Modeling Ionic Strength Effects on Hollow-Fiber Nanofiltration Membrane Mass Transfer

Area of Science:

• Environmental Science
• Chemical Engineering
• Materials Science

Background:

• Nanofiltration is vital for water purification, particularly for removing divalent ions like magnesium, contributing to water hardness.
• Understanding ion transport mechanisms through membranes is crucial for optimizing water treatment processes.
• Existing models like the homogeneous solution diffusion (HSD) model may not fully capture complex ionic interactions.

Purpose of the Study:

• To investigate the influence of feedwater ionic strength on divalent ion diffusion through hollow-fiber nanofiltration membranes.
• To evaluate the predictive capability of the homogeneous solution diffusion (HSD) model under varying ionic strengths.
• To develop an improved model that incorporates feedwater ionic strength for more accurate hardness removal predictions.

Main Methods:

• Experimental investigation of magnesium diffusion across nanofiltration membranes with controlled feedwater ionic strengths.
• Comparison of experimental results with predictions from the standard homogeneous solution diffusion (HSD) model.
• Development and validation of a modified HSD model (HSD-IS) incorporating an empirical term for ionic strength effects.

Main Results:

• Elevated feedwater ionic strength increased the solute flux of magnesium during nanofiltration.
• The HSD model under-predicted the nonlinear impact of ionic strength on magnesium diffusion.
• The modified HSD-IS model demonstrated a 77% improvement in root mean squared error compared to the HSD model.

Conclusions:

• Feedwater ionic strength is a critical factor influencing divalent ion diffusion in nanofiltration.
• The HSD-IS model provides a more accurate representation of magnesium diffusion, essential for predicting hardness removal.
• Incorporating ionic strength effects into modeling is recommended for optimizing nanofiltration processes for water softening.