Modeling prediction of the process performance of seawater-driven forward osmosis for nutrients enrichment: Implication for membrane module design and system operation

Abstract Seawater-driven forward osmosis (FO) has been successfully applied in wastewater nutrient recoveries in laboratory-scale studies. In this study, modeling simulations were performed to gain a better understanding on the performance of a large-scale FO with two practically applied module configurations, a plate-and-frame module and a submerged hollow fiber module. The mathematical models were derived based on the mass balance and permeate flux model, taking into account the water and solute bidirectional transportation and the influence of internal concentration polarization. Iterative method was adopted to solve the highly non-linear and implicit equations in the models. The models were afterward applied to simulate a seawater-driven FO process for enriching nitrogen and phosphorous in wastewater. The simulation results show that approximately 30–40% of bulk osmotic pressure difference is used as the effective driving force in the processes with both plate-and-frame and submerged hollow fiber modules. The FO process is terminated at the osmotic equilibrium state, which is independent of the module configuration. However, a submerged hollow fiber module can meet the equivalent performance with much more compact module dimension compared with a plate-and-frame module. In addition, the influences of membrane module dimensional and operational parameters, including channel height, membrane length, assistant hydraulic pressure, and inlet cross-flow velocity in feed and draw stream on process performance, were further discussed in a plate-and-frame module. These developed models can be applied to design membrane modules and optimize the operational conditions in scale-up FO processes in future studies and applications.