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accumulate in an anaerobic lagoon. A lagoon can bel designed with enough storage (Table 1 and Figure 1) to avoid having to remove any bottom sludge throughout its life. The rate of sludge buildup can bereduced Tay LneGtianical solids separation or gravity settling of the waste prio� to lagoon input. At some point the treatment capacity of most lagbons will be severely diminished by sludge accumulation. Table 4 reports some of the r3�arsarttaricrir_.s of poultry Ang*robic lagoon sludg . Orsanic nitrogen compounds and phosphorus tends to accumulate in the sludge causing nitrogen levels to be 3 times higher than lagoon liquid levels ad phosphorus to be up to 45 times higher than liquid levels. In addition to Igher nutrient levels, the bottom sludge may also contain significant noncentre}tions of heavy metals, salts and other trace elements. These factors di orate r.nA nAAA r.n bAVA rhe. sludge analyzed and expert agronomic advice sought prior to land application. Lagoon sludge solids contents average almosr 10 per6enz requiring careful selection of removal equipment. The .most frequently u�ed method consists of vigorous mixing of the sludge and lagoon liquid using a chopper-agitator impeller pump or pto propeller agitator. The sludge mix, ure is pumped through a large bore gun-sprinkler slurry irrigation system ant6 cropland followed by soil incorporation. Another alternative consists of partial lagoorn dew,aterit%g followed by sludge agitation and finally pumping the Llurry mixture into a liquid manure spreader for field spreading. A third (alternative is lagoon dewatering followed by dragiine dredging. The sludge may be hauled and applied directly to cropland by spreaders equipped to handle slurries, or stockpiled near the lagoon and allowed zo further drain �efore spreading. AEROBIC LAGOONS i t Naturg lly Aerobic Oxidation Ponds) The mart advantages of aerobic lagoons are that bacIterial digestion tends to be more complete than anaerobic digestion with relatively odor-free end Products. in naturally aerobic lagoons, oxygen diffusjion occurs across -che water surface. Algae also generate oxygen through photdsynthesis which takes { place when sunlight can penetrate the water depths. W7 ter depths are rather k shallow ranging £zoxn 3 to 5 feet. Because of the needl for oxygen transfer, p naturally aerobic lagoons are designed on the basis of surface area rathar than v*lume. Tlzc USDA Soil, co-nEervation Service rccosdmcnd-a a maxim= daily ' loading rate in North Carolina of 50 pounds of 5-day bio;chemi.cal oxygen demand (BOD5) per acre of lagoon surface. Vsing these design 6riteria, Table 5 gives the surface area required to maintain naturally aerobic lagoon conditions. Fable 4. Poultry ,Anaerobic Lagoon Sludge Chaslacteristics Bird type Total Chemical Oxygen Nitrogen Yhosphorus Potassium Solids Demand, GOD N P205 K20 *wb mg/L -------- ----- •--'------------- -------- Layer mmean ------- _-- 13000 �+__ . 5aB 2015 266 Std. dev. 7-7 - 212 281 Bo i