit was installed and operated for one year inside a controlled environment agriculture building cooled by the evaporation of seawater on the campus of King Abdullah University of Science and Technology in Thuwal, Saudi Arabia. Results collected from the operation included crop water use, water quality parameters, dissolved ion concentrations, outdoor/indoor climate data and crop output. Seawater-based evaporative cooling did not provide adequate indoor temperatures for the cultivation of lettuce during the hot and humid summer season. However, the combined aquaponics with seawater evaporative cooling was effective for fall, winter, and spring cultivation with a mixed crop of lettuce and tomatoes. Opposite to the vegetable production cycle, higher water temperature in the summer favored the production of Sabaki tilapia during the warm summer season rather than the cool winter season. Because of this dichotomy, the system showed promise for management and nutrient balancing on an annual basis rather than on seasonal or daily basis. From a fresh water use perspective, the average daily fresh water use by plants totaled only 4.6 L day-1 m-2 or 19 L kg-1 of crop harvested during the peak winter/spring growing season. Results demonstrated that an aquaponics system in combination with seawater-based evaporative cooling is capable of saving ~90% of fresh water as compared with traditional forms of agriculture in the region.