Civil Engineering Reference
In-Depth Information
CHAPTER 15
Membrane Treatment
INTRODUCTION
Membrane filtration processes for the treatment of potable water covered in this chapter
are reverse osmosis, nanofiltration, ultrafiltration, microfiltration, and electrodialysis
reversal. The reverse osmosis, nanofiltration, and in some cases ultrafiltration processes
use the ability of semipermeable membranes to separate aqueous salts, organic mol-
ecules, and metal ions from solutions. Ultrafiltration and microfiltration utilize physical
straining to remove colloidal and particulate contaminants, including microbial path-
ogens such as bacteria, and
Giardia
and
Cryptosporidium
cysts. Electrodialysis utilizes
electrically charged membranes to remove dissolved ions by dialysis.
In addition to a description of membrane processes, this chapter covers the prin-
ciples of membrane operation, including configurations and fouling mechanisms. It
also describes methods for disposal of concentrates from membrane processes.
MEMBRANE PROCESSES FOR DRINKING WATER
Membrane separation technology has been used for many years in the small-volume
treatment of pure and ultrapure water for many industries, such as beverages, phar-
maceuticals, and electronics. Membranes are increasingly being considered and utilized
for large-volume potable water treatment for the following reasons:
Membranes remove particulates by physical straining above a target size, so they
can reliably meet stringent drinking-water regulations for removal of microbial
contaminants such as
Giardia, Cryptosporidium,
and viruses.
•
Membranes have the ability to efficiently remove pathogens and may reduce the
disinfection chemicals required and the potential for formation of disinfection by-
products.
•
Increased water demands and limited high-quality raw-water supplies have forced
the use of lower-quality raw-water supplies with elevated levels of mineral or
biological contaminants. Membranes are able to treat these more difficult waters.
•
Membranes have the ability to remove organic precursors, leading to more bio-
logically stable water.
•
476
