Identifying and Overcoming Rate-Limiting Steps for Nitrogen Fertilizer Production from Urine

Abstract

Listen

Translate article

Wastewaters containing nitrogen have a deleterious impact when discharged to the environment. Conventional nitrogen removal techniques are resource-intensive and limited to settings with formal sewer infrastructures. Furthermore, these techniques treat nitrogen as an impurity to remove rather than a resource to recover. In 2018, we addressed all three of these issues by demonstrating a proof-of-concept for electrochemical stripping (ECS) of ammonium sulfate from source-separated urine. ECS does not require caustic chemicals, can be implemented in remote settings, and recovers the fertilizer ammonium sulfate. In 24 hours, our ECS setup achieved 93% nitrogen recovery. Our next step is to improve the time-efficiency of ECS, but because it is a novel technology, we lack guidance in the literature for optimal experimental ranges. To grasp a more mechanistic understanding of the steps bottlenecking nitrogen recovery, we develop a model as follows. First, we decompose nitrogen recovery into major transport and chemical transformation steps. Experimental data is then fit to the model with a goodness of fit test. Using these fitted values as a starting point, we perform sensitivity analyses for each major step in order to elucidate what parameters most crucially govern nitrogen recovery. Preliminary results (attached) suggest that ammonia volatilization contributes nontrivial nitrogen losses to the system. Our model will guide further developments of ECS technology by providing quantitative measures of how to overcome rate-limiting steps in nitrogen recovery. Figure 1