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Common Manure Handling Systems

Table 1. Manure Production per 200 Cows*
  Per Day (lb.) Per Year (LB)
Feces and Urine 24,100 8,800,000
Total Solids 3,360 1,230,000
Volatile Solids 2,800 1,020,000
Total N 126 46,000
Total P 26 9,610
Total K 812 23,600
*does not include wastewater and bedding
*estimates may increase with milk production

Cows differ considerably in the amount of manure they produce. Jerseys, for example, produce only 60% as much manure as Holsteins. With respect to many environmental rules, especially state regulations, however, no consideration is made for breed or body size. Composition of typical dairy manure is known (Table 1). Consideration must be given to the kind(s) of bedding used (Table 2) and the milking system (Table 3), both of which contribute to the amount of manure produced on a dairy farm.

Table 2. Bedding
  ft3/cow/day
Housing Type Chopped Straw Sawdust
Tiestall 0.8 0.1
Freestall 0.3 0.2
Loose Housing 1.1 ---
0.6 ft3 per cow is a good guide

 

Table 3. Wastewater
# Milking Cows gal/cow/d ft3
0 - 50 5 - 8 0.6 - 1.0
50 - 100 4 - 6 0.5 - 0.8
150 + 2 - 4 0.2 - 0.5
1 ft3 = 7.48 Gallons

Skidsteer loading a manure spreader

Skidsteer loading a manure spreader

 

A number of manure handling systems are utilized in dairy production. For tiestall barns, manure is collected in gutters behind the cows and removed from the barn as a solid material by a barn cleaner. Outside of the barn, the barn cleaner places the manure on a storage stack or directly into a manure spreader.

There are three types of manure handling systems used for freestall barns:

  1. Manual scraping,
  2. Flush systems, and
  3. Automatic alley scrapers.
Flush systems work very well

Flush systems work very well

Some freestall barns use slotted concrete floors above a pit, but these are quite rare in the U.S. With manual scrape systems, manure is scraped to the end of the barns by a skidsteer or mechanical loader with a scraping attachment. The manure is either stored temporarily in a solid stack, or loaded directly onto a manure spreader. Some barns are equipped with a freestall alleyway that is flushed with recycled wastewater to convey the manure to a storage pit or lagoon. Mechanical alley scrapers consist of a hinged v-shaped plough driven by a cable or chain. The plough is continuously or periodically dragged forward to draw manure to the end of an alley. When being pulled, the plough's blade splays across the entire alley between two curbs. After completing a pass, the chain or cable reverses direction and pulls the plough backward as the plough's blades fold together so as not to pull manure the opposite direction. Flush systems are comprised of a tank that delivers copious amounts of water to flush all manure off the alleys. Provided there is adequate slope along the channel and adequate water pressure from the tank, flush systems work very well. However, some concerns have been raised that a number of bacterial pathogens may be circulated through the barn by flush systems.


Storage containers

Storage Containers
Source: Al Sutton, Purdue University

Frequently manure from the freestall barn is stored temporarily in a storage pit and combined with more dilute waste from the milking parlor. Milking parlor waste often contains very little manure, but does have much residual milk from cleaning and may have various cleaning products as well. Manure from pits is agitated and then loaded onto a slurry wagon for application onto cropland, often with direct incorporation into the soil.

Effluent Drips Down for Collection

Effluent drips down for collection

Collection pits may also be used when solids are to be separated from the liquid portion of the manure. Solid separation can be mechanical, in which the liquid portion of the manure is squeezed though a screen. This provides a relatively dry solid that may be composted and perhaps even reused as a bedding material after drying. Sloped screen separators work by trickling the manure over a sloped screen so that the effluent drips through the screen with the solids sliding down for collection. Other mechanical separators draw an apron across the manure to force it across a screen. Concrete pit separators work by using a porous "weeping wall" in which the effluent is allowed to weep through the slots between boards or screens while the solids are retained. The solids then can then be removed as a semi-solid from the concrete pits. Composting is another option for solid manure management.

Settling Pond

Settling Pond

With sloping screen separators or other mechanical methods, the effluent may go into a settling pond to settle out even more solids before the effluent enters the lagoon. Many lagoons have been constructed with clay or compactible soil. In sandy or lighter soils, dairies must line the lagoons with compacted clay or synthetic liners.

New Technology

Recently, there has been much interest expressed in developing technology to utilize methane produced by anaerobic digestion of manure . As cost of the technology declines and pressure to manage manure and control odors on larger farm units increases, this technology will become more common. On some very large farms, these systems are used to generate electricity and hot water for the farm. Some are able to to sell electricity back into the grid through their local cooperatives. Cost of this technology remains too expensive for all but the largest producers at this time. Furthermore, anaerobic digestion should be viewed as a value-added process, but not as a solution to nutrient management difficulties, since nitrogen, phosphorus, and potassium remain in the effluent following digestion. Advantages appear to be in reduced energy costs, potentially reduced odors, and a more stable manure slurry.

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