The USEPA published regulations for the NELG and the NPDES Permit Regulations for CAFOs in January 2003. The final rule focuses on the largest operations and those having the greatest environmental risk. It strengthens the current regulations for reduction of pollution from AFOs and promotes innovation , Any AFO, according to the new regulations, must provide storage for manure and wastewater. The new rule ensures that land application of manure by CAFOs use nutrients for agricultural activities. Changes to the existing regulations include:
• All CAFOs, all large chicken operations, large swine nurseries, and heifer operations must apply for a NPDES permit;
• AFOs may elect to use innovative technologies and alternative management practices;
• CAFOs must implement nutrient management plans that include appropriate best management practices to protect waters;
• CAFOs must report key information about their operations annually.
23.4 LIVESTOCK WASTE STORAGE TECHNOLOGIES AND MANAGEMENT
Livestock and poultry wastes are normally stored in animal shelters of animal feeding operations until they are removed for treatment or utilization. An animal shelter can be an anaerobic lagoon, a. storage pond, a manure pit, a below/aboveground storage tank or other structure used to house animals in production agriculture. These systems should be properly designed, constructed, and managed to ensure that the waste has no adverse effects on the surrounding environments (ground and surface waters and odors).
In general, the service life and durability, foundation, structure loading, and structural design must be in accordance with the national, state, and local government standards and rules. Odors from livestock production facilities (e.g., H2S due to anaerobic digestion of manure) must be prevented from releasing to the environment. Hence, adequate separation distance between the production plants and residential areas, and the appropriate orientation of the plants must be ensured.
Anaerobic lagoons have multiple functions of storage and decomposition of manure. Biogas of methane can be produced during the anaerobic biological process. The volume of the lagoon consists of minimum treatment volume, sludge volume, livestock manure and wastewater volume, net precipitation volume (i.e. precipitation minus evaporation), volume due to a 25 year, 24 hour storm event, runoff volume, and additional safety volume (freeboard, normally height of >1 ft) . The minimum treatment volume can be estimated by the volatile solids loading rate ranging from 3 to 7 pounds per 1000 ft3 per day; the manure and wastewater volume is based on a storage period of 90-365 days. A typical depth of 8-20 ft is normally used. The sides of the lagoon should be sloped with a horizontal to vertical ratio of 2:1 to 3:1. Lagoons with two stages are usually used in the storage. A cover is used so that odors can be avoided and methane is collected. An optional solid separation unit can be used before the waste enters lagoons. Impervious liners are normally used for prevention of possible groundwater pollution. An extremely high hydraulic retention time (HRT) of more than 200 days is normal in the lagoon operation. The averaged removal efficiencies of COD, TSS, total nitrogen (TN), phosphorus, and potassium are 90, 94, 75, 87, and 45%, respectively .
A storage pond is similar to the anaerobic lagoon, except that the minimum treatment volume is not added. Thus, its function is mainly to store the manure, but not to actively treat it. The organic carbon, phosphorus, and nitrogen can be removed mainly because of physical actions, rather than chemical. The removal of sludge can lead to reduction of these three elements. Some nitrogen, in the form of ammonia, is reduced as a result of volatilization.
Solid wastes can be stored in manure pits that are located inside or outside of buildings. A typical storage period of 5 to 12 months is used. Semisolid wastes are often pumped to pits (Fig. 3), where solids are separated from liquids. A pit should be lined with an impermeable soil
Figure 3 A pit to contain semisolid or liquid wastes.
Figure 3 A pit to contain semisolid or liquid wastes.
(such as certain clays), concrete, and a heavy plastic liner in order to prevent groundwater contamination. The design life of earthen pits is approximately 10 years. Manure stored in earthen pits can form a nearly impermeable seal of organic matter and microorganisms on the bottom and sides.
The function of below/above ground storage tanks is the same as storage pits and earthen lagoons. The tanks are commonly constructed of moderate-cost concrete, higher-cost glass-lined steel, or others materials. Both tanks are suitable for storage of both semisolid (slurry) and liquid manure. Owing to the high cost of storage volume, tanks are not usually used to contain large volumes of lot runoff. It is important to minimize the runoff area draining into the tank to increase ease of management and reduce tank size. Storage tanks can be located above grade, below, or partially below grade. Below-grade tanks are easy to fill by scraping, whereas abovegrade tanks may require pumps for filling (Fig. 4). For open storage structures, it is important to minimize odor and sight nuisances. Tanks should be located at least 300 ft from water wells. Open tanks should be fenced, as necessary, to exclude animals and children. Tanks filled by scraping should have guardrails or grates to prevent machinery as well as animals and people from entering the tank.
Plumbing for the facility must be properly designed with safeguards against ruptures and leaks. Excess water into an animal shelter can result in possible environmental consequences. Dry waste can become wet waste and be harder to handle, while a wet waste system can have more liquid than the system is designed to handle. Ruptures of waste-handling pipes can result in direct discharge to the environment.
Proper ventilation design within the animal shelter optimizes animal health and minimizes odor emissions. Ventilation design should be in accordance with national standards. An erosion and sediment control plan should be developed for the facility to minimize erosion during construction. The finished surfaces should be shaped to provide positive drainage from the animal shelter. All the disturbed area for the construction of the animal shelters should be established to permanent vegetation according to national standards.
Animal manure storage systems should be regularly inspected to ensure proper functioning of all design features that protect the environment. Pipes that convey waste should be regularly inspected to repair any leaks. Concrete cracks or plumbing leaks that could release waste should also be immediately repaired. Dust within the shelter is known to contribute to odors and should be controlled or removed [12,13].
Figure 4 An aboveground storage tank for livestock manure.
Figure 4 An aboveground storage tank for livestock manure.
23.5 GENERAL INTRODUCTION OF LIVESTOCK WASTE TREATMENT
Solid livestock waste can be used as a fertilizer due to its nutritional values (e.g., N, P, and K) and converted to useful energy (as biogas of methane) because of its high organic carbon content. These benefits can be obtained only when the waste is carefully treated; additional facilities usually must be built and operational costs budgeted.
In most cases, however, the waste is usually discharged into nearby waters. Owing to the negative environmental impact, livestock and poultry waste must be treated before it is released. Depending on the goals and characteristics of the waste, solid-liquid separation, biological treatment, chemical treatment, conversion (to useful materials), and composting may be employed. In biological treatment, both aerobic and anaerobic processes may be used. The process configuration varies from lagoon, ponds, oxidation ditches, to plug flow reactor . Air pollution control, which is not a topic in this series, may also require consideration due to its greenhouse effect.
Solid-liquid separation technologies are used to separate the partial organic and inorganic solids from liquid manure. The goal is to reduce the solids content for subsequent handling and treatment, and to recover solids for further usage as fertilizer and/or other applications. Effective separation can lead to many benefits, such as reduction of organic matter in the liquid fraction, concentration of nutrients in the solid fraction, ease in transport and handling, reduction of odor emissions, reduction of size of the lagoon or storage pond, and flexibility for ultimate disposal and use of livestock waste.
The separated solids can be used for composting, soil amendments, animal feed supplements, or for generating biogas (methane). Composted material can have some applications, such as bedding in barns. The separated liquid fraction could be recycled as flush water or stored and land applied. A basic arrangement for a mechanical solid-liquid separation system is illustrated in Fig. 5.
Separation of solids from the liquid portion is normally achieved by using gravity or a mechanical device. Mechanical separation can be achieved via. screen, press, and centrifuge. The advantage of the mechanical separation is its higher efficiency, while disadvantages include higher energy consumption and difficulty in management. In addition, it may not be costeffective if used for small operations.
There are two characteristics of solids in liquids that are used as the basis for separation. One is based on the density difference between the solids and the water solution, while the other is based on the physical size and shape of the solids. A basic requirement for efficient separation is the continuous agitation of the manure. Otherwise, the relatively fast sedimentation processes that occur during storage can reduce its efficiencies [5,6].
Gravity settling is effective in a manure stream when it contains less than 1% total solids. Settling is typically accomplished through a series of sedimentation ponds or tanks. Y- and V-shaped gutters under slatted floors are useful for swine operations. The former is more difficult to build and clean than the latter, even though the operations are similar. The sideslope of the gutters is 1:1 and 0.75:1 for farrowing and nurseries operations, respectively [1,3-6].
In the screening process, solids in the liquid manure are collected on the screen while the liquids pass through. The separation efficiency is dependent on the size of the solids, physical properties of the screen (e.g., opening) and operating conditions (e.g., flow rate). Stationary screens, rotating drum screens, and vibrating screens are commonly used.
In addition to the above two types of separators, other separators use smaller screen sizes and pressure to "squeeze" the manure through screw press, belt press, or centrifuge. These processes can handle manure with higher solid content and are more efficient than typical screen separators; however, they often require more capital investment and operational costs.
Biological treatment is the most common and extensively used process for livestock and poultry manure wastes. Manure stored in earthen basins, pits, or tanks or spread on land undergoes biological reactions, which typically are not carefully controlled and take a long time. Therefore, well-designed and operated biological treatment systems become important for enhancing treatment efficiencies. The objectives of the treatment are stabilization of manure, removal of odor, removal of organic matter, nitrification, removal of nutrients, and recovery of energy (e.g., methane) [22,23].
Anaerobic decomposition is one of the most common natural processes and has been extensively used in waste treatment. In the absence of free oxygen, anaerobic microorganisms can decompose the complex organic compounds. If livestock manure is stored in a container at a temperature ranging from 0 to 150°C, the waste solids and dissolved organic compounds can be decomposed, yielding carbon dioxide, methane, ammonia, hydrogen sulfide, and a series of simple organic compounds. pH, temperature, presence of toxicity, and alkalinity are important to anaerobic processes. pH must be maintained above 6.5.
Manure is a complex mixture of carbohydrates, proteins, and fats, while anaerobic decomposition is a complex process involving numerous individual reactions and a variety of enzyme-excreting bacteria. The latter can essentially be considered as a breakdown process that converts complex manure constituents into simpler, more stable, and more easily used endproducts. The microorganisms responsible for the process experience survival, growth, and reproduction. The biodegradation can often be simplified and described as a three-stage process. The first stage is hydrolysis, which converts the complex organic compounds to fatty acids, monosaccharides, amino acids, purines and pyrimidines, and other simple compounds. The second stage is acid formation, in which compounds from the hydrolysis are converted to a series of simple organic acids (e.g., acetic acid). The third stage is the acid recovery stage, which involves a more sensitive group of bacteria, the methane formers, whose role is to metabolize the organic acids, converting them to carbon dioxide and methane.
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