Anaerobic Digestion Pre-Treatment Systems

McLanahan Anaerobic Digestion Pre-Treatment Systems remove grit and sand from manure streams, allowing dairy producers to ensure they have the cleanest material possible prior to their Anaerobic Digester.

How Anaerobic Digestion Pre-Treatment Systems Work

McLanahan Anaerobic Digestion Pre-Treatment Systems can consist of a Sand-Manure Separator (for dairies using sand bedding) and/or an Agricultural Hydrocyclone to capture sand and other grit materials from the manure stream.

The Sand-Manure Separator is the first step in the system and can remove up to 87% of sand and settleable materials from the manure stream. It consists of a rotating auger shaft inside an inclined washer box. Manure is pumped or augered into the feed end of the Sand-Manure Separator, where it is diluted with water. The heavier sand particles sink to the bottom of the tub and are conveyed out of the machine by the rotation of the spiral auger. The water, manure fibers and lightweight, fine-sand particles are removed via the overflow weirs surrounding three sides of the washer box.

The second stage of the Pre-Treatment System removes an additional 5 to 10% of the sand and grit from the manure stream. This is accomplished with an Agricultural Hydrocyclone. The Agricultural Hydrocyclone consists of a hollow, conical rubber lined cyclone. Overflow from the Sand-Manure Separator containing water, manure fibers and fine-sand particles is pumped into the Hydrocyclone. Centrifugal forces inside the Hydrocyclone cause the sand particles to the   walls of the cyclone, where they work their way down toward the discharge cone at the bottom. The liquid andmanure solids exit via the top of the Hydrocyclone.

If bedding on sand and using an anaerobic digester, additional sand (up to 5%) from the Hydrocyclone overflow can be removed by sending it to a sand lane to induce gravity settling. Sand lanes must be properly designed and managed to ensure optimal settling of the sand grains. Some manure fibers will also be lost to settling in the sand lane, reducing the volume of organic matter heading to the digester. The settled sand is scooped out of the sand lane, leaving the liquid portion for the digester.

With these three stages of separation, Anaerobic Digestion Pre-Treatment can recover up to 98% of the sand from a manure stream prior to the digester. The remaining 2% bypass sand is often so fine that it will remain suspended in the viscous manure and is not likely to settle out in the digester.

A fourth stage can be added to the Anaerobic Digestion Pre-Treatment System to form a closed-loop (circuit) operation. The liquid portion recovered from the sand lane can be processed through a Rotary Drum Separator, which recovers some of the course manure fibers by separating the liquid from the solids. The liquid portion discharged from the Rotary Drum can be used as dilution water in the Sand-Manure Separator in the first stage of the process, while the thickened manure or separated manure solids is sent to the digester.

Why McLanahan Anaerobic Digestion Pre-Treatment Systems

Anaerobic digesters often lack the means to remove any grit that is present in a manure stream – grit that can be problematic for digesters. Not only does grit accumulate in the digester, causing reduced tank capacity and reduced biogas output, but it can wreak havoc on the associated piping and mixing components. The accumulated grit then needs to be removed, which is a costly and time-consuming process that involves shutting down the digester and removing all the solids, liquid and gas. This cleanout process can take weeks to complete. After restarting the digester, even more time is required for it to reach full output.

McLanahan’s Anaerobic Digestion Pre-Treatment Systems remove sand and  grit ahead of the digester to lessen cleanout frequency, maintain tank capacity and maximize energy output.

McLanahan pioneered the use of mining-duty equipment as a means of sand-manure separation for the dairy industry. With proven high sand and grit recovery rates, these same Sand Separation Systems have been successfully used as anaerobic digestion pre-treatment systems to reduce costs associated with digester maintenance.

McLanahan Anaerobic Digestion Pre-Treatment Systems are designed specifically for the needs of your dairy, whether you have 100 cows or 100,000 cows. By partnering with McLanahan, you can transform your manure into a profitable revenue stream.

Bed On Sand And Make Use Of Anaerobic Digestion

Dairies wanting to utilize anaerobic digestors to produce methane from their manure stream have traditionally bedded on dried manure solids because sand can wreak havoc on digesters. However, sand is considered the gold standard of freestall bedding because it is an inorganic material that does not promote the growth of bacteria. It is moisture-wicking and non-absorbent to keep cows clean and dry. It also offers a cool, comfortable place for cows to rest and provides traction for cows to get up and down in the stall. Sand can also be recycled for reuse as clean bedding, reducing sand inventory and saving dairy producers money on purchasing new sand.

With Anaerobic Digestion Pre-Treatment Systems, dairies can realize the benefits of sand bedding while still being able to use an anerobic digester. Anaerobic Digestion Pre-Treatment Systems are comprised of sand separation equipment and are designed to remove as much sand as possible from the manure stream before it is sent to the digester. 

Frequently Asked Questions About Anaerobic Digestion Pre-Treatment Systems

Ask An Expert

Yes, dairies can bed on sand and still make use of anaerobic digestion! Dairy producers just need to ensure as much sand as possible is removed from the manure stream before it enters the anaerobic digester. McLanahan Anaerobic Digestion Pre-Treatment Systems can remove up to 98% of the sand for a manure stream, allowing producers to send a nearly sand-free effluent to the digester in addition to recycling sand bedding for reuse. Another best practice for bedding on sand and using a digester is to use concrete sand as bedding. Concrete sand contains minimal fine particles and will yield higher sand recovery. 

Anaerobic Digestion Pre-Treatment Systems can recover up to 98% of sand from a sand-laden manure stream. The first stage of the process is a Sand-Manure Separator, which recovers up to 87% of the sand. The second stage is an Agricultural Hydrocyclone, which recovers an additional 8% of the sand. The third stage is a sand lane, which recovers another 3% of the sand. The remaining 2% bypass sand has potential but is unlikely to settle out because it is often fine enough to remain in suspension due to the viscous nature of the manure. A fourth step uses a Rotary Drum to thicken the manure stream before anaerobic digestion by separating some of the liquid from the manure solids. This liquid can then be used as dilution water in the first stage of the process.

McLanahan Anaerobic Digestion Pre-Treatment Systems recover sand and grit from the manure stream ahead of digesters.

Features & Benefits
  • Bed on sand and still make use of anaerobic digestion
  • Recover up to 98% of sand from the manure stream
  • Save money and reduce inventory by recycling sand bedding
  • Reduce freshwater requirements
  • Designed specifically for your dairy
  • Simple to operate
  • Low maintenance

Need Some Help?

Our customer service team is here to help you 24/7. We can ship you parts, send field service technicians to your site and answer any questions you have. Whatever you need, we are here for you.