top of page

Manure Separation: Coarse Solid-Liquid Separation via Sloped Screens and Screw Press

alternative practice names:

Coarse Solids Separation; SLS

Coarse solid-liquid separation is a manure management technique that uses mechanical equipment to separate liquid and coarse solid manure materials before they enter manure storage. Coarse solids, such as undigested plant fibers and sand, are removed based on their particle size and density using mechanical action and pressure. This process allows the liquid portion to pass through the equipment while larger solids are retained.


Coarse solid-liquid separation results in two manure streams:


  • Coarse solids: The separated solids are high in organic matter and have a moisture content of 60-75%.

  • Liquid fraction: The liquid manure fraction that remains after coarse separation contains fine solids and is typically reduced in volume by 5-18% compared to the original slurry. This liquid fraction is high in nitrogen and potassium but lower in dry matter and phosphorus.


Some common mechanical coarse solid separation technologies include inclined screen/slopped screen, screw press, and roller presses/rotary drum screen.

When used, in what regions in the U.S. is the practice found: 

Northwest, West, Upper Midwest, Southwest, Northeast, Southeast

FARM SIZE 

When used, typically found on farms of the following sizes:

Over 500 cows

Case Studies.png

Practice Benefits 

Reduces build-up of solids in primary lagoons: By removing coarse solids before manure enters storage, farmers can significantly reduce the frequency of clean-outs. This is especially crucial for covered manure storage and passive covered lagoon digesters, where the cost of removing the cover is substantial.


Reduces the need to agitate manure in storage: Manure with few solids may not require mixing/agitation before being applied to the land. 


Nutrient management: The liquid fraction, known as separated liquids, is rich in nutrients like nitrogen and can be applied more precisely to crops as fertilizer. The solid fraction can be used separately and will capture about 10% nitrogen, 25% phosphorus, and 5% potassium. As a dry product, it can be transported to fields farther from the farm. 

 

Reduces volume for storage and transport: Separating solids reduces the overall volume of manure, making it more manageable for storage and transportation. 


Compatibility with transfer and irrigation systems: Removing solids from the liquid waste stream improves waste application by reducing clogging as manure is pumped through transfer lines, drag hoses, and irrigation equipment. 


Bedding material: Separated solids can serve as high-quality bedding material for livestock. This can enhance cow comfort and reduce bedding costs (see Bedding Management).


Prerequisite for advanced manure management technologies: Coarse and fine solid removal is essential for advanced manure management technologies such as ultra-filtration and reverse osmosis, which require a clean liquid fraction to operate effectively.


Diversified income: If the dried solids are not utilized on the farm, they can be composted and sold offsite.

Practical Insights.png

Implementation Insights

Site-specific or Farm-specific requirements 

farm-icon.png
  • Manure management: This practice is only applicable to farms that manage manure as a liquid or slurry.

Required Capital Expenditures (CapEx)

red-dollar-0.png
  • Separating system: The equipment best suited to separating coarse solids will depend on manure characteristics, total volume to be processed, throughput capacity, separation efficiency, and planned use of separated solids. If farms are using sand for bedding, it will need to be separated first via a different manure separation technique using either an inclined screen/sloped screen, roller presses/rotary drum screens, or screw presses (or some combination therein):

    • Inclined screen/sloped screen manure separator: This type of separator works by pumping diluted manure over a sloped or inclined screen. The liquid passes through the screen openings, while larger solids slide down and are collected at the base. It's effective for separating coarse solids from liquids, particularly when the manure has been diluted.

    • Screw press manure separator: A screw press functions by compressing manure inside a chamber, where a rotating screw pushes the material through a screen. This action squeezes out the liquid, leaving solids that are drier and easier to manage.

    • Roller press/rotary drum screen: A rotary drum screen separates solids from liquids by rotating a drum with perforated screens or wedge wire. As the manure passes through, the liquid filters out while solids remain on the drum and are conveyed for further processing. A roller press can be added to further reduce the moisture content of the solids by compressing the material.

  • Formed concrete: This is used for curbs, gutters, and basins as needed to perform tasks and to create a slab(s) for solid storage following separation.

  • Piping and pump(s): Pipes and pumps are used to transfer liquid waste to the designated locations.

  • 3-phase electric power: Farmers may need to upgrade power supply logistics to operate mechanical equipment. 

  • Roof or building enclosure: A new shelter may be required to protect equipment and store solids in cold weather until they can be moved to other storage facilities or utilized.

Required Operational Expenditures (OpEx)

orange-dollar-0.png
  • Equipment replacement: Screw presses often require new augers annually and the screens of sloped screens may need replacement up to three times per year. These replacement frequencies are influenced by factors like material type and volume processed.

  • Labor: Monitoring the performance of manure separation systems is important to prevent issues like clogging or equipment failure. Regular cleaning and lubrication help maintain the equipment’s efficiency. Additionally, the management of separated solids requires attention. In cases where storage capacity is limited, frequent removal of solids is necessary, often involving labor for transport to storage or utilization sites.

Implementation Considerations

implementation-complexity-1.png
  • Different types of manure: Farms that are accustomed to managing a single manure stream must adjust their nutrient management plans to account for two types of manure with different nutrient profiles and handling requirements.

Financial Considerations and Revenue Streams

FEDERAL COST-SHARE PROGRAM

Funding is available for this practice through USDA's Natural Resources Conservation Service (NRCS) Environmental Quality Incentives Program (EQIP).

Notes:

  • Check with the local NRCS office on payment rates and crop rotations relevant to your location.

  • To quality for EQIP funds, the dairy is required to obtain a Comprehensive Nutrient Management Plan (CNMP) to guide practice implementation.


FINANCIAL RESOURCES, TOOLS, AND CASE STUDIES

Research Results.png

Environmental Impacts

MAY REDUCE FARM GREENHOUSE GAS FOOTPRINT

Little scientific research directly evaluates the practice's impact on a farm's greenhouse gas (GHG) footprint. However, the removal of coarse and fine manure solids from liquid/slurry manure storage lowers the amount of organic matter and carbon available for methanogenesis, resulting in lower methane production potential. When separated manure solids are stored in predominantly aerobic conditions, emissions of ammonia and nitrous oxide may increase;¹ however, by eliminating the anaerobic conditions required for methane production, methane emissions are significantly reduced.


See research highlights below:

  • Fangueiro et al. (2008) found that separate storage of the liquid and solid fractions reduced CH₄ emissions by approximately 35% compared to the raw manure.

  • Aguirre-Villegas et al. (2019) showed that solid-liquid separation alone could reduce GHG emissions by up to 38% and that centrifugation was more effective than screw presses at separating solids.


IMPROVES WATER QUALITY

Solid-liquid manure separation supports farms in land-applying manure in a way that more closely matches crop demands with manure nutrient content. This is because the separation process allows for more precise management of nutrient application, tailoring the solid and liquid fractions to meet the specific needs of crops, thereby reducing the risk of nutrient over-application and subsequent runoff or leaching.


────────────────

¹ Amon et al. (2006) found that solid-liquid separation increased total NH₃ and N₂O emissions from storage and application by 77% and 19%, respectively. Conversely, Hai et al. (2015) observed no significant difference in N₂O emissions between separated liquids from unprocessed manure and reported that the separated solids show lower N₂O emissions than unprocessed manure in terms of the percentage of N applied. Neerackal et al. (2015) also found no significant difference in NH₃ emissions between raw manure and separated liquids.

REFerences

farm-assessment.png

Alignment with FARM Program

FARM Environmental Stewardship (ES) V2-V3 Alignment

FARM ES allows for users to specify their solid liquid separation in the manure section. FARM ES Version 3 offers an expanded list of solid liquid separators including; sand lane/gravity lane, settling basin, weeping wall, roller press, belt press, sloped screen, screw press, rotary screen or a custom solid liquid separator.

Contents

farm-icon.png
farm-icon.png
farm-icon.png
farm-icon.png
farm-icon.png
farm-icon.png
farm-icon.png

We're always eager to update the website with the latest research, implementation insights, financial case studies, and emerging practices. Use the link above to share your insights. 

We're always eager to update the website with the latest research, implementation insights, financial case studies, and emerging practices. Use the link above to share your insights. 

Contents

farm-icon.png

Practice Overview

Case Studies.png
Practical Insights.png
dollar.png
reference,png
Research Results.png
farm-assessment.png

Coarse solid-liquid separation is a manure management technique that uses mechanical equipment to separate liquid and coarse solid manure materials before they enter manure storage. Coarse solids, such as undigested plant fibers and sand, are removed based on their particle size and density using mechanical action and pressure. This process allows the liquid portion to pass through the equipment while larger solids are retained.


Coarse solid-liquid separation results in two manure streams:


  • Coarse solids: The separated solids are high in organic matter and have a moisture content of 60-75%.

  • Liquid fraction: The liquid manure fraction that remains after coarse separation contains fine solids and is typically reduced in volume by 5-18% compared to the original slurry. This liquid fraction is high in nitrogen and potassium but lower in dry matter and phosphorus.


Some common mechanical coarse solid separation technologies include inclined screen/slopped screen, screw press, and roller presses/rotary drum screen.

Practices and technologies

Manure Separation: Coarse Solid-Liquid Separation via Sloped Screens and Screw Press

alternative practice name:

Coarse Solids Separation; SLS