Estimation of Water Flux and Solute Movement during the Concentration Process of Hydrolysed Urine by Forward Osmosis

Abstract

Urine is rich in nutrients and can be applied as a fertilizer. The limitation on the application is the transportation cost for the farmlands. The cost estimation required 80% of the volume reduction for a feasible utilization of urine in the farmlands near urban areas. The volume reduction system by forward osmosis (FO) process was proposed to address this problem. In this study, the experiments on FO process with real and synthetic hydrolysed urine were performed to assess the FO performances, to evaluate the solute diffusion and to describe the water flux considering the activity of solutes. This study showed both real and synthetic urine can be concentrated to 2–5 times with 2–5 mol/L sodium chloride solution. High diffusivity of ammonia and carbonates were observed, but the diffusion of other solutes was low. The activities of the solutes in the non-ideal solution should be considered for estimation of the osmotic pressure of the solution which reflects the water flux. The software PHREEQC can be used for estimation of the activities in such high concentration solutions. The organic matter in real hydrolysed urine had a negligible effect on the osmotic pressure variations.