Odor Control 13

Treatment Lagoon Options

Unlike manure storages, lagoons are designed to treat (i.e. reduce the strength) and store swine manure. Lagoons can be designed to provide aerobic or anaerobic treatment.

Aerobic Lagoons

Aerobic microorganisms require free oxygen in the manure. Biological oxidation converts the organic matter in the manure to carbon dioxide, water, and microbe cells. Oxygen must be supplied mechanically to maintain the required level of dissolved oxygen in the manure for treatment.

The main advantage of an aerobic treatment lagoon for swine manure is very low odor. However, the high energy requirements of traditional aerobic treatment lagoons made aerobic treatment uneconomical for livestock manure. In the last few years, researchers, and swine producers have had a renewed interest in aerobic treatment of swine waste. Recent research has shown that the amount of aeration required to control odor is much less than required for significant treatment of the manure to reduce the biological oxygen demand. The new aerobic technologies include: low-rate aeration, pulse aeration, liquid-solid separation prior to aerobic treatment, and aerobic treatment following anaerobic treatment. Many of these new technologies are still in the development phase, and additional on-farm research is needed.

Anaerobic Lagoons

Anaerobic microbes decompose manure in an oxygen free environment. Anaerobic microbes dominate the microbial population in deep portions of an anaerobic lagoon. In the two to three feet near the surface facultative microorganisms are often present. These microbes can thrive in either an aerobic or anaerobic environment. Anaerobic lagoons can be used to decompose more organic material per unit volume than aerobic lagoons and at a lower cost. For this reason, the majority of the livestock waste lagoons in the United States, and South Carolina are anaerobic. The other advantages, and the disadvantages of anaerobic lagoons are pointed out below.

Other anaerobic advantages: (1) The long storage periods needed for biological treatment provide the flexibility needed to apply the liquid effluent to cropland before and while the crop is actively growing. (2) A large portion of the nitrogen is lost to the atmosphere thus reducing the land area needed for utilization of the remaining nutrients in the effluent. (3) Effluent can be recycled for use in flush or pit-recharge, gravity drain buildings. (4) The high degree of stabilization can reduce odors during irrigation of effluent as compared to waste storages. (5) A properly sized anaerobic lagoon can provide solids storage for long periods of time.

Other anaerobic disadvantages: (1) Foul odors can be given off from the surface whenever the biological activity is small relative to the loading of the lagoon. (2) Anaerobic treatment of manure converts organic nitrogen to ammonical forms that can be lost to the atmosphere. Therefore, a great deal of the fertilizer value of the manure is lost. (3) Sludge (a mixture of degradable and nondegradable solids) will accumulate in the bottom of the lagoon. If this sludge is not periodically removed and spread on cropland the treatment volume of the lagoon can be greatly reduced. The result can be high odor. The amount of cropland needed to apply lagoon sludge at agronomic rates will exceed the amount of land used for application of the effluent. (4) Much of the phosphorous, potassium, and valuable organic matter in swine waste is contained in the sludge. If the sludge is stored for 10 to 15 years these valuable soil amendments are not available for use in crop production.

The amount of odor that is emitted from a lagoon is highly variable. The primary factors that influence the amount of odor released are: Management and startup, Temperature, Loading rate, and Ration.

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