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Reverse osmosis water desalination

The reverse osmosis water desalination (RO) is a water purification method that can produce high quality water (such as distilled water, or drinking water) from saline or seawater sources. The reverse osmosis water desalination removes and purifies using membranes, or semipermeable membranes, all soluble salts, viruses and particles that are much thicker in molecular size. In addition to high pressure pumps, RO membranes, Pressure Vessel, pretreatment including carbon filter, sand filters and micro filters, as well as a set of controls and control valves that perform water purification they give.

Today, industrial water treatment and water desalination processes are widely used in reverse osmosis method. The reverse osmosis water desalination, in addition to its easy operation, provides very low initial and initial costs, plus high purity water compared to other purification methods. TARHOKAR Engineering Company in designing, manufacturing, installing various types of reverse osmosis water purification systems (RO) in various industries such as boiler water, industrial water, sewage treatment, drinking water, deep well water and Other fields of water purification are active.

Sea water desalination by RO

Description of the process of reverse osmosis water desalination

The reverse osmosis water desalination RO consists of two parts. The first part is pretreatment to be designed to protect membranes more efficiently and extend their useful life. The second part is the reverse osmosis system (RO). The water inlet to the reverse osmosis water purifier feeds into a sand filter and then a carbon filter through the feed pump. In these filters, suspended particles and opacity agents are adsorbed into silica particles and the indicators of turbidity and water slurry are reduced. In the carbon filter section, organic matter, chlorine remains and factors related to odor in water are removed. In the next step, the water passes through a micro filters. In these micro filters particles are removed up to 5μm in size. In this way, it can be ensured that the suspended particles do not enter reverse osmosis membranes and the water turbidity is reduced to an acceptable level.

In the second part of the reverse osmosis water desalination, the water enters the high pressure pump to provide the pressure needed to overcome osmotic pressure. Water then enters the membranes, where water molecules pass through membranes with pores smaller than one nanometer, but monovalent and multiplicity ions, viruses and bacteria, ions of metals and suspended particles pass through membranes they do not go along with the flow of waste water (Concentrate). Therefore, the water entering the membranes is split into two sections of the treated water and wastewater.

In addition to designing pre-treatment systems in the reverse osmosis water purifier, various chemicals are injected into the water entering the membranes, including antiscalant agents to prevent saturation of ions on membranes and acid Adjust pH and reduce Langeuli indexes.

Reverse osmosis membranes

The membranes are in the reverse osmosis water purification system of the RO as the core of the water purification unit. All soluble salts and what is generally referred to as TDS are removed and purified in this section. These membranes are made with very high effective surface and diameter of cavities less than nanometer of polyamide.
Polyamide membranes that are used in the reverse osmosis water purification process are sensitive to some chemical compounds. So Reverse Osmosis design engineers, therefore, try to prevent the introduction of such materials into reverse osmosis. In this case, the useful life of a membrane can be optimized for about 3 to 5 years.
The most important inputs that can reduce the useful life of reverse osmosis membranes include:

1.    The remaining free chlorine entering the reverse osmosis membrane RO should be less than 0.1 mg / lit.
2.    The amount of SDI should not exceed 5 units.
3.    The total chemical oxygen demand (COD) should be less than 10mg / lit.
4.    Oil & Grease should be less than 0.1 mg / lit.
5.    The amount of iron must be less than 0.05 mg / lit.

Pretreatment in reverse osmosis water desalination

Due to the limitations mentioned above, the design of a reverse osmosis water desalination system  is designed to prevent pre-treatment of particulate matter in order to prevent materials that damage membranes. The most important pretreatments used in reverse osmosis include sand filter, carbon and microfiltration and chemical injection, the uses and generalities of which include:

1.    Sand filter: This filter is designed to reduce the SDI index. In reverse osmosis water desalination system, the water turbidity agents and suspended particles are used to fill sand filters filled with silica, anthracite or gravel. These filters can absorb suspended particles.
2.    Carbon Filter: This filter is designed to eliminate remaining free chlorine and reduce COD. Since membranes are semi-permeable (membranes) made of polyamide and strongly react with the remaining chlorine in water, it is therefore necessary to ensure complete removal of chlorine before water is introduced into the reverse osmosis water desalination. For this purpose, an active carbon bed is used as an organic solvent and free chlorine absorber.
3.    Micro filtration: These filters trap polypropylene fibers in their pores, and improve the quality of the sludge index, the SDI of the water. As stated, the slurry indicator for the reverse osmosis water desalination package is considered as one of the main information related to the design of the RO unit.
4.    Injection of chemicals (antiscalant): In order to prevent the fouling of the smoke membranes, the injected antiscalant is injected inverted. This phosphate-based material prevents solute saturation on reverse osmosis membranes.
5.    Chemical Injection (SMBS): Due to the extreme sensitivity of reverse osmosis membranes to free chlorine or any other oxidizing agent, it can be injected into the chemical SMBS before water enters the RO, and the oxidizing properties of such substances completely destroyed.

Brackish Water treatment by RO

Membrane cleaning (CIP) in reverse osmosis water desalination

A reverse osmosis water desalination after 3 to 4 months of operation requires cleaning. Since many salts are isolated on the membranes and are removed from the water treatment system by the condensate stream, it is possible to saturate some of the compounds, such as calcium carbonate, magnesium sulfate compounds, and so on. In order to improve RO unit efficiency, periodic reverse osmosis requires the clean in place (CIP) of chemicals.

In this reverse osmosis operation, the clean in place (CIP) is said to be one of the key to keeping membranes in good shape. Depending on the type of membrane fouling, special chemical solutions are prepared, which rinses the reverse osmosis membranes. These solutions are mainly chloric acid, caustic soda, sodium tetraethyl EDTA and other compounds.

Results of using reverse osmosis desalination

The main results of using reverse osmosis include:
1.    Reduce TDS or the total dissolved solids.
2.    Reduced electrical conductivity (salinity).
3.    Reduction of temporary hardness and permanent  hardness of water Total Hardness
4.    Eliminating all microbial agents, organisms and germs and viruses.
5.    Reducing bivalent and cation ions such as calcium, magnesium and sodium
6.    Reducing water anions such as chloride, sulfate, and bicarbonate.
7.    The removal of nitrate (NO3), which is highly harmful to the health of drinking water.
8.    Removal of ions and rare but toxic elements, such as strontium, barium, boron and mercury
9.    Removal of heavy metals such as iron, cobalt, zinc and nickel.
Compared with other water treatment methods such as water softening, ion exchange and ultrafiltration, the reverse osmosis method produces better quality water.

Reverse Osmosis Applications

Today, in various industries, reverse osmosis water desalination is used to sweeten and purify water. The most important uses of this method are as follows:
1.    In the water treatment the boiler and produce the demine water.
2.    In the water treatment of cooling tower and heat exchanger.
3.    In industrial water treatment in steel factories, mines, food and dairy industries.
4.    In the production of distilled water by Double RO method
5.    Demine water production in pharmaceutical and pharmaceutical industries
6.    In Pure water production for use in starch factories, juices, detergents, sugar
7.    Brackish water treatment for animal use in cattle, chicken and ostrich breeding