UltraFiltration (UF) is a type of membrane filtration similar
to Reverse Osmosis, using hydrostatic pressure to force water
through a semi-permeable membrane.
UltraFiltration is a pressure-driven membrane process not
fundamentally different from reverse osmosis (RO),
microfiltration (MF) or nanofiltration (NF), except in terms of
the size of the molecules it retains.
The
pore size of the ultrafiltration membrane is usually 103 - 106
Daltons.
UF is a barrier to suspended solids, bacteria,
viruses, endotoxins and other pathogens to produce water with
very high purity and low silt density.
Suspended solids and solutes of
high molecular weight are retained, while water and low
molecular weight solutes pass through the membrane.
A
semi-permeable membrane, is a thin layer of material capable of
separating substances when a driving force is applied across the
membrane. Once considered a viable technology only for desalination,
membrane processes are increasingly employed for removal of bacteria and
other microorganisms, particulate material, and natural organic
material, which can impart color, tastes, and odors to the water and
react with disinfectants to form disinfection byproducts (DBP).
As advancements are made in membrane
production and module design, capital and operating costs continue to
decline.
The primary advantages of low-pressure
UF membrane processes compared with conventional clarification and
disinfection (post-chlorination) processes are:
• No need for chemicals (coagulants,
flocculates, disinfectants, pH adjustment)
• Size-exclusion filtration as opposed to media depth filtration
• Good and constant quality of the treated water in terms of particle
and microbial removal
• Process and plant compactness
• Simple automation
UltraFiltration is used to remove
essentially all colloidal particles (0.01 to 1.0 microns) from water and
some of the largest dissolved contaminants. The pore size in a UF
membrane is mainly responsible for determining the type and size of
contaminants removed.
In general, membrane pores range in
size from 0.005 to 0.1 micron. UF membrane manufacturers classify each
UF product as having a specific molecular weight cutoff (MWC), which is
a rough measurement of the size of contaminants removed by a given UF
membrane. Ours removes all molecules larger than .2 microns and many
smaller than that.
A 100,000 MWC UF membrane means that
when water containing a given standard compound with a molecular weight
of around 100,000 daltons is fed to the UF unit, nearly all of the
compounds will not pass through the membrane.
Substances with a molecular weight of
100,000 daltons have a size of about 0.05 microns to about 0.08 microns
in diameter.
UF membranes are used where
essentially all colloidal particles (including most pathogenic
organisms -- parasites and bacteria) must be removed, but most of the dissolved solids may pass
through the membrane without causing problems downstream or in the
finished water. UF will remove most turbidity from water.
The water flows through the UF membrane at a rate that
is slower than with other filtration media, but rapid enough to collect
without need of a holding tank or a long period of waiting to fill a
collection vessel.
