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NANOFILTRATION IN WATER
SUPPLY SYSTEMS
MEMBRANE PROCESSES
Generally, there are
four types of
membrane processes,
 Microfiltration.
 Ultrafiltration.
 Nanofiltration.
 Reverse Osmosis.
Filter type
Symbol
Microfilter
MF
Ultrafilter
Pore Size, m
Operating
Pressure,psi
Types of Materials
Removed
1.0-0.01
<30
Clay, bacteria, large
viruses, suspended
solids
UF
0.01-0.001
20-100
Viruses, proteins,
starches, colloids,
silica, organics, dye,
fat
Nanofilter
NF
0.001-0.0001
50-300
Sugar, pesticides,
herbicides, divalent
anions
Reverse
Osmosis
RO
< 0.0001
225-1,000
Monovalent salts
Applications of Micro- and Ultrafiltration:
 Conventional water treatment (replace all
processes except disinfection).
 Pretreat water for R.O and nanofiltration.
 Iron/Manganese removal (after oxidation).
 Removal of DBP precursors.
Applications of R.O. and nanofiltration:
 R.O. application mostly desalination.
 Nanofiltration first developed to remove
hardness.
 Nanofiltration can be used to remove DBP
precursors.
HISTORY OF NANOFILTRATION

During 1970s RO membranes with greater operating
pressures was developed.

This resulted in considerable increase in energy cost.

Thus, low-pressure RO membranes were developed
and came to be known as NF membranes.

By the second half of 1980s,NF became established.

Starting in early 1990s, it had became common and
various applications were found out.
NEED FOR NANOFILTRATION

Increasing demand of good quality water
due to increasing population.

Reducing the wastage and reuse of water.

Better reliability and durability of filter
membranes.

To reduce the overall cost of operation.
Materials used in NF membranes
•
Different polymers used are polyethersulfone,
polysulfone, polyphenylsulfone,
polytetrafluoroethylene, polyvinylidene fluoride,
polyacrylonitriles, nylon, polypropylene, cellulose
acetate (CA), regenerated cellulose, and composites.
•
Ceramic and cintered metals.
•
carbon nanotubes.
Two types of membranes:
i.
Spiral membranes: Cheapest, more sensitive to
pollution.
ii.
Tubular membranes: Most used, not easily
polluted.
But surface area of spiral membranes is greater than
that of tubular membranes and hence greater
capacity.
Benefits of Nanofiltration
Low cost of operation.

Low energy cost.

Lower discharge and less waste water than typical

Reverse Osmosis system.
Reduction of Heavy Metals (removes 95%).

Reduction of water hardness.

Reduction / Removal of viruses, bacteria, VOC’s, and

Pesticides.
Reduction of Nitrates and Sulphides.

Reduction of the salt content (brackish water).

Chemical - Free filtration (No use of salt).

pH of the water can be altered for better health.

Ideal for municipal water supply, well water, river

and rain water.
Removes Iron, Lime and other problem causing

chemicals often neglected by water softeners.
Distinct properties of Nanofiltration

The pore size of a NF membrane corresponds to a
molecular weight cut-off of 300-500g/mol. Hence,
separation of these components from higher
molecular weight components can be achieved.

Nanofiltration membranes have a slightly charged
surface. The dimensions of pores are close to
dimensions of ions and hence charge interaction takes
place. It can be used to separate ions with different
valences.
Two basic types of exclusion mechanisms:
1.
Steric exclusion mechanism: similar to
sieving. Geometric exclusion of solute
particles larger than pore size.
2.
Charge based exclusion mechanisms:
i.
Donnan exclusion: Due to charged
nature of NF membrane.
ii.
Dielectric exclusion: Due to difference
in dielectric constant.
Various Applications:
Industrial applications:
1.
•
Food and dairy sector.
•
edible oil processing sector.
•
Petroleum industry.
•
Drug industry.
•
Paper pulp industry
2.
Water treatment.
3.
Desalination of water.
4.
Water softening. LINK\app.docx
Drawbacks of the process of Nanofiltration:
1.
Membrane fouling.
2.
Insufficient separation.
3.
Treatment of concentrates.
4.
Membrane lifetime and chemical resistance.
5.
Insufficient rejection for individual components.
There are various ways to reduce the fouling
such as:
Periodic pulsing of feed.
Periodic pulsing filtrate (backwashing).
Increasing shear by rotating membrane.
Vibrating membrane.
Pretreatment.
Pretreatment of feed water greatly influences the
performance of NF installations.
The application of a pre-treatment has several
benefits:
 Membranes have a longer life-span when pretreatment is performed.
 The production time of the installation is
extended.
 The management tasks become simpler.
 The employment costs are lower.
CASE STUDY
Nanofiltration Membranes for Removal of
Colour and Pathogens in Small Public Drinking
Water Sources:

Small public water supplies that use surface water
as source for drinking water are frequently faced
with elevated levels of colour and NOM which are
precursors for chlorinated DBP formation.
NF systems can prevent DBP formation by

removing colour and NOM before chlorination.
Research studies were conducted in Fall Lake water

in Minnesota and dechlorinated potable water
spiked with NOM in Ohio by using
nanofiltration(Fyne process).
Fyne process
Developed in Scotland in 1994 to treat highly
coloured surface waters.
Requires no pretreatment of feed water other than a
coarse screen to prevent the entry of large solids.
Chosen because of its minimal pretreatment and
chemical cleaning requirements and its unique
mechanical cleaning feature.
The process uses a tubular semi permeable
membrane to allow clean filtered water to pass
through while retaining microbial contaminants and
most of the colour producing organic materials
dissolved in water.

Surface water treatability studies were conducted in Fall lake
water, Minnesota, for removal of microorganisms and organic
matter in 2008 and 2009.
Additional studies were conducted with the same Fyne
process pilot unit using dechlorinated potable water spiked
with NOM in Ohio.
Pilot unit was fitted with two 3 ft vertical membrane modules
made of acrylonitrile butadiene styrene plastic.
Each module contained 72 individual 0.91m tubes.
PCI type ES404 polyethersulfone membrane with a 4,000
Dalton MWCO, PCI type CA2PF cellulose acetate membrane
with a 2,000 Dalton MWCO and in 2009, the ES404 membrane
was tested again in Minnesota, along with a PCI type AFC30
polyamide film membrane with a MWCO of 350 Daltons,
potentially offering better DBP precursor removal.

NF membrane flux results from Minnesota (2008)
Results
ES404
CA2PF
Flux rates
624L/m2/day
608L/m2/day
Apparent colour
removal
99%
95%
Removal of
particles>2µm
2.5log
2.4log
Iron and
Manganese
Complete removal Complete removal
Calcium
25%
25%
Magnesium
13%
13%
Flux declined by 18% & 7% respectively for the two membranes.
NF membrane flux results from Minnesota(2009)
Results
ES404
AFC30
Flux rates
624L/m2/day
400L/m2/day
Colour removal
efficiency
90.7%
93.3%
Removal of
particles>2µm
2.2log
2.3log
Iron and
Manganese
Complete removal Complete removal
Calcium
42%
63%
Magnesium
29%
100%
Both flux rates are greater than design flux rates.
DBP studies in Minnesota.

In 2008, the ES404 and CA2PF membranes
removed 92 and 73% of TOC respectively.

ES404 and CA2PF reductions of ultraviolet (UV) 254
were 96 and 69%, respectively.

In 2009, the ES404 membrane removed only 76%
of TOC, whereas the AFC30 removed greater than
91%.

The results of the tests indicate that ES404 and
Particle count results from Minnesota (2008)

Above table represents the 2 & 3µm particle removal
results, same size range of Cryptosporidium.

Influent water-average particle count of 3440/ml.

Effluent water, for ES404-average particle count-
14/ml.

Effluent water, for CA2PF- ES404-average particle
count-17/ml.

Thus,99.6 and 99.5% removal, respectively for both
the membranes.
Colour removal results from Minnesota.
TOC and colour removal results from Ohio (2009)
CONCLUSIONS:
In Minnesota, the ES404 membrane showed
noticeably better performance in colour removal
than the CA2PF membrane.
The ES404 and CA2PF membranes both showed
99.5% removal efficiency for particles in the 2 and 3
μm size ranges (the size range for Cryptosporidium).
The colour removals achieved by the ES404 and
AFC30 membranes in treating Fall Lake water were
also satisfactory.
In Ohio, the Fyne process membranes
demonstrated good colour and TOC removal.
The results of this study indicate that the Fyne process
nanofiltration system could be used at very small
(serving 25–500 people) public water systems to reduce
colour and microbial pathogens in drinking water. The
TOC removal exhibited by the nanofiltration membranes
would also reduce the formation of DBPs after
chlorination.
Thus, It is evident that nanofiltration will play a
vital role in providing a quality, usable form of
water in the future.
THANK YOU!!