Manure is the linchpin of biocircularity in dairy production systems. Nutrients in cow manure are recycled back to the land to produce crops, which are used as animal feed.
As herds grow and farms consolidate, this recycling can become challenging, both by the longer distances manure needs to be hauled, or by the fact that more manure is generated than acres to responsibly apply it to. These situations may necessitate advanced manure treatment systems to consolidate and partition manure nutrients to facilitate their transport or export from the farm. While still largely emerging practices, innovation and development over the last 10 years have started to make advanced manure treatments that consolidate and partition nutrients into more feasible solutions for large, consolidated dairy farms.
Advanced manure treatments systems are typically implemented sequentially, starting with solid-liquid separation. A screw-press, the most common primary separation system used by dairy farmers in the region, can reduce manure slurry volume by five to 15 percent, and capture around 45 percent of the total solids, 15 to 20 percent of the total organic and inorganic nitrogen (N), and 10 to 20 percent of the total phosphorus (P) and potassium. This alone may be an adequate reduction in volume and nutrients for some farms, and facilitate longer-distance pumping of separated liquids, or hauling of separated solids. Separated solids can also be composted, which may facilitate their export to other farms or potential marketing to consumers. Sequential separation (e.g. belt press, centrifuge) can further improve removal efficiency, achieving closer to 60 percent solids capture and doubling the nutrient recovery.
Treatments like composting and anaerobic digestion are important parts of the dairy manure treatment systems, but do not meet all the objectives of advanced manure treatment as they do not effectively partition nutrients nor substantially reduce manure mass or volumes. They can also be a source of nutrient losses, primarily in the form of ammonia, which is emitted during the compost process and from the open-air storage of digestate.
If primary separation cannot adequately reduce manure volumes or partition nutrients to address the disconnect between herd size and land base, additional practices and technologies can be utilized to preferentially target P or N recovery. Phosphorus, which is typically found in dairy manure as insoluble calcium or magnesium salts, can be recovered using chemically enhanced fine solids separation, ultrafiltration, intentional struvite (MgNH4PO4 ∙ 6H2O) formation, or biological removal. Intentional struvite formation and biological removal are not yet commercially feasible, due to higher calcium than magnesium content in dairy manure, which limits struvite recovery, and the challenges of maintaining P-accumulating algal and bacterial cultures. However, chemically enhanced fine solids separation and ultrafiltration are increasingly feasible on large dairy farms.
FINE SOLIDS SEPARATION
Chemically enhanced fine solids separation uses a ferric coagulant or polymer to clump together and settle out P-rich fine suspended solids. While early systems using dissolved air flotation were large, energy demanding, and did not produce a reliably stackable nutrient-dense solid, newer and more efficient moving disk presses can generate stackable solids (25 percent dry matter) containing 85 to 95 percent of the influent P and organic N. Solids may be over 20 lbs./ton of organic N and 15 lbs./ton of phosphate equivalent, leaving a low-P “tea water” containing 10 to 15 lbs./1,000 gal of N and potash equivalents. The primary challenge to these systems remains the cost of the ferric coagulant or polymer, which for some farms may be as high as $0.25/cow/day.
P RECOVERY
Ultrafiltration systems, where membranes are used to selectively remove P-rich fine solids, can reliably achieve 95 percent total P and 40 percent total N removal efficiencies. Select membranes can be used in series to preferentially generate higher or lower P and N streams. The low solids and nutrient content of the final permeate also lend itself to treatment by reverse and forward osmosis, where clean water, representing a third of the original manure volume, can be generated for use on farm or in some cases is permitted for discharge. Ultrafiltration is an energy-demanding treatment with substantial operating and maintenance costs currently feasible on dairy farms with herds in excess of 7,000 cows.
N RECOVERY
Several approaches can also be used to target N recovery following P partitioning, though vermifiltration is only emerging at the commercial scale. In a vermifiltration system, low-solids manure is trickled through a passive bed reactor with layers of wood shavings, composting worms, castings and other porous media. Nutrients are sequestered in worm castings as liquids are polished. Capable of capturing over 85 percent of N and P, vermifiltration has a large footprint, requires careful management, and due to its dependence on worms, are best suited for dairy production regions of the country, like California’s central valley. Other strategies like biological conversion of ammonium and nitrate to atmospheric nitrogen gas or ammonia stripping, where pH shifts are used on high ammonium post-digested manure to volatilize and then capture ammonia in an aqueous stream, have not been deployed commercially, though pilot studies are promising.
PLAN BEFORE INVESTING
Investment in advanced manure systems can be substantial and careful assessment of your need and ability to purchase, maintain, and manage these systems is essential. All advanced manure treatment systems require primary separation pre-treatment and thoughtful integration with the current farm manure system. They have an energy demand and often require three-phase power. Consideration must also be given to the handling and storage of new manure streams, how these can be utilized on-farm, or what their marketability is off-farm. Explore the vendors offering these technologies, visit farms using them, and discuss with your advisors the fit of these technologies to your farm, and if they will in fact address your consolidation challenges and needs to transport and export manure nutrients.
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This article appeared in PRO-DAIRY's The Manager in November 2025. To learn more about Cornell CALS PRO-DAIRY, visit PRO-DAIRY. |
