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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs 2 Animal Feeding Operations INTRODUCTION Understanding the place of animal feeding operations in the U.S. agricultural economy is a necessary prelude to effective public management of the adverse effects of their air emissions. This chapter starts with information on the overall size of the major livestock feeding operations (cattle, swine, dairy cows, and poultry) and their relationship to crop agriculture. It then turns to the general economics of livestock agriculture and the structure of the livestock industry. It ends with a discussion of the economics of emissions and manure management and potential methods of livestock operation emissions control and mitigation. LIVESTOCK AGRICULTURE Livestock agriculture is concerned with raising and maintaining livestock, primarily for the purposes of producing meat, milk, and eggs. Livestock agriculture also includes wool and leather production and may include animals kept for recreation (riding or racing) and draft. Livestock and livestock products generated from $87.1 billion to $96.5 billion annually (46 to 48 percent of U.S. cash receipts from farm marketings) between 1995 and 1998 (U.S. Department of Commerce, 2000, Table 1109). Livestock agriculture is the market or consumer for a significant portion of U.S. crop agriculture. Annual U.S. feed and residual use of feed grains (corn, sorghum, barley and oats) amounted to 154.6 million to 157 million metric tons (1994-Livestock Agriculture and
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs 1995 through 1997-1998 crop marketing years), 55 to 63 percent of U.S. feed grain production during this period (USDA, 2000a). Corn provided 18.2 percent of cash receipts from farm marketings of crops between 1994 and 1998 (U.S. Department of Commerce, 2000, Table 1109). Sorghum and barley added another 2 percent of cash receipts from farm marketings of crops. Hay is consumed by livestock and represented 3.8 percent of cash receipts from farm marketings of crops during this period. Livestock agriculture is also the market or consumer for soybean meal and other oilseed meals. Soybeans accounted for 14.7 percent of cash receipts from farm marketings of crops between 1994 and 1998 (U.S. Department of Commerce, 2000, Table 1109). Approximately 37 percent of U.S. oilseed output was consumed domestically as oilseed meal during the 1994-1995 through 1997-1998 crop-marketing years (USDA, 1996b, 1997b, 1998, 1999a). In summary, livestock agriculture directly accounts for nearly half of U.S. cash receipts from farm marketings and provides the market for a significant fraction of the remaining portion of U.S. agricultural output. The leading states in terms of annual cash receipts from livestock and products in 1997 and 1998, in decreasing order, include Texas ($8.2 billion), California, Nebraska, Iowa, Kansas, North Carolina, Wisconsin, Minnesota, Georgia, Arkansas, Oklahoma, Colorado, and Pennsylvania ($2.85 billion). In many states, livestock agriculture accounts for more than 65 percent of cash receipts from farming. Examples include Alabama, Colorado, Delaware, New Mexico, New York, Oklahoma, Pennsylvania, Utah, Vermont, West Virginia, and Wyoming (U.S. Department of Commerce, 2000, Table 1113). Livestock agriculture provides the basis for the meat, dairy, and egg processing industries. Meat products represent 49.8 percent of all non-metro food processing employment and 1 of 16 rural manufacturing jobs (Drabenstott et al., 1999). Finally, meat, dairy products, and eggs are important components of the U.S. diet (Table 2-1). ECONOMICS OF LIVESTOCK AGRICULTURE Economic characteristics of livestock agriculture addressed here include markets and prices, production costs, and industry structure. Markets for Livestock and Products Prices for livestock and products are determined in competitive markets. With the exception of federal marketing orders for dairy (see Blayney and Manchester, 2001, for a description of U.S. milk marketing programs), markets for livestock
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs TABLE 2-1 U.S. Per Capita Consumption of Meat, Dairy Products, and Eggs in 2001 Product Retail weight per year (kilograms) Broiler chicken 34.7 Beef 30.0 Pork 22.8 Turkey 7.9 Milk and products 264.4a Eggs 252.6b a1998, kilograms of milk equivalent on a milk fat basis (USDA, 1999b). bNumber rather than kilograms. SOURCE: USDA (2002c, p.11) and products are unrestricted. Producers respond to market prices for livestock and their products and to prices of feed ingredients by increasing production following periods of high profit and decreasing production following periods of losses. Biological lags in production response are a fundamental characteristic of livestock agriculture. The gestation or hatching periods of livestock and poultry plus the period from birth to market weight or to milk or egg production impose minimum times in which livestock and poultry farmers can respond to price or profit signals. This period approaches one year for swine and two to three years for cattle. Broiler producers are able to respond within a few months, while egg and turkey producers may require 6 to 18 months to respond. The result of the lagged response is a cycle in production, prices, and profits as producers are constantly adjusting output by expanding or exiting production. Prices and profits in any single year may not be representative of the equilibrium price and profit of a livestock sector due to the length of cycles in prices and profits. Volatility in prices is evident. Feed cost is generally the largest component of total cost and varies directly with ingredient (corn, soybean meal, hay) prices. Recent U.S. Department of Agriculture (USDA) benchmark cost series show feed to be about 60 percent of the cost of broilers, turkeys, table eggs, and pigs. Feed is more than 70 percent of the benchmark cost of weight gain in high plains cattle feeding operations. Volatile prices for feed ingredients and market animals, combined with biological lags in production response, result in extremely volatile profit margins. Extended periods of losses (sometimes severe) and profits are common in the livestock sector. Confined animal feeding operations have a large share of the nation’s livestock and account for an equal or larger share of the products. For example, beef cattle feedlots with more than 1000 head of cattle, which sold an average of
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs 10,983 head in 1997, accounted for 85 percent of the beef cattle sold (EPA, 2001a). The largest size categories for other kinds of livestock operations have similarly large shares of the number of animals and production. Nevertheless, the large number of operations in even the largest size categories keeps any one, or any group, of them from having sufficient market power to affect the prices of their products. Farms in general, including animal feeding operations, are “price takers.” Because of the large number of farms of most kinds, each farm faces an elasticity of demand that is “nearly infinite” (Carlton and Perloff, 1989). Various methods of vertical coordination between meat processing organizations and animal feeding operations (AFOs) are in use (Martinez, 2002). Broiler, turkey, and some swine processors use production contracts. Production contracts are generally defined as contracts between owners of livestock and independent farmers to have the farmers raise the livestock on their farms. Typical production contracts have the livestock owner (frequently, but not necessarily, a processor) provide livestock, feed, medication, and managerial and veterinary support, while farmers provide buildings, labor and management, land, manure management, utilities, repairs, and supplies in exchange for a fee per head or per pound produced. Marketing contracts or agreements are another method of vertical coordination between processors and livestock producers. Marketing contracts or agreements may be defined as contracts to deliver livestock, and establish the base price and price increments for specific attributes (e.g., weight, condition, backfat depth). Marketing contracts are distinguished from production contracts in that farmers retain ownership of the livestock and provide feed and other inputs until the livestock are delivered to the processor. It is the individual farms, whether they sell on “spot” markets or operate under contract, that produce the air emissions that are the subject of this report. Producers of livestock and poultry compete in an international market. Beef and pork are both imported and exported. Net exports range from 3 percent of pork production to 18 percent of broiler production. Although exports constitute a relatively small fraction of total production, they add significantly to agricultural income. Increased production costs can decrease the international competitiveness of U.S. agricultural production sectors and shift income to foreign producers. A significant cost increase in the U.S. livestock sector could shift production (and emissions) across political boundaries. Farm Numbers, Inventory, Farm Size, Production, and Productivity The number of farms in the United States peaked in 1935 at about 6.5 million and has been declining steadily as farm size and productivity rise. There were 1.91 million farms (defined as places selling at least $1,000 of agricultural products in a year) in the United States in 1997 (USDA, 1999c). The fraction of U.S. farms that keep all types of livestock and poultry has also been declining steadily since about 1910.
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs Increased specialization has accompanied increased productivity. There has been little change in the number of pigs in the United States since 1920. The number of cows being milked peaked at 25 million in 1944 and has since dropped to about 9 million. Milk production per cow increased markedly from 2073 kilograms per year in 1944 to more than 8,000 kiograms per year in 2001 (USDA, 2002c, 2002d). Annual production of livestock and products has risen steadily over the past century, although production cycles are evident in the data. Also evident is a steady increase in livestock productivity (defined here as the quantity of meat, milk, and eggs produced annually from a given inventory of livestock). Productivity gains arise from an increased number of animals born and raised per breeding animal per year, increased growth rates and market weights of animals intended for slaughter, and increased milk or egg production per animal per year. In addition to producing more from a given inventory of animals, livestock farmers have greatly decreased the quantity of feed required to produce a pound of meat, milk, or eggs. Productivity gains have been accomplished through genetic selection, as well as through improvements in diet formulation and processing, housing and environmental controls (e.g., improved buildings, manure removal, and ventilation), veterinary medical care and medications, and management. Havenstein and colleagues (2002) demonstrate that a 2001 strain of broiler chicken fed a current diet requires about one-third the feed and one-third the time to produce a 4.0 pound (lb) live broiler as a 1957 genetic strain chicken fed a diet used in 1957. Since modern broilers are grown to heavier weights, the actual efficiency gains are altered. The modern broiler raised to 5.9 lbs in six weeks requires about 27 percent of the time and 42 percent of the feed per pound of live bird that the 1957 strain required. The 1957 strain required about 103-105 days to produce a 4.0-pound bird. These productivity gains are consistent with those cited by Martinez (2002, Table 3). Note that reduced feed consumption per pound of product results in a proportionally larger reduction in the quantity of excreta on a dry weight basis. For example, if feed consumption is reduced to 42 percent of the original quantity, and if 15 percent of the original quantity was and is retained in the product, then the dry weight excreta would be 31.7 percent of the original quantity excreted ([0.42 − 0.15] / [1.0 − 0.15]). Farm Size, Production and Market Organization, and Contracts Dairy. In the United States, there were 79,318 dairy farms with more than three milk cows reported in the 1997 census of agriculture (Kellogg, 2002). Of these, 16 percent were very small (<35 USDA animal units [AUs]), 33 percent were small (35 to 70 USDA AUs), 40 percent were medium sized (70 to 210 USDA AUs) and 9.8 percent were large (>210 USDA AUs). USDA animal units differ from Environmental Protection Agency (EPA) animal units (Appendix E) and are equivalent to 454 kg (1000 pounds) live weight accounting for all animals on the farm. In contrast to other food animal industries, the dairy industry is not
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs vertically integrated. Farms are owned and managed independently of processors. Most dairy farms raise their own replacement heifers but sell bull calves. Fluid milk is sold to processors, which may be controlled by cooperatives or by private or public corporations. (See Blayney, 2002, and Manchester and Blayney, 1997, for further exposition of structure and trends in the U.S. dairy sector.) Beef Cattle. The number of beef cattle in the United States peaked at 132 million head in 1975. USDA estimated that in 2001 the U.S. cattle inventory was 96.7 million head and that there were 1.05 million cattle operations (operations with at least one or more head of beef or dairy cattle). Many of these are cow-calf operations, with cattle fed on pasture, that are not considered AFOs. For example, 0.65 million cattle operations had fewer than 50 head of cattle and accounted for 11.5 percent of the United States cattle inventory in 2001 (USDA, 2002e). Feedlots vary in size, from a great many operations that hold only a few animals to a small number with a one-time occupancy capacity of more than 100,000 head. The cattle feeding industry has not developed integration or contractual arrangements to the extent that the poultry or swine industries have. Most feedlots are privately held; an owner may have more than one, but ownership of a feedlot does not necessarily mean ownership of the cattle being fed there. Custom feeding is common where an investor who owns the cattle may have no active involvement in cattle feeding or agriculture except through an investment portfolio. Cattle farmer-feeder operations are those in which much of the feed used in the feedlot is derived from owned or rented cropland that is part of the operator’s overall agricultural operation. These operations may involve feedlots with capacities as large as 10,000-12,000 head. Most farmer-feeder operations probably have a one-time capacity of <2500 head. Large commercial feedlots may have a substantial land base for feed production but in most instances would have to purchase a significant portion of the feed needed. Custom feeding (housing and feeding cattle on a feedlot for a fee; the cattle are not owned by the feedlot owner) is common. Cow-calf operators who do not have a feedlot may also utilize custom feeding after their cattle have been weaned. The proportion of custom-fed cattle within a feedlot is not necessarily related to overall size of the feedlot. It has become increasingly common for smaller farmer-feeder operations to use custom feeding as a way to decrease risk or to capitalize expansion. Pigs. Almost all of the U.S. inventory of pigs in each of the three phases of production is housed in buildings. There were 81,130 farms with at least one pig on December 1, 2001. Of those, 84.6 percent had fewer than 1000 pigs in inventory and maintained 13.5 percent of the 58.8 million pigs in the country; 8.6 percent have at least 2000 pigs in inventory and maintained 74.5 percent of the U.S. inventory of pigs (USDA, 2001).
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs The U.S. markets for pigs include a mix of spot markets, contracts, and processor ownership. For example, USDA (2002a) indicates that 14.1 percent of market hog sales on October 21, 2002, were spot market transactions (where prices are negotiated within 24 hours of the delivery of pigs to market); another 67.4 percent were conducted through marketing contracts. The remaining 18.5 percent of hogs slaughtered that day were packer owned. USDA also estimates that 33 percent of the U.S. pig inventory on December 1, 2001, was under production contract to operations that owned at least 5000 pigs (USDA, 2001). Many of the entities that own pigs and contract them out under production contracts are pig producers and not pork processors. Some pork processors own pig farms, and some own pigs and contract them out to farmers under production contracts. Some Midwestern states including Iowa prohibit packer ownership of pigs prior to slaughter. Poultry. Almost all broilers (young chickens raised for meat) and turkeys are raised in buildings, as are egg-laying chickens. Martinez (2002) indicates that more than 80 percent of broilers are raised under production contracts and the remainder are raised on farms owned by the processors. He also reports that 56 percent of turkeys are raised under production contracts and another 32 percent are owned and raised by turkey processors. Martinez (2002) indicates that 60 percent of chicken eggs are produced on farms owned by the processor and another 38 percent are produced under production contracts for the processor. Although not substantially concentrated economically in terms of being able to affect prices for their output, the animal feeding operations (as distinguished from the large processing firms, referred to as “integrators” in the case of swine and poultry) are regionally concentrated (Box 2-1). The cumulative shares of production based on number of animals for the top four and next four states are shown in Table 2-2. As improvements have been made in poultry housing, and equipment for feeding, watering, and ventilation, the number of birds that an individual farmer could care for has increased. A flock of 1000-2000 birds was considered huge in the 1920s. Presently, one broiler farmer can easily manage and care for 150,000 or more birds. Complexes housing laying hens for the production table eggs may have 1.5 million birds that are typically managed by a crew of approximately 15. Again, economics have caused poultry farmers to look for more efficient and effective methods of producing more animals per unit of labor. State and regional specialization, as shown in Table 2-2, is the result of various factors that affect the livestock industry. The cost of animal feed, the importance of which is evident in the frequent high rankings of states in the Midwest, is obviously significant. Transportation costs—both for getting feedstuffs to the feeding operations and for getting products to markets—are also important, although their importance tends to be reduced by practices such as shipping feed grains in unitized trains, which can significantly lower transportation costs for
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs BOX 2-1 Poultry Production in the United States Poultry production in the United States was essentially a farm sideline until the 1930s. Economically disadvantaged farmers, primarily in areas of the country where soils, climate or other conditions were not conducive to traditional row crop agriculture, were the early pioneers in transforming poultry production into a primary farming opportunity. For example, poultry production is purported to have begun in north Georgia due to the continued failure of cotton crops in the region. Farmers were desperate to develop an alternative. In northwest Arkansas an apple blight was the economic incentive, and on the Delmarva peninsula, declines in shellfish harvests and disease problems in the region’s traditional truck farming (fruit and vegetable) crops made farmers desire a reliable cash crop (Gordy, 1974). As the industry evolved, it looked for ways to become more efficient. Jesse Jewell in Gainesville, Georgia is generally credited with advancing the idea of vertical integration in poultry production. He understood that bringing hatcheries, feed mills, and processing plants together as coordinated units would greatly improve scheduling and reduce costs. Vertical integration resulted in an infrastructure being developed (hatchery, feed mill, processing plant) that further localized poultry production into regions. It was advantageous from a transportation standpoint for all of these aspects of poultry production to be in close proximity. Generally the farmers who produced the poultry were located within 50 miles of the feed mill. Thus, the concentration of the poultry industry in discrete areas of the United States has been due to economics (Sawyer, 1971). large operations. Other factors such as climate, differences in cost of labor and land, population density, and state regulation of the livestock industry are also important, but their effects are not obvious in the rankings. TABLE 2-2 Leading Livestock Production States by Animal Sector Sector Top Four States Percent Next Four States Percent Total Beef cattle TX, KS, NE, CO 60 IA, CA, OK, MN 16 76 Milk cows WI, CA, NY, PA 44 MN, TX, MI, ID 17 61 Swine IA, NC, MN, IL 57 IN, NE, MO, OH 21 78 Broilers GA, AR, MS, NC 48 TX, VA, DE, MO 16 64 SOURCE: EPA (2001a).
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs Animal Feeding Operations and Concentrated Animal Feeding Operations Animal feeding operations and concentrated animal feeding operations (CAFOs) are classifications of livestock and poultry farms used by the U.S. Environmental Protection Agency for regulation under the Clean Water Act. An AFO is defined as “a lot or facility where animals have been, are, or will be stabled and confined and fed or maintained for a total of 45 days or more in any 12 month period, and where crops, vegetation forage growth, or post harvest residues are not sustained in the normal growing season over any portion of the lot or facility” (40 CFR part 122.23(b)(1)). An AFO is defined as a CAFO if it confines more than 1000 EPA animal units at any time during the year. EPA defines animal units differently than USDA. One EPA animal unit of each type of livestock is indicated in Table 2-3. Threshold farm sizes are published by EPA to distinguish CAFOs for each animal type. An AFO is defined as a CAFO (based on EPA regulations prior to December 15, 2002) if it has more than the following numbers of animals of any species: 1000 feeder and slaughter cattle, 700 mature dairy cattle, 2500 swine weighing more than 55 pounds, 55,000 turkeys, 100,000 laying hens or broilers if the facility has continuous overflow watering or 30,000 laying hens or broilers if the facility has a liquid manure system, and 5000 ducks. The critical distinction between AFOs and CAFOs is that CAFOs are potentially regulated as point sources and required to obtain National Pollutant Discharge Elimination System (NPDES) permits. These definitions are solely for the purpose of determining which farms are to be regulated by various methods, with the largest farms receiving the most stringent oversight. USDA has a different definition of an animal unit, which can lead to confusion in comparing EPA and USDA statistics, including confusion in estimating air emissions because of differences in the animal base on which estimates of air emissions are predicated. The committee suggests that estimates of air emissions in the future be based on a modeling approach that is more flexible than has been TABLE 2-3 Number of Animals per EPA Animal Unit Animal Type Head Slaughter or feeder cattle 1.0 Mature dairy cow 0.7 Pigs weighing 25 kg or more 2.5 Turkeys 55.0 Chickens 100.0 Sheep or lambs 10.0 Horses 0.5
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs used to date and that is consistent with continuous, rather than periodic, estimates of animal growth. This leads to Finding 1: FINDING 1. Much confusion exists about the use of the term “animal unit” because EPA and USDA define animal unit differently. RECOMMENDATION: Both EPA and USDA should agree to define animal in terms of animal live weight rather than an arbitrary definition of animal unit. Production Systems Production systems vary substantially across the country and from farm to farm. This section describes basic elements of the most prevalent systems. Dairy. Most dairy farms are diversified crop and animal production systems. Some feeds are purchased, but dairy producers usually grow their own forages (whole plant feeds such as hay or silage) and raise their own replacement stock. Most dairy farmers sell their bull calves and raise heifers as replacement animals. The advantage of raising heifers on farm is that it helps prevent introduction of diseases when animals are introduced to the milking herd. In a typical herd, mature cows calve every 12 to 14 months, producing a female calf 50 percent of the time. Milk production per day increases for about 10 weeks and then decreases for the remainder of lactation. Typically, the lactation period lasts about 10 to 12 months. Some farmers use bovine somatotropin injections in mid-lactation to sustain higher amounts of milk production per day. Cows are bred artificially when behavioral and physiological signs of ovulation occur about 60 to 120 days after calving. Lactation continues until two months prior to the next predicted calving. Cows are culled from the herd and slaughtered for low-grade meat production because of failure to become pregnant, low milk production, or chronic health issues. Calves, growing heifers, and dry cows are often housed separately from lactating cows. Young calves are frequently housed in separate hutches or grouped together with animals of similar age in pens or pasture. Replacement heifers are bred, usually by artificial insemination, between 14 and 17 months of age and calve 9 months later. A typical herd with 100 lactating cows may also include 18 dry cows and 86 growing heifers (Dunlap et al., 2000) for a total inventory of 204 head. Young dairy calves consume casein or soy-based milk replacer until adjusted to grain and eventually forage-based diets as they mature. Lactating cattle in peak production consume diets with as much as 60 percent of dry material from grains and high-energy by-products and 40 percent from forages (whole plant crops such as hay or silage). Lactating cattle at lower levels of production and mature cattle between lactations consume diets comprised mostly of forages.
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs Beef Cattle. Most of the cattle in feedlots in the United States are referred to as yearlings. They enter the feedlot weighing 340 to 410 kg and are fed high grain diets for 130 to 150 days. They are harvested at an average of about 590 kg. There are wide variations on this theme, so these generalizations are less accurate than for other specie production systems. As an example, Holstein steer calves are commonly placed in feedlots on high grain diets when they weigh 160 kg and fed for more than 300 days. In backgrounding yards, calves enter the feedlot weighing 180 to 230 kg and are usually fed high-roughage diets until they weigh 360 to 410 kg. These cattle may then be sold to another feedlot for finishing, or they may remain in the same feedlot and be fed high-grain diets. Large feedlots typically have a continual movement of feeder cattle in and finished cattle out. Occupancy will have seasonal highs and lows, but there are always cattle on feed. Many smaller operations feed one group of cattle each year. In these systems, calves (500 pounds or 227 kg) enter the feedlot in the fall and are marketed the following summer. During a portion of each year, these operations have no cattle on feed. Many combinations of these production system themes exist in the industry. Feedlot designs vary by region and type of operation. The most common design is an open pen with 0-15 percent of the surface paved. The balance of the pen surface is earthen. Space allocations range from 70 to 500 square feet per animal. The proportion of paving applied to the pen surface increases in regions that receive more rainfall. Typically, area-per-animal allotments decline as more paving is used. Bedding is not generally used in earthen pens with large area allocations per animal. Bedding during winter months (and in some instances year-round) is used in paved pens. It is common to include housing in colder or higher-precipitation regions. When housing is provided with open pens, the housing is generally paved. Shedded area allocation is approximately 20 square feet per animal, and bedding is used only in winter months. Feed bunks are usually included in the housed area of these operations. Total-confinement systems refer to pens completely under roof. Some systems use partial or fully slatted floors with either deep (storage) pits or shallow pits that are flushed or scraped. Other systems have paved floors and use bedding throughout the year. Space allocations will be as low as 25 square feet per animal in total-slat, deep-pit facilities and 40 to 50 square feet in paved floor, bedded, confinement barns. Pigs. Almost all pigs are raised in total confinement. Pig farms are organized around three phases of production. Farrowing operations maintain a breeding herd of mature females and produce weaned pigs that are typically 3 or 4 weeks old and weigh 5.4 to 7.3 kilograms. Nursery operations receive the weaned pigs and produce feeder pigs that are typically 10 to 11 weeks old and weigh 20-27 kilograms. Finishing operations receive feeder pigs and feed them to market
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs cal scrapers. Most U.S. dairies with fewer than 100 cows use this means for cleaning barns (USDA, 1996a). Free-stall barns are often cleaned using mechanical scrapers that pass through the alleyway. Most farms with more than 200 cows use this means of cleaning (USDA, 1996a). Flush systems are increasingly common on large farms. However, flush systems require greater storage capacity than mechanical scrapers because more liquid is added to the animal manure despite recycling from a storage pond or lagoon. Dry lots or bedded packs can be used to house cattle in dry climates, with manure removed only occasionally with a tractor. Dairy cattle manure is either stored dry in piles on concrete or earthen pads, stored as a slurry in a concrete or lined lagoon or storage tank, or mixed with flush water in earthen or lined lagoons which may be covered with biological material (e.g., straw), covered with impermeable material (e.g., synthetic polymers), or left uncovered. Beef Cattle. Manure management in feedlots varies with the range of facilities described previously. Earthen-floor pens are routinely scraped, and the solids are collected into mounds within the pens. The manure mounds are removed on schedules that depend on the climate, region, and class of cattle involved. Solids removal from these systems may occur monthly, quarterly, semiannually, or annually. Some feedlots do not remove the manure yearly; rather a mound is created in the fall and peeled over winter, allowing the manure to dry in summer and be mounded again. The one-turn-per-year feedlots typically remove solids only once a year. When there is a continuous flow of cattle and pens are on feed less than 150 days, solids removal likely coincides with the sale of cattle from a pen. Pens with extensive paving require regular (weekly, semiweekly) removal of solids. Primary factors affecting the frequency of scraping are stocking density in the pen, precipitation, and use of bedding. Solid-floor, total-confinement barns with bedding are generally cleaned every month. In all of these systems, the disposition of removed solids depends on season and region. It is often necessary to stockpile solids at a location outside the pen until the material is spread onto cropland, perhaps weeks or months later. Some operations compost the solids, but this practice is not prevalent because of climatic conditions, costs, and additional management requirements. Permitted feedlots with outside pens have runoff controls ranging from vegetative filters to settling basin pond systems to lagoons. Settling basins are handled as solid waste usually when the material is dry. Ponds may be allowed to evaporate or be used as a source of irrigation water. Lagoons are pumped, usually each spring and fall, with liquid manure applied to cropland. Slatted-floor confinement designs with flush systems typically incorporate some degree of solids separation to allow recycling of flush water. The high solids content effluent fraction would be stored in lagoons or slurry store-type structures. Deep-pit facilities are usually emptied each spring and fall.
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs Local ordinances are having an increasing influence on manure handling and management. These are highly variable and often specific to an individual feedlot. The result of federal, state, and local regulations and stipulations is a checker-board of manure management strategies. This creates confusion in the permitting process, may accommodate specific optimums by location, and may lead to a real or perceived disparity of requirements. Pigs. Manure management for pigs varies widely with climate, geographical characteristics, and size and type of operation. A small proportion of farms in Iowa and other states has adopted a deep-bedded system in the past decade, in which pigs are kept in hoop buildings on deep straw beds. The bedding material and manure are removed periodically and spread on land. More prevalent systems include slurry handling systems, common in the upper Midwest, and anaerobic lagoon and flushing systems, with land application of liquid lagoon effluent, common in the Southeast. A variant of the anaerobic lagoon system can be found in the arid West where liquid is evaporated rather than applied to cropland. The slurry handling systems include collection of manure, spilled water and feed, and wash water in under-floor concrete pits or gutters. The floor of the pig buildings consists partially or totally of concrete gang slats, steel tribar, or woven wire such that manure can fall through gaps in the flooring. The undiluted manure is referred to as slurry and may contain 5 to 10 percent solids. The slurry may be stored in a deep pit beneath the building, or it may be pumped to an outside storage tank (usually open topped and made of concrete or glass-lined steel) or an earthen slurry basin. Slurry is pumped out of storage and applied to land with tractor-drawn equipment in either the fall or the spring. The application rate is limited to the amount of manure that will meet the plant available nitrogen requirements of the crop to be produced there. A recently revised NRCS standard has caused some producers to shift to applying manure to more land, at a lower rate that will not exceed the plant available phosphorus requirements of the crop. The anaerobic lagoon and sprayfield system of manure handling is characterized by an anaerobic treatment and storage lagoon with a flushing or pit recharging system for frequent removal of manure from the buildings. Concrete slats or other flooring with openings allow manure, spilled water, and feed to fall into a shallow pit or a flush gutter beneath the floor. In the pit recharge system, less than 2 ft of liquid depth is maintained in the shallow pit and a standpipe-plug is pulled on a regular schedule to allow the liquid and accumulated manure to drain to the anaerobic lagoon. The pit is then recharged with lagoon liquid. The flush system does not maintain liquid in the flush gutter, but a flush tank at the higher end of the building is filled with several hundred gallons of lagoon liquid and released into the flush gutter every few hours. The flush liquid and accumulated manure drain into the anaerobic lagoon. The anaerobic lagoon is a large earthen structure in which a minimum treatment depth of several feet of liquid must be maintained at all times. This treatment depth maintains an anaerobic environment that sup-
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs ports anaerobic microbes employed to digest the organic matter in the manure. In addition to the treatment volume, the lagoon is also designed to contain temporary storage volume (six months to one year of manure volume and rainfall accumulation), emergency storage (a 25-year, 24-hour storm accumulation, plus a chronic rainfall accumulation in some states), sludge accumulation depth, and freeboard. Lagoon effluent generally has less than 1 percent solids and a small fraction of the nutrient content of manure slurry. Liquid lagoon effluent is land-applied using automated irrigation equipment. Liquid effluent is applied at a rate that meets the plant available nitrogen or phosphorus requirements of the crop. Annual land application volume is equal to the volume of manure, spilled water and feed, water used to wash the building interior, and rainfall accumulated in open structures, minus evaporation from barns and open structures. A variant of the anaerobic lagoon system uses the high rate of evaporation and low rainfall in some locations to decrease effluent volume. Broilers and Turkeys. Many broiler and turkey grow-out buildings have earthen floors. The floor is covered with a bedding material such as wood shavings to collect and dry the manure. The relatively low moisture content of poultry manure makes this approach practical. The bedding material and accumulated manure (called litter) are generally removed from the buildings and replaced once each year. The surface of the litter is generally raked to remove feathers and caked material, and then new shavings are added between flocks. Once removed, the litter is generally directly land-applied, but it may be stacked and stored in covered piles or in a litter storage shed until it is loaded into a manure spreader (a truck- or tractor-drawn implement) and land-applied. In arid regions, thin bed drying may be used. Eggs. A variety of manure management systems are used for layer operations. Most caged layer buildings have concrete floors. In the high-rise layer system, manure falls onto a concrete floor, accumulates there, and is removed periodically as a dry material that can be spread mechanically on land. Anaerobic lagoon and flushing systems have also been used on layer farms, but are becoming less and less common. There are also cage systems with manure belts that pass beneath the cages and convey the manure to a collection point. The manure is then augured out of the building for storage until it is eventually spread on land. Economics of Emissions and Manure Management Farmers generally behave as profit maximizers; that is, they try to use inputs and produce products such that the difference between total revenue and costs is maximized. Farm practices to limit emissions and manage manure can be considered in this context. Since manure management can affect rates and composition of emissions, it is given considerable attention in this and the following section.
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs Farmers are willing to incur costs to store, transport, and land-apply manure up to the value of additional revenues generated and costs avoided. In the case of manure management, the costs avoided include the purchase and application of commercial fertilizer. Costs avoided may also include those associated with nuisance complaints. In some cases, manure utilization is thought to increase yields more than commercial fertilizer. Such a yield increase would be an example of additional revenue generated. An example of the economic definition of a waste product would be if the costs of utilizing manure as a fertilizer exceed the value of benefits generated. A product that costs more to use than the value of benefits generated by its use is a waste. Once a product is identified as a waste, profit-maximizing behavior seeks the least cost (total cost minus total revenue) option for waste disposal. Manure treatment (as opposed to simple storage and land application) may become the most profitable or least costly option in some circumstances (e.g., Drynan et al., 1981). A variety of factors affect the economic attractiveness of treatment. High transportation and land application costs, low commercial fertilizer prices, and low treatment costs create incentives for manure treatment. High transportation costs arise from long distances between livestock and fields. Hauling distances are increased by having small and noncontiguous fields, low-yielding soils and crops (low fertilizer requirement per acre), higher nutrient concentrations in manure, larger farm sizes, and by regulations. Some costs of treatment decline (on a dollar-per-gallon basis) as farm size increases. Manure treatment may include stabilization (decomposition of organic matter to prevent odor and flies), decreased pathogens, concentration of components that must be transported (such as nutrients), separation of low-value material (e.g., water, organic matter, grit) for application to nearby land, or other modification of form to produce more useful by-products. Emissions and manure management become a policy issue when not all costs and benefits of livestock production are realized by the farmer. Costs and benefits realized by others in the absence of a negotiated exchange (purchase or sale) are referred to as externalities. Negative externalities are costs incurred by others, such as loss of environmental quality or adverse health effects. Positive externalities are benefits received by others such as increased income, employment, and improved public services arising from a larger tax base. Policy is generally designed to maximize social welfare by maximizing total benefits (private and public) minus total costs (private and public). Where externalities are present, governments may adopt policy to intervene in the market. Intervention may take the form of regulation and enforcement, investment in research and education, and/or support for the development of markets that allow externalities to be partially internalized. A maximizing social welfare solution may be difficult to identify; it is more feasible to identify policy changes that increase social welfare. A policy change that creates benefits that are valued more than the costs imposed is one that increases social welfare. Thus, the policy ob-
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs jective with respect to emissions and manure management on livestock farms may be to limit emissions to the rate at which the value of marginal benefit (marginal health and environmental damage avoided) is greater than or equal to the marginal cost (marginal cost of emissions mitigation to farmers, the community, and consumers). Critical components of the benefits estimation procedure include (1) accurate measurement of the marginal changes in emissions due to various mitigation strategies, (2) accurate measurement and prediction of changes in environmental quality and public health that arise from such changes in emissions, and (3) accurate estimation of the dollar value that society places on the marginal changes in environmental quality and public health. Critical components of the cost estimation procedure include (1) accurate measurement of the incremental investment, annual operating costs, occasional costs, and operating revenue incurred by the farmer to adopt each mitigation strategy; (2) estimation of the distribution across farms of farmers’ responses to the additional cost (continuing to operate, altering or decreasing production, or closing the operation); (3) estimation of the effect on equilibrium production and prices across regions, states, and countries; and (4) estimation of the secondary loss of income, employment, and property tax base in communities that lose livestock production. (See Chapter 5 of the committee’s interim report for further exposition of cost-benefit analysis; NRC, 2002a). Efficient policy change can be defined as a change in policy such that no other policy would generate the same value of benefits at lower cost or generate greater benefits at the same cost. A final important consideration in policy change is the Pareto criterion. This criterion requires that no one be made worse off by a policy change and at least one person be made better off. If a policy truly creates benefits of greater value than the costs imposed, then those receiving benefits can compensate those bearing the costs and still be better off than they were. The costs of a policy change to individual farmers and to communities may be inadvertently overlooked in a national comparative statistical analysis comparing the equilibria before and after a policy change. The costs of transition can be great where policy change has different effects across regions. Application of the Pareto criterion decreases the displacement during a transition by compensating those bearing the costs. Elimination or minimization of individual welfare loss decreases opposition to policy change. Where manure is considered a waste or a product of little value, farm practices to limit emissions and to manage manure are driven by regulatory requirements (such as the EPA CAFO rule and state rules) and nonregulatory guidelines (such as NRCS standards and Cooperative Extension Service recommendations). Costs and benefits of manure utilization have not been well documented in surveys, but some budget estimates (with their inherent limitations) are available. Regulatory requirements and nonregulatory guidelines are important to cost analyses of various manure management systems if they affect the rate at which
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs manure can be land-applied and the size of storage and treatment structures. Drynan et al. (1981) have published a detailed analysis of manure management costs for several systems applied to North Carolina swine farms. They concluded that “the cost estimates suggest that almost all operations will choose to use a lagoon in preference to hauling manure with tank wagons.” Cox (1993) budgeted costs of irrigation systems for lagoon effluent on various sizes and types of pig farms in North Carolina. His estimates of total irrigation cost per 1,000 gallons of effluent were in the range of $1.50 to $2.00. Lorimor and collegues’ (1999) survey of custom rates for tractor-drawn drag-line injection of manure slurry in Iowa reflected rates averaging $6 to $8 per 1000 gallons injected, with additional charges if the slurry had to be transported more than 1 mile. Roka (1993) budgeted total costs and value of fertilizer saved for lagoon and sprayfield systems in North Carolina and slurry systems in Iowa. Zering (1998, 1999) adapted the budgets provided by these authors and calculated finishing farm costs of $1.10 to $1.90 per hog finished for an anaerobic lagoon and sprayfield system in North Carolina. He also calculated costs of $2.85 per hog finished in an Iowa finishing operation and value of fertilizer saved at $2.44 for a net cost of $0.42 per hog finished. Note that the lagoon system was the least costly alternative in North Carolina, while the slurry system was less expensive in Iowa. These results are consistent with the differences in field size, crop yield, and climate (anaerobic lagoons must be up to 40 percent larger in cooler climates to achieve the same level of treatment) between the two states and the observed practices. Each of these estimates is a result of a series of assumed coefficients; together they illustrate the sensitivity of resulting estimates to changes in each parameter and variable. Information needs arising from the economics of emissions and manure management are substantial. Several critical components of cost and benefit estimation are listed earlier in this section. Accurate measurement of emissions from current and proposed livestock production and manure management systems is one of the most critical components. The economic basis for measurement of emissions is that society cannot rationally decide how much cost to incur to decrease emissions without knowing the extent to which emissions will be decreased and the value of the benefits that will be generated by that decrease. Alternative Manure Management and Emission Mitigation Strategies Air emissions from livestock and poultry farms arise from many sources spread across the entire farm and the emissions are matters of concern. Sources include manure storage and handling facilities within and outside buildings, transport and land application of manure and effluent, and feed storage and handling facilities. Options for control or mitigation of air emissions from livestock and poultry operations are limited. Several research efforts around the country involve some of the technologies and management practices that may prove useful
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs in decreasing air emissions from AFOs. Some technologies not discussed here may prove as efficacious as those listed. Discussion of possible emission modification or control strategies is presented in broad categories including strategies for animal feeding, animal health, and manure management. Animal Feeding and Animal Health Strategies. Animal feeding strategies to protect the environment have been studied closely in recent years (e.g., Kornegay, 1996). A possible method to decrease emissions is to decrease the source of the material being emitted. Several approaches for decreasing the quantity of nitrogen excreted in manure are available. One approach is to continue to increase the productivity of livestock and poultry. Increasing production per animal (faster growth rate, increased milk production) decreases the number of animals required to fill the market demand for those products. The animal’s requirements can be divided into needs for maintenance (maintaining basal metabolism) and production. Meeting maintenance requirements results in a fixed amount of nitrogen excretion for each animal in the herd or flock. Since fewer animals are required with increasing production, the nitrogen losses to manure are decreased. Dunlap et al. (2000) showed that increasing milk production of dairy cows—by administering bovine somatotropin, increasing photoperiod using artificial lighting, and milking three times daily instead of two—would decrease manure nitrogen by 16 percent for a given amount of milk produced. Increased productivity has been accomplished through genetic selection, improved diet, improved housing and environmental controls, improved veterinary medical care, and improved management. Animal health is important to emissions control since unhealthy animals have decreased growth or decreased milk or egg production but their maintenance needs to remain the same, and they continue to produce emissions and manure. A second approach to decreasing the quantity of nitrogen excreted is to more precisely match diets to requirements of groups of animals at various stages of growth, reproduction, lactation, and egg production. Since most animals are fed in groups, diets are composed to meet or exceed the requirements of all or nearly all of the animals within the group. Like human beings, animals also have species-specific requirements for essential amino acids (NRC, 1994, 1998a, 2000, 2001a). Grouping animals with similar requirements enables meeting the requirements of each animal more closely with the same diet. For example, grouping growing animals by age and gender allows a substantial decrease in the amounts of nutrients fed and excreted. Feeding broilers four different diets during their grow-out period, rather than the standard practice of three diets, resulted in decreasing nutrient requirements by 5 percent (Angel, 2000). (This practice is referred to as phase feeding.) Grouping dairy cows into separate production groups on a farm was predicted to decrease nitrogen excretion by 6 percent compared to feeding all lactating cows the same diet (St-Pierre and Thraen, 1999). Such reductions have great economic importance since profit margins tend to be small.
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs Many commercial operations have already adopted phase feeding; all-in, all-out production; and separate gender feeding. A third approach is to increase the precision with which digestible or metabolizable amino acid, mineral, energy, and other nutrients in the diet match the current requirements of the animal. Feeding amino acid supplements has had the greatest impact of all recently adopted practices on decreasing nitrogen excretion to manure. Animals require a specific profile of amino acids for optimal production, which most feeds do not provide. When balancing the diets of animals, corn products and legumes are typically mixed to provide a complementary set of amino acids. Corn is high in methionine but low in lysine, while legumes are the reverse. By blending grain and soybean meal diets to ensure adequate inclusion of the most limiting amino acids, nutritionists invariably include excess quantities of other amino acids (included in crude protein). Synthetic amino acid supplements can be used to further decrease protein feeding without sacrificing production or health. Sutton et al. (1996) showed that corn and soybean meal diets for growing pigs supplemented with lysine, tryptophan, threonine, and methionine decreased ammonia and total nitrogen in freshly excreted manure by 28 percent. Amino acids protected from degradation in the rumen of cattle have been developed and shown to decrease needs for feed nitrogen by approximately 10 percent (Dinn et al., 1998). Exclusion of feed ingredients that are not highly digestible or metabolizable by animals decreases the quantity excreted. Some researchers are also examining the inclusion of enzymes and other compounds to increase the digestibility of feed ingredients. Feed efficiency is expected to continue improving for the foreseeable future. Increased precision in diet formulation may preclude the feeding of some crop and food processing by-products because their digestibility is low or their nutrient composition profile does not match that required by the animal. As a result, this material may become waste and be land-applied or otherwise disposed of. Rapid changes in feed efficiency and resulting excretion rates leave many published coefficients obsolete. There is a need for recurring measurement of typical performance and updating of published numbers for variables such as volume excreted per day, nitrogen excreted per day, volatile solids, and biochemical oxygen demand (BOD) or chemical oxygen demand (COD) of excretion per day. This need for updated data is apparent in attempts to budget nitrogen emission factors using dated estimates of nitrogen excretion. Manure Management Strategies. A wide variety of manure management technologies and strategies have been considered over the last 30 years (e.g., ASAE, 1971). The systems and strategies now in wide use are those that proved the most cost-effective and reliable at achieving their design objectives. For the most part, those objectives did not include minimization of emissions of ammonia or methane, but rather focused on odor and dust control, avoidance of direct
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs discharge to surface water, and land application at agronomic rates. Recent attention to air emissions reveals that very few data exist on emissions of some compounds from these systems. This section is intended to highlight air emission issues related to some of the manure management technologies being considered. It is important to keep in mind that water quality protection, nuisance avoidance, animal environment protection, and worker health protection remain as considerations in manure management system design, not to mention cost and risk minimization. Manure naturally undergoes microbial decomposition that produces a number of inorganic gases and organic compounds. Manure handling and treatment can have a large influence on the physical, chemical, and biological properties of manure and consequently on the production and emission of gaseous compounds. Many treatment technologies are available that may be important in emission mitigation. However, the effectiveness of most of these technologies is not well quantified. Some technologies may decrease emissions of certain gases or compounds but increase those of others (e.g., sprinkling water on feedlots to suppress dust emissions may increase organic decomposition and the emission of ammonia and odorants). Other technologies may suppress emissions during one stage of manure management only to increase those in subsequent stages. A complete farm system approach to emissions measurement is required. Treatment technologies have to be analyzed with clear objectives as to what emissions are to be mitigated. Two white papers recently published by the National Center of Animal Manure and Waste Management (Lorimor et al., 2001; Moore et al., 2001) review various animal manure handling and treatment technologies that have been used on farms, or have been extensively researched. Recently, USDA NRCS initiated a project to identify and evaluate the emerging animal manure treatment technologies that will most likely be used by animal producers in the next 5 to 10 years. The following discussion includes manure handling and treatment technologies that have been identified by the project and have relevance to air emissions (Melvin, personal communication, 2002). Storage covers for slurry storage tanks, anaerobic lagoons, and earthen slurry pits are being studied as a method to decrease emissions from these containments. Covers being studied, both permeable and nonpermeable, range from inexpensive chopped straw (on slurry containments only) to more expensive materials such as high-density polyethylene. Covers can decrease emissions from storage, but their net effect on emissions from the system depends on how the effluent is used on the farm. Anaerobic digestion in closed containment has been studied for many types of applications. This is the process that occurs in anaerobic lagoons. When conducted in closed vessels, gaseous emissions including methane, carbon dioxide, and small amounts of other gases (possibly ammonia, hydrogen sulfide, and volatile organic compounds) are captured and can be burned for electricity generation or water heating, or simply flared. An in-ground digester being tested on a swine
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs farm in North Carolina is an example of the ambient temperature version of this technology (there are also mesophilic and thermophilic designs). The concentration of ammonia remaining in effluent from that digester may be higher than that which can be volatilized from lagoon effluent once exposed to air. The primary effect of anaerobic digestion is to decrease the amount of volatile solids (corresponding to COD or BOD). Pathogens may also be decreased in the process. Complete anaerobic digestion substantially decreases odor. Emissions from combustion of digester gas should be measured. The State of California recently awarded a $5 million grant to Inland Empire Utilities Agency to develop a centralized waste processing facility in Chino, California, and also provided $10 million as cost sharing for dairy farmers to build anaerobic digesters. Aeration of liquid or solid waste streams is accomplished by mechanically forcing air through the waste. The objective of aeration is to maintain some concentration of (dissolved) oxygen in the waste stream to support aerobic microbes that digest the organic material in the manure. Aerobic digestion generally produces carbon dioxide rather than methane, and decreases the amount of ammonia produced, producing nitrate and organic forms of nitrogen instead. Aerobic treatment is generally more expensive than anaerobic treatment because of the equipment, electricity, repairs, and management required. Westerman and Zhang (1995) found that the typical electricity cost to completely treat finishing hogs’ manure using aeration was $14 per pig space per year at $0.09 per kilowatt-hour (kWh). This amounts to $5.38 per hog finished at 2.6 groups per year. These authors found that $2.34 in electricity costs per hog finished would be required to attain partial odor control with aeration. Aerobic treatment produces several times the volume of sludge produced by anaerobic digestion. Costs, benefits, and emissions arising from sludge management must be considered. Solid-liquid separation is used on some farms now and is being considered as part of several alternative manure management systems. Zhang and Westerman (1995) reviewed engineering studies of solids separation. They reported that from none to roughly half of total Kjeldahl nitrogen (TKN), phosphorus, and COD can be removed. Costs of separation increase as the fraction separated increases and as the use of polymers increases. The costs, benefits, and emissions from solids storage and land application after separation are important considerations. Solids separation may decrease the volatile solids load on a subsequent treatment process and may increase the land required to receive swine manure nutrients. Further treatment (composting or dewatering) may add to cost but allow less expensive transport off the site. Effects of solid separation on odor concentrations at the property line remain to be determined. Composting is a method of stabilizing organic solids and decreasing pathogens by allowing aerobic or anaerobic microbes to digest the material. Composting requires space, labor, and management and can affect emissions positively or negatively. Its primary benefit is to decrease volume and produce a more acceptable soil amendment.
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs Other manure management technologies and strategies have been or are being considered (e.g., Burton, 1997; Miner et al., 2000) and an extensive research program is under way. Many of these have been applied in municipal and industrial settings (e.g., Crites and Tchobanogolous, 1998). On July 25, 2000, Smithfield Foods, Inc., entered into a voluntary agreement with the Attorney General of the State of North Carolina to provide resources to be used in an effort to develop innovative technologies for the treatment and management of swine wastes that are determined to be technically, operationally, and economically feasible (Williams, 2001). Performance standards require comprehensive analyses of odor and ammonia emissions, pathogens, and economics for each technology. Currently, 18 technologies or systems are being studied. Other technologies and practices such as livestock housing design and operation affect air emissions. A considerable research and development effort has been devoted to evaluation of inexpensive filters for exhaust air from buildings and of “windbreak walls” to deflect and disperse the exhaust airstream from buildings. Land application methods to decrease emissions are also being studied. In summary, many options of varying cost and effectiveness are being evaluated for reducing emissions and managing manure on livestock and poultry farms. Measurement of air emissions from existing and alternative systems on commercial farms is needed for both emissions of local concern and those of regional and national concern. SUMMARY The structure and management practices of the animal feeding sector respond mainly to economic dictates as influenced by government regulations. Both economic factors and regulations affecting this sector change as understanding of their effects and the effects of responses to them also change. This chapter provides what amounts to a recent snapshot of the sector’s structure and operations. While the exact direction of changes in economic factors and regulations, and thus the future structure and operation of the industry, may not be predictable, users of this report should expect change to occur.
Representative terms from entire chapter: