Investigation of Recycling by Separating and Concentrating Ammonia Nitrogen Contained in Methane Fermentation Digestive Fluid

Abstract

In this study, in order to concentrate ammonium nitrogen (NH₄-N) in methane fermentation digestive fluid and to recycle it as nitrogen fertilizer, we attempted to concentrate NH₄-N in the digestive fluid by vacuum distillation with reference to the literature. Since digestive fluid contains substances other than NH₄-N, diluted ammonia water (simulated digestive fluid) was used to examine the experimental conditions. Evaporated NH₄-N was absorbed in distilled water or dilute sulfuric acid, or recovered by reaction with CO₂ were attempted. Vaporized NH₄-N was absorbed in distilled water or dilute sulfuric acid, or recovery by reaction with CO₂ was attempted, and the results were used in experiments with digestive fluid. The NH₄-N concentrations before and after the experiment were measured to confirm the amount of reduction. The amount of deposit was determined gravimetrically, and the composition was estimated using an infrared spectrophotometer. In experiments with simulated digestive fluid, the NH₄-N concentration decreased by 37-44%, and when CO₂ was introduced, ammonium carbonate was deposited by the reaction with vaporized ammonia. In experiments with digestive fluid, the NH₄-N concentration decreased by 37% at maximum, and ammonium carbonate was deposited even without the introduction of CO₂, and NH₄-N was concentrated and recovered as a solid.