A Comparative Study of Forward Osmosis Systems: An Integrated Experimental, Modeling, and Techno-Economic Analysis

Draw solution chemistry is a design parameter in forward osmosis (FO), governing hydraulic performance, organic rejection, fouling dynamics, and process economics, yet these dimensions are rarely evaluated together, particularly under wastewater feed conditions. This study addresses that gap through an integrated experimental, modeling, and techno-economic framework using three draw solutions (NaCl, MgSO₄, and sodium acetate), each prepared at an initial osmotic pressure of 30 bar, and two feed solutions (deionized water (DI) and real municipal wastewater (WW)). Water flux (J _w), reverse salt flux (J _s), and chemical oxygen demand (COD) flux (J _COD) were monitored over 4 hours. Water fluxes ranged from 1.8 to 4.0 L m^-2 h^-1, and substituting DI with WW reduced J _w by 8.1-46.2% depending on draw solution chemistry. A dynamic MATLAB finite-difference model coupling concentration polarization with membrane transport accurately reproduced experimental J _w and J _s profiles, with Root Relative Mean Square Error below 1.9% and 6%, respectively. A phenomenological COD sub-model partitioned organic matter dynamics into three pathways and introduced a dimensionless ratio P _COD/K _foul as a selectivity screening metric. Techno-economic analysis identified NaCl as the most economically viable draw solution, achieving a levelized cost of water of USD 1.04 m^-3. Monte Carlo analysis confirmed this advantage was statistically robust with complete non-overlap of NaCl 's 95% confidence interval and those of MgSO₄ and sodium acetate. MgSO₄ demonstrated superior COD rejection, lower initial fouling accumulation, and more stable flux decay kinetics within the initial-to-intermediate fouling regime examined, making it preferable where selectivity and effluent quality are prioritized.