Recovery of ammonia from anaerobic digester centrate to produce ammonium nitrate

Abstract

Ammonia runoff and subsequent accumulation in water sources leads to eutrophication, while on the other hand, NH3 is a valuable chemical for use in agricultural fertilizers and in the chemical industry. Most of the practices for NH3 production are energy intensive and contribute to global warming, therefore, developing new methods for removal and recovery of NH3 it’s an interesting line of research. Although most lines of research are working with Forward Osmosis (FO) processes, using gas-permeable hydrophobic membranes, there may be a better solution with not hydrophobic membranes. In this project, an alternative process was studied. Instead of using a hydrophobic membrane, it was used a water-permeable membrane for the FO process. Instead of the acid solution, an ammonium nitrate high concentrated solution will be used. These type of solutions are typically used to fertilize crops. Farmers, instead of diluting the solution in water before using it, will get free ammonium nitrate and water to enlarge their quantity of fertilizer, and the Waste Water Treatment Plant (WWTP) will get rid of ammonia and an excess of Waste Water (WW). Beyond enhancing circular economy, ammonia concentration in WW will be significantly reduced, limiting the effects of eutrophication. First, an exhaustive research of FO ammonia recovery’s actual situation was carried out, showing that the majority of research lines are working with hydrophobic membranes. Then, Reverse Osmosis (RO) simulated experiments were carried out with ROSA software to obtain the membrane parameters. With the results obtained, FO simulated experiments were carried out with Visual MINTEQ (VM) and an own created mathematical model, which gave promising results about water and ammonia reduction in the feed solution