Valorise the Nitrogen Surplus of Highly Intensive Livestock Areas as Renewable Resource Through a Simplified Ammonia Stripping Process

In highly intensive livestock areas, the surplus of nitrogen (N) contained in manure can be responsible for environmental problems. A slow-release ammonia stripping process can be used to recover the N surplus in manures as mineral fertilizer. In a laboratory scale experiment, digestate was treated at ambient temperature to evaluate different ratio between the slurry surface exposed to air and the volume, of 24, 30, 40 e 60 cm2/dm3. After 21–25 days of treatment, increasing N removal efficiencies, ranging from 67 to 88%, were observed as the surface/volume ratio increased. Then a pilot plant was developed to demonstrate the feasibility of introducing this treatment in livestock farms. The tests on pig slurry, cattle slurry and digestate lasted between 15 and 32 days, resulting in recovery efficiencies of 42–72% of total N and 50–79% of ammoniacal N. The ammonium sulfate solution obtained had an average N concentration of 41.7 g/kg. The pilot plant was easily manageable and modulated in relation to nitrogen removal needs. Stripping would make it possible to obtain a highly efficient fertilizer from livestock slurries with significant environmental benefits.