Page 485 - Water and wastewater engineering

12-2 WATER AND WASTEWATER ENGINEERING

12-1 INTRODUCTION

The membrane used in membrane filtration is a synthetic material that is semipermeable; that is,
it is highly permeable to some constituents and less permeable to others. To remove a constituent
from the water, the water is pumped against the surface of a membrane, resulting in a separation
of product and waste streams as shown in Figure 12-1 .
Membranes can be described by a variety of criteria including (Jacangelo et al., 1997):
• Membrane pore size,

• Molecular weight cutoff (MWCO),
• Membrane material and geometry,
• Targeted materials to be removed,
• Type of water quality to be treated, and/or

• Treated water quality.
Along with these criteria, membrane processes can also be categorized broadly into pressure
driven and electrically driven processes. This discussion is limited to pressure driven membrane

processes. Figure 12-2 summarizes the various pressure driven membrane processes and selected
materials removed by each. As used in water treatment, membranes are classified into two broad
categories: (1) those that are used to separate ions from solution, that is, reverse osmosis (RO)
and nanofiltration (NF) and (2) those that are used to separate suspended particles from water,
that is, microfiltration (MF) and ultrafiltration (UF). RO and NF were presented in detail in
Chapter 9. This chapter focuses on MF and UF.
A brief description of MF and UF provides a delineation of their differences.

Feed stream
Waste stream containing
particulate matter (reject or
concentrate)

Semipermeable
membrane
Product stream
(permeate)
FIGURE 12-1
Schematic of separation process through semipermeable mebrane.