Capturing the Nitrogen That Escapes from Stored Manure: An Acid-Scrubbed Vent for a Covered Store, Its Nitrogen Budget and Its Break-Even Herd Size

A covered livestock manure store loses a large share of its nitrogen as ammonia gas before the manure reaches a field. This paper designs an acid-scrubbed vent for a covered store serving an 800-cow dairy herd (store 40 m by 40 m by 5 m deep) and computes its nitrogen budget from an accompanying script: the store surface emits 7,358 kg N per year, the scrubber captures 6,919 kg N per year (94.0 percent) using 4.01 kg of commercial sulphuric acid per kilogram of nitrogen captured, and the captured nitrogen is worth $11,071 per year against a total cost of $10,744 per year. Capture stops paying below a herd of 720 cows, below a mean slurry temperature of 11.3 degrees C, and above a vent rate of 0.76 air changes per hour. All performance figures are simulated, not measured.