SOLID OPPORTUNITIES FOR MANAGING SWINE MANURE

BioCycle December 2003, Vol. 44, No. 12, p. 45

Jody Tishmack
A recent USDA Economic Research Service report predicts that pending environmental regulations will require a much larger land base for manure application from confined animal feeding operations (CAFOs). The regulations will require large livestock operations to meet nutrient application standards when applying manure to land. The USDA report states, "If all CAFOs [are required] to meet the nutrient standards outlined in the new regulations, increases in production costs could be felt throughout the food and agricultural industry." It is

clear from the report that livestock producers will need to find better ways to manage manure and improve profitability. This situation applies particularly to management of swine manure because the swine industry has embraced the trend of concentrating more pigs on fewer farms.

In part, the difficulties of managing swine manure are related to the way in which the manure has come to be handled. As discussed in Part I (see October 2003), most swine manure is handled as a liquid. Manure falls through a slotted floor into either a gutter or a concrete storage pit and then is pumped, flushed or drained to an outside storage area or lagoon. In storage, the organic matter begins to decompose anaerobically which causes odors. Periodically, liquid manure from storage pits or lagoons is hauled in tankers and applied to fields. It is injected beneath the surface or broadcast and incorporated after application to control loss of volatile ammonia and release of odors. In remote areas, liquid manure may be pumped directly to the land application site and then irrigated onto cropland, an efficient but odorous option. Handling manure as a liquid is expedient and labor-efficient, but it dilutes nutrients and adds to the volume, weight, and odors associated with manure management. The liquid consistency makes transportation more costly and composting impractical. Liquid manure generally must be land applied near the farm, which concentrates the nutrients near the farm and leads to nutrient overloading.

Because of the limitations with liquid manure, there is interest in returning to managing swine manure as a solid. Historically, swine manure was handled as a solid, either deposited directly by grazing animals, or collected in bedding placed on solid shelter floors to absorb the urine. Pastured animals spread the manure over the land as they grazed. Manure deposited on solid floors was typically stored where it fell, with more bedding added as needed to maintain dry conditions. Once in storage, solid manure and bedding decompose, similar to static pile composting. Nutrients were recovered by spreading the aged manure/bedding on cropland to complete the nutrient cycle. The problem with solid manure management is that it is more laborious to handle. It doesn’t flow and pump like the liquid stuff. Also, for swine manure to retain a solid consistency, additional water from cleaning and precipitation has to be either eliminated, absorbed or removed.

Livestock producers, engineers and researchers are developing swine production systems that overcome these disadvantages in order to make solid manure handling more convenient for swine producers. This part of the article discusses three such systems — Hoop structures, the High-RiseTM Hog House, and the liquid/solid isolation system. These technologies effectively manage swine manure as a solid. Because the manure is collected as a solid, these systems are more easily coupled with composting to improve or expand the use of manure and its nutrients. All three of these systems have reduced or eliminated odor problems at swine facilities.

HOOP STRUCTURES
Hoop structures are low cost "quonset hut" style livestock housing in which pigs are raised on a solid floor — a pack of well-bedded solid manure that accumulates as the pigs grow. In Iowa, Minnesota, and Canada, hoop structures have become an increasingly popular alternative for swine barns since the mid-1990s. The first hoop structures in Iowa were built in 1995. In 1997, the Leopold Center for Sustainable Agriculture formed an interdisciplinary group of researchers from Iowa State University to study swine production in hoop structures. The "Hoop Group," as they call themselves, continues to conduct research on deep-bedded hoop swine production.

A typical hoop structure is 30 feet wide by 72 feet long, and houses approximately 180 hogs. The structures are spanned by arched steel tubes and covered with a polypropylene tarp. They have 4 to 6-foot high solid sidewalls, typically made from treated lumber. The end walls are left open in the summer for natural ventilation and covered in the winter. The buildings are not insulated. Heat is generated by the animals and by the aerobic decomposition of the bedded-pack. During the summer, water misters are used to cool the barn. About one-quarter of the floor area is occupied by a raised concrete pad that contains the feed and watering equipment. The remaining floor is typically packed soil that is covered with enough bedding to absorb the manure and urine and keep the hogs dry. Bedding consists of corn stalks, straw, wood shavings or any other carbon-rich material. Initially, eight round bales (approximately 1,200 pounds each) of straw or cornstalk are placed on the compacted floor, and one or two additional bales are added weekly. Bedding must be replenished on a frequent basis in order to maintain dry conditions. Cycling continuous groups of 180 hogs through a hoop requires about 100 large bales of bedding per year per hoop barn.

The bedded-pack is normally removed two to three times a year, after each group of pigs is sold. Once the bedded-pack is removed, the material is either directly spread on the fields, stored for later use or composted to reduce the volume and stabilize the nutrients prior to land application. Tom Richard, with Iowa State University, says that farmers do not spend a lot of time making compost. Most farmers remove the bedded-pack from the barn, stockpile it, and then spread it on fields when the time is optimum. Richard has explored the distribution of moisture, nitrogen, and temperature of the bedded-pack inside the hoop barn, and he has evaluated different composting strategies. Manure characteristics vary within the pack because of the pigs’ habit of dunging in specific areas. However, on average, the concentrations of nutrients and moisture are ideal for composting (30:1 C:N, 50 to 60 percent moisture). Richard has found that temperatures are highest in areas where the manure is concentrated. A simple pile built with a front end loader and no turning appears the most effective in reducing nutrient losses, and even with turning, nutrient variability is still high in the compost.

The main advantage of hoop structures is their low-cost and ease of assembly. Building costs range from $9,000 to $16,200, about one-fourth to one-half the cost of a conventional swine barn. This equates to $55 per pig capacity compared to $120 per pig for conventional barns (including a lagoon). The lower capital investment means lower debt and makes it easier for some farmers to grow hogs when the market is good, or stop temporarily if the market is bad. The average labor expenditure in hoop barns is 0.45 hours per pig compared to 0.25 to 0.35 hours per pig in large conventional facilities. Producers who have used the system for several years say that once they learn how to manage their hoop barns, their labor is about the same. "It depends on how you want to raise pigs," says Richard. "Farmers in Iowa that have hoop barns may spend more time managing their systems but they seem to enjoy it. It gives the farmers more hands-on time with the pigs. They see problems and correct them earlier, such as treating or removing a sick pig from the herd."
Researchers and producers have found that hoop-raised pigs grow faster during the summer but slower in the winter compared to conventionally confined pigs. However, feed intake, growth rate, feed efficiency, and mortalities are comparable on an annual basis. Some of the research has shown that animal health statistics are better in hoop structures than conventional swine barns. Animal behaviorists at Iowa State University have found that hoop-raised pigs fight less and respond to stress better than conventional confinement-raised pigs. Their studies have shown lower levels of hormones produced by pigs under stress and a reduction in "stereotypic" behavior such as tail biting. Improved animal health could translate into less need for antibiotics. This has attracted the attention of farmers producing pork for niche markets such as antibiotic-free pork or "natural pork."

Whatever the reasons, many farmers in Iowa appear to like hoop barns given that there are more than 2,100 hoop structures currently in operation at 770 farms in Iowa. About half the swine producers compost some of their hoop manure and almost 40 percent use the compost to handle swine mortalities. An estimated four percent of Iowa’s annual pig production is now done in hoop structures, a significant change in only about five years.

HIGH-RISE HOGS
The High-RiseTM Hog House was developed in Greenville, Ohio by Tom Menke, president of Menke Consulting, Inc. and the EnviroLogic Corp. The design is modeled after high-rise poultry barns, where the animals live in the upper story and manure is deposited on dry amendments in the lower story. Unlike chickens, swine produce urine and manure with a slurry-like consistency, so the poultry barn design had to be modified. In 1993, Menke began working with a poultry industry consultant, Bob Mackin, to design a two-story hog barn that can support solid manure management. They called their new design the "High-Rise Hog House." Along with two other partners, they built the first prototype in 1998 — a 1,000 head hog finisher barn in Ohio. About half a dozen barns have since been built in Ohio and Indiana, including: four finishing, one sow, and one nursery unit. In addition, a Canadian company, Avonbank Farm Equipment Ltd., built a variation of the High-Rise Hog House on an Ontario farm.

The upper floor of the High-Rise Hog House is similar to a conventional slotted floor swine barn (Figure 1). The difference is in the lower level. Where a conventional swine barn has a pit below the pens for liquid manure, the lower level of the High-Rise Hog House is at ground level and contains a 2 to 3-foot deep layer of dry absorbent amendment such as wood shavings, corn fodder, or wheat straw. The amendment is placed below the slotted floor to absorb the feces and urine produced by the pigs. Perforated PVC pipes, located in the floor beneath the amendment, blows air upwards to aerate and dry the manure. The air pressure is kept strong enough to keep the pipe holes open. Ventilation fans in the sidewalls of the lower story pull air out of the building from the attic through continuous baffle inlets down through the slots in the floor. This airflow helps keep the upper floor dry (a source of odor) and provides fresh air for the pigs.

At the start of the pig production cycle, one and a half feet of fresh bedding is placed below the slotted floor. As the feces and urine fall through the slots onto the bed of straw, air moves upwards and across the bedding to dry it. Periodically additional bedding is added, particularly in areas where dunging patterns are concentrated. Pigs tend to pick one location in their pen for dunging and this concentrates the liquid in the bedding below, giving rise to an uneven manure distribution in the pit. The designers are still working on ways to compensate for this.

Overall, the anticipated cost savings for the system include: 1) elimination of liquid manure handling equipment, spreaders, and the labor to operate them; 2) improved growth and health of herd due to better environment in the barn; 3) reduced transportation costs of handling solids; and 4) the ability to process the manure further through composting to eliminate odors, pathogens, and weed seeds, which increases its market value. A study comparing pig performance in the High RiseTM barn with that of 11 other conventional barns found that the performance of hogs in the High RiseTM building was better than the average for conventional barns. The High Rise barn produced a lower percentage of mortality and culls plus a greater weight gain and only a slightly lower feed conversion ratio compared to the averages in the conventional barn. Harold Keener, an agricultural engineer with Ohio State University, has been monitoring air quality in the high-rise hog house for several years. He has found that ammonia measurements in the upper level are between 0 to 8 ppm (parts per million) compared to 20 to 30 ppm in conventional deep pit finishing barns. There has been no hydrogen sulfide detected in the building. Harry Hoitink, also with Ohio State University, has been researching the composting aspects of the project. According to Hoitink, the compost has slightly lower nutritional content compared to liquid manure because some of the nitrogen is lost during the composting process. However, the reduction in volume of composted manure lowers transportation costs, allows manure application to more distant fields and there are possible revenues from the sale of compost.

I visited the facility in Greenville, Ohio with a group from Ohio State University. We toured both upper and lower floors of the barn and I was impressed by the lack of odors both inside and outside of the building. I stood outside next to one of the ventilation fans and could not detect any of the strong, characteristic smell of hog manure. Manure and bedding in the lower level begins to compost in-place. We dug into areas of the bedding and found it had an "earthy" smell; there was visible mold present indicating active composting. The bedding is removed from the barn about once a year, or after three groups of pigs have been moved out of the barn. A year’s worth of manure and bedding only gets about 2.5 to 3-feet deep because of the reduction in volume as the materials compost and dry. The bedding is usually piled up outside of the barn to finish composting statically. Some of the finished compost is used for mortality composting.

The apparent benefits associated with the High Rise Hog House come at a slightly higher expense in construction and operating cost. According to Tom Menke, the construction costs for the first barn were about 10 to 15 percent higher than conventional deep pit buildings, in part due to more stringent permit specifications. However, changes in permits in Ohio for all new barns are raising the cost for conventional barns as well. Some operating costs (mainly power) are slightly higher due to increased ventilation, but the elimination of hydrogen sulfide in the barn should result in longer equipment life and lower maintenance costs. As Menke observes, "producers are amazed at the High Rise Hog House concept but many have a hard time justifying additional cost of construction and operation when there is no immediate financial reward for it. Most of the people looking to build new barns are contract hog growers. It always comes down to the bottom line. Real change may only happen when regulations or societal pressure forces it to change." Most producers with odor problems are still hoping that the answer will be a retrofit technology that they can add on to their existing system. They have put a lot of money into their systems, and don’t want to lose that investment. Perhaps as new regulations for manure nutrient management take effect, the High-Rise Hog House will become more economically attractive.

LIQUID/SOLID ISOLATION
The Liquid/Solid Isolation system, which was developed at Michigan State University (MSU), is similar to a conventional swine barn but with a radically different manure handling system. When MSU began looking into designs for their new Swine Research and Teaching Facility, several things had to be considered. Since the site of the new swine facility was less than a mile from the main campus, it was necessary to reduce odors. It was also necessary to adopt a technology that would make it easier to transport manure because of phosphorus (P) loading. Michigan adopted Generally Accepted Agricultural Management Practices (GAAMPS) for land application of manure, which is based on soil Bray P1 test values. If, according to the tests, the soil contains less than 75 ppm P (or about 150 pounds per acre), manure may be applied at crop nitrogen use rates. But if soil contains more than 75 ppm P, then manure may only be applied at crop P2O5 uptake. If the soil contains more than 150 ppm, manure may not be applied. Compliance with GAAPMS limits the amount of manure that can be land applied near their facility.

In 1995, MSU graduate student, Carrie Tengman, found that about 94 percent of the phosphorous in swine excrement is in the feces. Their research showed that when you capture feces separately from urine, the phosphorous in the fecal matter is isolated from the liquid portion. By collecting the feces separately from the urine, there would be much less liquid to transport and land apply. When Maynard Hogberg, then chairman of MSU’s animal science department, heard about Tengman’s research, he recalled a system he had seen while in Japan 10 years earlier. Hogberg and Robert von Bernuth, then chair of MSU’s agricultural engineering department, arranged a visit to Japan so other researchers could see the system. They were impressed by what they saw and decided to build something similar at MSU. Jerry Wille of Curry-Wille & Associates, designed the system for the new MSU facility, a 250 sow farrow-to-finish operation with scrapers beneath the gestation, farrowing, and finishing rooms.

They call their design the liquid/solid isolation system. It has slatted floors in the stalls typical of deep pit systems, but under the pens is a concrete V-shaped floor that is slanted towards a central notch (Figure 2). As urine and feces are deposited on the floor below the pens, the urine flows down into the central notch of the V shaped floor and is collected with slotted PVC piping. Cable driven scrapers move the feces from the V shaped floor to a channel outside the pen area. A conventional dairy scraper moves the feces outside the building. A plug attached to the scraper ensures that the urine flows out the end of the pipe to a separate holding tank. The liquid is pumped through an ozone contactor tank to remove odors, and is then stored in a large commercial steel tank for later land application. Solids are moved to a composting area where they are mixed 3:1 with straw and wood shavings bedding from the nearby pavilion, mainly from horse shows. Some of the finished compost is used in their mortality compost bins and the rest is land applied on nearby cornfields.

Al Snedegar, manager at the swine facility, says the five-year-old system has been trouble free. When asked if he thought the system would be attractive to large swine producers, he said that all the moving parts might scare off many producers, but he’s been very happy with it so far. Snedegar notes the operating costs are about the same as a conventional barn, or only slightly higher with the labor associated with composting. "It’s pretty hard to beat lagoons when it comes to low labor," said Snedegar. Researchers at North Carolina State University are studying the feasibility of using inclined belts instead of mechanical scrapers to separate the feces and urine. The belts can be located under the slotted floor of a conventional swine barn and act as a conveyor moving manure to the end of the barn for collection. Jeanne Koger, project director, believes it should be possible to retrofit swine barns with plastic belts positioned at an angle so that urine runs off and solids remain on the belt.

The main advantage of the liquid/solid isolation system, according to von Bernuth, is that the feces, which contains most of the phosphorous, remains separate from the liquid phase. When feces and urine are allowed to mix to form a liquid, solids separation techniques can then only effectively remove about 50 percent of the phosphorous, leaving the other half in the liquid portion to be land applied. However, when the two are kept separated, one can capture over 90 percent of the phosphorous, thus allowing more liquid to be land applied based on nitrogen needs of the crop. The system also reduces 75 to 80 percent of the odors, mainly ammonia and hydrogen sulfide (there is almost no ammonia or hydrogen sulfide detectable). Urine contains an enzyme called urease, which chemically releases the ammonia from the feces. Feces also contain volatile solids that quickly become anaerobic in liquid manure handling systems. Data collected at the facility has shown that the nitrogen to phosphorous ratio of the liquid waste stream is about 2.85. A crop rotation of corn, soybean, and wheat uses nitrogen and phosphorous at a ratio of about 2.9. By capturing the manure for composting and moving it off the farm, MSU is able to balance the animal and crop production without greatly increasing production costs.

It is clear that the future of swine manure management is changing, due to societal pressures and environmental regulations. Technologies that eliminate odors and improve nutrient management are going to be more important to U.S. pork producers. Perhaps technologies such as those discussed in this article will give producers more options to reduce odors while managing manure nutrients safely. Much of this may depend on the willingness of both livestock and crop producers to see the value of manure as a resource.

Jody Tishmack is with the Agricultural and Biological Engineering Department at Purdue University.

Copyright 2004, The JG Press