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Centrifuges a Good Option for Dairy Manure Nutrient Management

Dairy manure phosphorous extraction made easier.
Dairy manure phosphorous extraction made easier.

Some dairy farms in BC produce more manure phosphorus than is required by their crops resulting in the gradual buildup of surplus phosphorus in their soils. The reason for this buildup is that phosphorus is imported onto BC dairy farms in the form of feedstuffs and fertilizers, while a smaller amount of phosphorus is exported off farms in the form of milk. This imbalance increases if dairy herd sizes increase without an equivalent increase in farm land on which to spread dairy manure.

Due to this phosphorus buildup in some soils, an alternative to the current land application of dairy manure is required by some BC dairy farmers. This need is potentially becoming more urgent due to increased discussion concerning development of new regulations for agricultural waste.

A centrifuge was tested on seven dairy farms in the Fraser Valley to assess how much phosphorus can be extracted from dairy manure. This project was funded and supported by the BC Dairy Association, BC Agriculture Council, the seven participating dairy farmers, and by the governments of Canada and British Columbia through programs delivered by the Investment Agriculture Foundation of BC.

Centrifuges are capable of extracting phosphorus from dairy manure because most of the phosphorus in manure is bound to small solids. By using high speeds to create centrifugal force, centrifuges separate solids from liquids, extracting phosphorus from dairy manure into a solid product. This solid product, with dry matter of approximately 25%, is easier and cheaper to transport off the farm than dairy manure.

Used widely in a large number of industries to separate solids from liquids, from oil and gas to food and beverage processing, centrifuges are now being used on dairy and hog farms in Europe and the United States. Until now, testing on BC dairy farms has been limited.

Six of the test farms have scrape manure collection, while one farm has flush manure collection. On the six scrape manure collection farms, phosphorus extraction of 50-60% was consistently achieved, while highest extraction achieved on any one farm was 75%. For the flush manure collection farm, phosphorus extraction of 40-50% was consistently achieved.

During phosphorus extraction, some nitrogen and potassium are also extracted. While this isn’t ideal for most BC dairy farms, as nitrogen is often the limiting nutrient for most crops, this is simply a reality of the technology.

“These results clearly show centrifuges can be used to extract a high percentage of phosphorus from dairy manure,” explains project manager, Matt Dickson of Hallbar Consulting. “Furthermore, because the results were consistent across all seven farms, we are confident they can be achieved on almost every BC dairy farm.”

“Perhaps more interesting and relevant,” according to Environmental Farm Plan advisor and project co-ordinator, Dave Melnychuk, “is that based on the test results, if all seven participating dairy farmers were to use a centrifuge and transport the high-phosphorous solid product off their farms, they could expand their herd size by at least 15% and still be able to meet the requirements of a nutrient management plan, even without purchasing or renting additional land. As more quota is issued, herd sizes increase and land prices continue to rise, centrifuge technology starts to look promising.”

After centrifuge extraction solid product is easier and cheaper to transport.
After centrifuge extraction solid product is easier and cheaper to transport.

Unfortunately, the solid product produced by a centrifuge doesn’t seem to have much value, especially in the Fraser Valley. “As such,” cautions Dickson, “centrifuges rarely pay for themselves. Instead, they should be seen as a cost of doing business.”

“Due to the availability of many other sources of organic matter, such as poultry litter and spent mushroom compost, it looks like most BC dairy farmers may have to give the solid product away, or somehow transport it outside of the Fraser Valley,” explains Dickson. “However, the economic feasibility of transporting the solid product over long distances is currently unknown, and therefore more work is required before farmers should consider this option.”

While required next steps for technology adoption are still under discussion, this is exactly the type of work BC’s dairy sector supports. “The BC Dairy Association is always looking at ways to ensure dairy farming delivers a positive impact on our community,” says Holger Schwichtenberg, Mainland Milk Producer Chairman. “This is why we chose to support this study through the Dairy Industry Research and Education Committee.”

To request a copy of the full study or the study factsheet, readers should contact Matt Dickson at Hallbar Consulting Inc

[infobox title=’Mathew Dickson’]

Mathew DicksonMathew Dickson is an experienced sustainability professional with experience in industry, government and non-profits. With a strong background and keen interest in sustainable resource management, renewable energy, waste management and agriculture, Mathew works with clients to maximise their renewable energy, waste management and agricultural opportunities, or overcome challenges they face.



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