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accumulate in an ansa <br /> is lagoon. A lagoon can be designed with enough <br /> storage (Table 1 and F 1) to avoid having to re, any bottom sludge <br /> throughout its lift. The rate of sludge buildup can be�teduced by mechanical <br /> solids separation or gravity settling of the waste prig I to lagoon input. <br /> At some point the treatment capacity of most lagoons will be severely <br /> diminished by sludge accumulation. Table 4 r ports some of the <br /> nbArAntArigtiCS Of P01,11try AWL*robiC lagoon rludgj. Organic nitxogen <br /> compounds and phosphorus tends to accumulate in the sludge causing nitrogen <br /> levels to be 3 times higher than lagoon liquid levels a,d phosphorus to be up <br /> to 45 times higher than iiquid levels. In addition to Igber nutrient levels, <br /> the bottom sludge may also contain significant concentra ions of heavy metals, <br /> salts and other trace elements. These factors di curare rhA nAAA to 'hAVA. 111P. <br /> sludge analyzed and expert agronomic advice sought prior to land application. <br /> Lagoon sludge solids contents average almost 10 perlcenL requiring careful <br /> selection of removal equipment. The most frequently u4ed method consists of <br /> vigorous mixing of the sludge and lagoon liquid usi4 a chopper-agitator <br /> impeller pump or pto propeller agitator. The sludge mixture is pumped through <br /> a large bore gun-sprinkler slurry irrigation system onto cropland followed by <br /> soil incorporation. Another alternative consists of partial lagoon dewatering <br /> followed by sludge agitation and finally pumping the �lurry mixture into a <br /> liquid manure spreader for field spreading. A third <br /> ,alternative is lagoon <br /> dewatering followed by dragline dredging. The sludge may be hauled and <br /> applied directly to cropland by spreaders equipped to handle slurries, or <br /> stockpiled near the lagoon and allowed to further drain �efore spreading. <br /> AEROBIC LAGOONS <br /> Naturally AerobiSj {Oxidation bonds <br /> The main advantages of aerobic lagoons are that bacterial digestion tends <br /> to be more complete than anaerobic digestion with relatively odor-free end <br /> products. In naturally aerobic lagoons, oxygen diffusion occurs across the <br /> water surface. Algae also generate oxygen through photdaynthesis which takes <br /> place when sunlight can penetrate the water depths. Water depths are rather <br /> shallow ranging from 3 to 5 feet. Because of the needy for oxygen transfer, <br /> naturally aerobic lagoons are designed on the basis o� surface area rather <br /> then v*lume, Tht USDA Soil Conservation Service racorAmOndc a maximum daily <br /> loading rate in North Carolina of 50 pounds of 5-day biq6hemical oxygen demand <br /> (BODS) per acre of lagoon surface. Using these design criteria, Table 5 gives <br /> the surface area required to maintain naturally aerobic lagoon conditions. <br /> Table 4. Poultry Anaerobic Lagoon Sludge Characteristics <br /> B -d type <br /> ix Total Chemical Oxygen Nitrogen Fhosphorus Potassium <br /> Solids Demand, COD N P205 K20 <br /> 9s wb mg/L -------- -------- <br /> ---------------------- <br /> 5,5,8­1------0,152"---------6-6--- <br /> Layer mean 9.4 13000 <br /> std. dev, 7-7 - 2281 80 <br />