| The past several decades have seen an increase in the growth of so-called "factory farms" for swine production. With this growth has come the inevitable problem of increased swine effluent. This has forced the industry and scientists to develop innovative technologies that treat it onsite in a way that is environmentally sensitive and financially practical.
The US produces about 105 million head of market hogs and necessary breeding stock per year, and has a consistent base population of approximately 60 million pigs. These animals, according to estimates from the National Swine Research and Information Center in Ames, IA, create roughly 21-25 billion gallons of waste each year, or 100-104 million tons of waste per year.
Hog waste in the southeastern US is currently piped into clay-lined pits called lagoons, where solids fall to the bottom and the liquid at the top is sprayed onto grass fields. In the past decade, some lagoon walls have broken during hurricanes or torrential rains, causing waste to flow into rivers and streams.
Minimizing the impact of livestock waste on the environment is one of the major challenges in American agriculture. In Iowa and North Carolina, first and second in hog production in the country respectively, local populations have had concerns about tremendous odor problems and the growing threat of lagoon leakage with subsequent pollution of area streams, rivers, and—ultimately—estuary environments as well.
North Carolina risks damaging its reputation as a vacationland of clean air and water unless it deals with the smell and runoff, according to Gerry Hancock, general counsel for the North Carolina Travel and Tourism Coalition.
"If we do not manage this problem intelligently, then we put at risk a reputation that, like all reputations, is by its nature fragile. And we put at risk all the jobs, all the economic benefits that depend on the travel and tourism industry," Hancock says.
Concern with this problem has grown to the point that the state issued a moratorium on construction of new large hog farms or additions to existing farms owned by Smithfield Foods, according to the state's Attorney General's office. Clearly it's an issue of great concern for both the population and business community in the state.
In the 1990s hurricanes and other weather-related impacts on the North Carolina hog farm lagoons resulted in much environmental damage. When waste escapes into the surrounding environment's surface water, the nitrogen and high chemical oxygen demand in the waste causes oxygen depletion, resulting in extensive deaths of fish and other organisms.
"What has happened in the past was that we've had some lagoon breaches when the concentrated hog waste would come out over the landscape and escape into streams and rivers," says Dr. Michael Mallin, research professor with the Center for Marine Science at the University of North Carolina, Wilmington. "During the course of one of these accidents in 1995 the waste material entered the New River and the New River Estuary, where it started a 'bloom' of the toxic dinoflagellate Pfiesteria. This organism thrives on organic nutrients. The result was a big fish kill out in the estuary. This event did not start because of a hurricane but simply resulted from a period of heavy rain experienced in the area."
Since then a number of hurricanes caused hog farm lagoons to overflow. "When that happened the result would be a big slug of this organic material would get into the rivers," Mallin says. "The problem with this scenario is that sudden influx causes something called 'biochemical oxygen demand' to drop the dissolved oxygen content in the river to almost zero, directly causing fish kills—effectively asphyxiating the fish."
According to Mallin, although the Cape Fear River Estuary area has not had any recent spills, it does have problems dealing with the rising levels of ammonia in area rivers. "This has been a growing concern particularly in the rivers adjacent to areas where the hog farms are located," says Mallin. "The levels of ammonia in our rivers have been increasing significantly over the past 10 years—in particular, over 300% in the northeast Cape Fear River. Ammonia can either travel through the groundwater or enter the ecosystem as atmospheric ammonia where it is eventually deposited somewhere."
Though the ammonia levels at present are too low to cause toxicity to fish, the levels are significant enough to stimulate bacterial and algae growth. Mallin is aware of proposed North Carolina state legislation to phase out hog farm lagoons by 2010. "At that point the legislation recommends that the lagoons are to be shifted over to new technology, which will help to ease this problem," says Mallin.
System Developed for Onsite Treatment
In 2000, the North Carolina State Attorney General's Office, and Smithfield Foods, (along with Premium Standard Foods and a group known as Frontline Farms), reached an agreement to find an environmentally superior replacement for lagoons and spray fields. Out of some 100 proposals submitted, the 18 most feasible were finally narrowed down to two systems that looked the most promising.
The good news for those most interested in an onsite water treatment solution is that three scientists with the USDA's Agricultural Research Station (ARS), in Florence, SC, have recently been able to create treatment systems capable of replacing hog lagoons. The scientists are Patrick Hunt, Matias Vanotti, and Ariel Szogi.
Some 12 to 14 years ago, the swine wastewater problem came to be especially noticeable by residents in the areas around factory farms, and started to become a subject of media coverage. "In the early 1990s, the USDA started a water-quality initiative that included the management of livestock waste from swine, poultry, and the dairy industry," says Hunt.
Hunt, Vanotti, and Szogi plunged in and attempted to find an engineering solution to the problem. They attacked the problem in three different ways. In a municipal or industrial system one would typically treat the organic materials in a huge, large-capacity plant for all the suspended solids; in dealing with animal manures, however, that's not necessary. "Solids have been used in agriculture as crop fertilizer since antiquity," Hunt says. From the onset, the scientists determined that if an effective way could be found to separate the solids from the liquids there would be a great reduction in the amount of material that would have to be treated at the farm. The cost and the complexity of the job would decrease tremendously.
Solid-Liquid Separation
The scientists set about finding a way of separating or flocculating the solids from the liquids. They used a flocculant called a polyacrylamide. It is typically used in agriculture, food processing, and municipal waste. The team decided that if it could find the correct polyacrylymide it could quickly flocculate the solids to efficiently separate them from the liquid in any number of different ways, from filter presses and sand filters to rotating drum filtration. In this way, the scientists found that they could separate out 95% of the solids from the liquid. In a normal filtration without flocculant addition, perhaps 15% of the solids will be separated out. But if polymer is added, another 80% increase in the amount of solids is removed. "We showed that we could do this far superior separation in both theory and practice," says Hunt. "We also saw that there are several different ways that you could do that in full scale."
Biological Nitrogen Treatment
The next factor to consider was the fact that, in working on the swine waste problem, the team was dealing with very high levels of ammonia nitrogen. Japanese scientists developed a technology with which they were able to immobilize nitrifying bacteria into polymer pellets and, in so doing, they were able to keep the concentrations of the bacteria in the reaction tank about a thousand times higher. Consequently, a small tank could be used. In Japan, this technology is being used for municipal wastewater treatment. The team worked cooperatively with Japanese scientists and engineers and found that it did indeed work with animal waste. Over the decade of working with it, they discovered many things about improving nitrification of animal waste.
Sequence Is the Key
The immediate result of the treatment is that the lagoons are much cleaner, with much less volatile ammonia and odor. Manure solids are no longer going into the lagoon, but going off to composting where it can be blended into growth medias and distributed over the landscape—as opposed to being limited to the hog farm.
The phosphorous problem is one of the other issues of livestock waste. Through some basic chemistry, the researchers discovered that when they eliminated the ammonia they were also producing acid. That eliminated the bicarbonate buffer, and the remaining wastewater was then very weakly buffered. "A small amount of calcium hydroxide—an alkali—could then be added, raising the pH and at the same time precipitating out the phosphorous as calcium phosphate," Szogi says.
"A final payoff in all this is that raising pH also kills off all the bacteria and the viruses," says Vanotti. "You end up with a disinfected effluent."
Impressive First Results
The researchers have received a US patent for their system, filed on July 13, 2001. Retrofitting an existing operation with a lagoon with this new wastewater treatment system cleans up the lagoon rather quickly according to Hunt. The change is startling. "It turns from this rank color and odor into something that is odor-free with the blueness of a typical pond instead of a manure-treatment lagoon."
"Everything that we predicted would happen, did in fact happen that way," Vanotti says. "The parameters were the same in our pilot study as the system we developed that is operating now. It is just on a much bigger scale by a factor of 25."
After two years, the system is still running in North Carolina and the scientists are still receiving consistent data. "With the second generation of the project, we are trying to eliminate a lot of the redundancy found in the first one," Vanotti says. "You come to find you can do this much cheaper as well."
The third scientist on the project, Szogi, was involved chiefly in the phosphorous removal patent with Vanotti, using a small amount of chemical and recovering the phosphorous in the form of calcium phosphate. The typical way for calcium phosphate to be obtained is to mine it out of the rock it is found in and treat it with enormous amounts of sulfuric acid to make it plant available. "Basically, the calcium phosphate we are making is quite pure, very low in heavy metals and it can be used for plant fertilizer pretty much as it comes out, with very little processing," Szogi says.
At present, Szogi is running greenhouse experiments with the calcium phosphate from the system—as is—to see how well plants respond to the fertilizer. The researchers think that the system can be adapted for use in Midwest states such as Iowa or Missouri, which are also heavy swine producers. The water from the lagoon, though not potable, is perfectly safe for any type of irrigation. "It is also recycled back into the barns for cleaning, though it is not used for drinking water for the pigs," Szogi says.
Putting It to the Test
A yearlong evaluation was conducted using a full-scale version of the new system built at Goshen Ridge Farm, a 4,360-head swine-finishing facility in Mount Olive, NC. The inventors and the Clinton, NC--based private firm, Super Soil Systems USA Inc., implemented it. Construction was part of an agreement between Smithfield Foods of Smithfield, VA; Premium Standard Foods of Kansas City, MO; and the North Carolina Attorney General's office in an effort to "use environmentally superior technology to replace current waste lagoons," according to an article in Agricultural Research (2005) by the USDA.
The system is fully automated, featuring sensors integrated to a programmable logic controller for full-time operation. During the trial, at its peak, the system processed on average 12,700 gallons of manure, containing 176 pounds of nitrogen, per day.
The first module in the assembly line is the Ecopurin Solid-Liquid Separation Module, which quickly separates solids and liquids. SELCO MC, a firm based in Spain, developed the module. "This conserves much of the organic fraction of the waste," Hunt says. Polyacrylamides—high-viscosity, water-soluble polymers—are used there for coalescing the solids.
In the second module—the Biogreen Nitrogen Removal Module, developed by Hitachi Plant Engineering and Construction Co. in Tokyo—the biological removal of ammonia takes place. "Once solids are removed, a relatively smaller amount of suspended organic waste remains in wastewater, but it still contains significant amounts of soluble ammonia and phosphorus," says Vanotti. "This biological process consistently removed more than 95% of the ammonia and total organic nitrogen present in the manure after separation—even during winter, with below-freezing temperatures."
In the third and final step, the wastewater flows by gravity to the Soluble Phosphorus Removal Module. Developed by Vanotti, Szogi, and Hunt, it recovers phosphorus as calcium phosphate and destroys pathogens through alkaline pH. It also turns the removed phosphorus into a solid, marketable fertilizer, and it converts leftover effluent into a liquid crop fertilizer that's more environmentally friendly than manure.
A trip through the three modules has been shown to remove more than 97% of total suspended solids from wastewater, greater than 95% of total phosphorous, 99% of wastewater ammonia, 98% of the copper, 99% of the zinc, greater than 99% of the wastewater's biochemical oxygen demand, and over 97% of the water's odor-generating components. All these benchmarks were achieved in addition to creating both a marketable fertilizer and an environmentally friendly effluent.
In the course of nine months of operation, the new plant produced 285 bags of calcium phosphate containing 1,160 pounds of phosphorous. The plant performed equally well in hot and cold weather conditions.
Research From the Opposite End
Brian Kerr, research leader and scientist with training in swine nutrition with the USDA Agricultural Research Service in Ames, is working on the problem of swine waste at the other end of this problem—no pun intended, of course. Kerr is trying to work out part of the problem through addressing nutritional methods of reducing nutrient losses and odor generation from swine-production facilities. "We are working on the problem through the nutrition end of things while the Carolina group is handling it through engineering methods," says Kerr. "In essence, we are trying to reduce the problem before it becomes a problem, by changing the composition of the manure before researchers receive it."
Kerr's unit is relatively new. It has been working on the study for only four years. This group is changing the diet in terms of the feeds used for the hogs, either in protein or fiber components. They are also looking into trying novel ingredients, but have not tried this yet.
Kerr notes the differences in how effluents have been handled by the large hog farms before the development of this new system. In the Carolinas more lagoons are used. Some of the liquid evaporates off, but some of that water and sludge can be used for nutrient purposes. In the Midwest, the effluent is placed in 8-foot-deep pits under the facilities, which result in less evaporation. This material is also used for nutrients for crops. Both of these methods create odor problems. "The scientists in South Carolina are working on the issues of odor and manure processing from an engineering standpoint," Kerr says. "There are different processes that you do on the manure to reduce odor and utilize nutrients in the manure. We can change the diet and reduce ammonia losses or change the diet and hold more of the nitrogen in the manure, whereas Hunt might work on liquid/solid separation and then process both of those streams in a different fashion to minimize nutrient losses and odor losses and therefore have a better fertilizer for crops."
The Sweet Scent of Success
During the course of their work on the onsite hog waste solutions, Hunt, Vanotti and Szogi published an award-winning paper in Transactions of the ASAE, the Journal of the American Society of Agricultural Engineers (2003), on their groundbreaking work.
This success did not come without demands and challenges. Szogi found that the greatest challenges came in going from the prototype to the full-scale treatment system.
"Though we weren't certain our prototype's success would be repeated in full-scale operations, we are thrilled that on this first try the system is still working and doing what we predicted," Szogi says. "Our expectation is that we will have two or three farms implementing a second-generation version of the wastewater treatment system, and at the same time we can make some economical evaluations also of the cost of this new technology."
"The excitement for me also came in our ability to follow this project from bench scale to pilot scale all the way to full scale," Vanotti says. "In each stage of the research we made some discoveries and that was the rewarding part—seeing something move from an idea to something fully operational."
If this new system is used for most of the hog farms in the Southeast, it will clearly have to deal with the two issues most on the minds of North Carolina hog farmers. As one such farmer offered in a coastal Carolina news report: "We know technological change is coming, but any new technology must do two things: It has to be truly better than the system we already have, and it has to not cost more than what we're already doing. It would be unwise for a politician—or anyone else—to force a change if those two parts aren't met." So far it looks as though the new system meets both of those criteria.
PETER HILDEBRANDT writes extensively on engineering and
scientific subjects.
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- September/October 2005
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