Caleb Andrew's blog : Membrane Filters Explained: Definition, Working Principle, and Applications
Membrane filters are a type of a barrier that is used to
separate a contaminant from a body of water or remove the contaminating
particles from the water. Membrane is a common denominator in various
filtration processes, including reverse osmosis, ultrafiltration, and
nanofiltration. One of our Master Water Specialists, John Woodard, gives
insights into how a membrane filter works and how it is used in various water
filtration systems.
What Is Membrane Filtration?
Membrane filters also come in various configurations. There
are reverse osmosis (RO) membranes, ultrafiltration (UF) membranes, and
nanofiltration (NF) membranes.
How Does A Membrane Filter Work?
In reverse osmosis, pressure is exerted on water to a
semi-permeable membrane. During this process, the water molecules pass through
the membrane and any dissolved chemical or inorganic compounds are flushed down
the drain. Water is therefore separated into two outlets or systems.
GMI Research reports that the Membranes Market is projected
to hit USD 13.9 billion in 2032.
Use Cases:
Desalination of sea and brackish water.
Purification of drinking water.
Ultrafiltration isn’t a separation of water like a reverse
osmosis membrane does. It is simply a filter of ultra-fine particulates or
sediments. With mechanical filtration, particulates down to 0.025 microns won’t
pass through the ultrafiltration membrane.
Use Case:
Cleaning drinking water. Removal of microbes and large organic molecules.
As a pre-treatment to reverse osmosis to reduce the amount of fouling.
Nanofiltration membrane technology works similarly to
reverse osmosis, the difference being that filtration is not as fine.
Nanofilters have the exact same pores but on the extreme end of the pore size
range, 0.001 to 0.01 µm. The membrane can efficiently reject divalent ions like
calcium and magnesium, heavy metals, and even some organic compounds.
Use Cases:
To soften water and to remove heavy metals from industrial wastewater.
What’s the difference between a reverse osmosis and an ultrafiltration
membrane?
These two processes, Reverse Osmosis and Ultrafiltration,
differ in that reverse osmosis is able to reject dissolved minerals in water,
while UF can only filter out solids or particulates. Reverse osmosis can
eliminate dissolved inorganics which will pass through the UF membrane.
What materials are filters made out of?
Membranes can be constructed of a wide range of materials.
For reverse osmosis, they’re usually called thin-film composite membranes.
Historically, reverse osmosis membranes were made out of cellulose triacetate
(CTA), which is no longer produced. CTA membranes were the first incarnation of
the RO membrane, which had low pH tolerances and produced low quantities of
water per square inch. Thin-film technology enables RO systems to make far
greater quantities of water in less space, meaning larger membranes are now
possible in smaller housings.
How can membrane filters be cleaned?
You can skip cleaning the membrane filter in a residential
POU system. To dislodge some of the scale or particles that are clogging the
membrane, use chemical agents. Given that trying to flush or clean the membrane
is far less cost-effective, it is definitely cheaper to replace it every few
years.
UF membranes are flow through membranes and not separation
membranes. When you ultrafiltrate membranes, you need to pull the air out of
the membranes when you flush them at the beginning of the process. When you
flush a reverse osmosis system each time you start it, it is to help
re-saturate the system because the membranes are usually manufactured, dried
and stored. For a POU system, fill two or three tanks and let them drain before
using the system.
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