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Nitrogen Enrichment of Organic Wastes by Ammoniation

Dep. of Agronomy, Louisiana State Univ., Baton Rouge, LA 70803.

^* Corresponding author (gbreite{at}unixl.sncc.lsu.edu).

ABSTRACT

The benefits of amending soil with cellulosic organic wastes generated during the processing of agricultural products are limited by their low nutrient value, occasional strong odors, and high costs of transportation. The objective of this study was to develop a chemical process to enrich the N content and reduce the water content of cellulosic organic wastes to enhance their value as nutrient supplements. Various combinations of pressure (300–9000 kPa), temperature (60–240°C), and O₂ and NH₃ concentrations were used to identify optimal parameters for N enrichment of various wastes by reaction with anhydrous NH₃. Total N contents of sugarcane (Saccharum officinarum L.) milling wastes, rice (Oryza sativa L.) hulls, and several composts were increased 5.9 to 17.1 times under the optimal combination of reaction parameters tested. Ammoniation resulted in dry, dark brown organic products containing 50 to 90 g N kg^–1 and having negligible odor. Nitrogen enrichment increased as the organic C content of the organic wastes increased. For all materials studied, the optimal N enrichment was obtained at a reactor pressure of 7200 kPa. Optimal reaction temperature varied between 80 and 180°C. Maximum fixation was attained in <120 min for all materials studied. Products ammoniated under optimal conditions contained 87 to 93% of their N as organic N. Increasing reaction temperature decreased the proportion of water soluble to insoluble organic N in ammoniated materials. Anaerobic incubation of soils amended with ammoniated bagasse indicated about 20% of N in this material was released as mineral N within 14 d.