Presentation presented at UNISCO Chair fo water and water recourses, SUDAN
Published on: Mar 3, 2016
Transcripts - Nanofiltration
- Khalid Omer
- Mohamed Elhady
- Altohamy Alshamy
Dr.Hassan Ahmed Sulieman
Nanofiltration is one of a group of similar
membrane processes (including reverse
osmosis, Ultrafiltration , and microfiltration)
used most often with low total dissolved
solids water such as surface water and
fresh groundwater, with the purpose of
softening (polyvalent cation removal) and
removal of disinfection by-product
precursors such as natural organic matter
and synthetic organic matter.
Membrane Filter in brief:
The membrane filter uses a relatively thin
material with a well-defined maximum pore
size and the particle retaining effect takes
place almost entirely at the surface.
Membranes offer the advantage of having
well-defined effective pore sizes, can be
integrity tested more easily than depth
filters, and can achieve more filtration of
much smaller particles.
Nanofiltration is a membrane filtration -based
method that uses nanometer sized cylindrical
through-pores that pass through the membrane
at 90. Nanofiltration membranes have pore sizes
from 1-10 nanometers. Membranes used are
predominantly created from polymer thin films.
Materials that are commonly use include
polyethylene teraphthalate or metals such as
Nanofiltration membrane modules:
Membrane types are mainly classified into; hollow fiber type, tubular
type, capillary type , flat sheet type and spiral wound type
depending on its construction method. For Nanofiltration , spiral
wound type membranes are the most commonly used style of
Spiral wound type provides:
-- Available in a range of standard diameters (2.5”, 4” and 8”)
to fit standard pressure that can hold several modules in
series connected by O-rings.
-- The module uses flat sheets wrapped around a central tube.
- The membranes are glued along three edges over a permeate
spacer to form ‘leaves.
- The permeate spacer supports the membrane and conducts
permeate to the central permeate tube.
- Between each leaf, a mesh like feed spacer is inserted.
The NF separation mechanism:
The NF separation mechanism can be identified as a sum of convection and
diffusion transport mechanisms,
** Convective transport of ions with the water flux through the membrane
is caused by the pressure difference between feed and permeate sides.
** diffusive transport is a consequence of the concentration gradient as
achieved by the rejection of solutes Electromigration is caused by a
“streaming potential” difference across the membrane.
** streaming potential is caused by the electric current generated by the
convective flow of a fluid that is necessarily charged through the pores of
a charged membrane
** For uncharged molecules, sieving or size exclusion is primarily
responsible for separation and is controlled by molecular size in solute
** Multivalent ,viruses , bacteria , suspended solids are removed by
Effectiveness of NF:
Micro-pollutants like herbicides and insecticides, as well
as low-molecular components like colorants and sugars
can be very successfully blocked using a Nano-filtration
NF can be implemented for removing the following
parameters (removal yield indicated in brackets):
- Dissolved matter (>75%).
- Harmful micro-organisms, e.g. bacteria, protozoa,
algae, fungi (>90%).
- Persistent organic matter (50-75%).
- Organic compounds (50-90%).
- Nutrients (incl. phosphates).
- Metals (50-90%).
- Inorganic salts (e.g. sulphates).
Applications of NF:
* Food and dairy sector.
* Edible oil processing sector.
* Petroleum industry.
* Drug industry.
* Paper pulp industry
3-Desalination of water.
- Lower discharge volumes, lower retentate
concentrations than RO for low value salts.
-- Reduction salt content and dissolved matter
content (TDS) in brackish water.
-- chemical-free. e.g. needs no salt or
chemicals during operation.
- pH of water after Nano-filtration is normally
- Higher energy consumption than UF and MF
(0.3 to 1 kWh/m³).
- Limited retention for salts and univalent ions.
- Membranes are sensitive to free chlorine
(life-span of 1000 ppmh). An active carbon
filter or a bi-sulphite treatment is
recommended for high chlorine