16-Feb-09 3:00 PM CST
Aquaculture Irrigation Combination
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.
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.|
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.
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.”
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.
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.
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.
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.”
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.
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Source: David Engle
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