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