On a recent trip to the UK, I visited Lower Farm in Warwickshire, a dairy farm where they were separating out the solids, liquid and sand in the manure. It is common to see manure separation in Europe as a whole, primarily to just separate the liquid and solid fraction, however this was of interest as they were attempting to retain sand as a means of becoming more sustainable.
In picture 1, you can see the layout of the outdoor manure separating area. Picture 2 is a close-up of the NC Engineering separator, which is a roller and screen device. These models work on the principle of slurry being fed into the top of the unit through a spinning, perforated drum. The liquid passes through the holes in the drum while the solids gather and fall through into a collecting area, to the left of the separator.
This machine isn’t specifically intended for sand separation, but simply by the way it is designed, the sand falls through the screen with the liquid fraction. Without sand, the life expectancy of these separators is roughly 25 years and we would expect close to this given the lack of mechanical movement of the sand, but just gravity.
Picture 3 shows the sand and liquid then flow down a gradually sloping raceway. The liquid passes through a weeping wall into a lagoon and the sand remains, to be collected with a tractor loader once a week and stored outdoors in pile for between 4 and 6 months. During this time, dirty water continues to drain from the sand pile and into the lagoon.
After this time, the sand is moved into another, cleaner pile (picture 4), where it sits for a further 2 months, until it is stored ready for use in the stalls for bedding once again.
Whilst the owner admits this is a crude system, he manages to reclaim approximately 50% of the sand. The reason this is not higher is down to lengthy spells of wet weather, which means they wouldn’t bring the sand back into the barn for bedding.
Another advantage of separating the solids and liquid is that most of the degradable carbon is in the solid fraction. Research has shown that separating out the carbon from the liquid fraction reduces the potential for methane emissions. Methane is a greenhouse gas, with approximately twenty-five times the global warming potential, compared to carbon dioxide.
The approximate cost for this separation set up was £60,000 (CAD $96,000) and the owner claims he made that back in 1.5 years through savings in reclaiming the sand. There is also significant savings in manure transport costs. The sand adds a lot of bulkiness to the manure, resulting in more trips to the field to empty a lagoon. Less trips are also good for reduced GHG emissions from land application and is more labour efficient. Separating out much of the sand also adds to the life expectancy of the manure application equipment through less wear and tear.
Submitted by Dan Mosely, Perennia Dairy Specialist
Interested in learning more about manure management? Check out our upcoming webinar: Manure Management to Improve Nitrogen Efficiency, Soil Health and Reduce Greenhouse Gases coming up on January 31st from 12:00 – 1:30. Register here!