Teaching Sustainability Through Aquaponics

You may have heard of hydroponics (growing plants without soil), but have you heard of aquaponics? Aquaponics couples aquaculture (raising aquatic animals such as fish, crayfish, snails or prawns in tanks) with hydroponics, where nutrient-rich aquaculture water is fed to the hydroponically-grown plants. 

Although it sounds confusing, the idea behind it is actually pretty simple: fish enrich the water with nitrogenous waste, which is then pumped to the plants via solar-powered pumps. The filtered water drains from the plants back into the fish tank, making it a 100% self-sustaining system. 

As construction wrapped up at Richfield High School during distance learning, Science Teacher Matt Brown saw large plastic totes being used by contractors to contain heating and cooling fluid—coincidentally, the same totes that are often used in aquaponics. Building an aquaponics system had been an idea in his mind for awhile, and when he saw the totes he realized it was the perfect opportunity. 

The construction foreman was more than happy to give the totes to Mr. Brown when they were done with them. Together with the RHS Green Team, Mr. Brown cut a tote in half to create a “top” and “bottom” for the aquaponics system and, slowly but surely, began to set it up. As the 2021-22 school year began and students were back in the building, his CIS: Climate Crisis* class took on the project and worked together to find solutions to a few of the problems it faced. 

“The students had great ideas about it,” said Mr. Brown. “They’re the ones who figured it out.” 

There are multiple parts to the aquaponics system that work together to create a functioning system. The first one is the power: where does it come from? The CIS: Climate Crisis class was able to set up solar panels to provide electricity for the pumps. The solar energy collected from the panels is put into a charge controller, which then charges batteries connected to a timer that, in turn, controls the water pump system.

Another major part of the system is the siphon that drains water from the plant basin back into the fish tank on the bottom. 

“We were struggling with making the siphon system work,” said Mr. Brown. “If the plants have constant water, with no drying out process, there can be a lot of mold growth.” 

The cycling of water into the siphon valves allows the plants to dry out, while the clay pebbles (which contain needed bacteria) stay wet. The CIS: Climate Crisis students invested time, energy and ideas into how to make the siphon valves work (and found a solution). 

The third component involves transforming the ammonia from fish waste and from uneaten food into nitrates that can be taken up by the plants to make chlorophyll, amino acids and other nitrogen-based biomolecules. This process is completed through nitrogen-fixing bacteria that live on the extruded clay pebbles.

“The plants need to use a slightly different version of nitrogen than what would come out in the waste of animals,” explained Mr. Brown. 

After months of hard work, the CIS: Climate Crisis class held Richfield’s first-ever salad party, where students enjoyed the fruits of their labor with fresh lettuce cut from their aquaponic system.

So, what’s next in the future for our first aquaponics system? Hopefully, another one! Mr. Brown has more bins and now that the trial-and-error process is complete and the current system is functioning properly, all that’s left to do is find the perfect spot to put the next project. 

Check out the video below to see how the system works and hear from CIS: Climate Crisis students about the aquaponics system and their thoughts on sustainability.

* CIS stands for College in the Schools, which is an educational program available at RHS for high school students, run by the University of Minnesota. It allows students to take college-level classes in their high school and, as a result, earn college and high school credit.

While the CIS: Climate Crisis class achieved the full operation of the system, many students from the RHS Green Team worked to get the materials and fish ready. We would also like to thank Beacons for its generous donations of equipment and to the DOW We Are Innovators Grant for additional funding for the project.