Ion-selective membranes for the recovery of ammonium and potassium

Our planet is expecting a population growth in the coming years and so a higher demand of food production (i.e., crops) that will require higher crop yields. The demand of fertilizers (chemical or natural) is going to increase as they contain one or more of the essential elements (nutrients) necessary for plant growth: phosphorus, nitrogen, and potassium. Urine is considered as a possible source of such nutrients because of its composition. In urine, sodium (Na+), potassium (K+) and ammonium (NH4+) are competitive cations in separation and the recovery process as they have the same valence (+1), very similar hydrated radii and very similar diffusion coefficient which renders separation by charge, size, and mobility unsuitable. This research is based on the development and characterization of membranes selective for the recovery of potassium and ammonium - two of the essential nutrients. A membrane-based technology was chosen due to its possibilities in continuous systems as well as the feasibility to incorporate selective phases (organic and inorganic) to the polymeric matrix. Polymers, selective inorganic and organic phases and additives were studied for their chemical effects on the transport of the target nutrients across the membranes. The research performed shows that membrane technology is a promising tool for the separation and recovery of potassium and ammonium from competitive cations and that the transport mechanism is key to understand the membrane performance.