Dairy: You can handle sand-laden manure

Bedding stalls with sand isn’t an obstacle if manure-handling systems are designed and managed with sand in mind.

For all of sand bedding’s benefits to cow comfort, it has traditionally been challenging to contend with in manure-handling systems. Sand bedding is a mixture of two different materials: Manure, a pumpable material, and sand, a stackable material, produces a mixture that can’t be readily pumped or stacked. (See Not all sand is the same).

Manure’s relative flowability typically determines manure-handling methods. Flowability standards suggest that manure at 35% solids content (bedded pack manure) is stackable and can be handled as a solid. But at 35% moisture, sand-laden manure isn’t stackable or readily pumpable because sand doesn’t absorb liquid like organic bedding does.

Solutions that work

The traditional challenges to handling sand-laden manure stem from using systems designed for materials other than sand. Until recently, equipment hasn’t been available to dairies to handle sand’s abrasiveness.

Compared to manure-handling equipment, sand-handling equipment is constructed with abrasion-resistant alloys rather than mild steel. It uses large tolerances that prevent sand grains from grinding between metal surfaces. Standard manure equipment, on the other hand, relies on close tolerances and high speeds.

Four traditional disadvantages of handling sand-laden manure can be solved with the right equipment matched to the type of sand being used:

PROBLEM: Increased load and wear on alley cleaning equipment.

SOLUTION: Rubber scraper blades work best to clean alleyways when sand is used as bedding. They’re durable, can withstand sand’s abrasiveness and create less wear on flooring surfaces than steel scraper blades.

With alley scrapers, select units designed to handle the increased load and wear resulting from sand-laden manure. For better wear, select heavy-duty scrappers with fewer moving parts. Retrofit steel scraper blades with reinforced hard rubber.

PROBLEM: Accelerated wear on equipment that mechanically moves manure to storage or separation areas.

SOLUTION: Properly designed and installed pumps and horizontal augers can effectively move sand-laden manure. Select equipment manufactured from abrasive-resistant steel components. This equipment should operate at low rotational speeds – RPMs – to increase equipment wear resistance. Quality equipment will minimize contact of steel-to-steel moving parts.

Centrifugal pumps can be used but since they generally operate at high speeds and small clearances, they’re susceptible to wear and clogging.

Piston pumps are better suited to handling sand-laden manure because of their large intake and discharge lines and few moving parts. But since piston pumps don’t provide a continuous high velocity flow, pipes may clog. Where pump discharge pipes are buried, space clean-outs liberally – every 60 feet – throughout the system. Sand particle size makes a big difference in how this equipment functions.

Horizontal augers, designed to be wear-resistant, potentially eliminate the need to “turn” or “chase” manure out of barns. Horsepower requirements range from 5 to 15 hp, depending on auger length, usually limited to 132 feet. Multiple horizontal augers can be positioned end-to-end or piggybacked to exceed that length.

PROBLEM: Clogged pipes and channels.

SOLUTION: Gravity flow of undiluted sand-laden manure is never recommended because sand particles settle and clog pipes and channels.

If the velocity of the liquid required to keep the largest sized sand particles suspended is maintained, sand-laden manure that has been diluted by flush cleaning or flush-flume conveyance can be gravity flowed. Consult an engineer for specifics on pipe slope for a given channel size and water-flow rate.

Designing a system to handle the particle size of the sand being used is critical to the effectiveness of this, and all, sand-manure handling systems.

PROBLEM: Separating sand from manure.

SOLUTION: With proper separation techniques, the sand fraction can be reused as bedding and the manure fraction pumped to a site for further processing or to remote storage where it can be stored long term. It can be irrigated or spread onto fields. Either method reduces field compaction compared to spreading raw sand-laden manure.

Two sand separation systems work well:

     * Gravity separators rely on sedimentation where water is used to separate materials based on their
       specific weight and size. Sand traps, used exclusively with flush cleaning or flush-flume systems,
       function by slowing the water velocity to less than 1-foot-per-second for a retention time of
       approximately one-minute. Course sand grains and some manure settle. Sand traps must be emptied
       regularly to avoid sand accumulation. The type of sand determines how much of it is captured. Sand
       with large quantities of fines isn’t recommended since fine particles can remain suspended with manure
       that passes through the trap. Since sand recovered from a sand trap contains some organic material,
       it’s generally not suited for reuse as bedding.

     * Mechanical sand-manure separators differ from mechanical manure separators. The sand separated
       from manure in sand-manure separators can be reused as bedding. Manure separators separate
       manure solids and some sand from water.
        An inclined auger usually delivers material to a sand-manure separator.
        Once in the separator, it’s mixed with air and recycled water to suspend the manure solids. Sand
       settles in the separator and is recovered by a mining-duty auger. Sand, discharged at 10 to 12%
       moisture with less than 2% organic matter, can be reused for bedding.
        The method works best with course-grained sand that has minimal fines such as concrete or mason
       sand. Manure discharged from mechanical separators is relatively sand free and can be pumped or
       gravity flowed to storage.

Not all sand is the same

The gradation of sand differs. When deciding what type of sand to use, consider what works best in stalls and with your manure handling system.

For bedding material, sand with fewer fines, such as concrete and mason sand, is preferred. This type of sand more readily conforms to a cow’s body, provides better drainage, requires less stall maintenance and doesn’t adhere to cows’ bodies like sand with more fines. Sand with fewer fines can also be separated from manure with either mechanical sand-manure separation or sedimentation systems.

A sieve analysis quantifies sand samples with the results plotted on a graph to determine gradation. (See graph.) Sands with high amounts of fines have a higher percentage of particles passing through the larger screen openings of the sieve. This results in graph plots with increased horizontal sections of the curve at the larger sieve sizes.

Sands with less fines have more material retained on the larger sieve openings, resulting in a gradation plot with less of a horizontal curve at the larger sieve openings.

Reputable sand supplies can supply sieve analysis. Or you can have an analysis run on a sample of your bedding material.

By Curt Gooch and Andrew Wedel
Cornell University PRO-DAIRY program
Published at DairyBusiness Communications newsletter

^{* Curt Gooch is a professional engineer in Cornell University’s department of biological and environmental engineering. He heads up the dairy facilities component of the PRO-DAIRY program.

* Andrew Wedel is a professional engineer with the McLanahan Corporation located in Hollidaysburg, PA.}

Communities in English

Communities in Spanish

Communities in Portuguese

Dairy: You can handle sand-laden manure