The nutrient management manager at TeamAg in Lancaster County, PA describes his experience
with separated digestate on ten American farms with anaerobic digesters.
There are plenty of opinions about the properties of the digested, then separated, solids and liquids that are produced by a methane digester. Lots of conclusions, theories…and uncertainty.
In the United States, a country of only two hundred sixty agricultural biogas systems, the longtime nutrient manager at ten of those farms has some valuable observations. Jedd Moncavage’s base is Lancaster County, PA, the home of one of America’s very few digester clusters. A total biogas support industry has evolved in Lancaster including generator service, parts and plant operators. Just as important is the “knowledge sharing” that benefits all the region’s farms.
While hosting a visiting Chinese agricultural group, Jim Muir asked Jedd questions of interest to potential digester owners in the United States as well. His responses result from an education in soil science at Penn State, work at NCRS and most importantly, real-life experience, He has handled nutrient management at multiple farms with digesters over an eighteen year period.
Digested bedding solids and Mastitis reduction. (:37)
Increased “plant available” nitrogen, reduced phosphorus in liquid digestate and increased phosphorus in solid portion. (1:02)
Benefits of spreading liquid digestate including land absorption (:47)
Liquid digestate facilitates “no till” farming and weed seed reduction (2:17)
Meanwhile in Vermont… the Chaputs share much of the Pennsylvania experience described in the four videos above. Their American style complete mix design digester was installed in 2010 and currently supplies over $100,000 worth of bedding…for free.
These “digested solids” contain few pathogens so somatic cell counts and Mastitis rates remain low, however, Mike points out that bedding solids only work well if they are used fresh. He says “the sooner the better and the material should be in the stalls at our two sites on the same day or that night. If they sit for 2 days or more in a pile, pathogens and SSC can definitely build up and so the material should be discarded”.
Reg adds that while their digester and separator only processes the manure of the 1,000 cows at their main location, it produces much more than is needed there, so they can supply their other dairy of 400 cows as well.
Another interesting point is that the Chaputs are aware that some Phosphorus migrates from the liquid to solid fraction during digesting and mechanical separating. Nevertheless, the Phosphorus levels at the farm near where bedding is kept have not increased abnormally. This was confirmed by their nutrient management specialist and matches the experience of TeamAg (above) at their ten Pennsylvania farms.