New innovations in recirculating systems and flow-through water treatment push fish farmers towards zero waste.
By Dan Rafter
Til-Tech Aquafarm produces more than 6 million young tilapia, or fingerlings, each year. The aquafarm, located 30 miles north of New Orleans in the small town of Robert, LA, hatches these fingerlings in an indoor facility that covers 50,000 square feet of climate-controlled ponds. It then ships them to ethnic restaurants across the region.
How much wastewater does this busy facility discharge? Nearly none.
Til-Tech, like most tilapia farms, relies on an indoor recirculating system to treat its wastewater. The system, designed 16 years ago as a prototype by engineers at nearby Louisiana State University, uses bead-filter technology—a floating polyethylene bead in a vessel grows bacteria that captures solids—to treat the farm’s water and constantly recycle it. Til-Tech, for more than 15 years, has discharged such a small amount of liquid waste that it has never had the need to discard its effluent offsite.
The tiny amount of waste that the facility does generate has its own benefits, and stays close to home. Til-Tech employees use it to fertilize the fruit trees at an onsite orchard.
“If you want to look at a model of zero pollution, we’re as close as you’ll ever get to it,” says Steve Abernathy, owner of Til-Tech.
Fortunately, Til-Tech is not alone. Critics have long pointed to the aquaculture industry—fish farming, basically—as one that places great strains on the environment. The growers of trout, salmon, and catfish, critics contend, too often operate without considering the impact their farms have on their surroundings.
Some of this criticism is deserved. Environmentalists and scientists especially target the oceanic net-pen industry used to cultivate much of the salmon purchased in US supermarkets and restaurants as having potentially dire effects on the environment. Much of the salmon industry grows its fish in pens directly located in ocean waters. These pens discharge nearly all their waste into the surrounding waters. The impact may be minimal in large bodies of water; in smaller bodies, though, the discharge of nitrogen and phosphates can harm other fish and aquatic life.
But most fish farmers and aquaculture facilities have little impact on their surrounding environments; say researchers who study the fish-farming industry. Catfish growers, for example, rely on natural ponds for treating their wastewater. And tilapia growers—a rapidly expanding portion of the US aquaculture industry—employ advanced recirculating systems that produce barely a trickle of wastewater discharge.
In all, say the scientists who have helped create a cleaner aquaculture business, fish farmers have a negligible environmental impact compared to most other large-scale industries.
“There are times when this industry has been portrayed unfairly,” says Joseph Hankins, director of the Shepherdstown, WV–based Freshwater Institute, an arm of the non-profit Conservation Fund that works with government and industries to help foster the environmentally responsible management of water resources.
“Very few agricultural sectors have evolved as quickly as the aquaculture industry has over the last two to three decades,” Hankins says. “It’s essentially grown up from a fairly modest industry to a major food-production sector. The Clean Water Act, wetlands protection, all the environmental rules we have today, as that social background has evolved, the aquaculture industry has had to evolve with it. It’s done that successfully. Have there been bumps? Absolutely. But few other industries have had to change and grow up in the same kind of environmental climate.”
The growing tilapia industry is leading the way in these innovations. The industry’s recirculating systems, though expensive, are extremely efficient, producing quality water with little or no waste discharge.
The best news? Industry officials and observers expect more sectors of the domestic aquaculture industry to follow the tilapia growers’ example.
A Wide Range
It’s little surprise that scientists and environmental experts would take a close look at aquaculture. It’s increasingly becoming the means by which much of the world’s consumers get their fish.
A report created by the United Nations Food and Agriculture Organization in 2002 stated that worldwide aquaculture has increased at an average compounded rate of 9.2% every year since 1970. That compares with only 1.4% yearly growth for capture fisheries.
In 2003, aquaculture facilities provided 41.9 million tons’ of worth of products to consumers.
The aquaculture industry relies on four main systems for treating the wastewater discharged from its facilities while producing these fish.
Natural ponds are the most common, the dominant production technology in the US aquaculture industry. These are used for species such as catfish and crawfish. Ron Malone, a professor of civil and environmental engineering at Louisiana State University and an aquaculture expert, refers to ponds as “Mother Nature’s recirculating system.” Ponds, as long as their owners take some care to maintain them, internally treat or process nearly all the waste that the fish living in them produce, Malone says.
Malone has more problems with fish farms that use flow-through water treatment methods. These are most common with farms that are producing trout. As the name suggests, under flow-through treatment systems, water is used, treated, and then discharged from the facility. Malone worries that the discharged water can cause ecological changes down the stream, especially because many fish farms use an extensive amount of water.
There is a bright side, though. Many farms that use the flow-through method are now capturing a greater amount of their treated discharge and reusing that water in their facilities. It is Malone’s hope that these farms will eventually graduate to recirculating systems that constantly reuse treated water and discharge nearly no waste.
“With some exceptions, based on where the facilities are located, I think flow-through is a dead technology,” Malone says. “Today we are spending so much money to protect the environment. With some exceptions, then, this is probably a technology that is past its time. These systems are being pressured away by environmental regulations, mostly at the state level. If you are capturing so much water and retreating it anyway, you might as well go with a recirculating system.”
Malone, though, stops well short of calling for an end to flow-through systems. In some portions of the country, mostly in the Western United States, flow-through technology can actually prove beneficial to the surrounding environment, Malone says. In the dry West, the wastewater from flow-through systems is often diverted and used for irrigation. That, Malone says, is a smart use of flow-through technology.
Like most environmentally minded engineers, Malone also has issues with net-pen salmon farming. These pens discharge nearly all their waste directly into the waters surrounding them. If the body of water is small, the nitrogen and phosphorous can cause it serious damage.
Also like many observers and researchers in the aquaculture industry, Malone is most excited about the recirculating systems used in the growing field of tilapia farming. There are two reasons for his optimism: Recirculating systems reuse treated water on a near constant basis, meaning that aquaculture facilities that use them discharge only tiny amounts of waste. Secondly, the US tilapia system is on the verge of serious growth. This means that more fish-farming facilities will be relying on recirculating systems.
“The recirculating systems have minimal environmental impact,” Malone says. “The BOD [biological oxygen demand] is totally removed. The solids are totally removed. We are virtually able to close down the tap, turn the discharge down to a negligible amount of water.”
And with demand from restaurants and ethnic markets in the United States for live tilapia constantly increasing, the opportunity to further refine recirculating systems is now present, Malone says.
“Tilapia production is nowhere near as large as it is going to become,” he says. “Essentially, tilapia will be one of our main production animals in the future. It will be analogous to the chicken or pig in the grocery world.”
A Good Fit
Tilapia farmers have gravitated toward recirculating systems not necessarily because they are good for the environment, but because for them they make economic sense. Even though such systems are typically more costly, they work well with tilapia stock.
Tilapia is a tropical or warm water fish, and cannot survive the winters in the United States in most regions north of Florida. With indoor recirculating systems, though, farmers can control the temperature of their waters. This way, the tilapia industry can have farms in the country’s northern and colder states. Malone, for instance, is currently working on plans to help construct a tilapia indoor farm facility in South Dakota.
Then there are cost issues. Recirculating systems are more costly than are flow-through and pond systems. To cover those extra costs, facilities that rely on recirculating systems need to produce a fish that will be able to fetch a better price from buyers. Tilapia is one of those fish, says Steven Summerfelt, director of aquaculture systems research at the Freshwater Institute.
And researchers see an even brighter future for recirculating systems. Summerfelt sees a time, not too far from now, when the cost of recirculating systems will drop enough so that they’ll be affordable to a greater number of fish-farming operations.
“We are getting much better. With economies of scale, you are seeing the cost of production dropping,” Summerfelt says.
But even though recirculating systems will become more common, they still have a long way to go to replace the far greater number of pond and flow-through systems currently in operation, Summerfelt says.
“I don’t think people will shift away from flow-through systems unless they are regulated for discharge limits so hard,” he says. “They just can’t afford right now to install technologies that are extremely advanced to treat their huge flows.”
This is a shame, Summerfelt says. The aquaculture industry has a bad reputation mainly based on salmon farms and their net-pen technology, he says. If consumers understood that most aquaculture industries did a sound job of either discharging no waste or clean waste, the industry’s reputation would be significantly better.
While recirculating systems are the most environmentally friendly of the methods fish farms use, it’s not the only one that places minimal strain on the environment.
The catfish industry, for example, is extremely green. Catfish farms don’t use recirculating systems because their profit margins are so tight, Summerfelt says. Any extra expenses—such as the costs of installing and maintaining a recirculating system—could take a significant bite out of those profits. But by using ponds for their farms, catfish producers also discharge a minimal amount of waste. They retain water and rely on natural systems to treat it.
Even flow-through treatment is becoming more environmentally friendly. The systems’ improving technology means that they do capture more particulate matter before discharge. Many farmers also have experimented with their feed to reduce the amount of nutrients and waste solids that their fish generate. The flow-through systems still have a ways to go before they could be called green technology, Summerfelt says, but they are, at the least, improving.
These improvements shouldn’t stop any time soon. Everyone from consumers to environmental activists to government regulators is now expecting aquaculture farms to discharge ever-cleaner effluent.
“People are expecting more out of this industry across the board,” Hankins says. “Whether you are a fish farmer or are working in any other kind of agricultural enterprise, the expectations that society is placing on your production system for safety, security, wholesomeness, and organic issues are all increasing. This is not necessarily a bad thing. The management skills required [and] the capital investment required for even a modest aquaculture facility has dramatically changed.”
Hankins says he’s been impressed with many of the changes that he’s seen from aquaculture facilities. He does hope, though, that consumers understand a basic law when it comes to improving these facilities: Fish-farming industries can make technological changes to improve the quality of and reduce the amount of effluent they discharge. But these improvements aren’t free. Someone will have to pay.
And consumers shouldn’t be surprised if they’re asked to chip in part of this cost.
“The good people and companies in this industry are handling all the new requirements being placed upon them by making investments when they can and then passing those costs onto their customers,” Hankins says. “As consumers’ expectations increase, their willingness to pay for products that can get certified as green, organic, or sustainable can allow farmers to cover the costs of these improvements. Of course, that doesn’t happen all the time. Often, society expects more and expects the costs to remain the same. Then you have an unsolvable problem. Hopefully, technology can help change that.”
Additional Challenges
When members of the public think about the waste streams generated from aquaculture facilities, they naturally picture waste generated from fish production. But for large aquaculture facilities, this is only part of the picture.
Larger facilities employ many workers. They, of course, generate a significant amount of domestic sewage waste. This waste stream also has to be treated separately from the normal aquaculture effluent. Other facilities boast modest water-quality laboratories that create analytical waste that needs to be treated.
Some large aquaculture operations may even have a processing facility located onsite. Such facilities will have to treat the blood water and other processing wastes generated from that stream.
All of these waste streams have to be handled in different ways. And aquaculture facilities have to apply for and receive permits to treat each of them. Because of the nature of aquaculture, many facilities are located in remote sites, far from utility grids. The facilities, then, have to generate their own power onsite.
Juggling all these challenges doesn’t make for a simple process.
“The world is a complicated place with all kinds of permits,” Hankins says. “And that’s not even getting into the environmental aspect of permitting. A fairly simple matter suddenly becomes awfully complicated. That said, fish farmers are pretty astute managers; they understand environmental issues. If you manage tons and tons of sensitive aquatic organisms, you have to maintain an extremely high water quality; otherwise your product isn’t going to be produced. Your fish won’t grow. The link between environmental quality and business economics is absolutely clear. Fish farmers understand that.”
Tilapia Farmers Lead the Way
Mark Willows, with North American Fish Farmers Cooperative, handles the marketing for tilapia farms. He, then, understands just how advanced are the recirculating systems that the operations use.
Not enough people understand just how environmentally friendly these farms are, Willows says.
“I don’t think that many people do know that,” he says. “All the discharge that does come from a recirculating system, and there isn’t much, usually goes into municipal sewage treatment. Other, usually larger, farms have their own settling ponds. They build their own ponds, line them, and then drain the pond out once or twice a year. They take the sludge out and fertilize their drain fields. It’s very highly confined.”
Tilapia farmers can tap into this advanced technology because of the nature of the fish they raise.
Kevin Fitzsimmons, a professor in the department of soil, water, and environmental science at the University of Arizona and secretary/treasurer of the American Tilapia Association, says that tilapia are naturally attuned to the conditions that indoor recirculating systems replicate. In East Africa and the Middle East, for example, the bodies of water that provide homes to tilapia evaporate significantly during the warmer months. Tilapia over the years have evolved as they were crowded out, and learned to handle fairly poor water quality compared to most other fish. They have evolved, then, into extremely hardy fish.
This is a perfect species, then, for indoor recirculating systems, Fitzsimmons says.
“In a recirculating system, you have with tilapia a huge functional capacity to raise your fish,” he says. “They thrive under conditions that would kill most other fish. Their physiology can handle these conditions without stressing.”
Because of this, tilapia farmers can grow more product in a smaller amount of space. Fitzsimmons compared the tilapia industry to the typical trout farm: A tilapia farmer using a recirculating system can grow 500,000 pounds of tilapia in the same space that a trout farmer using the same system would be able to grow just 100,000 pounds of fish.
Tilapia also does best in warm water, with temperatures in the range of 80°F to 82°F. It can prove expensive to keep water at this heat. This also works well with recirculating systems. If facilities are heating the water, their operators, to save money, will want to keep reusing it, which is what recirculating systems do, Fitzsimmons says.
“Tilapia are just such a forgiving fish,” Fitzsimmons says. “Trout need really good, clean water. Tilapia can take more salt in the water. They can take more waste materials in the water.”
Tilapia farmers can then reuse almost all the water in their facilities, discharging maybe 1% to 2% of the water volume of the entire farm every day, Fitzsimmons says. Because they discharge such a small amount of water, the tilapia farmers can use the little effluent they do have to irrigate a field crop or tree crop. If the farms are located in an urban setting, they can then discharge their small amount of effluent into city sewers, Fitzsimmons says.
The market for US–grown tilapia continues to grow. Most of the tilapia consumers see frozen in supermarkets, though, come from overseas. Domestic producers of the fish sell it mainly to restaurants and ethnic food stores who are more frequently offering tilapia on their menus.
The American Tilapia Association says that tilapia is now the fifth most popular seafood consumed in the United States. According to association officials, US fish farmers produce about 22 million pounds of tilapia every year. The vast majority—about 95 %, according to the association—is sold live into ethnic Asian grocery stores and restaurants.
Battling a Bad Rap
Tilapia farmers, despite their ecologically sound method of treating their waste, do run the risk of suffering the same negative reputation that much of the fish-farming industry seems to incur, Fitzsimmons says.
Like others, Fitzsimmons blames this bad rap on salmon industries and their net-pen methods. Salmon pens continue to incur the anger of environmentalists and scientists.
“It’s really unfortunate,” Fitzsimmons says. “It’s like saying that all agriculture is bad without differentiating between organic farmers, family farmers and big corporate farms using pesticides. There are a small number of bad actors in the aquaculture industry, and they’ve made it bad for everyone else.”
Summerfelt also points to the net pens used by salmon fisheries as the main reason for aquaculture’s shaky reputation among the public.
“The salmon net-pen industry is taking a tremendous amount of environmental pressure right now,” Summerfelt says. “It has zero containment of waste. Those pens are just sitting there in the ocean currents. Waste and waste feed are not captured at all. It’s kind of like hogs, poultry, and cattle. They are distributing the waste. It depends on the location to see how well the net pens distribute the waste away from the farm. In some places, there is not good distribution by currents. Other places, it does.”
Dan Rafter is a technical writer based in Illinois.
OW- November/December 2007
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