IEEE Spectrum June, 2013 - 62

The age of plenty

"The roots can remain small because the nutrients are everywhere, so the plants grow faster," says Huy Tran, PAES's plant expert.
"A head of lettuce planted in soil takes 50 days to mature. One in
an aquaponics system takes 35 days or so." The flow of water and
nutrients through the system can be tightly controlled, allowing
Urban Organics to vary production according to market demand.
Finally, there's the advantage of growing food practically down
the street from the consumer. While the fish will provide some
revenue, it's the high-value greens such as arugula, baby lettuces,
and microgreens and fresh herbs like basil that Urban Organics
is counting on to make its real money.
According to agricultural economist David Weatherspoon of
Michigan State University, a successful business model for indoor
aquaponics depends in part on the proximity of the farm to the
tables where its produce will be eaten. Being able to harvest
produce in the morning so chefs can have it on lunch plates that
afternoon is, Weatherspoon admits, "a good marketing point for
the leafy vegetables. And that might be where the sweet spot is."

The fIrsT TIme I vIsITed Urban organIcs lasT sepTember, haIder
showed me one of the aquaponics systems that he had originally
set up in his basement. A polystyrene raft full of lettuce seedlings
floated in a tank, with a few tilapia swimming below and a fluorescent bulb glowing from above.
He took me through the first two floors, showing me how they'd
been completely gutted and repainted. Now they were empty,
except for some massive, 5.5-meter-tall load-bearing columns
and eight big blue tanks placed at even intervals on each floor.
Haider and his partners already knew what crops and fish
they wanted to grow-tilapia and greens. They also knew exactly
which markets they would serve. They had distributors lined up
for their fish and produce and were working on deals to supply
various restaurants as well as the St. Paul and Minneapolis public schools. But the systems design for the farm was still a work
in progress when PAES came calling last November.
"We were following news stories, and we reached out to Dave
Haider and Fred Haberman," says Bob Miller, PAES's vice president for aquaculture. "We had lunch together up in St. Paul and
talked about what we could bring to the table in terms of design
services and equipment and founded the relationship off that visit."
The Urban Organics team-led by Losordo on the aquaculture
side and Tran and Haider on the plant side-took the Rakocy system and added a few high-tech wrinkles to optimize fish health
and plant growth in an indoor environment. The setup's also
designed to allow the fish and plant sides to operate independently should one part have to go off line.
To get a picture of how the system will work, just follow the water. It starts in 13 200-liter fish tanks (circular and self-cleaning),
62

jun 2013

north american

SPectrum.ieee.orG

half baked

Gone
Adrift

raising seafood in offshore cages
just isn't practical

each containing 1000 to 2000 tilapia that feed on a high-protein
soy mixture. Next, it drains under gravity into a radial flow separator, where the solid waste-fish poop and uneaten food-gets filtered away in stages. First the heavier stuff settles and is shunted
to a wastewater treatment system in the basement; then the remaining water is filtered through a screened drum, which catches
the larger particles and releases them for treatment when rinsed.
What's left is clarified water, which drains via gravity to a fiberglass tank about the size of a Volkswagen Beetle. In this tank,
called a moving-bed biofilter, a blower aerates the water, removing carbon dioxide and adding oxygen to the water so that the
biological filtering can work.
Thousands of plastic paddle wheels small enough to fit in the
palm of your hand accommodate two kinds of helpful bacteria,
which cover the surfaces in a thin film. As the water flows over
this biofilm, the first kind-Nitrosomonas-converts ammonia from
fish waste into nitrites, and the second kind-Nitrobacter-breaks
illustration by

Jason lee

http://SPectrum.ieee.orG

Table of Contents for the Digital Edition of IEEE Spectrum June, 2013