Aquaponics is an ecosystem approach to food production. In one recirculating system, aquaponics maintains a school of fish, a variety of plants, and a healthy colony of beneficial bacteria. The bacteria are the real heroes here. They rapidly consume toxic ammonia waste produced by the fish and turn it into nitrates on which the plants can thrive.
It all boils down to the nitrogen cycle. The fish feed contains nitrogen in the form of protein, which is the primary source of energy for the fish. As part of their digestion and respiration, the fish excrete nitrogen as ammonia both directly from their gills and indirectly through their solid waste. This waste ammonia will rapidly accumulate in recirculating aquaculture systems, and is quite toxic to fish even at relatively low levels. For aquaculture, ammonia must either be flushed out of the system or consumed in a biofilter.
A biofilter is nothing more than an elaborate bacteria condominium. In the biofilter, there is a lot of substrate surface area for bacteria to call home. Two kinds of bacteria have been identified as the main beneficial actors in a biofilter: Nitrosomonas and Nitrobacter. In turn, these bacteria convert ammonia into nitrite and then nitrate. This is good for the fish because nitrate is far less toxic than ammonia. This is great for the plants because nitrate is great plant food.
After the bacteria in the biofilter have eaten up the ammonia and spat out nitrate, the plants uptake these chemicals and prevent them from building up. Thus, the plants effectively purify the water for the fish in the aquaculture system.
The plants get great fertilizer, the fish get pristine water, and the bacteria make it all happen.
Unlike aquaculture, aquaponics allows no effluent to leave the culture system for the environment to break down. Unlike hydroponics, aquaponics systems do not require the entire system’s water to be dumped down the drain every two weeks. With aquaponics, you can produce edible fish and plants, waste little water, and produce no external effluent.
Aquaponics at the University of Miami
At the University of Miami (UM) Experimental Hatchery, the main focus has been on raising marine pelagic finfish in semi-recirculating tank systems.
By leveraging the considerable aquaculture experience available in the faculty, staff and students at the hatchery, a successful aquaponics system has been started at the UM Experimental Hatchery to showcase the technologies relied upon in aquaponics systems. We are raising Tilapia in a completely recirculating aquaponics system, with no wastewater going down the drain.
For the hydroponic component of our aquaponic system, we are using a media bed filled with expanded clay and we are experimenting with a vertical tower system which allows greater production per square foot. We are currently growing two crops: basil and spearmint. If you have eaten the pesto at the restaurant SALT on campus since late in the fall semester of this year, there’s a good chance you’ve enjoyed the basil grown in our aquaponics system.
The Aquaponics program at the UM Experimental Hatchery continues to grow. Aquaponics is a great way to eliminate the waste effluent being produced at aquaculture facilities and hydroponic plant production facilities. We are engaging with a variety of commercial and educational facilities which are interested in developing aquaponics operations.
–Joshua Grubman, UM Rosenstiel School part-time lecturer