114 which is rich in CO2, goes to the greenhouse. The ammonia in this air is removed by a biological air scrubber (with wood chippings), that has been placed between the building and the greenhouse. After being fermented, the manure is separated into a solid and a liquid fraction (digestate). The solid fraction is spread on the land. After being separated in a compactor, the liquid fraction is also used as fertilizer for the duckweed. The duckweed is fed to the calves, thereby completing the closed cycle. Duckweed needs nitrogen (N) and phosphorus (P) to grow, which it derives from the liquid fraction. This means that some of the minerals so that less ammonia is released. The solid fraction goes to a fermentation plant. The urine, which contains large quantities of nitrogen but hardly any phosphorus, is used partly for spreading on the land and partly as feed for the duckweed, which is cultivated in a pond situated above the stables. The moist warm air from the calves, and other residual products (CO2, water, heat) can be used again within the farm. Moreover, the duckweed is a protein-rich cattle feed, that reduces the need for imported soya. The fermentation of the solid fraction produces biogas, which is burned in a unit for cogeneration of heat and power (CHP unit) to convert it into heat and electricity. The electricity is used by the farm itself and supplied to the grid; the heat is stored in a hot-water tank before being used by an adjacent veal farm. The various flows are shown in the diagram below. Figure: Flow-chart of the ECOFERM closed-cycle farm system. 4.5 g/kg (N) and 0.5 and 1 g/kg (P2O5) in the urine. This nitrogen and potash-rich fraction, which contains hardly any phosphorus, is used on the farm’s own grass and corn fields, and is also supplied to nearby arable farms. On a yearly basis, 16,761 tons of slurry and the Processing manure In the old veal farm there is room for 2,000 calves. Slurry is stored here, under the animals. In the new building, which accommodates 1,600 animals, the urine is separated immediately from the solid manure by a manure scraper and a sloping drainage floor. The separation ratio is around 50:50 for faeces and urine. The urine amounts to 4,789 tons every year (with some faecal contamination). In the manure samples from recent years, there was between 2.5 and Pagina 121
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