Reverse Osmosis

Reverse Osmosis

ABSTRACT Earth is the only planet, which has water in abundant and in ready to use forms. So we have to consider only his water in our discussion. About 97% of water available on earth from the area under sea, remaining 3 % is found in continent and in atmosphere. But more than 70% of this later portion is locked in glaciers and icecaps. The main reason for water shortage is uneven distribution of rain. Many other reasons are also there. Most of the water available is being polluted. So though there is water, we cannot use it as in the same form. For using the water we have to do some chemical and physical operation on this water. Bio-filtration is one of the operations for the purification of water. But we have large part of water by desalinizing the seawater. Seawater has salination value is 35000 ppm. But according to WHO for human consumption salinity should be 500 ppm. In desalination process actual value is brought to 500.

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Reverse Osmosis

INTRODUCTION Reverse osmosis is a physical process by which the dissolved material in the solvent may be separated from that solvent with the assistance of a semi-permeable membrane. By application of pressure in excess of the natural osmotic pressure to the feed water the membrane will preferentially allow the solvent (i.e. water) molecules to pass through and high percent of electrolytes and dissolved organic materials will be rejected. The raw water is pressure fed into a chamber containing semipermeable membrane. Only the pure water (known as permeate) can pass through the membrane, while the impurities are rejected and ruin to waste (known as concentrate). Reverse osmosis is operated as a continuous process.

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Reverse Osmosis

WHAT IS OSMOSIS AND REVERSE OSMOSIS It is the phenomenon of water flow through a semi-permeable membrane that blocks the transport of salt or other solutes through it. Osmosis is a fundamental effect in all-biological system. Osmosis is applied to water purification and desalination, waste material treatment and many other chemical and biochemical laboratory and industrial process.

Reverse Osmosis : 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. If there are solute molecules only in one side of the system, then the pressures that stop the flow is called osmotic pressure. By the application of pressure in excess of the natural osmotic pressure to the feed water the membrane will preferentially allow the solvent molecules to pass through and high percent of electrolytes and dissolved organic materials will be rejected. The raw water is pressure fed into a chamber containing semi permeable membrane. Only the pure water can pass through the semi permeable membrane, while the impurities are rejected and run to waste. Reverse osmosis is operated as a continuous process. C.O.E. & T., Akola

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Reverse Osmosis

PRINCIPLE OF REVERSE OSMOSIS Reverse osmosis is a membrane process that act as a molecular filter to remove 99% of all dissolved minerals, upto97% 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. Reverse osmosis is a misnomer, since application of pressure lo overcome osmotic pressure reverses only the flow of solvent but not the direction of flow of solute. As shown fig. (a), which depicts a semi permeable membrane separating pure water and a salt solution is pure water passes in opposite direction in process called natural osmosis. The driving force for the two flows is the difference in chemical potential between the two solutions. The water now continues until the pressure aerated by osmotic head equals-the osmotic pressure of salt solution in fig. (b). The two liquids are in equilibrium, by applying an external pressure; a salt solution in fig. (c) the flow of solvent may be revised. The reversal of flow has given the process the name REVERSE OSMOSIS.

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Reverse Osmosis

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Reverse Osmosis

OPERATION Fill the overhead tank with saline tract water up to full capacity. Open the outlet valves of overhead tank, multiple media filter and activated carbon filter. Multiple media filter will remove the particles in the range 0.01 to 0.1mm. The activated carbon filter will remove the colour pigments, oderous compounds and suspended particles in the range 0.001 to 0.01 mm from water. Let the storage tank be filled up to its full capacity. Before starting the pump make sure that. The valves are in V1 opened, V2 closed, V1 opened, V4 closed position. NEVER run the jump with V1 valve closed it may damage the membrane. Valve V1 is by pass valve you can adjust the pressure required for membrane with it. Start the pump. Slowly start closing valve V1. Never close the valve V1 fully. While closing V1 a situation will come when the water will start coming from the outlet of module. At this point adjust this outflow rate of 8lit/hr. At this point stop closing V 1. After some time ( 1-1 ½ hr) you will get the water require quality.

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Reverse Osmosis

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Reverse Osmosis

MEMBRANE Definition : Membrane can be defined as essentially as a barrier; which separates two phases and restricts transport of various chemicals in a selective manner. Membrane is a heart of every membrane process. The membrane can be made of an inorganic or organic, synthetic or biological product. Membrane of reverse osmosis system permeable for solvent and impermeable for solute. Material used for membranes in RO Membranes are prepared from almost every available material. In large-scale production commercial thermoplastic and cellulosics are primarily used. 1. Cellulose acetate. 2. Aromatic polyamide 3. Polyamide 4. Polyphyenylene oxides

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Reverse Osmosis

MODULES TYPES FOR REVERSE OSMOSIS SYSTEM The several forms of Reverse Osmosis membranes are sold packaged in devices to contain the steam pressure and to separate the feed and reject stream from the permeate streams. The device; usually called a module, is designed to control the feed stream-velocity and turbulence in order to reduce concentration polarization. There are three types of modules related to the types of membrane. a) Spiral wound b) Tubular c) Plate and frame

a) Spiral wound module: Pressure vessel can contain 1-6 membrane element in series, resulting in low pressure vessel to produce water cost. Having productivity of 15-30 Gal. Of product /sq. fit of membrane area. It is least prone to fouling through leading edge of the first element is the most pronelocation for fouling, biological degradation and wash out. Large membrane

areas are required

for adhesive attaching

membrane back to back in each leaf. These areas are non productive. Flow appears to be well distributed through out the membrane area. Product recovery for each element is appox 5-15 % of feed flow rate.

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Reverse Osmosis

b) Tubular type module : In this module the membrane system is parked in a shell and tube arrangement similar to heat exchanger. The membranes are tubular shaped with diameter 0.7-2.5 cm up to 30 tubes can be incorporated in series in tubular type module. In this module, each tubular membrane is held in stainless steel tube. There are two types of arrangements available, in first case brine is kept inside the tube and permeate flow outside and in second case brine is outside the tube and permeate flow inside the tubes.

c) Plate and frame module : It uses flat membrane cut in a unique, serial order and unidirectional feed flow coverage. In principle plate and frame module consist of non specified number of support plates of special contours with inter space membrane backing plates. This configuration resembles the filter press in vertical-position. This type of module has unique advantage that it can be tailored to the separation problem at hand, which can range from desalination of ultra filtration.

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Reverse Osmosis

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Reverse Osmosis

FOULING C.O.E. & T., Akola

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Reverse Osmosis

Membrane fouling is one of the most serious problems in case of Reverse system. This affects directly on the performance of the reverse osmosis system. It may cause permanent damage to membrane. The main reasons of fouling are: 1. Membrane scaling 2. Metal oxide ppt. 3. Device plugging 4. Biological growth inside device. 5. Colloidal fouling. Membranes scaling : Membrane scaling is caused by ppt of the salts dissolved in feed water. The salts in feed water are usually concentrated by a factor of two to ten in RO process, their solubility limits can be exceeded thus ppt can occur. The most common scales encountered in water treatment application are calcium carbonate and calcium sulfate. But ether compounds such as silicate, strontium sulfate, beryllium sill late and calcium fluoride also can scaling.

Metal Oxide Precipitation :

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Reverse Osmosis

Soluble species in feed water can be oxidized in the reverse osmosis system ahead of the permiator or in the permiator itself, to form insoluble species, which can deposit into permiator. Both manganese and iron can cause fouling by this mechanism, but iron fouling is most prevalent. Device plugging : Plugging is caused by mechanical filtration in which particles too large to pass through the feed brine passage are trapped in device. Device plugging problem. Biological fouling : Biological fouling occurs mainly due to growth of micro-organism in RO device. Micro-organisms may itself grow in membrane and when feed water is filtered these bacteria's may enter in product water. Colloidal fouling : Colloidal fouling is caused by entrapment of colloids on membrane surface in RO. Colloidal fouling is also caused by coagulation of colloids during RO process.

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Reverse Osmosis

APPLICATION OF REVERSE OSMOSIS TECHNIQUE Reverse osmosis system or technique has a many application over other conventional techniques; so in industry it is most widely used technique. Some of them are as follows. a. The most wide use of RO is in the desalination of sea water. b. RO is also used in sewage water treatment plants for the removal of nitrates phosphates or the non-biodegradable surfractants. c. RO is used in the treatment of hard water. d. Paper and pulp industry also use this technique for the treatment of waste water. e. Electroplating and electro painting industries also needs RO. f. RO is used in the removal of common water pollutants like nitrates, borate, fluorides, phosphates, alkyl benzene sulphonate. g. RO is used in pharmaceutical and electronic industries.

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Reverse Osmosis

ADVANTAGES AND DISADVANTAGES Advantages of reverse osmosis 1. Thermal damage of product is eliminated 2. Retention of original aroma and taste is retained 3. Reduction is energy consumption 4. Easy in operation 5. Compact size 6. Low maintenance.

Disadvantages ;  High Cost  Less membrane life

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Reverse Osmosis

CONCLUSION Today's day water is basic need and the availability of pure water is little quantity on earth. So desalination is necessary for today's world and selecting Reverse Osmosis process we can solved water problem to some extend to use of membrane technology. 1. Reverse osmosis is most efficient and convenient hyper filtration process of water purification. 2. Reverse osmosis process gives more promising result. 3. Reverse osmosis is simple and effective method than any other purification method. 4. Organic matter removal and particle colloidal reduction are effectively controlled by RO.

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Reverse Osmosis

REFERENCES 1. Indian Journal of Environmental Protection Vol.19, No.8 2. Indian Journal of Chemistry

Vol. 31 A.

3. www.dairyconsultant.co.uk/filtration.htm 4. www.desaline.com

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