The Effect of Untreated and Acidified Biochar on NH₃-N Emissions from Slurry Digestate

The development of new options to reduce ammonia (NH₃) emissions during slurry manure storage is still required due to the shortcomings of the current technologies. This study aimed to identify to what extent untreated and acid-treated biochar (BC) and pure acids could reduce ammonia nitrogen (NH₃-N) volatilization and increase nitrogen retention in slurry digestate. The NH₃-N emissions were effectively reduced by H₂SO₄ and H₃PO₄ acids, untreated BC when applied mixed into the digestate and acidified BC treatments applied on the surface of the digestate. Acidification increased the specific surface area and number of O-containing surface functional groups of the BC and decreased the pH, alkalinity and the hydrophobic property. Compared to untreated BC, the ability of BC to reduce NH₃-N emissions was greater when it was acidified with H₂SO₄ and applied to the digestate surface. The effect on digestate pH of acidified BC when applied mixed into the digestate was not different, except for H₂O₂, from that of the addition of the respective pure acid to digestate. The total N concentration in digestate was not significantly correlated with NH₃-N emissions. These findings indicate that acidified BC could be an effective conditioner to reduce NH₃-N emissions from slurry digestate storage.