IEEE Spectrum June, 2013 - 61

growing it

15 000, had dwindled to 396. A couple of
small demonstration fish tanks burbled
quietly in one corner, lonely vestiges of
the lush green farm that TV foodie Andrew Zimmern visited for his "Appetite
for Life" Internet show just a few months
before. A new fish house and the greenhouses next to it are where Sweet Water
hopes to raise greens and rise again.
What went wrong the first time around? Mark Haase, who's engineering the new process, says that the Sweet Water team had
taken the original building's built-in sunken railroad bed, partitioned it into rectangular tanks, and lined them with sheets of
synthetic rubber, much like the setup Allen describes in his book.
A two-tier wooden rack system lit by T5 fluorescent bulbs held
long trays filled with water that sat above the tanks. Polystyrene
rafts perforated with holes that cradled seedlings were placed
on top of the water, which was pumped up from the fish tanks.
The plants absorbed nutrients from the water, which flowed back
down to the tanks.
If you've ever tried to keep a tank of tropical fish clean, you might
guess what happened next. Fish excrement collected in the corners and fouled the rafts. "One of the drawbacks of the Will Allen
system," Haase explained during a tour, is that "the sump pumps
are right in the fish tanks. Those pumps are grinding up the solids
and suspending them, and that makes it harder to filter out."
The system was also overcrowded. Fifteen thousand fish in a
34 000-liter system might have seemed like a recipe for commercial
success at first, but it was ultimately unsustainable. Scores of fish
died or had to be destroyed, some suffering "inflamed gills, friable
livers, and distended gall bladders," according to an investigative
article in the Bayview Compass, a local weekly. Most of the employees, a number of whom had gone without pay for weeks, left.
After the exodus, the task of reviving the operation fell to Haase,
who has an undergraduate degree in limnology (the study of
inland waters) and 25 years of experience in industrial wastewater treatment and environmental monitoring. Having inherited
parts of a new system designed by Charlie Price of Aquaponics
U.K., Haase googled around and came upon the work of the man
widely regarded as the father of modern aquaponics: James Rakocy,
yet another Milwaukee native, who'd spent 30 years perfecting a
commercial-scale aquaponics farm at the University of the Virgin
Islands, and who at one point had Charlie Price as a student.
Haase is now tweaking Price's design according to Rakocy's setup:
an insulated fish house where water from the sump gets pumped
up into two 4500-liter fish tanks and then drains out again through
a filter to the greenhouses. Then it goes back again to the sump.
"The cleanest water in the system is the sump, and that goes to
the fish tanks," Haase points out.
the seeD of the
idea for urban
organics germinated in this aquaponics setup that
David haider built
in his basement
two years ago.

" I c oU l d h av e To l d [sw e e T waT e r ] f r o m T h e v I r g I n I s l a n d s T h aT
[they were] on the wrong track," Rakocy said when I reached him
via Skype at his home in Pattaya, Thailand, where he retired in 2010.
"For one thing, we don't use square tanks because it makes it
hard to remove solids," he said with the exasperated air of someone who has seen too many aquaculture operations botched by
amateurs. "They never even had a mechanism to remove the
solids, so they let the waste accumulate on the bottom of the
tank, which starts to decompose and give off ammonia, take up
more oxygen, and give off other toxic gases, like hydrogen sulfide."
The aquaponics world is small, and even in retirement Rakocy
is at the center of it, traveling widely to conduct workshops. In
March he spoke in Abu Dhabi with Thomas Losordo, PAES's aquaculture expert and one of his coauthors
on the seminal article about aquaponics.
Twice a year, Rakocy teaches a class for
PAES in Florida. It's no wonder then that
Rakocy has recently taken a keen interest
in the St. Paul project.
450 000
He is, however, concerned about the
kIlograms
prospects
for urban indoor aquaponics.
that's how much
He points out that the rules and regulalettuce and fresh
herbs Urban
tions against farming in an urban setting,
Organics expects
which
vary from city to city, can be expento harvest by
sive and time-consuming to comply with.
2014, along with
23 000 kg of fish
Ventilation is also an issue. "Aquaponic
per year.
systems put out a huge amount of water
vapor, and these warehouses aren't built
for that moisture load," Rakocy says, add35 days
how long it takes
ing that carbon dioxide can also build up
for a head of
indoors. "I think they're taking that into
lettuce to mature
account at the Hamm's brewery."
in an aquaponics
Haider confirms that each floor in Stock
system versus
50 days for lettuce
House #3 will have five ceiling fans to cirplanted in soil.
culate the air, plus two ventilation fans,
one each on the north and south walls.
And heat pumps will capture the latent
heat in the humid ambient air and transfer it back into the fish
tanks, reducing the humidity substantially.
Then there's the cost of powering the pumps, filters, and especially the fluorescent lighting, which combined will tally $5000
to $8000 per month. Rakocy points out that greenhouse-based
aquaponics operations don't have lighting costs, relying instead
on natural sunlight.
But there are countervailing benefits from farming indoors under
the lights, argues the Urban Organics team. Growth continues around
the clock, 365 days a year. Crops are not exposed to harsh weather
conditions. And plants grow faster in an aquaponics system than
on a conventional farm-much faster.
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Table of Contents for the Digital Edition of IEEE Spectrum June, 2013