Newly emerging pond system reclaims wastewater for hydroponics, fisheries, and endlessly renewable fuel.
Call it aquaculture efficiency or,
perhaps better, ultra-everything efficiency-conserving freshwater is only the
first-stage benefit here. Beyond this comes water reclamation for reuse, then
tightly integrated energy efficiency (virtually, all free, low-tech solar), and
next, food production efficiency, free fertilizer byproduct efficiency,
bounteous biomass production efficiency surpassing—by at least two- or
three-fold—any other known biomass source, and, at the end, a virtually
unlimited loop of water recycling efficiency.
Properly speaking, the system
itself is called the integrated modular production system (IMPS). Just now it is
being implemented at one pilot site to relieve water-challenged cattle feedlots
in Texas, and is gaining a foothold internationally. Its inventor Clifford
Fedler, a professor of civil engineering and associate dean at the graduate
school at Texas Tech University in Lubbock, coined the name in the course of
spending a dozen years testing and developing it.
Fedler’s IMPSs essentially take
self-cleaning wastewater treatment ponds and equip them with hydroponics. Added
in the latter stages are tertiary ponds in which, he explains, “the water has
been naturally denitrified by the right combination of plants and sunlight,”
sufficient to support pools teeming with fish and enormous, almost
hard-to-believe aquaculture crops.
How IMPSs Evolved, Operate
Fedler first got the design idea
two decades ago while chatting with the man who had devised a predecessor
version, Ray Dinges (then nearly 90 years old). Back in the early 1960s, Dinges
had dug some basic, multi-stage ponds for a south Texas farm. Hearing about his
concept, Fedler quickly grasped its potential for wastewater treatment, and
better water recycling of all kinds. The key, he realized, would be simply “to
ensure, in the anaerobic portion, a deeper section of the first pond,” excavated
“down to more than 15 feet in total depth.” Dimensions for the adjacent ponds
can be more flexibly varied as needed, once the basic facultative depth is
right.
As another inspiration, Fedler
also credits the late William Oswald of UC Berkeley, the innovator of Advanced
Integrated Wastewater Pond Systems (AIWPS). Oswald pioneered the extensive use
of algae and sunlight for advancing treatment. Thousands of his AIWPSs have been
installed since the 1960s, primarily in the rural US and abroad.
In Fedler’s IMPS treatment
sequence, wastewater first flows into the deep anaerobic section of what is
called an integrated facultative pond (IFP). Methane gas is produced there and
can be easily captured. Afterwards comes aerobic treatment, to further remove
biochemical oxygen demand (BOD), pathogens, and fecal coliforms. Algae boost the
oxygen level. Some phosphorous removal begins to occur by the growth and
harvesting of aqueous plants. Nitrification/denitrification happens with the aid
of bacteria. At a later stage, algae must finally be either settled or filtered
out.
Through the processes, water
chemistry becomes balanced enough to support hydroponic vegetable production and
many species of fish (for example, koi, red shiner, bluegill, tilapia, platty,
molly, and largemouth bass) or other exotic aquarium species. All have been
tested by Fedler in this setting and found to thrive, feeding on the
already-present algae and other plants.
Of course, plants grow remarkably
quickly in nutrient-rich water; and rapid changes in crops or fish species are
easily made, if desired.
 |
| After a successive treatment of the natural nitrification/denitrification and sewage water cleaning process is completed, the water is clean enough to support hydroponic vegetable growth or fisheries. |
One perhaps surprising and
potentially far-reaching crop for this fecund pool, Fedler suggests, is water
hyacinth. This plant turns out to be both the fastest growing hydroponically and
also one of the highest yielding in biomass. Growth is so prodigious that
harvesting could occur daily. Usage options of this output are also remarkably
varied and versatile: hyacinth can be chopped into silage for animals, scattered
as land fertilizer, fed to fish as food, or gasified into a low-btu,
carbon-neutral fuel. The latter can be burned onsite for heating or even tanked
and piped to a generator for electric power.
Given the extraordinary
characteristics of water hyacinth, and favorable economics of aquaculture
production, the potential of IMPSs for renewable energy generation is quite
spectacular.
As for the wastewater reclamation
aspect, total cycle time ranges-depending on conditions-from 25 to 45 days.
Clarified outflow (BOD and total suspended solids less than 20) will qualify for
reuse right onsite, filling water troughs or being used as wash water. Thus, the
cycle can repeat endlessly. Or, water meets EPA standards for waterway
discharge.
Alternatively, with less treatment
it can be piped out to irrigate land crops (meeting World Health Organization
and EPA 60 to 100 BOD guidelines).
Potential Economic Value
Though currently designed
primarily to serve livestock pens, the ponds can easily do similar work at a
wide range of sites—say, a desert country club, remote Andean village, an
abattoir in the Australian Outback, or an urban wastewater treatment plant. In
fact, practically anywhere that freshwater is or may soon be in short supply—but
wastewater and land are not—would likely profit. The system design (which is not
proprietary) is such that it can be scaled up or down to suit anything from a
family farm to big city waste.
In every case, the IMPS would not
only recycle and conserve water, but it would save power resources on an
enormous scale since it relies only on sunlight.
And, because the ponds consist of
little more than lined basins in the ground, capital costs are pared to a
decimal fraction of engineered treatment plants.
With these advantages in view,
potentially many thousands of sites doing agricultural, livestock, and food
production/processing worldwide would benefit immensely.
So, too, would the planet’s water
tables. United Nations Educational, Scientific, and Cultural Organization
(UNESCO) estimates that about 70% of the world’s groundwater is now being
squandered on agriculture, at a time when such a precious resource should truly
be preserved for drinking and domestic use. After pooling in the muck of animal
pens or at a cannery, dirty water is often summarily dumped into nearby
waterways untreated, further compounding human problems. In many countries,
groundwater is also being extracted faster than it can be recharged.
Obviously, multiple water crises
loom, and anything that can relieve the burden on the earth’s resources is a
godsend. As Fedler observes, “Every gallon of wastewater that we recycle saves a
gallon of freshwater for human consumption.”
Still another virtue of water
recycling combined with food or energy production, is the prospect of generating
revenues. Thus, instead of a community needing to raise taxes or sell bonds to
pay for sewage treatment, an IMPS could be had for a tiny capital cost, and it
will soon pay for itself. Given good commercial management, it would become a
long-term source of income and jobs. A study by Eugenia Olguin and Gloria
Sanchez, published in Sustainable Development (CRC Press, 1999), concludes that
such systems “could be the most rewarding low-cost technology for waste
recycling that can be applied to both rural and urban waste and wastewater,” and
they envision for-profit development.
Fedler adds that, in an
agricultural setting, “It’s difficult not to come out showing that you can have
a fairly decent income from these.”
Current and Pending
Projects
Though aimed at stretching water
in drier agrarian settings, IMPS can be cost-justified in other applications as
well. A few jobs in progress illustrate:
- At a relatively new IMPS just
getting underway for Colorado City, TX (population 6,000), after wastewater
treatment is done by the ponds, the secondary effluent will irrigate a field of
crops for cattle feed, notes Ken Martin, P.E., of Jacob and Martin Engineering,
in Abilene, TX. The city plans on growing “a pretty salt-tolerant field of
coastal Bermuda grass,” he says. The original design has already been revised
and recently expanded, to include treating the water from a nearby 5,000-inmate
prison as well. This will raise the total waste output to 1.2 million gallons
per day (gpd), and, eventually, this first-ever IMPS should be irrigating about
300 acres, for a rich grazing crop.
- By watering fields with this
nitrogen-saturated secondary instead of denitrified tertiary water (although the
latter is easily attainable), crop yields truly soar. Fedler notes that,
whenever watering or fertilizing, the two must always be paired to achieve
maximum efficiency.
As a result, Colorado City will
reap two or three mowings a year. This can be baled and sold to feed livestock
and will net many thousands of dollars in annual revenues for the city. Output
will be especially valuable during the area’s frequent drought periods, adds
Martin. Pond systems, too, he notes, “have very low maintenance and low
operating cost” and are ideal for small cities, if local soils are
impermeable.
Hypothetically, if Colorado City
ever wanted simply to discharge its treated effluent, the quality would easily
meet strict Texas standards. Thus, the new ponds are relieving Colorado City
from paying for the much costlier plant it otherwise would need. On that
score:
- The border town of Rio Hondo,
TX, commissioned similar ponds a few years ago, at an estimated cost of just
one-twentieth the expense of a conventional plant.
- Other IMPSs will soon be
commissioned in Texas at Presidio and Valentine. Reclaimed water at these will
grow alfalfa or other animal foods, notes Roberto Gil, who is project engineer for both.
- In a recent design proposed for
a new tribal casino in California, the IMPS would do anaerobic treatment of
sewage, and then support a wetland and a pond of exotic fish. Luxurious lawns
and gardens will flourish from the tertiary irrigation, serving as a
recreational park. To keep it green year-round, little or no freshwater will be
needed.
-
A housing developer in the
Southwest is considering using IMPSs near a stand of trees to irrigate roots,
with reclaimed wastewater being piped below ground.
- In mid 2008, an abattoir in
Narrikup, Western Australia, needed to expand its existing wastewater plant.
Having heard of IMPSs, company managers asked Fedler if his ponds could be used
to supplement an existing plant infrastructure. “Yes, easily,” he told them. In
a quick design draft, a single-process hydroponic treatment pond looked like it
could also yield enough fuel to provide the site one-third of its total
electrical and hot water load and, along with it, thousands of gallons of
fertilizer-enriched water for adjacent croplands. Managers took barely hours to
render enthusiastic approval.
A Role in Developing
Nations?
Given the ponds’ high value and
low initial costs, it would seem that their greatest potential for doing good
may lie in the world’s poorest regions.
Exploring this possibility, in
2004, Fedler visited a village in the Andes Mountains of Peru of which he says,
“The sun goes down early… and then they have no light to read by, which inhibits
their ability to be educated easily.
“So, I asked them, ‘What do you do
with all the waste?’” he continues.
“They said, ‘We throw it on the
ground.’
“I said, ‘That’s an energy
source!’ So, we designed a little digester that they could build out of local
materials. It’s a strange design, but, nonetheless, it has worked quite well,”
turning human and animal wastewater into reusable effluent and fuel. The latter
provides heat for cooking by day, and there’s enough left over to keep lights
burning all night.
“Now the most important result is
the kids have light to study by and are receiving education,” says Fedler.
At another site in that
high-altitude region, residents were found dumping 10 million gpd of raw sewage
into a stream. Consequently, “everything is dead for miles downstream,” he says.
“It should be growing trout, but it is not even clean enough to grow
catfish.”
A simple pond was designed, which
would remove 80% of the biological load and provide reclaimed wastewater to grow
land crops. “The flow was so simple that there was nothing they could do to make
the system go wrong,” notes Fedler. The only maintenance chore was periodic
cleaning of a filtration screen.
Unfortunately, local politics
somehow intervened, and further progress and communication ceased.
Several years ago, Fedler was also
sought by officials from Mexico City, who were canvassing US engineering firms
for proposals on handling 2 billion gpd of urban effluent. Construction bids
came back in the hundreds of millions. Fedler’s demonstration site in Lubbock
was their last stop on the return leg home.
When the visitors told Fedler
about the massive centralized plants other engineers had pitched, he suggested
they consider digging a patchwork of simple IMPSs. These would easily knock out
“about 80% of the waste load” all naturally, he told them. A quick calculation
came up with a comparative cost at about one-fifth the next lowest.
With IMPs in the developing world,
Fedler sees almost endless potential. “There are a lot of good things that can
result, if we can just get the technology out there to them,” he says.
Risks, Challenges
Yes, there are good things, but,
naturally, things also go wrong, Fedler candidly explains.
One—noted above by Martin—is the
risk to vegetation posed by the high salt content of this treated effluent. If
not adequately evaluated and dealt with, it can choke or even destroy, rather
than nourish, a cropland. Miscalculations on this issue are a leading cause of
earlier-generation AIWPS failures. Risks are greater with municipal rather than
agricultural wastewater, but in any case, he advises, “Pond designers need to
pay close attention to the water, nutrient, and salt balance.”
Besides salty water, two other
undesired byproducts are insects and odors. Inland bodies of water always
attract bugs, but designing for surface aeration can reduce problems, says
Fedler. Cropping nearby vegetation and stocking with insect-eating fish also
help. Applying new, money-saving multi-enzyme products can further control odors
naturally, but he concedes, “Some stink is inevitable.”
Another challenge: Being small
ecosystems rather than machines, ponds sometimes come up with hard-to-diagnose
idiosyncrasies. Despite good management, they do not always function as
expected. Eventually, with skillful troubleshooting or outside expertise, issues
are almost always correctable.
One illustration: One of the very
first AIWPS systems—built for the City of St. Helena, CA, over forty years ago
and still functioning—has faced a number of challenges during its long
operation.
On the positive side, chief
operator Michael Sample reports, “We love this system; it is great. We have no
piping infrastructure to maintain, and this community has very, very low sewer
rates.”
With this system, “The city has
saved millions and millions of dollars,” he says, compared to the cost of
building and running a conventional waste treatment plant. Also, the ponds have
never needed dredging.
On the negative side, though, the
treated effluent is no longer of any use and is now simply land-discharged,
rather wastefully. A slew of obstacles have piled up over the years to defeat
the original reuse goals, such as: ratcheting-up of EPA water discharge
standards, increased volumes and organic loading, city policies favoring low
growth, very high bids for corrective engineering, and lack of consensus on what
to do with reclaimed water. Increased BOD has also caused imbalances to the pH
during warm months, and algae control has been a problem (both, mechanically
correctable).
Fedler observes that, were it not
for these barriers, a pond like St. Helena’s—which he visited years ago with
designer Oswald—“should be able to produce a crop of alfalfa hay at an extremely
low cost.”
What It Takes to Get One
As described above, the IMPS
comprises from two to six ponds positioned in a sequence; an IFP receives raw
sewage, and then other ponds take the flow through successive steps and uses,
until discharge or return. Designing one thus means, “doing a mass balance on
the water, nutrients, biomass, food, energy, and mechanization or labor needed
for harvest,” says Fedler. As for the hydroponics, these are customized to
achieve whatever outputs are sought under given conditions.
Because similar earlier-generation
AIWPSs are already an established technology, qualified environmental or
agricultural engineers can probably do the design of IMPSs, suggests Fedler,
provided they do have “extensive prior experience with pond systems.” Doing the
computer-aided design and earthmoving calculations becomes straightforward.
Once properly commissioned, a
system should become virtually self-sustaining. Maintenance will be minimal; in
the case of basic ponds treating waste to secondary or tertiary levels, the care
could be as modest as just a filter cleaning every 2–4 months. If the system
supports a fishery or hydroponics, of course the care and harvesting of stocks
will add some work. If wastewater from livestock or onsite processing operations
is also present, the system is really a multi-faceted agri- and aquaculture
site: it will need capable employees and commercial management.
As earlier examples showed, sites
can be tailored to accomplish assorted end goals ranging from landscape
enhancement to food crop production, or simply for lowest-cost wastewater
treatment. With such versatility they can suit the needs of either public or
private sector operations.
Trying to win support in either
setting has brought to the fore a range of “interesting” results, according to
Fedler. In some cases, like the above-noted wastewater plant expansion in
Australia, the decision was a “no-brainer:” The upside was all good and the
downside minimal, given the very low first cost.
In other instances, IMPSs seem to
face the hurdles that any new process does, in that industry practitioners
simply do not know about, have not heard of, or do not understand IMPSs, hence,
they wait for someone else to go first. Engineering contracting firms also
prefer big-ticket projects, and many will not explore a system that promises
only modest profits.
In still other cases, like cattle
ranches, the shift from doing “the roundup,” to reclaiming water in order
harvest aquatic biomass and wholesaling exotic fish—though it makes sense on
paper—can turn out to be something of a cultural shock.
Then again, the thought of reaping
acres of green alfalfa—and never having to touch groundwater for it again—seems
to be catching on.
And, wherever in the world a
water, food, or sanitation crisis is already causing hurt, it’s probably no
longer a question of whether an IMPS, but when.