McLanahan Lists Best Practices for Dairies Using Sand Bedding with Anaerobic Digestion Systems
Many dairy producers choose to bed their cows on sand due to the many benefits sand provides. Traditionally, sand bedding has caused manure handling challenges, especially when used with anaerobic digesters and biogas plants since sand can settle in tanks and cause equipment wear.
Can I bed on sand and use an anaerobic digester?
While typically manure solids are the traditional bedding of choice for anaerobic digestion systems, sand bedding can be used on dairies with digesters. However, as much sand as possible should be separated from the manure prior to digestion.
Utilizing mechanical sand-manure separation equipment to separate the sand from the manure has proven successful on dairies over the long term.
Sand-manure separation as anaerobic digestion pre-treatment consists of four stages: primary sand-manure separation with a Sand-Manure Separator, fine sand recovery with an Agricultural Hydrocyclone, gravity settling with a sand lane and manure thickening with a Rotary Drum Separator. When using a washed concrete sand and with adequate process water, the first three stages of separation can recover up to 98% of the sand for reuse, and the fourth stage can increase the total solids going into the digester.
Here are some best practices for using anaerobic digesters with sand bedding:
1. Use a concrete sand for bedding.
Not only is concrete sand great for cows, but it also is great for separation. Because concrete sand contains minimal fine material, higher sand recovery is possible. This means less fine sand will bypass the Sand-Manure Separation System and end up in the digester.
2. Use a Closed-Loop Sand-Manure Separation System.
A Closed-Loop Sand-Manure Separation System is a system that relies on minimal water addition to achieve separation. It uses water separated from the manure to dilute manure to enable conveyance and/or separation. This is good for the digestion process, as it reduces the volume of liquid headed to the digester, and it ensures consistent system operation.
3. Use a sand lane to capture any remaining fine sand particles ahead of the digester.
Sand lanes capture a majority of the fine sand discharged from the Hydrocyclone using gravity to settle out the fine particles from the manure effluent. Removing as much fine sand as possible ahead of the digester prevents the digester from filling with unwanted sand that is challenging and costly to handle.
Using Sand-Manure Separation Systems and following these best practices, dairies can have all the benefits of sand bedding while at the same time handling manure in an environmentally friendly way.