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Reverse Osmosis Basics


Reverse Osmosis Basics


•    Osmosis is a natural phenomenon that provides water to all animal and vegetable cells to support life

•    Water moves from a high concentration of water (less sugar/salt dissolved in it) to a low concentration of water (more salt/sugar dissolved in it) across a semi-permeable membrane

•    This means that water can cross a selectively permeable membrane from a dilute solution (less dissolved in it) to a concentrated solution (more dissolved in it)

Reverse Osmosis (RO) is a technology used for purification of water. RO water purifiers are used to remove ions, molecules and large particles from contaminated water. In osmosis process, the solvent in water moves from area of low concentration solute to area of high concentration solute through a membrane.

While this movement occurs naturally, reverse osmosis requires an external pressure to reverse the movement of solvent. Reverse osmosis helps in removing dissolved bacteria and other pollutants from water. RO water purifiers contain a semi-permeable membrane that does not allow large particles to pass through. This membrane is designed to eliminate fine impurities from water.

RO purifier water has merits as well de-merits, and while it may pose some negative health effects over short and long terms, it cannot be categorised as “very dangerous for us”.First let’s see the merits (assuming its use for household level drinking water purification). The membrane is a non-chemical, non-residue leaving, physical process of removal of contaminants from water.

The removal of contaminants is dependent on the size of the pores in the RO membrane. Because of its very small size (of the order of 0.001 microns) the membrane is capable of removing practically everything from water, giving highly purified water. This water could also be used for surgical and pharmaceutical purposes.Reverse osmosis is a highly economical and efficient way of obtaining drinking water from sea through desalination. Other methods like distillation are highly energy intensive, for desalination.

The demerits arise in the process of reverse osmosis, which must necessarily reject a concentrated solution containing all the contaminants. This rejected water is highly contaminated that needs to be disposed of properly, which is never done at the household level. Also the yield of purified water is very low at the household level. Out of every 5 litres of water input into the RO purifier, only 1 litre is obtained as purified water.

Reverse Osmosis Basics

Osmosis: What is it?

•    A semi-permeable membrane is a membrane which will allow only

certain molecules or ions to pass through

•    Osmosis is very important in biology as it provides the primary means by which water is transported in and out of cells

Net Movement of Water Molecules

Reverse Osmosis: What is it?

•    RO is a form of filtration using osmosis in reverse

•    Water passes from a more concentrated solution to a less concentrated solution

•    To accomplish this a force or pressure MUST be applied

•    RO requires 1 psi of pressure for every 100 ppm of TDS

•    RO is used to remove dissolved solids from water but it can also improve taste, odor & color of water

•    RO membranes have the capability to remove particles as small as ions i.e. magnesium ions or sodium ions

•    RO membrane will reject most compounds based largely on size

•    Dissolved ions, such as salts, carry an electric charge and will also be rejected by membrane

Reverse Osmosis Schematic

Ro water plants How does it work?

•    Feed water flows into RO unit with the force of line pressure

•    Water is forced through membrane by cross flow filtration

•    Cross flow filtration is most commonly used in RO as it allows membrane to continually clean itself

•    Membrane then either rejects or repels contaminants

•    Two exit streams generated: waste & product stream

•    Waste stream consists of: A concentrate (reject) stream which carries contaminants (compounds too large to pass through membrane)

•    Permeate stream consists of: Product water which has been forced through the membrane & is virtually free of TDS

RO Membrane:

•    Membrane is the work-horse of an reverse osmosis system

•    When choosing an RO system you must do so wisely – taking into account water quality is very important

•    Three main types of membranes:

CTA    Cellulose acetate/triacetate blend

•    Provides lowest cost per gallon of water

•    Resists chlorine but has a lower flow rate limit in applications of high water consumption

TFG mawferaflfe: Thin film/thin layer composite

•    Can handle high flow, has a high rejection rate & can handle high water consumption •    Cannot handle chlorine concentrations; water must be carbon pre-filtered

TFC Membrane:

•    TFC membranes are intolerant to chlorine – will cause deterioration of membrane

•    Must use a carbon pre-filter for TFC membranes

•    TFC membranes have a much higher rejection rate of many chemicals than CTA membranes

•    Carbon pre filters are vital in the life of this membrane & must be changed regularly

RO Production Rate vs. Feed Water Conditions:

RO Systems can remove the following contaminants:

•    Dissolved solids = TDS (salts & minerals) – UP TO 2000 ppm

•    Most Heavy metals (lead, mercury, silver)

•    Most radioactive elements

•    RO systems may not be capable of removing nitrates to recommended levels

Air-Gap Faucets:

•    ‘Air gap’ faucet is a plumbing device designed to provide a siphon break for an under*sink reverse osmosis unit

•    It is a valve used to isolate one part of a water system from the drain

•    Air gaps are designed to prevent backflow by incorporating a “backflow prevention” method called an ‘air gap’

•    Purpose of an air gap faucet is to assure that no water from a stopped-up sink can possibly be forced backward into your reverse osmosis system unit via its drain connection

•    Some plumbing codes do enforce the use of an Air Gap faucet

RO System Maintenance:

When to Replace prefilters:-

•Every 6 months for normal installations.

•After a Boil Water Advisory (BWA)

When to Replace Postfilters:-

Every 6 months, depending on water conditions.

Noticeable decrease in water production indicates that the prefilter should be changed.

After microbiological contamination, such as in a Boil Water Advisory (BWA)

RO System Maintenance:


•    Typically, every 18 months to 3 years

•    Test using a TPS (total dissolved solids) meter. Replace a membrane below 80% TDS reduction.

•    This will depend on influent water quality, usage, pre & post filter maintenance

•    Maintain filters, lengthen life of membrane!!!




TDS stands for total dissolved solids, and represents the total concentration of dissolved substances in water. Common inorganic salts that can be found in water include calcium, magnesium, potassium and sodium, which are all cat-ions and carbonates, nitrates, bicarbonates, chlorides and sulfates, which are all anions.

Nitrate is a compound that is formed naturally when nitrogen combines with oxygen or ozone. Nitrogen is essential for all living things, but high levels of nitrate in drinking water can be dangerous to health, especially for infants and pregnant women.

The federal standard for nitrate in drinking water is 10 milligrams per liter (10 mg/l) nitrate-N, or 45 mg/l nitrate-NO3. when the oxygen is measured as well as the nitrogen. Unless otherwise specified, nitrate levels usually refer only to the amount of nitrogen present, and the usual standard, therefore, is 10 mg/l.

Water fluoridation is the controlled adjustment of fluoride to a public water supply to reduce tooth decay. Fluoridated water contains fluoride at a level that is effective for preventing cavities; this can occur naturally or by adding fluoride.

fluoride levels in drinking-water of <0.05–0.2 mg/litre (non-fluoridated) and 0.6–1.1 mg/litre. (fluoridated) have been reported in municipal waters.

Raw Water & Treated Water  Parameter  (View As a LAB REPORT With Help of One Example) :-

RO Plant Inspection Report

PHED Division
MLA Costituency
Gram Panchyat
Village / Hab.:
RO Plant Installed:
Capacity of Plant:
Water ATM Card/Physical card(In case of phase-I) Iss
Status of RO Plant as per physical Inspection

High-Pressure Pump (HPP) – The high-pressure pump is responsible for compressing the fuel supplied by the electric fuel pump to bthe pressure required for high-pressure injection up to 20 MPa (200 bar)

Raw-water pump -This pump does the bulk of the engine’s cooling. It draws raw water (this may be seawater, fresh water or whatever mixture of the two the boat is floating in) into the engine’s open or raw-water cooling circuit using a rubber impeller


filters continue to supply filtered water even during the flushing cycle. The water flows into the filter through a pre-filter, and then to the inside of the screen.

An illustrative embodiment of the air filter assembly includes a generally cylindrical air filter housing having a filter housing interior; a carburetor opening provided in the air filter housing and communicating with the filter housing interior,- a first housing inlet arm and a second housing inlet arm carried by the air filter housing in spaced-apart relationship with respect to each other and communicating with the filter housing interior; a first air filter and a second air filter communicating with the first housing inlet arm and the second housing inlet arm, respectively; and an air flow deflector provided in the filter housing interior at generally a center of the air filter housing.


A sediment Filter captures and removes particulate matter like dirt and debris from your water. Sediment is a generic term for all the particulate matter in your water that is not liquid. Flakes of rust can enter your water supply from corroded galvanized plumbing. Rainwater can carry silt, clay, soil, and grains of sand into your well groundwater supply. Flow changes in your water main can also transport sediment to your home. The sediment filter is the first line of defense against this dirt and debris. It prohibits all this solid particulate from entering your water supply and impeding the performance of your water filtration systems.

A sediment filter traps and removes suspended solids from your water supply. Debris from storm water  runoff and rust flecks from aging pipes can leave your water discolored and unappetizing. Sediment build-up can wreak havoc on appliances, clogging up valves and fixtures and ruining hot water heaters. Sediment also prevents filtration systems like reverse osmosis and ultraviolet purification from operating efficiently. Sediment filters keep your water clear and are an integral component of the water filtration process. A sediment filtration system is the guardian of your home and your water. 





In water treatment membranes are barriers that allow water to pass through but stop unwanted substances from passing through with it. Working much like the cell walls in our bodies, technical membranes filter out salts, impurities, viruses, and other particles from water.

A membrane process is any method that relies on a membrane barrier to filter or remove particles from water. Fluid is passed through the membrane because of the pressure difference between one side of the membrane and the other. Contaminants remain on one side. Although many types of filtering media are used for water treatment — for instance, clay, silt, and sand — one of the properties that distinguishes membranes is their ability to separate smaller substances such as salts and ions from a liquid

Ultra filtration (UF) is a type of membrane filtration in which hydrostatic pressure forces a liquid against a Semi permeable membrane. Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through the membrane.


Ultraviolet light is a type of electromagnetic radiation that makes black-light posters glow, and is responsible for summer tans — and sunburns. However, too much exposure to UV radiation is damaging to living tissue. Ultraviolet (UV) light falls in the range of the EM spectrum between visible light and X-rays.


A dosing pump is a small, positive displacement pump. It is designed to pump a very precise flow rate of a chemical or substance into either a water, steam or gas flow. Dosing pumps are used in a variety of applications from agriculture, industry, manufacturing to medicine.

Solenoid Valve

A solenoid valve is an electromechanical device used for controlling liquid or gas flow. The solenoid valve is controlled by electrical current, which is run through a coil. When the coil is energized, a magnetic field is created, causing a plunger inside the coil to move.


The flow meter checks compliance with the flow rate required for reasons of hygiene and therefore reports any clogging or leak. The pipes are made of stainless steel, with a diameter of up to DN100, and can reach temperatures of up to 100°C during cleaning cycles

Multiport valves are designed for maximum performance and working pressures. Available in 1 ½ and 2 inch for top mount and side mount models. These valves feature a solid constructed of molded ABS mixed UV materials with heavy-duty plastic handles, PVC socket which permits leak-free solvent welds to PVC piping, which is purposed to top position of world standard by the strict quality controlling systems . We offer manual, semi or fully automatic multiport valves of different sizes.

A multiport valve has a rinse setting which is basically a “filter to waste” setting that runs the water forward through the filter and then sends it to the waste line so that any debris that may have collected is not sent back to the pool.


A simple method of measuring flow rates of Newtonian fluids in pipelines based on the dimensionless velocity at a certain radial position is proposed. This technique makes use of the experimental observation that the dimensionless velocity profiles as scaled by the cross-sectional average velocity intersect each other at almost the same point over.


Water flow sensors are installed at the water source or pipes to measure the rate of flow of water and calculate the amount of water flowed through the pipe. Rate of flow of water is measured as liters per hour or cubic meters.

Working Principle

Water flow sensor consists of a plastic valve from which water can pass. A water rotor along with a hall effect sensor is present the sense and measure the water flow.

When water flows through the valve it rotates the rotor. By this, the change can be observed in the speed of the motor. This change is calculated as output as a pulse signal by the hall effect sensor. Thus, the rate of flow of water can be measured.

The main working principle behind the working of this sensor is the Hall effect. According to this principle, in this sensor, a voltage difference is induced in the conductor due to the rotation of the rotor. This induced voltage difference is transverse to the electric current.

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