Removing manure from freestall alleys

Flushing
Barn floors are sloped and water is delivered at a fast rate to erode sand and manure from alleys. The steeper the alley, the less water is needed. Use 2.5 to 4 percent (3 percent preferred) alley slope. Water can be pumped from a second- or third-stage storage at high rate (greater than 5 feet per second) directly to the alley or at a lower rate to a flush tank (high head pressure).

The flush tank is emptied by gravity at high rate (greater than 5 feet per second) into the alley. Flushing requires a large amount of added water and is prone to freezing in the alleys. Downstream handling systems must be designed to handle manure without settling sand until it is desired. Recycled manure storage water can cause odor problems in the barn and community.

Tractor/skidsteer alley scrape
A vehicle with a blade or half tire makes multiple passes to push manure to a reception area. No water is added to clean the barn. The downstream system is not so prone to sand settling. Equipment requires an operator, contributing to labor cost. Some owners prefer skidsteers because of their maneuverability while others prefer a small tractor to avoid damage to stalls, gates and buildings.

Vacuum tanker
A tractor or truck-mounted vacuum tanker is driven through the alley in one pass, and manure is sucked into the tank. Manure does not contact moving mechanical parts to cause wear. The tanker drives to a location on the farm where manure is treated, stored or field-applied. Downstream terrain or farmstead arrangements do not limit manure-handling design. No water is added to clean the barn.

The downstream system is not so prone to sand settling. Equipment requires an operator, contributing to labor cost. A vacuum pump is noisy. Tankers require periodic sand removal. Tanker weight can cause floor cracking (use a 6-inch concrete floor thickness).

Removing manure from barn

Gravity flow of flushed manure
Pipes or channels convey manure to the transfer system. High velocity (greater than 5 feet per second) must be maintained to avoid sand settling in the conveyance. Periodic sand cleanout may be necessary. There are no moving parts to wear.

Gravity flow with sluice gate
Manure and sand (no water) in a narrow channel or pipe is conveyed across the barn by gravity when a sluice gate at the end of the channel is opened. This requires about 10 feet elevation difference between the barn floor and high water mark of storage to work properly. Sand settling is minimized by emptying the channel soon after barn is cleaned.

Selecting sand with smaller particle size will reduce the rate of settling in the channel or pipe. Periodic sand cleanout may be necessary. There are no moving parts to wear. Do not push frozen manure into reception channel/pipe.

Cross auger
A horizontal auger mounted below the floor in a shallow channel conveys sand and manure to a reception area. There is little sand accumulation to clean out. There are minimal moving parts, but bearings require periodic replacement.

Flush flume
Recycled water from second or third stage of manure storage is pumped at 1,800 to 2,400 gallons per minute through a narrow across the barn channel as alleys are scraped into the channel. Velocity is used to erode manure and sand out of the channel. Use 5 to 8 feet per second liquid velocity for a half-filled pipe. Periodic sand cleanout may be necessary. There are no moving parts to wear.

Transfer to storage or treatment

Gravity through pipe or channel
Where terrain allows, manure can be moved to the next stage by gravity. Velocity must be maintained (greater than 5 feet per second) to avoid sand settling. Some systems try to maintain an empty pipe/channel when not being used to keep sand from settling in a full conveyance. Periodic sand cleanout may be necessary. There are no moving parts to wear.

Pump
Pumps are used to elevate manure to storage or treatment. Pumps are usually mounted in a reception pit which acts as a reservoir for the manure. Pit agitation or periodic cleanout is necessary to avoid rapid sand accumulation in the pit. Select a pump designed to provide a good service record when moving sand-laden manure.

Auger
An inclined auger is a special type of pump. It is generally a low- capacity device. There is little sand accumulation to clean out. There are minimal moving parts, but bearings require periodic replacement.

Sand removal treatment – mechanical

McLanahan sand-manureseparator machine
Sand-laden manure is metered into a hopper at a controlled rate from a reservoir tank. Recycled wastewater (less than 1 percent solids) delivered at the rate of 15 gallons per minute is combined with manure in the hopper. Compressed air is introduced to the hopper to promote mixing and separation of particles. Sand settles in the hopper and is removed by an inclined auger.

Clean water is sprayed onto the sand at a rate of 1 to 2 gallons per minute as it moves through the auger to wash out fine organic particles and dissolved organic matter. The spray water flows into the hopper to provide dilution water to facilitate sand settling. The manure/water mixture overflows the hopper and is delivered to further treatment or storage.

Removal efficiency will be in the range of 80 to 95 percent with coarser sand having the higher removal efficiency. Sand can be reused for bedding after several days of draindown and storage. Added water increases storage volume. There are minimal moving parts, but bearings require periodic replacement. The system should be protected from freezing.

Parkson Tru-Grit machine
Sand-laden manure is pumped from a reservoir tank into the top of this machine while recycled water from second or third stage of manure storage is pumped into the bottom. A mixing device within the cone-bottomed tank blends the manure and water. Sand that settles is removed from the bottom of the cone by an inclined auger. Liquid manure overflows from the top of the tank to flow to further treatment or storage.

Removal efficiency will be in the range of 80 to 95 percent with coarser sand having the higher removal efficiency. Sand can be reused for bedding. Added water increases storage volume. Minimal moving parts. Bearings require periodic replacement. System should be protected from freezing.

Accent Manufacturing machine
Slurry manure is pumped into a rotating drum screen. Liquids flow through the screen to further treatment or storage. Solids (a mixture of sand and manure particles) are moved through a roller press to better remove liquids. Water is not added to the system. Sand is not clean enough to be considered a replacement for clean sand bedding. This machine has been used to remove organic manure particles following other sand removal systems. Minimal moving parts. Bearings require periodic replacement. System should be protected from freezing.

HydroCyclone
Several companies offer a hydrocyclone as a post-sand removal treatment to remove the finer sand particles from the liquid discharge steam. Wastewater is pumped (at a tangent to the circumference) at the side and top of a cone-shaped cyclone separator. Sand particles are forced to the side of the cyclone and settle to the bottom where they are removed. The liquid manure overflows the top and flows to storage or further treatment.

Sand removal treatment – settling

Settling basin/tank
Sand-laden manure is introduced to a basin/tank and water is added from the milking center or precipitation. Sand and heavy organic manure particles settle to the bottom over time. These storages are often sized to represent about one-third to one-half the total manure storage volume. Concrete basin/tank bottoms and drive-in ramps are usually used to allow settled solids to be removed. Gravity flow or pumps are frequently used to decant the manure from the basin/tank to the second stage of storage.

Some producers agitate the contents of the basin/tank to improve water-manure mixing which facilitates sand removal. Mixing the contents of the basin/tank to entrain sand prior to pump-out has not been done very successfully as quite a large amount of simultaneous agitation is required. Consequently, most producers dewater the system before attempting to remove the sand/manure solids.

Front end loaders are a common method for removing the settled solids. After decanting most of the manure from the basin/tank, some producers have used highboy tractors with a blade to drive through and mix a thick slurry of sand and manure before pumping the mixture into a tank spreader. Manure entering the second stage of storage will carry some sand particles where they will settle. Some producers have used drag lines to remove sand from storages not designed for driving on the bottom. The sand/manure solids mixture is not suitable for reuse in stalls.

Sand traps
Sand traps are small shallow (3 to 4 feet deep) tanks used in systems where sand-laden manure is mixed with an appreciable amount of water used with a flume or flush transport system. The relatively large amount of water allows for rapid sand settling, thus a smaller chamber can get the job done. The residence time for the liquid is three to four minutes before it discharges through a pipe. Sand traps can be designed for up to 21 days of sand storage and can achieve 60 to 70 percent sand recovery.

J. Houle & Fils, Inc., a division of WestfaliaSurge, has designs for a sand trap system that allows for flush-flume water recycling. When sand trap tanks are located at the end of a flushed barn, the tank can be used as a short-term manure storage by scraping manure into the tank.

Weeping wall solids settling chambers
In the weeping wall system, flush water is introduced into one end of a long narrow chamber that has one long perforated wall. Sand tends to settle at the inlet end while organic solids tend to settle toward the far end. The water drains through the perforated wall. The weeping wall should be 15 to 30 percent porous. The maximum distance for water to drain to the weeping wall is 40 feet.

These systems are usually set up with two chambers separated by a drainage channel. The weeping walls face the drainage channel. Flush water is directed to one chamber while the other is being drained and emptied of solids. These chambers have concrete bottoms and drive-in ramps or removable walls at the far end for solids cleanout. Dewatering the chamber is done by gravity. The weeping wall system can achieve 60 to 70 percent sand recovery. However, much of the sand may not be reusable for bedding.

Sand settling lanes
Sand settling lanes are a very shallow version of the sand trap. With sand lanes, flush or flush/flume water containing sand-laden manure is introduced into a shallow, long and narrow channel (lane) at a high delivery rate. An energy dissipation system is usually installed at the head end of the lane to slow the velocity of the water and distribute the flow over the width of the lane. The bottom of the 12-foot-wide lanes should be sloped 0.2 to 0.25 percent. The water velocity slows to 1 to 2 feet per second in the lane which allows the sand to settle out while washing most of the organic matter from the sand.

After the excess water has been allowed to drain, ramps installed along the sides of the lanes allow front end loaders to drive into the shallow lanes to remove the settled sand. Many producers using this system install large concrete pads adjacent to the lanes to deposit the sand. The sloped pads allow drained water to reenter the lanes. The drained sand is often moved and mixed several times to condition it for reuse as bedding. When this is done properly, no feed particles are visible.

Because of the constant use of the sand lane throughout the day, two sand lanes work much better than a single lane. Two lanes allow one to drain down before sand removal. The shallow nature of sand lanes and the large surface area of the sand draindown pads expose the sand to freezing conditions. This system may have to be abandoned during extended periods of low temperatures.

Beach sand removal system
In this system, flushed sand-laden manure is directed onto the base of a gradually up-sloping concrete ramp. The energy of the flow forces the liquid up the slope. The energy dissipates and the water and manure solids retreat gradually down the slope much like it does on an ocean beach. The slow retreat leaves the sand deposited on the slope.

After the excess water has been allowed to drain, front end loaders drive onto the slope to remove the settled sand. Many producers using this system install large concrete pads adjacent to the beach to deposit the sand. The sloped pads allow drained water to reenter the channel used to remove the water from the system.

The drained sand is often moved and mixed several times to condition it for reuse as bedding. When this is done properly, no feed particles are visible. The shallow nature of the beach system and the large surface area of the sand draindown pads expose the sand to freezing conditions. This system may have to be abandoned during extended periods of low temperatures. ANM

—Excerpts from 2007 Midwest Dairy Expo Proceedings