ABC Farm is the first fully automated farm in City of XYZ. It occupies an area of 10.4 hectares. It houses 500,000 chickens in 16 layers houses (where the eggs are laid and collected) and 6 grower houses (where the chicks are reared). The daily production of eggs is about 290,000.
The mechanical washing operation and transportation heavily contributes to the pollutant load due to egg breakage. It is estimated that about 5-10% of the eggs are broken, spilling contents into the washwater. The total volume of egg washwater is small, only about 5-10% of the plant's total water usage; however, it contains a high concentration of pollutants.
The waste treatment process is illustrated in Figure 12. The first unit operation is the screening, a mechanized sloping stationary screen solid-liquid separation device shown in
Figure 13. It is used to retain solid waste such as poultry feathers, broken eggs, wasted feed, and manure. Solids separation may exclude as much as 50% of layer manure solids.
The screen is a wedge-wire screen and the screen surface is medium, ranging from 0.01 to 0.1 in. The device is specially designed to be in a triangular shape as this helps the solid waste to "slide" down the screen (through gravity) to the lower edge of the device where the solids are collected. The separated solids, due to the high nutritious value (broken eggs, manure, and feed), are then used as fertilizers. The effluent is transported to the anaerobic tank for further treatment. A completely mixed anaerobic activated sludge system is used. The temperature of the reactor is maintained between 30 and 38°C. Anaerobic processes can achieve high levels of organic removal, with an efficiency of up to 99%. The sludge produced in the anaerobic reactor is directed to the sludge digester, where the sludge is stabilized. Methane produced is collected and used to generate electricity to run the farm. The unremoved nitrogen and phosphorus is then directed to the VIP process for further treatment.
Odor from the lagoons is particularly severe when temperature increases to the point that biological activities become more intense. One method to reduce the odor is to reduce the loading rates, or to increase the treatment volume relative to organic loading. Lagoons in the warmer regions can be sized at higher loading rates because warmer water temperatures promote more rapid biological breakdown. Chemical and biological additives, masking agents, and other proprietary products can be used to improve lagoon performance, liquefy the accumulated solids and reduce odors. Another method is to add a lightly loaded, second-stage lagoon to an adequately sized primary anaerobic lagoon. The purpose of this second-stage lagoon is to further treat and store the effluent so as to lower the odor potential of the effluent. In this way, effluent can be used in land application or recycled as flushwater. For more detailed information on various biological treatment processes see Ref. 22-23.
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