Slurry Separation – A Systems Approach to Manure Management

The Livestock and Urban Waste Research (LUW) Team at the University of Illinois explains its manure management system, which involves the separation of the solid and liquid fractions of pig manure. From Swine Waste Economical and Environmental Treatment Alternatives (SWEETA).
calendar icon 1 January 2012
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Separation of municipal waste water into its solid and liquid components is a technology that has been utilized by municipal sanitation departments for decades. Removal of the biosolids fraction cleans the liquid portion sufficiently that the waste water can be added to the surface waters of Illinois and the US. Many city waste water treatment departments use polymer-assisted separation systems that combine the use of chemical flocculents, gravity belt thickeners and belt presses to remove the solids fraction from waste water.

The Livestock and Urban Waste Research (LUW) Team has adapted this technology to economically separate liquid swine manure into its biosolid and liquid fractions. This systems approach allows the biosolids fraction to be composted for ultimate use as either an on-farm or off-farm soil amendment while producing a liquid fraction with low odor, low solids and low phosphorus concentrations that can be irrigated as a nitrogen fertilizer for row crops.

LUW Team Separation System

All slurry pits in all the swine buildings at the ISU Farm farrow to finish swine operation are drained once or twice each week and recharged with 2-3 inches of separated effluent. The raw slurry is drained by an underground sewer line to the slurry processing building. The raw slurry is passed across a gravity screen-roll process separator to remove separable solids. The separated slurry is mixed with polymer and passed across a gravity belt thickener to remove suspended solids. The resulting biosolids are transported to the compost site, mixed with landscape waste and composted. The resulting separated effluent is stored in a slurry store® until land applied during the corn/soybean growing season via a center pivot irrigator.

Slurry Processed
1,067,237 Raw slurry, gallons
971,160 Separated effluenta, gallons
96,077 Biosolids, gallons
a91% collection rate

Slurry separation provides an efficient and cost effective system for managing the odor and nutrient overload associated with swine manure while improving animal welfare, reducing non-point source pollution concerns, and providing a source of beneficial soil amendments for crop production.

Land Application of Separated Effluent

The separated effluent, which makes up 90 per cent of the raw slurry volume, is transferred to a slurry store® tank or other appropriate storage tank where it is aerated before being land applied using center pivot or subsurface irrigation. Because the total solids have been reduced by more than 98 percent in the effluent, clogging in irrigation equipment and piping is not a concern. Additionally, no odor problems have been associated with the use of separated effluent even with above ground irrigation systems.

Land Application of Separated Biosolids

The biosolids, which make up 2-10 per cent of the raw slurry volume, are collected, composted and then land applied.

Component Characteristics

Both the composted biosolids and the separated effluent provide a comparable alternative to using inorganic fertilizers for crop production.

Separation Costs

Total separation costs, including equipment, labor, polymer and fuel, come in at less than 1.0 cent per gallon of raw slurry.

Separation Costsa
Equipment $100,000
Labor $15:hour .35/.34¢ SE/RS
Polymerb $1.60:lb .14/.13¢ SE/RS
Fuel $2.10:gal .15/.14¢ SE/RS
Main 2%:year .08/.07¢ SE/RS
Depr. (15yr) 6.7%:year .27/.25¢ SE/RS
acosts reflect 2007 prices
b560 mg:gal SE, 510 mg:gal RS

Separation/Application Cost (¢:g)a
Item Seperation Irrigation Total
RS 0.90 0.10 1.0
SE 0.99 0.10 1.09
RS Direct Injection= 0.70-1.70
acosts reflect 2007 prices

BMPs for Effective Slurry Separation

  • Frequent separation of slurry
  • Fresh slurry (no older than 7 days) is easier and lower cost (requires less polymer) to separate than anaerobic slurry
  • Not all liquid manure is the same, slurry composition can vary
  • Select a polymer specific to the slurry produced
  • Have adequate storage for separated effluent
  • Separation equipment should be housed in a heated building to allow year around processing
  • Match equipment size (gallons:minute processed) to slurry production
  • Have appropriate storage for separated biosolids or an adequate sized compost facility

Further Reading

- You can view the other articles in this series from SWEETA by clicking here.

January 2012
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