MP

membrane filtration 101024

INTRODUCTION

  • Membrane filtration, also known as "Millipore filter technique"

  • Separation process utilizing a membrane barrier for particle/solute separation in liquid or gas based on size or molecular weight

  • Commonly used for samples with low microbial content

  • Process involves applying pressure to force the feed solution through the membrane.

MECHANISM OF MEMBRANE FILTRATION

  • Membrane filter functions by removing unwanted particles while allowing water to pass through

  • Water sample is placed on a membrane filter and incubated, allowing typical colonies to grow post-filtering.

TYPES OF MEMBRANE FILTRATION

1. Microfiltration

  • Definition: Physical separation method that removes microorganisms and suspended solids.

  • Pore Size: 1.0 – 0.01 microns

  • Operating Pressure: <30 psi

  • Materials Removed: Clay, bacteria, large viruses, suspended solids.

2. Ultrafiltration

  • Definition: Low-pressure, cross-flow separation technique for fine particles.

  • Pore Size: 0.01 – 0.001 microns

  • Materials Removed: Viruses, proteins, starches, colloids, silica, dyes.

3. Nanofiltration

  • Definition: Rejects particles approximately 0.001 microns; pressure-driven process.

  • Pore Size: 0.001 – 0.0001 microns

  • Materials Removed: Sugars, pesticides, herbicides, divalent anions.

4. Reverse Osmosis

  • Definition: Efficiently separates dissolved salts and inorganics, primarily for drinking water purification.

  • Pore Size: 0.0001 microns

  • Materials Removed: Monovalent salts.

5. Other Filtration Types

HEPA Filtration

  • Definition: High Efficiency Particulate Air filters that remove at least 99.97% of particles sized at 0.3 microns.

Seitz Filtration

  • Definition: A disc filter with extremely fine pores, preventing bacteria passage. Composed of highly fibrillated cellulose fibers.

Diatomaceous Earth Filter

  • Definition: Utilizes diatomaceous earth for filtration, available in food-grade and filter-grade types.

APPLICATIONS OF MEMBRANE FILTRATION

  • Heavily used in pharmaceutical product purification and downstream processing.

  • Effective in separating heat-sensitive substances and volatile liquids in the cosmetics and perfumery industries.

  • Acts as a barrier for contaminant removal in water treatment processes.

ADVANTAGES OF MEMBRANE FILTRATION

  • Applications in water and wastewater treatment.

  • Utilized in food and beverage industries.

  • Important in pharmaceutical and biotechnology sectors.

  • Supports healthcare and environmental protection initiatives.

  • Capable of continuous operation with minimal complex instrumentation.

DISADVANTAGES OF MEMBRANE FILTRATION

  • High cost associated with implementation.

  • Potential skin irritation from exposure.

  • Handling challenges may arise.

  • Requires considerable energy inputs; involves high electricity costs and pressure drops.

PARTICLE REMOVAL EFFICACY

Protozoa and Helminths

  • Easily removed as they are significantly larger than MF and UF membrane ratings, with over 7 log rejection observed.

Bacteria

  • Generally removed below detection limits by MF and UF membranes.

Viruses

  • Virus rejection varies by species and membrane type; significant variability in log removal values (LRV).

MECHANISMS OF PARTICLE REJECTION

  • Straining: Larger particles are physically retained due to size.

  • Adsorption: Smaller particles enter pores and stick to their walls.

  • Cake Formation: Small particles accumulate on the membrane surface, trapping larger particles.

FLOW AND MEMBRANE RESISTANCE

Hydraulics of Flow

  • Darcy's law applied to describe flow characteristics through membranes.

  • Transmembrane pressure development is crucial for efficient membrane operation.

Example Calculations

  • Detailed calculations for membrane resistance coefficient and specific flux are outlined, supporting operational assessments.

SUMMARY

  • Membrane filtration serves as a crucial separation technology across various industries, particularly in pharmaceuticals and environmental applications. It effectively separates contaminants, particularly in water treatment processes.