The Magazine of The Sierra Club
Why Aquaponics Could Revolutionize Food Production
Inside a former brewery in St. Paul, Minnesota, a company called Urban Organics is perfecting a new model of aquaponic food production. This version combines fish farming with hydroponic vegetable cultivation to create an efficient closed loop system, where water and nutrients are perpetually recycled. The indoor farm, which is about the size of four tennis courts, uses 2 percent of the water that would be required by a conventional farm with the same square footage.
In Urban Organics' current pilot phase, about 800 tilapia swim in each of four fish tanks, chowing down on soy-based feed for about a year. The company harvests the mature fish, sending about 200 pounds each week to local restaurants.
The tilapia's waste drifts down to a drum screen filter, which removes the heaviest particles. As the drum rotates, a high-pressure jet of water washes the concentrated sludge down a channel for collection. Urban Organics is exploring the possibility of using this nutrient-rich material to grow mushrooms in the building's basement or selling it as fertilizer.
After the heavy waste has been separated out, the water flows into a 12-foot-long biofilter. Inside, thousands of penny-size plastic disks (they resemble rotelle pasta) tumble in the current, providing the surface area on which two types of bacteria grow. As the wastewater flows through, the bacteria convert its ammonia into nitrates, the main component of fertilizers.
Finally, that nitrate-rich water flows into long rubber troughs where plants flourish under grow lights. The hydroponic setup uses no soil; the plants' roots dangle directly into the water, whence they absorb nutrients. Urban Organics harvests kale, Swiss chard, lettuce, and herbs three times a week and sells the produce to local restaurants and grocery stores. The quick trip, says Urban Organics co-founder Tom Haberman, guarantees that each leafy green arrives fresh and full of nutrients.
