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Milkhouse Wastes: Handle with Care |
KEVIN JANNI
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The newly revised Minnesota Feedlot Rules (7020) clarify requirements for properly treating and handling milkhouse wastes to prevent water pollution. The wastes can be surface-applied to cropland (a good way to recycle nutrients). They can also be treated and applied to an infiltration field. If you need to upgrade your milkhouse wastewater treatment and handling to comply with the new regulations, evaluate several options and select the one that best fits your farm. Systems you may want to consider include:
Each option has advantages and disadvantages. All require an investment, management changes, and maintenance. When choosing among them, consider initial and operating costs, long-term reliability, performance (in both cold and hot weather), maintenance, management, and space, soil, and slope requirements. Short-Term Storage/Land ApplicationWith this option, milkhouse wastes are placed in below- or above-ground storage and land-applied daily or weekly. Septic tanks are commonly used for below-ground storage. Single-day storage is generally not recommended because it lacks flexibility. The cost of this option depends on storage size. Also, if you handle manure as a solid you will need to buy a spreader for the liquid milkhouse wastes. You will also need a pump to fill or empty the storage. Agitation is needed occasionally to keep solids from building up in the storage. A major consideration is that this option requires land for application in wet weather, the cropping season, and winter. Land application under this and other options must meet nutrient rate standards, setback distances, and soil and slope requirements of the revised feedlot rules. Also, think about where you will store the spreader during cold weather to keep it from freezing up. Long-Term Storage/Land ApplicationLong-term storage with land application once or twice a year is commonly used by operations with long-term liquid manure storage. Manure storage capacity is increased to accommodate the milkhouse wastes, and the milkhouse wastes are simply added to the liquid manure storage. The option is less economical if you haul manure daily or handle manure as a solid because of the cost of the storage structure. Concrete or glass-lined tanks or lined earthen basins can be used for storage. Hiring a custom applicator eliminates the need to buy equipment for agitating and emptying the storage unit. Milkhouse wastes in a separate open liquid storage would likely emit noticeable odors in warm weather. |
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TIP: When selecting and sizing a milkhouse waste management system, be sure to consider future milking herd expansion. |
Organic Filter BedsSeptic tanks with conventional infiltration (drain) fields typically fail within five years of installation because the fats, bedding, and manure are hard to digest and tend to plug the soil in the infiltration fields. Organic filter beds are an alternative to conventional infiltration fields. In this system, milkhouse wastes are pretreated in a septic tank, where heavy solids settle out and lighter materials float to the surface and form a scum. The liquid in between is drawn off and applied to an organic filter bed, a flat area with a surrounding berm (approximately one foot high) filled at least two feet deep with high-carbon organic matter such as wood chips, sawdust, or straw. The organic matter provides a carbon source for the aerobic microorganisms and a surface for them to grow on as they treat the wastewater in the bed. It also helps prevent the soil from freezing so the bed can operate all winter. Organic matter must be added every fall. If properly sized and maintained, this system should work well in cold climates. However, detailed design, construction, and management guidelines are needed for Minnesota conditions. Soil conditions and high water table may limit its use in some areas. Treatment TrenchesWide, stone-filled treatment trenches are another alternative to conventional infiltration fields. They can be used on fairly permeable soils but not on highly permeable soils. Like the organic filter bed, this system uses a septic tank for pretreatment, settling of solids, and scum removal. The stone-filled treatment trenches are about three feet wide and filled with two feet of gravel. A four-inch perforated sewer pipe is laid near the top of the gravel. The stone-filled trench and sewer pipe are covered with fabric and soil backfill. Effluent from the septic tank is evenly distributed throughout the trenches. The gravel provides an aerobic environment for more treatment. Proper trench construction and septic tank maintenance are critical to long-term performance. Lime FlocculatorLime flocculator treatment of milkhouse wastes was adapted from the wastewater treatment industry. It removes solids from wastewater so they can be handled with conventional solid manure-handling equipment. The liquid can then be sent to a septic tank with an infiltration field. About three pounds of lime are added to 400 gallons of wastewater, mixed for about 20 minutes, and allowed to settle for two hours. Automated units for treating milkhouse wastes are available. The tank and equipment must be housed in a heated building to prevent freezing. |
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TIP: Minimize milkhouse waste treatment and handling system size and cost by reducing water use in the milkhouse. Save water by scraping floors before washing down, reusing pre-cooler water, avoiding use of excessive water for washing and rinsing equipment (follow manufacturer's recommendations), and fixing leaks promptly. |
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Other milkhouse wastewater treatment systems include grass filters, aerobic lagoons, constructed wetlands, and spray irrigation. While these are not prohibited in Minnesota, they generally are not suitable here because they don't work well in winter. |
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