Effective Methods for Handling
Sand-Laden Dairy Manure

Brian J. Holmes
Department of Biological Systems Engineering
University of Wisconsin-Madison

Dairy cows must be kept clean, dry and comfortable to remain productive. When the udder is kept clean and dry, the incidence of udder infection (mastitis) from environmental organisms is kept to a minimum. Cows with healthy udders produce more and higher quality milk for which the dairyman receives more income. Dirty udders require more cleaning effort prior to milking. This increased cleaning labor and equipment run time increases the cost of harvesting milk. Keeping cows cleaner helps to reduce cow preparation time prior to cleaning. Well-managed sand based stall beds are very effective at keeping cows clean.

Comfortable cows will behave in a more natural manner and will not be limited in productivity by their environment. One aspect of dairy cow environment is the stall bed and the walk alley of freestall barns. Sand based stall beds are preferred by cows over many of the other alternatives. The softness of the sand encourages cows to remain in a lying position for extended periods of time. Cows, which have access to a comfortable stall, will spend more time lying in the stall and less time standing. Research has shown that blood flow rates to the udder increases in a lying vs. a standing position. Blood flow rate to the udder is related to milk production. Sand based stalls provide good footing during rising. Good footing increases a cow's confidence in the use of the stall, which encourages future stall use.

Sand kicked from the stall increases traction on slippery manure coated concrete alleys. The improved traction allows cows to confidently move to feed bunks and waterers as well as express estrus. Each of these behaviors has significant impact on animal productivity with ultimate impact on profitability. The amount of sand kicked from the stall depends on many factors including: sand type and particle distribution, frequency of sand addition, ratio of cows to stalls, method of placing sand in stalls and method of armoring stall base. Stowell and Bickert (1995) reported 60% of dairymen using between 2 and 8 cubic yards of sand per stall per year.

All of these benefits attract dairymen to consider sand-based stalls. However, there are drawbacks to handling sand-laden dairy manure. Sand is abrasive and wears equipment at an excessive rate. Alley scraper cables, chains and blades are worn quickly. Centrifugal pump housings, impellers and bearings wear rapidly. Propeller type pit agitator blades are rapidly worn. The high-wear rates increase the cost of manure handling compared to where no sand is used.

When sand-laden manure is stored, sand settling occurs. The rate of settling increases with increasing sand particle size and decreased manure viscosity. Much of the sand will settle where milking center wastewater and/or precipitation are mixed with the sand-laden manure. This is an important design consideration when deciding where to introduce milking center wastewater to the manure handling system (Wedel and Bickert, 1996).

The preferred method for removing sand-laden manure from freestall alleys in northern climates is a rubber half-tired scraper mounted on a small tractor or skid steer. The tire is not worn as quickly as a steel blade. Flushing systems are more popular on large dairies in warmer climates.

Many of the sand-laden manure handling problems can be avoided by not using any storage. Loading manure into a spreader with a push-off ramp, bucket or manure auger with subsequent field spreading eliminates the problems of moving manure into and from storage. Where the practice of daily haul is allowed and surface water quality can be protected, this is probably the lowest cost, most easily managed system of handling sand-laden dairy manure.

The manure should be moved to storage as quickly as possible to avoid sand settling in the handling system. Systems which satisfy this criteria include: scrape over a wall to top load the storage; scrape manure into several stand pipes which bottom load directly into the storage; narrow channel with gate controlled discharge into gravity flow pipe to storage; small capacity pump chamber. A heavy duty, horizontal cross auger with wood bearings is being used on at least one farm to move manure across the barn to a pump.

Locating manure storage at some distance from the barn requires a transfer system that will not be impaired by manure settling. Pumping manure at high velocity through small pipe can keep sand from settling during pumping and can re-entrain sand which may settle during the off cycle. This system will require sand with smaller particle size.

Gravity transfer through an 18-24 inch diameter pipe with a gate valve control at the intake works well when there is 10 feet of head between the high water mark of the storage and the barn floor. When the gate is opened, manure rushes through the pipe, keeping sand from settling in the pipe and keeping sand from sealing the discharge end of the pipe in the storage. Where settling would occur in a pipe (low head site), open and closed top box culverts can be used as an alternative to a pipe to transfer manure by gravity. The box culvert is sized to allow a front-end loader to drive from the storage into the culvert to remove the settled sand. The culvert can extend across the width of the barn to form a reception pit. Some method of limiting the effects of freezing in the box culvert is often beneficial to keeping the system operational in cold weather. Covers on the manure entrance opening to the box culvert can limit wind blowing through the box culvert. Carpet, curtain material and wooden doors are used at the discharge of the culvert to prevent wind from entering the box culvert. These closures must be flexible enough to cope with a rising manure surface that can be frozen. Sand accumulated in the box culvert is removed after the liquids are removed from the storage by driving a front-end loader into the culvert. Efforts must be made to protect the equipment operator from the hazards of working in a confined space. Manure gases and lack of oxygen pose a serious threat to the operator. Self-contained breathing equipment should be used in addition to forced ventilation of the box culvert. The forced ventilation maintains oxygen, removes loader carbon monoxide, hydrogen sulfide and carbon dioxide and minimizes the potential for methane gas explosion.

Most of the sand settles close to where the manure enters the storage. Adequate storage space must be provided for the sand so it doesn't interfere with delivery of manure to the storage. Thus, it is better to direct a discharge pipe through a long wall or a comer than through a short wall of the storage. Top loading manure should allow for multiple push in points to accommodate freezing manure and/or accumulated sand that could prevent manure loading as the storage fills.

Those who use a single large storage for sand-laden dairy manure find sand covering the floor throughout, but the vast majority of sand accumulates near the intake point. Trying to agitate this sand into suspension for pump out requires continuous agitation while pumping. Otherwise the sand will settle in areas not being agitated. A better solution is to pump out the manure solids and liquids and remove the sand separately. Methods for removing the sand include a front-end loader, a dragline or a dredge. The dredge may require a supplemental source of liquid to effectively remove the sand. The extra liquid can come from a separate manure or milking center storage.

Some producers have attempted to devise systems for removing sand from manure before moving it to storage. The techniques that have been tried can be divided into two categories: separation equipment and settling chambers. MeLanahan Corporation, Hollidaysberg, Pennsylvania, has introduced an aerated grit chamber type separator. This system uses water addition to encourage sand settling along with air addition to encourage manure solids removal. A final water spray is used to remove fines from sand being augured from the bottom of the grit chamber. Research on this technology was reported by Wedel and Bickert (I 995).

Inclined screens can remove some sand along with some manure solids but work best with flushed manure. The holding tank prior to pumping the flushed manure over the screen should be designed for convenient sand removal. Much of the sand will settle from this dilute waste in the holding tank. Access by a front-end loader is desirable.

Some dairies, using flushing in warm climates, design shallow settling basins in the conveyance moving flushed manure to the storage. The settled sand is removed with a front-end loader. Work by Burcham, et al. (I 997) showed the settling basin to be much more effective at removing sand from flushed dairy manure than was an inclined screen.

In an attempt to separate the sand from the manure containing limited dilution water, some dairymen have constructed a settling chamber with liquids overflowing into storage. The settling chamber is sized to bold the settled sand for an extended period and yet large enough to minimize sand spillover into the storage. The settling chamber should be small enough to be conveniently agitated if sand pump-out is planned. Sand pump-out or removal with a dredge will probably require a supplemental source of liquid. A separate milking center wastewater storage or manure storage can provide the supplemental liquid. A ramp and driveable bottom is probably a good investment for a sand-settling chamber.

The overflow structure from the sand-settling chamber into the storage must accommodate freezing conditions and solids accumulation. One method of accomplishing this is a square notch weir in the top of the wall or berm separating the settling chamber from the storage. It is also useful to prevent erosion of the soil embankment.

Sand-laden manure is moved to the field by pumping through hoses and into tank spreaders. Sand will settle in tank spreaders, requiring periodic clean out. Hose lines need to be cleaned as well. Sand can be hauled to the field in dump trucks as well.

Sand based stalls are very comfortable for cows. The sand helps to keep the cow clean which reduces the incidence of mastitis and speeds milking throughput. Sand entering the manure causes handling problems for many conventional manure handling and storage systems. Several methods for handling sand-laden manure have been developed which help to reduce some of the problems encountered with sand-laden dairy manure.

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