We installed a closed-loop aquaponics food production system in our residential dining hall, the Food Zoo. This is an extension of our larger campus food production program and is a way to grow indoors, year-round, to the delight of our students and guests.
Aquaponics is an integrated sustainable food production system that combines traditional aquaculture (raising seafood) with hydroponics to produce food and fertilizer and manage waste all in one self-contained system. Fish are raised in tanks where they produce waste in the form of ammonia. This ammonia is perfect for feeding plants, but isn’t yet in a form that is useful for plants. So the water in the tanks is inoculated with microbes that convert the fish ammonia into nitrogen that is useful for plants. The water is then pumped into the growing area where it makes its way through four levels of plants and volcanic rocks that take up the nutrients and effectively filter the water. The clean water is then returned to the fish tank and the cycle continues.
We had a student who had an internship with us last semester, and it was part of his responsibilities to help build this system. The system is set up as an 80-gallon tank with standard baker’s racks on either side. On those racks we built four wooden boxes that extend beyond the dimensions of the rack. In the middle of the tank are a pump and a PVC pipe system that pump the water up to the very top of the baker’s racks. It drops the water into our custom containers, which are filled with the volcanic rock. You set trays of the plants on top of that volcanic rock. There’s basically a hole in each of those racks and when it gets too full, it drains. When the water goes up there, it’s laden with nutrients from the fish. It fills the container and the plants suck it up from the bottom.
We use our system to produce nutrient-dense microgreens as well as tilapia. The microgreen harvest is used in both our residential dining operations as well as in catered events. Last year we produced 150 pounds of microgreens. At the market rate of $36 per pound from our local growers, that equals $5,400 worth of product.
The tilapia grow in the tank and once they are large enough we harvest them. We just replenish them when they get too big. You can use other types of fish if you’d like. We still need to find out how to close the loop on the fish. Our biggest learning was all these little intricacies about the system, like you have to buy a certain bacteria to eat the fish waste before the plants can absorb it. Little things like that we had to learn with no local resource to guide us.