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 PHRE-EQC 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.

Forward Osmosis as Concentration Process: Review of Opportunities and Challenges

“…Several recent studies demonstrated the potential of FO as a concentration/separation process for ammonium and phosphorous recovery from source separated urine. The feasibility of urine concentration by FO was demonstrated, with up to a 5-fold concentration using a 5 M NaCl solution [ 171 ]. If phosphorous and potassium are concentrated, one main challenge is the relatively poor rejection of nitrogen especially under urea form by FO membranes (50–60%) [ 171 ].…”

“…The feasibility of urine concentration by FO was demonstrated, with up to a 5-fold concentration using a 5 M NaCl solution [ 171 ]. If phosphorous and potassium are concentrated, one main challenge is the relatively poor rejection of nitrogen especially under urea form by FO membranes (50–60%) [ 171 ]. In that context, the improved rejection of nitrogen (50−80%) in hydrolysed urine was observed in comparison with the low rejection of neutral organic nitrogen (urea-N) in fresh urine [ 168 ].…”

Desalination of Municipal Wastewater Using Forward Osmosis

“…Other forms of improvement of the FO process are in the membrane module development and draw solute improvement to reduce reverse solute flux. On the subject of FO, most studies have focused mainly on the concentration of FS with the aim of volume reduction for discharge or for resource recovery [ 34 , 35 , 36 , 37 , 38 ], at relatively high DS and FS flow rates (>1 L/min).…”

Synthesis and Characterization of Magnetic Nanoparticles as a Candidate Draw Solution for Forward Osmosis

“…Indeed, the draw solution should provide enough pressure to achieve five times the concentration of urine and be easily recovered in households. The osmotic pressure of 5 times concentrated urine is reported as 8 − 11 MPa which is higher than that of 2.5 MPa for seawater [8]. It is mentioned that high osmotic pressure can be easily generated by inorganic salts and organic compounds, although its recovery is difficult and energy-intensive.…”

“…Latest investigations proved the possibility to concentrate urine and recover a major portion of the nutrients it contains using FO [8]. However, it should be noticed that a critical aspect is the selection of appropriate draw solution to con-centrate urine at household level by FO.…”