.OSMOSIS & REVERSE OSMOSIS | REVERSE OSMOSIS SCIENTIFIC SCENARIO | APPLICATION DESALINATION | WATERMAN REVERSE OSMOSIS SYSTEM

 

          orOsmosis is a natural process involving the flow of a concentrated solution across a semi-permeable membrane barrier. Consider a tank of pure water with a semi-permeable membrane dividing it into two sides. Pure water in contact with both sides of an ideal semi-permeable membrane at equal pressure and temperature has no net flow across the membrane because the chemical potential is equal on both sides.

          

        If a soluble salt is added on one side, the chemical potential of this salt solution is reduced. Osmotic flow from the pure water side across the membrane to the salt solution side will occur until the equilibrium of chemical potential is restored {Figure 1(a)}. In scientific terms, the two sides of the tank have a difference in their "chemical potentials," and the solution equalizes, by osmosis, its chemical potential through out the system. Equilibrium occurs when the hydrostatic pressure differential resulting from the volume changes on both sides is equal to the osmotic pressure. The osmotic pressure is a solution property proportional to the salt concentration and independent of the membrane.

 

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What is Reverse Osmosis ?
Reverse Osmosis (RO) is a modern process technology to purify water for a wide range of applications, including semi conductors, food processing, biotechnology, pharmaceuticals, power generation, seawater desalting, and municipal drinking water. From initial experiments conducted in the 1950’s, which produced a few drops per hour, the reverse osmosis industry has today resulted in combined worldwide production in excess of 1.7 billion gallons per day. With demand for pure water ever increasing, the growth of the reverse osmosis industry is poised to continue growing well into the current century.

This section will provide historical background on the development of R O, and introduce the concepts of osmosis and semi-permeable membranes.

Historical Background
Research on Reverse Osmosis began in the 1950's at the University of Florida, where Reid and Breton were able to demonstrate desalination properties of Cellulose Acetate Membrane. Loeb and Sourirajan continued the development of the RO technology with the creation of the first asymmetric cellulose acetate membrane.

Research on these promising developments spawned new and better configurations of RO elements; today the industries produce predominately spiral wound elements, or in some cases, hollow fibre elements. In the early 1980's, research in US Government Labs resulted in the first Composite polyamide membrane. This membrane had significantly higher permeate flow and salt rejection than cellulose membranes. Today, with the introduction of the ESPA3 by Hydranautics, the industry has attained a 20-times increase in flow per pressure over original cellulose membranes, with an order of magnitude decrease in salt passage.

What is Semi-permeable ?
Semi-permeable refers to a membrane that selectively allows certain species to pass through it while retaining others. In actuality, many species will pass through the membrane, but at significantly different rates. In RO, the solvent (water) passes through the membrane at a much faster rate than the dissolved solids (salts). The net effect is that a solute-solvent separation occurs, with pure water being the product. In some cases, dewatering is desired to concentrate the salts.
Reverse Osmosis
With the tank in Figure 1(a), the water moves to the salty side of the membrane until equilibrium is achieved. Application of an external pressure to the salt solution side equal to the osmotic pressure will also cause equilibrium {Figure 1(b)}. Additional pressure will raise the chemical potential of the water in the salt solution and cause a solvent flow to the pure waterside, because it now has a lower chemical potential. This phenomenon is called Reverse Osmosis.

Flow diagram of Reverse Osmosis R.O. system

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Reverse Osmosis need pre treatment as well as post treatment as required according to the quality of raw water as well as the quality required of treated water at the end of the system or for final use of the water.

Pre Treatment
The pretreatment of water is required to remove the Dissolved, Foreign, Organic and Biological impurities.

Dissolved impurities include Calcium, Magnesium, Silica, etc. which can damage the porosity and Brine channels of membrane element.

Foreign impurities like Suspended Solids, Turbidity, etc. can damage the porosity and Brine channels of membrane element.

Organic impurities like Oil & Grease and Biological impurities like Algae, Fungus and harmful Bacteria, that can grow by multiple effect in the empty space in the membrane element because of stagnant water present in the element, can damage the element physically.

Usually, the pretreatment includes the following :

907bbalb.gif (874 bytes) Softening, Acid dosing, Suitable antiscalent dosing, etc.

907bbalb.gif (874 bytes) Pressure Sand Filtration, Micron Filtration, Coagulant dosing, etc.

907bbalb.gif (874 bytes) Activated Carbon, Chlorination – Dechlorination, Sterilization, etc.

Post Treatment
The post treatment for RO treated water is necessary if RO treated water may not be useful for further use, or may require some sort of treatment which can enable to use the RO treated water for process, drinking purpose, etc. Most effective post treatment for industries, drinking purpose and general use may vary depending on the raw water quality and the type of application.

Softening, degassification, dealkalisation, demineralization, Mixed bed deionization, Chlorination or Sterilization are the types of post treatment usually applicable to RO treated water.

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Desalination is the process to desalt the water which is having dissolved salts as ions. For desalination, following treatment are available in the world :

907bbalb.gif (874 bytes) Solar Distillation

907bbalb.gif (874 bytes) Vacuum Distillation

907bbalb.gif (874 bytes) Demineralization

907bbalb.gif (874 bytes) Distillation

907bbalb.gif (874 bytes) Reverse Osmosis

A brief description of these processes are as described below :

Solar Distillation

Water is desalted by means of solar energy. It requires huge space for desalting by evaporation through solar heat energy. It is very costly and is dependant on the availability of sunlight.

Vacuum Distillation

Water is desalted by means of vacuum distillation. It is based on the principle that the water can evaporate at 65 o C temperature under vacuum. It requires high power heaters as well as vacuum columns. Because of the salt present in the water, it can precipitate in the distillation columns thereby causing operational problems. It may not prove to be a continuous process for desalination due to scaling.

Demineralisation

Demineralization is a process wherein exchange of ions take place in the water by using cation and anion exchange resin. It requires charging of the resin by using Hydrochloric Acid and Sodium Hydroxide after getting the calculated quantity of desalted water. Due to the use of acid and Caustic, it can create problems of wastewater as well as handling problems. Moreover, timely charging in the demineralization process, it proves to be expensive.

Distillation

Distillation of water by evaporation process consists of steam generation followed by condensation,. Because of the process, operation cost is very high and it is not useful for continuous operation because of salts present in the water. Impurities and scale can deposit in the steam generator unit. Frequency of cleaning is high. Maintenance is costly. So it is used only in the pharmaceutical industries where the quantity of water required is very less.

 

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Reverse Osmosisrs

Osmosis is a natural process involving the flow of a concentrated solution across a semi-permeable membrane barrier. Consider a tank of pure water with a semi-permeable membrane dividing it into two sides. Pure water in contact with both sides of an ideal semi-permeable membrane at equal pressure and temperature has no net flow across the membrane because the chemical potential is equal on both sides.

If a soluble salt is added on one side, the chemical potential of this salt solution is reduced. Osmotic flow from the pure water side across the membrane to the salt solution side will occur until the equilibrium of chemical potential is restored {(Figure 1(a)}. In scientific terms, the two sides of the tank have a difference in their "chemical potentials," and the solution equalizes, by osmosis, its chemical potential throughout the system. Equilibrium occurs when the hydrostatic pressure differential resulting from the volume changes on both sides is equal to the osmotic pressure. The osmotic pressure is a solution property proportional to the salt concentration and independent of the membrane.

With the tank in Figure 1(a), the water moves to the salty side of the membrane until equilibrium is achieved. Application of an external pressure to the salt solution side equal to the osmotic pressure will also cause equilibrium {Figure 1(b)}. Additional pressure will raise the chemical potential of the water in the salt solution and cause a solvent flow to the pure waterside, because it now has a lower chemical potential. This phenomenon is called Reverse Osmosis.

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The driving force of the Reverse Osmosis process is applied pressure. The amount of energy required for osmotic separation is directly related to the salinity of the solution. Thus, more energy is required to produce the same amount of water from solutions with higher concentrations of salt.

Features

907bbalb.gif (874 bytes) Simple unit for process of purification and separation.

907bbalb.gif (874 bytes) Easy operation.

907bbalb.gif (874 bytes) Low energy and operating costs.

907bbalb.gif (874 bytes) Due to compact construction, it requires low space area.

907bbalb.gif (874 bytes) Operating flexibility due to modular system.

907bbalb.gif (874 bytes) Removes ionic and non-ionic impurities.

907bbalb.gif (874 bytes) Chemicals required are very less than other technologies.

907bbalb.gif (874 bytes) Environment friendly process.

907bbalb.gif (874 bytes) Diminishes water disposal problems.

907bbalb.gif (874 bytes) Easy and low maintenance.

907bbalb.gif (874 bytes) Wide range of application including sea water

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Applicationsap

907bbalb.gif (874 bytes) Process and utilities like boiler feed, cooling tower make-up, etc.

907bbalb.gif (874 bytes) Product dilution

907bbalb.gif (874 bytes) Rough Demineralization

907bbalb.gif (874 bytes) Sea Water Treatment

907bbalb.gif (874 bytes) Drinking Water Plants

907bbalb.gif (874 bytes) Recycling of effluents

 

Area of Application in Industries

907bbalb.gif (874 bytes) Water utilities

907bbalb.gif (874 bytes) Food and Beverages

907bbalb.gif (874 bytes) Tube and Micro Circuit manufacturing

907bbalb.gif (874 bytes) Pharmaceuticals

907bbalb.gif (874 bytes) Hotels & Resorts

907bbalb.gif (874 bytes) Hospitals

907bbalb.gif (874 bytes) Mineral Water Processors

907bbalb.gif (874 bytes) Power Generation

907bbalb.gif (874 bytes) Domestic Applications

907bbalb.gif (874 bytes) Electronic Component manufacturing

907bbalb.gif (874 bytes) Semi conductors

Configuration of Reverse Osmosis Elements

 

The Reverse Osmosis elements are of the following configuration :

Hollow Fine Fibres

The hollow fine fibre RO membranes are the fibres bound in cylindrical bundle. They provide large surface area. Feed water passes through the walls of fibre and passes through the bore. Brine or the concentrate is rejected through the Brine outlet.

Spiral Housing

In spiral wound configuration, the RO membrane is spirally wound around a permeate collector tube. The pressure vessel can house a number of elements with necessary seals and inter connector contaminants remain on the outside surface.

Tubular

Tubular membranes are housed in the inner surface of support tube. An appropriate number of membrane tubes are connected in parallel within a modular container with manifolds, which provide connectors for feed permeate and concentrate. Pressurized water flows through the tube and permeate passes through the tubular membrane
along the entire length.

Because of Spiral Wound construction, it has resistivity against immediate fouling in element and easy cleaning process by membrane cleaning chemicals with wide application from low salinity water to high salinity sea water. Nowadays, spiral
wound membrane is used widely.

Waterman design the Reverse osmosis /Desalination to get maximum efficiency from
the system ,With easy operation in single valve, Atomization.

The material of construction of the system may be Fiber glass reinforced plastic, Stainless steel ,PVC, etc…as suit to our requirement.

Waterman Manufacturing REVERSE OSMOSIS with highly technocrat personals.  our design in very wide range, i.e. for Home application, Hotel Application to Industries with wide production capacity.

Waterman is OEM of KOCH MEMBRANE SYSTEMS, USA., Which is manufacturing, R.O.Membrane elements from last--------years., Which is with different ranges & sizes Products in Membrane elements.

Waterman Works in Trunkey as well as part work for Reverse osmosis & Desalination Systems for water treatment application.

Waterman Manufacture the system from 60 ltrs to 1,00,000 ltrs per Hour and above As desired by the client & suit the client requirement. Waterman R.O. Systems depends On Present water quality, End water quality required by the client.Rsys

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Revised: September 22, 2000