Environmental Engineering: Fundamentals and Design - Chapter 10

BOOK TABLE OF CONTENTS
CHAPTER TABLE OF CONTENTS
TOC > Ch. 10 > 10.8 Membrane Processes

# Chapter 10 Drinking Water Treatment

David W. Hand and Qiong Zhang

## Membrane Processes

Membrane processes, including microfiltration, nanofiltration and reverse osmosis have gained acceptance as means of producing a safe, high quality drinking water. These technologies offer the advantage of accomplishing many of the objectives of traditional treatment (removal of turbidity, inorganic and organic chemicals and pathogenic microorganisms) in a single unit operation.

The raw water (feedwater) is pumped under pressure through a membrane. The treated water or permeate is that passing through the membrane and continues to disinfection. The rest of the water or retentate contains those constituents removed by the membrane and is wasted.

The size classes of constituents removed and the transmembrane pressure required to remove them varies as a function of the pore size of the membrane. As pore size decreases, removal efficiency increases as does the required transmembrane pressure and the associated energy costs.

This animation provides examples of the various size classes of constituents of interest in drinking water treatment and illustrates the operation of three membrane technologies used to remove them.

Treatment Process | Pore Size (µm) | Primary Application | Target Constituents | Transmembrane Pressure (psi) | Cost ($/1000 gal)
--- | --- | --- | --- | --- | ---
traditional | - | freshwater (total dissolved solids, TDS, < 1000 mg/L) |  | - | $1.00 – 1.50
microfiltration | 0.1 – 2.0 | freshwater | particles, protozoa | 10 | $0.21 – 1.00
nanofiltration | 0.0001 – 0.001 | brackish or sea water (TDS > 1000 mg/L) and freshwater; pre-treatment for reverse osmosis | hardness and natural organic matter | 75-100 | $0.75 – .00
reverse osmosis | 0.00001 – 0.0001 | freshwater and brackish or sea water | salt and other dissolved substances, e.g. nitrate, radionuclides, synthetic organic chemicals | 200-1200 | $2.00 – 4.00

#### Credits

Water Filtration animation: © 2008 Michigan Technological University.

| Previous | Book TOC | Chapter TOC | Next