Osmotic pressure estimation using the Pitzer equation for forward osmosis modelling

Area of Science:

• Water treatment technologies
• Chemical engineering
• Membrane science

Background:

• Forward osmosis (FO) offers low-energy water production potential.
• Accurate prediction of water flux is crucial for optimizing FO systems.
• Existing models often struggle with complex interactions in inorganic draw solutions.

Purpose of the Study:

• To develop and validate a new model for predicting water flux in FO systems.
• To incorporate the effects of concentration polarization (ICP and ECP) and water activity.
• To improve the correlation of experimental data compared to traditional methods.

Main Methods:

• Developed a nonlinear model for FO water flux prediction.
• Incorporated Pitzer's model for water activity to calculate osmotic pressures.
• Utilized a laboratory-scale cross-flow single cell unit with inorganic draw solutions.

Main Results:

• The new model accurately predicts water flux, outperforming the van't Hoff equation.
• Water activity-based calculations provided better experimental data correlation.
• The model improved estimates for the membrane's structural parameter (S).
• Temperature and solution concentrations significantly impacted water flux.

Conclusions:

• The developed model offers improved prediction accuracy for FO water flux.
• Accounting for water activity and concentration polarization is key for inorganic draw solutions.
• The model enhances understanding of factors influencing water flux in FO systems.