Introduction

Livestock and poultry production involves the conversion of raw feeds such as grass into valuable products such as meat, milk, and eggs to meet daily human consumption. In the United States, the total amount of chickens consumed increased by 27.5% from 1992 to 2001. The chicken consumption per capita is projected to grow from 78 pounds in 1992 to 92 pounds in 2004 (Fig. 1). The US Department of Agriculture forecasted US agricultural exports for fiscal year 2003 at $57.5 billion, a $4 billion increase over the expected $53.5 billion for fiscal year 2002. Export sales at this level would be the highest since 1997, only $2.3 billion below the all-time record of $59.9 billion in 1996.

In the past half century, livestock and poultry agriculture has experienced a rapid transition from small flocks and herds to large-scale intensive (concentrated) productions in a few locations due to global industrialization. This has served to reduce operational costs as well as improve profitability and increased coordination between animal feeding operations and processing firms. Operations have tended to cluster near slaughtering and manufacturing plants as well as near end-consumer markets, which has encouraged safety standards in the food supply and convenience of food delivery [1].

The consolidation and intensification of production, while perceived as sound from economic and management perspectives, often do not give full consideration to the potential environmental impact. One of the obvious problems is considerable odorous emissions produced from livestock and poultry production sites. In recent years, attention has shifted to their impact on water, soil, and air quality. One new challenge is the increase of methane in the atmosphere, a potent greenhouse gas, which can contribute to global climate change. The gas is produced by ruminant animals, such as cattle, sheep, buffalo, and goats. Because of their special digestive systems, they can produce methane. Globally, ruminant livestock produce about 80 million tons of methane annually, accounting for about 22% of global methane emissions from human-related activities. Livestock production systems can also emit other greenhouse gases

Figure 1 Chicken consumption in United States from 1992 to 2004.

such as nitrous oxide and carbon dioxide. The most promising approach for reducing methane emissions from the US livestock is to improve the productivity and efficiency of livestock production [2-6].

Unavoidable and less desirable livestock and poultry waste is excreted in solid, liquid, and gaseous forms. In past years, especially before industrialization, the livestock and poultry excreta was predominantly used as fertilizer and soil conditioner, which was termed as manure. The geographic concentrations of livestock production has led to a challenge in land availability. The volume of the excreta or manure generated today could become a major obstacle to future development of the livestock and poultry industries if the environmental impact is not properly managed. For example, North Carolina is one of the leading states in livestock and poultry production. In 1999, there were approximately 5.5 million animal units (AU) in the state. Animal production operation produced about. 33 million tons of fresh manure, which consisted of 240,000 tons of nitrogen (N), 182,000 tons of phosphorus (P2O5), 169,000 tons of potash (K2O), and other nutrients [26].

Potential pollutants are mainly nitrogen and phosphorus; others are solids, pathogens, and odorous compounds. Manure can also be a source of salts and various trace elements (e.g., zinc and copper), as well as pesticides, antibiotics, and hormones. It is well known that manure has nutrients (i.e., N, P, and K) that have potential value as fertilizers [7]. However, the nutrients are of relatively low concentrations, which makes them more costly to store than apply as fertilizer. Fresh swine manure, for example, contains 0.6% N, 0.45% P, and 0.45% K. The pollutants can be released into the water environment through discharge or runoff if the manure and wastewater are not properly handled and managed. As a result, laws and regulations have been applied to restrict agricultural practices and impose penalties for exceeding land application limits in an effort to control agricultural impacts. In the future, sound nutrient management practices will be mandated to manage both feed and manure to minimize the environmental impact of livestock and poultry agriculture (USEPA, 2003) [3-6].

23.2 CHARACTERISTICS AND IMPACT OF WASTES

23.2.1 Livestock and Poultry Wastes

Livestock and poultry wastes are mainly composed of excreta and associated losses, bedding, washwaters, sprinkling waters from livestock cooling, precipitation polluted by falling on or

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