Membrane technology for the recovery of nutrients in wastewater

Abstract

The main problems are ammonium and phosphate, which are present in many nutrients for animals and plants. The large farms that have grown in recent years, especially slurry, are fed with a high nitrogen content and eliminate of it in nature in the form of urea. Most of the urea is composed of ammonium and leaches into the soil, where it can also end up contaminating the water. This situation creates the need for water purification. Reverses osmosis membrane technology is a possibility. The study consists of the permeation of ammonia using a reverses osmosis membrane. First, the membrane performance was characterized by permeation of pure water and NaCl solutions at different temperatures. The different alkaline media were made for NaCl with the same purpose. In addition, the solute transfer coefficient was estimated to evaluate the effect of polarization. Subsequently, the permeation of ammonia to different effluents was evaluated, as well as solutions of NH4Cl and (NH4)2SO4. Moreover, the influence of temperature and pH on water permeability was quantified. Likewise, the permeability of ammonium and ammonia under these conditions was investigated. The ammonia nitrogen transfer coefficient was also estimated. At the end of the investigation, it could be demonstrated that both solute and water permeability increase with increasing temperature, since it follows the Arrhenius equation. On the other hand, the influence of pH is related to the equilibrium of the reaction. As the alkalinity of the media increases, more ammonia is formed and permeates the membrane. In contrary, ammonium ions hardly permeate and will be retained in the membrane. Also, the transfer coefficient was obtained, and it was deduced that it presents moderate polarization. This study takes a small step forward in reverse osmosis membrane technologies. As well as innovating, improving, researching, and developing new membrane structures to expand their industrial applications. In addition to improving water quality, ammoniacal nitrogen could be recovered at pH > 10.5 in the permeate. Thus, it could be used as a raw material for many chemical industries.