Treatment of Water Through Reverse Osmosis Plant

Osmosis is a natural process that provides water to all vegetable and animal cells to support life. In this case, water flows from a higher concentration of water to a lower concentration of water. This means water can cross a selectively semi-permeable membrane from a dilute solution to a concentrated solution.

Reverse osmosis (RO) is a reverse form of filtration which is opposite to osmosis. Water passes from a concentrated solution to a diluted solution. 

RO is used to remove soluble solvent from water but can also improve the taste, aroma and color of water. RO membranes have ability to remove small particles as sodium or magnesium ions. The RO membrane will reject many elements depending on the size. Dissolved ions, such as an electric charge-carrying salts will also be rejected by membrane. The feed water flows to the RO unit with the line pressure force. Water is forcefully passed through membrane by a cross filtration. Cross flow filtration is extensively used in RO as it allows membrane to clean itself continually. The membrane then either refuses or returns the impurities.

Two different types of exit streams generated: waste & product stream

• Waste stream consist of: It is a stream (reject) which carries contaminants (compounds too large to pass itself)
• Permeate stream consists of: It is a product water which has been passed through the membrane and is must be free from total dissolved solid (TDS).

Components of RO Unit:

• Turbines: 

Ground water is obtained with the help of turbines. They have capacity of 100,000 liter per hour. Two turbines in total are present at the moment and they both contain same capacity.

• Raw water tank:

From turbines water directly moves to the storage tank of raw water. The capacity of raw water tank is 100 ton. In raw water storage tank chlorine is dosed about 1-3 ppm. The addition of chlorine has a specific function of killing microbes.

• Bag Filter:

There are 2 bag filters placed at the entrance of the plant. They have the mesh size about 20-50 microns. They are placed to remove the unwanted particles or other foreign undesired particles.

• Ultra-filtration:

This is also a filtration processing unit to provide aid in the filtering of water. It has several tubes to perform certain function. It has mesh size of 0.01 microns. It helps in removing colloidal materials, larger substances and inorganic and organic polymeric molecules. Low molecular organics weight is not removed such as magnesium chloride, calcium, sodium and sulfate are not removed. Low applied pressures are therefore sufficient to achieve high flux rates from an ultra-filtration membrane.

• Ultra-filtration product tank:

This acts a buffer tank.  And it has a capacity of 20,000 liters.

• Carbon filtration:

It consists of water washers, sand beds, activated carbon bed. The main function of carbon filtration is to remove chlorine from the water as it was added intentionally earlier for the removal of the microbes.  The capacity of the carbon filtration tank is 74 tons. Carbon filtration also has the gravels present in them which has a size of 2-8mm.

• Cartridge filter (1):

This is also used to filter certain particles and aid in the cleaning of water. This has a mesh size of 5 microns and has 40 inch length.

• RO membrane plant:

This contains several membranes which are used to purify the water to extreme extent. Membrane is the workhorse of a reverse osmosis system. The water is treated in two phases. The first phase has a product water and rejected water. The rejected water from first phase is again treated and then it also divides into two streams of water. The product water is sent to further processing and the rejected one is drained. The one which is used in the MBL has the capacity of 50 tons per hour. HCL is also dosed in treated water coming directly from the RO processing. HCL is used for the decreasing of the pH. Anti-scalant is used for the removing of calcium, magnesium or the other sulphates present.

• High pressure pump:

This pump is used to pump the product water coming from RO to the product storage tank and it has pressure about 188psi.

• Product tank:

The water coming from RO is stored in product tank. The product storage tank has the capacity of 100 tons.

• UV-light:

This is placed to cleanse the water coming from the product tank in order to remove the bacteria or any other sort of microbes.

• Cartridge filter (2):

This is also used to filter or clean the water coming from the UV-light because the light contains glass tubes and due to high pressure, there is chance of breakage of the tubes. In order to get rid of this possibility that is why this filter is placed after UV-light. This has a mesh size of 1 micron and has 40 inches length.

• Supply:

There are three lines of product treated water which are used for the utilities, Tetra pack and filler for beverage.

Water Analysis:

There are following water analysis tests which are as follow:

• Total hardness
• Calcium ions
• Magnesium ions
• Chloride test
• Total alkalinity
• Turbidity

• Total hardness:

1. Take sample 100ml.
2. Add ammonia buffer solution 2ml.
3. Add EBT 1-2 drops.
4. Titrate with EDTA 0.01M.
5. End point will be light blue. Blue color indicates hardness is zero.
6. If the color is red titrate the solution with 0.01M EDTA containing burette with constant agitation. Check the end point as blue color and burette reading x10.

• Calcium ions:

1. Take the sample 25ml.
2. NaOH 1N 4-5 drops.
3. Murexide with EDTA 0.01 M.
4. End point will be purple color.
5. Burette reading x16.04.

• Magnesium ions:

1. Total hardness burette reading – (Ca++) reading.
2. Answer x9.78.

• Chloride test:

1. Take the sample 25ml.
2. Potassium chromate indicator 4-5 drops.
3. Titrate with AgNO3 0.02 M.
4. End point brick red.
5. Burette reading x40.

• Total alkalinity:

1. Take sample 100ml.
2. Methyl purple indicator.
3. Titrate with H2SO4 0.02 N.
4. End point will be light pink.
5. Burette reading x10.

• Turbidity:

1. Take the sample in burette (in the sample bottle).
2. Put it in the photometer.
3. Check for 2-3 times.

• TDS:

1. Total dissolved solids are check with the help of TDS meter. Normal range will be in between 25-30 in treated water. TDS are checked for both treated as well as raw water.

• Chlorine test:

1. Take 2 tubes. Fill one tube with waste water and other with the treated water from carbon filter tank. Presence of chlorine is checked with the help of the help of DPD tablet. Presence of pink color indicates the chlorine.

• pH:

1. pH of water is checked with the help of pH meter.

• Raw water pH(7-8)
• Treated water pH(greater than 4.9)

Conclusion:

RO plant has various health benefits as it lowers the risk of various water borne diseases by lowering the levels of total dissolved solids (TDS). RO filtered water is beneficial to both local population as well as any person coming from outside country. So, its consumption should be implemented to improve health of general population.