Biochar Application Rate and Adsorption Capacity Effects on Nh3 Losses Mitigation from Buffalo Digestate Storage

Livestock effluent storage contributes to the release of ammonia (NH3) into the atmosphere; thus, it represents an aspect of farm manure management to be optimised. A possible solution could be adopting a tank floating cover or adding manure additives. Previous studies have shown that biochar is promising in reducing ammonia (NH3) emissions for manure storage, as a floating cover for manure storage tanks or a manure additive for its adsorbent properties. Nevertheless, there are still some interesting and relevant aspects to be addressed, related to the mechanism leading to the mitigation of ammonia emissions and the biochar application method and dose. For that purpose, this work aimed at studying the NH3 emissions reduction by investigating: (i) different biochar applications by simulating digestate storage conditions and (ii) the potential biochar adsorption capability and the main mechanisms involved. Results show that the amount of biochar applied cannot be reduced by under 4% of the total digestate weight stored, without increasing the ammonia losses by 44%. On the other hand, findings confirmed that the biochar produced at 550 °C, acts as an adsorbent material, both for NH4+ and NH3, despite NH3 proving to be adsorbed on the biochar surface in form of NH4+ after H+ abstraction from the acid groups. Nonetheless, the additional resistance to the gas transfer by biochar is even more affecting than the adsorption in the NH3 emissions reduction