Development of a Nitrification System for Ammonium Nitrate Production

Abstract

The rising global population increases the demand for nitrogen fertilizers, requiring a more sustainable method to produce them. The Atmonia Nitrification System utilizes an enriched consortium of wild-type microorganisms to convert ammonia to potassium nitrate. This project aimed to characterize this enrichment and use it as a base for ammonium nitrate production, which has a higher nitrogen content and a hundred times bigger market, to develop a sustainable alternative to the Ostwald method for nitrate-based fertilizers production. The parent enrichment was characterized through activity assays, scanning electron microscopy, and 16S rRNA gene sequencing. Bioreactor experiments were performed in 20 L moving bed biofilm bioreactors to transition the system to ammonium nitrate production. In the activity assays, nitrite-oxidizing bacteria were more active under standard operating conditions, while ammonia-oxidizing bacteria and/or archaea were more resilient to changes in those conditions. Intricated biofilm structures were observed with scanning electron microscopy. The 16S rRNA gene sequencing detected a diverse community of microorganisms, including known nitrite-oxidizing bacteria and ammonia-oxidizing bacteria (8,5% and 1% average abundance respectively). No ammonia-oxidizing archaea were detected. The newly developed bioreactor system for ammonium nitrate production processed the same ammonia feed rate as the parent bioreactors, 0.8 g N/L carrier/day, rendering a product with a mass ratio N:K five-fold above that of the system for potassium nitrate production. These results show the feasibility of ammonium nitrate production in this biological system and suggest opportunities for improvement in the biomass.