(373a) New Material and Process Design for Sustainable Nitrogen Fertilizer Management

Managing nitrogen cycle is one of the 14 Grand Challenges for Engineering in the 21st Century set forth by National Academy of Engineering. This effectively raises a chief question: can nitrogen fertilizer synthesis be decoupled from the need to utilize natural gas as a hydrogen source? Developing a system for harnessing nutrients and producing advanced new fertilizers derived from manure or other organic residues to the scales needed for US agriculture is theoretically possible. While a direct comparison of the N amount available in biogenic waste with that consumed needs to be approached cautiously, the amount of the total N confined in biogenic activity end products generated in the US is ∼10.5 million tons. According to USDA, about ∼14 million tons of N were consumed in the US annually, suggesting that N confined and otherwise eventually released to the environment can be converted into functional fertilizer and recycled for crop growth. Several strategies to recover nitrogen from liquid waste, including anaerobic digestion liquid, and transform it into nitrogen efficient fertilizer materials will be presented.

An emerging source of solid materials that can be derived from digestate that contains solid nitrogen that does not need equimolar amounts of H₂SO₄ is ammonium bicarbonate (ABC). ABC was one of the main fertilizers used in China some 20 years ago until it gave way to urea. This is due to its poor environmental stability since it readily decomposes back into NH₃ and CO₂ at room temperature. It is excluded from the organic fertilizer register in the US, not allowed as a standalone fertilizer in the EU and is currently used as a fumigant. If the methods can be developed by formulating ABC into solid materials that do not have any negative impacts on the biota (does not function as a fumigant), do not volatilize spontaneously as ABC does and contribute nitrogen to the plant growth, a tremendous benefit to the agriculture section would result. The technologies to extract solid ABC from digestate should be available on a large scale for distributed operation and have already been estimated cost and environmental impact efficient. The path in physicochemical stabilization of ABC potentially lies in green mechanochemical technologies of stabilization as recently shown when addressing urea environmental stability problem. In particular, we mechanochemically combined laboratory grade ABC (or ammonium carbonate) with either MgCO₃ or ZnCO₃ to form double salts, Mg(NH₄)(CO₃)₂ and Zn(NH₄)(CO₃) as well as the combination of other salts. Laboratory experiments as well as field tests will be presented that shows improved nitrogen use efficiency. Technology development to obtain stabilized ABC materials using solar energy via distillation will also be presented.