Less well known is “denitrification,” a so-called downstream technology that can be applied to digestion. This technology was developed in cooperation with the dairy cooperative FrieslandCampina and is already in use in the Netherlands. “People are less familiar with it, but that doesn’t mean the technology is still in its infancy,” Dejonghe says. “The first denitrifiers were commissioned three years ago and the installations are now ready for the third generation.”
Nitrogen stripping is a very complementary extension of pocket fermentation. The process requires heat, which the biogas plant can provide. Nitrogen (ammonia) is “striated” from digestion and converted to ammonium sulfate. “By operating in a gas-tight environment, ammonia cannot escape. This is released in a controlled manner in a denitrifier and washed away with sulfuric acid,” explains Dejonghe. The installation reduces the company’s nitrogen emissions by 65 percent.
Alternative to fertilizer
The produced ammonium sulfate can ideally be used as an alternative to fertilizers. Today fertilizers are purchased by the farmer. It is produced using Haber-Bosch technology, a chemical process that requires more than 1 percent of global energy production. So the fertilizer production on the farm is perfectly suited to circular farming.
In addition to this fertilizer alternative, a low-nitrogen liquid residue remains, which still contains particles of organic nitrogen. “If you run this on Earth, hardly any emissions are released. Plus, there’s no irritating odor. It’s basically pure organic nitrogen,” says Dejungi. “This way you gain a lot in terms of nitrogen emissions, you produce your own fertilizer and you have a lot of nutrients left over to grow the fields. In other words, the cycle is complete.”
Currently, four nitrogen boosters are connected to a Biolectric pocket fermenter, all installed in the Netherlands. “The facilities are for farm-scale dairy farms, on the order of 100 to 400 cows. Be warned, these are not high-tech farms, but regular cattle farms fully committed to sustainability,” emphasizes Dejonghe.
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