A variety of sand separation and cleaning technologies have been used to separate and clean sand that has been used for free stall bedding. These techniques rely on gravity and sometimes centrifugal forces, or maybe a combination of the two, to differentiate sand from the water and other particles in the manure. It’s fairly common that a properly designed sand separation system can recover up to 90% or more of the bedding sand from the manure. This recovered bedding sand contains varying amounts of moisture and is usually stacked and allowed to dewater for weeks or months before reintroducing back into the stalls. During this time, money remains tied up in sand inventory.
Why Is It Important?
Sand piles that are allowed to dewater can represent a significant investment in sand volume.
Additionally, these sand piles are routinely moved and restacked to facilitate dewatering, which takes machine and man hours. In most regions, regulations require that the sand is stacked on a concrete pad so the leachate can be collected and diverted to the manure storage(s).
Benefits of Dewatered Sand
Another option for dewatering sand is to mechanically remove the water from the sand as it comes off the sand separation system. This can be accomplished with what is commonly referred to as a dewatering screen. Dewatering screens mechanically remove free water from the sand and produce a drip-free sand product that is commonly reused within several days.
One of the most obvious benefits of mechanically dewatering sand is the immediate reduction in moisture. Separated bedding sand typically contains 20-30% moisture as it comes from the separation process. Immediately putting that sand through a dewatering screen reduces this moisture by up to 40%. This yields a sand product that will readily stack with minimal water leaching from the pile. This is important for several reasons. The sand can often be reused immediately. There is no need for large stacking areas to contain the recycled sand and leachate. The sand also needs little or no conditioning, which means less operator interface. All this equates to less time and money spent on recycled sand.
The benefits of dewatered sand go further than just having drier sand, less inventory and smaller stacking areas. As water travels out of the sand, it carries with it fine manure particles – measured as volatile solids (VS). These manure fibers act as sponges, which hinder dewatering, and become the food for any bacteria that may be in the sand. Sand that is mechanically dewatered is not only drier, it is also cleaner.
How Does It Work?
A dewatering screen contains an inclined vibrating screen deck. Wet sand is fed onto the screen deck, which is inclined toward the discharge point. Two counter-rotating motors create a linear motion to the deck, which throws the sand uphill, toward the discharge. As the sand is accelerated up and forward, water and fines begin to drain through the sand and screens. This motion rapidly repeats itself, causing the sand to move toward the discharge. A discharge weir at the end retards the sand and determines the bed depth. The dewatered sand discharges over the weir, while the separated liquid is directed away.
Dewatering screens are available in different sizes depending on the required capacity of the system, with the largest screens capable of more than 200 tph. These capacities are dependent on the type of sand being processed. Sand composed of larger particles will dewater faster and easier than sand composed primarily of small particles.
Who Can Benefit?
Any dairy producer who beds with sand and manages a sand separation system can benefit by adding a dewatering screen to their system. In a mechanical sand separation system, the sand is discharged from the sand-manure separator directly onto the screen deck of the dewatering screen.
Sand dewatering screens can quickly and positively affect the recycled sand quality of a dairy by reducing the water and VS content of the recycled sand. This improves the sand quality as well as reducing sand inventories, labor interactions, and sand stacking areas.