WATER USE ANALYSIS OF DECOUPLED AQUAPONICS SYSTEMS TO SUPPORT OLIGOTROPHIC CULTURE CONDITIONS FOR HIGH VALUE FISH SPECIES

Aquaponics systems can be classified into two general groups, coupled and decoupled systems.  A coupled aquaponics system is one where the fish and the plants symbiotically coexist in the same water and requires the pairing of fish and plants that have similar water quality requirements.  This normally includes fish that can sustain eutrophic environments and is often associated with fish species that have low market values.  High value fish species, in general, required oligotrophic conditions, colder temperatures or saline conditions.  These are not ideal growing conditions for most plants and therefore required the decoupling of the systems to accommodate the disparity in culture environments.  

There are apparent challenges associated with decoupling the fish and plant production aspects of an aquaponic system.  The low nitrate-nitrogen (N) concentration required by the fish result in high water exchange rates that flush away nutrients needed to sustain the high plant production.  Micronutrients required by the plants are not tolerated by the animals on the fish side.  Through decoupling, each system can be managed relatively independently for water quality criteria such as nitrate-N, temperature and pH.  By utilizing an interim process between fish and plants, key nutrients can be removed quickly from the fish side, converted to soluble nitrogen and delivered to the plant side before they can deteriorate water quality conditions for the fish.  

Mass balance calculation for solids, ammonia, nitrate-N and water losses through evapotranspiration (ET) indicate that by decoupling the fish and plant production aspects of an aquaponics system and creating an intermediate solids retention, mineralization and biofiltration system, you can achieve a nitrate-N disparity of up to 40% between the fish and plant system without additional water use or loss of nutrients.  This strategy also allows for limited individual manipulation of TSS, temperature, pH and other micronutrient in each system based on the needs of the plant and animals being produced.

A comprehensive analysis of the consumptive water use rates was evaluated using an equivalent evapotranspiration rate (mm/day) for all water losses associated with the complete aquaponics systems.  This is compared to irrigation requirements of similar plant species grown using modern soil based agriculture methods and technologies as a reference.