162931615 Reverse Osmosis
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Transcript of 162931615 Reverse Osmosis
REVERSE OSMOSIS
Presentation
REVERSE OSMOSIS
Reverse osmosis (RO) is a membrane-
technology filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side.
When two water or other solvent volumes are separated by a semi permeable membrane, water will flow from the side of low solute concentration to side of high solute concentration. The flow may be stopped or even reversed, by applying external pressure on the side of higher concentration. In such a case the phenomenon is called reverse osmosis. RO is a-physical process.
Reverse osmosis is a membrane process that act
as a molecular filter to remove 99% of all dissolved
minerals, up to 97% of most dissolved organic
matter, more than 98% of biological and colloidal
matter can be removed from water having
concentration from 50 ppm to 60,000 ppm.
STAGES OF FILTRATION
The modern RO system is a unit consisting of a
sediment pre-filter to remove particulates, turbidity,
sand and rust; an activated carbon pre-filter to
remove the chlorine, pesticides, herbicides,
disinfectants, and VOCs which might otherwise
damage the reverse osmosis membrane; the
reverse-osmosis membrane which removes
virtually everything such as heavy metals, lead,
salt, chromium and dissolved solids; a storage tank,
and an activated-carbon post filter.
Sediment Stage: removes rough particles, sand and rust.
Carbon stage: removes chlorine and chemicals which would otherwise damage the TFC reverse osmosis membrane. Multiple carbon stages my be necessary at this point depending on the carbon quality and contact time.
Reverse osmosis stage: removes dissolved solids nd virtually everything larger than the water molecule itself. This is where the bulk of the purification is accomplished.
Remineralization Stage: water purified by reverse osmosis is highly pure and slightly acidic. The Tap Master Artesian Full Contact remineralizes with calcium and magnesium to balance the pH, improve the taste and introduce healthy minerals.
Storage tank
Optional or application specific water treatment stage(s): UV filter to destroy microorganisms, nitrate/arsenic/fluoride/deionization selective filters to remove whatever small amount remains of these contaminants.
Final Carbon stage: also known as a "polishing" filter this carbon filter removes any tastes or odors the acidic RO water has "picked up" from the storage tank. In other words the acidic water produced from systems without the Artesian Full Contact technology will dissolve some of the rubber in the storage tank which the final carbon filter then removes.
HOW REVERSE OSMOSIS WORKS
A semi permeable membrane, like the membrane of a cell wall or a bladder, is selective about what it allows to pass through, and what it prevents from passing. These membranes in general pass water very easily because of its small molecular size; but also prevent many other contaminants from passing by trapping them.
Reverse osmosis filters have a pore size around 0.0001 micron. After water passes through a reverse osmosis filter, it is essentially pure water. In addition to removing all organic molecule sand viruses, reverse osmosis also removes most minerals that are present in the water.
Reverse osmosis removes monovalent ions, which means that it desalinates the water. To understand how reverse osmosis works, it is helpful to understand osmosis.
Two fluids containing different concentrations of dissolved solids that come in contact with each other will mix until the concentration is uniform. When these two fluids are separated by a semi permeable membrane (which lets the fluid flow through, while dissolved solids stay behind), a fluid containing a lower concentration will move through the membrane into the fluids containing a higher concentration of dissolved solids.
After a while the water level will be higher on one side of the membrane. The difference in height is called the osmotic pressure. By pursuing pressure upon the fluid column, which exceeds the osmotic pressure, one will get a reversed effect. Fluids are pressed back through the membrane, while dissolved solids stay behind in the column. Using this technique, a larger part the salt content of the water can be removed.
1. Water flows from a column with a low dissolved
solids content to a column with a high dissolved
solids content
2. Osmotic pressure is the pressure that is used to
stop the water from flowing through the membrane,
in order to create balance
3. By pursuing pressure that exceeds the osmotic
pressure, the water flow will be reversed; water
flows from the column with a high dissolved solids
content to the column with a low dissolved solids
content
RO MEMBRANES:
Four common types of membranes:
Nanofiltration
Ultrafiltration
Microfiltration
Common membrane materials include polyamide thin
film composites (TFC), cellulose acetate (CA) and
cellulose triacetate (CTA) with the membrane material
being spiral wound around a tube, or hollow fibres
bundled together. Hollow fibre membranes have a
greater surface area and hence capacity but are more
easily blocked than spiral wound membranes.
ULTRAFILTRATION
An ultrafiltration filter has a pore size around 0.01
micron. A microfiltration filter has a pore size around
0.1 micron, so when water undergoes
microfiltration, many microorganisms are removed,
but viruses remain in the water.
Ultrafiltration would remove these larger particles,
and may remove some viruses. Neither
microfiltration nor ultrafiltration can remove
dissolved substances unless they are first adsorbed
(with activated carbon) or coagulated (with alum or
iron salts).
NANOFILTRATION
A nanofiltration filter has a pore size around 0.001
micron. Nanofiltration removes most organic
molecules, nearly all viruses, most of the natural
organic matter and a range of salts.
Nanofiltration removes divalent ions, which make
water hard, so nanofiltration is often used to soften
hard water.
MICROFILTRATION
Microfiltration is a low-pressure cross-flow
membrane process for separating colloidal and
suspended particles in the range of 0.05-10
microns. Microfiltration is used for fermentation,
broth clarification and biomass clarification and
recovery.
PH ADJUSTMENT
The desalinated water is very corrosive and is
"stabilized" to protect downstream pipelines and
storages, usually by adding lime or caustic to
prevent corrosion of concrete lined surfaces. Liming
material is used to adjust pH between 6.8 and 8.1
to meet the potable water specifications, primarily
for effective disinfection and for corrosion control
LOW PRESSURE (RESIDENTIAL) SYSTEMS
Low pressure RO systems generally refer to those systems
with a water feed pressure of less than 100 psig. These are
the typical countertop or under sink residential systems that
rely primarily on the natural water pressure to make the
reverse osmosis process function; a typical system is shown
schematically below.
FACTORS:
There are two factors that are most relevant to
determine how effective a membrane filtration process
is. these two factors are selectivity and productivity.
Selectivity is expressed as a parameter called retention
or separation factor (expressed by the unit l/m2/h).
Productivity is expressed as a parameter called flux
(expressed by the unit l/m2/h). Both these factors i.e.
Selectivity and productivity are dependent upon the
memberane.
Membrane filtration can be divided into a few ranges. It
is divided between micro and ultra filtration on the one
hand and nano filtration and reverse Osmosis (also
called hyper filtration) on the other hand.
APPLICATIONS
Drinking Water Purification: Such systems typically include a number of steps:
a sediment filter to trap particles, including rust and calcium carbonate
optionally, a second sediment filter with smaller pores
an activated carbon filter to trap organic chemicals and chlorine, which will attack and degrade TFC reverse osmosis membranes
a reverse osmosis (RO) filter, which is a thin film composite membrane (TFM or TFC)
optionally, a second carbon filter to capture those chemicals not removed by the RO membrane
optionally an ultra-violet lamp for disinfecting any microbes that may escape filtering by the reverse osmosis membrane
Membrane pore sizes can vary from 0.1
nanometres (3.9×10−9 in) to 5,000 nanometres
(0.00020 in) depending on filter type. "Particle
filtration" removes particles of 1 micrometre
(3.9×10−5 in) or larger. Microfiltration removes
particles of 50 nm or larger. "Ultrafiltration" removes
particles of roughly 3 nm or larger. "Nanofiltration"
removes particles of 1 nm or larger. Reverse
osmosis is in the final category of membrane
filtration, "hyperfiltration", and removes particles
larger than 0.1 nm.
FOOD INDUSTRY
Reverse osmosis is extensively used in the dairy
industry for the production of whey protein powders and
for the concentration of milk to reduce shipping costs. In
whey applications, the whey (liquid remaining after
cheese manufacture) is concentrated with RO from 6%
total solids to 10–20% total solids before UF
(ultrafiltration) processing. The UF retentate can then be
used to make various whey powders, including whey
protein isolate used in bodybuilding formulations.
Additionally, the UF permeate, which contains lactose, is
concentrated by RO from 5% total solids to 18–22%
total solids to reduce crystallization and drying costs of
the lactose powder.
CAR WASHING
Because of its lower mineral content, reverse
osmosis water is often used in car washes during
the final vehicle rinse to prevent water spotting on
the vehicle. Reverse osmosis is often used to
conserve and recycle water within the wash/pre-
rinse cycles, especially in drought stricken areas
where water conservation is important. Reverse
osmosis water also enables the car wash operator
to reduce the demands on the vehicle drying
equipment, such as air blowers.
REEF AQUARIUMS
Many reef aquarium keepers use reverse osmosis systems for their artificial mixture of seawater. Ordinary tap water can often contain excessive chlorine, chloramines, copper, nitrogen, phosphates, silicates, or many other chemicals detrimental to the sensitive organisms in a reef environment. Contaminants such as nitrogen compounds and phosphates can lead to excessive, and unwanted, algae growth. An effective combination of both reverse osmosis and deionization (RO/DI) is the most popular among reef aquarium keepers, and is preferred above other water purification processes due to the low cost of ownership and minimal operating costs.
Where chlorine and chloramines are found in the water, carbon filtration is needed before the membrane, as the common residential membrane used by reef keepers does not cope with these compounds.
EFFECTIVENESS:
RO can treat water TDS concentrations up to
40,000 – 45,000 mg/L
RO treatment produces lower water recovery rates
(approximately 40%-65%) or a higher brine stream
relative to thermal treatment processes with high
TDS concentrations.
RO is typically more cost effective since the
technology requires less energy to operate relative
to thermal treatment processes
Reverse Osmosis has proved to be the most
reliable and cost effective method of desalinating
water, and hence its use has become more and
more widespread. Energy consumption is usually
some 70% less than for comparable evaporation
technologies. Advancements have been made in
membrane technology, resulting in stable, long lived
membrane elements.
IN PAKISTAN ,INDUSTRIES USING RO:
Nishat mills capacity of 4 m3/hr in lahore
Coca cola beverages Pak ltd capacity of 35 in
Lahore , 120 in Lahore and 20 in Multan
Engro fertilizers ltd capacity of 170 in dharki
Karachi
And many more others working on this process in
Pakistan