Water Softening:// theory of Ion- Exchange and Reverse Osmosis (RO) method, advantages and Affects on Ecosystem

 

Why do we need soft water?

Groundwater is typically Hard Water because it contains dissolved minerals. Hard water can be defined as the water that has a very high concentration of Ca⁺² and Mg⁺² (multivalent cations). Hard water can cause serious handling issues in residential and commercial application like:-

·         Hard water can cause plumbing, clogging and scaling on Plates of the boiler, if Sodium Carbonate is present then it will cause hydrolysis ultimately the Boilerplates will destroy and structure will be collapsed.

·         Ca⁺² and Mg⁺² ions in household water can cause corrosion of supply pipes, curding of soaps (increasing its utilization) and other such issues.

 

Water Softening:-

Water softening is the process in which dissolved water hardening agents (probably Calcium and Magnesium ions) are removed for the efficient domestic and industrial uses and to avoid errors in processing.

There are many methods of water softening used but two are commonly used stated below

1.      Ion-Exchange Method

2.      Reverse Osmosis Method

Ion-Exchange Method:-

Ø Executive Theory of Ion-Exchange Method:-

Ion-exchange is a water treatment technique to undesirable contents from water through exchange with non-objectionable or less-objectionable ionic substances. Both contaminants and the exchanging substance must be dissolved in water. Importantly, both have the same charge. It also aims to eliminate various charged molecules like Nitrates, Sulfates and Fluorides etc. it can get rid-off toxic metals which can cause scaling or corrosion.

Ø Ion-Exchange Resins (IERs):-

Commercial ion-exchange resins are microporous beads that are very small (diameter ranging from 0.1 mm to 0.3 mm). They are synthesized by using mainly polystyrene or polyacrylate. They have a 50% composition of water dispersed homogeneously in gel-structured sites of material.

Since water is present all over the substrate so the movement of water-soluble species is free. They can randomly move inside out. As there are Functional Groups present to each monomer unit. These functional groups will essentially get in contact with water-soluble entries especially ions and will form a relationship with each other. Since functional groups are also charged; they will interact with oppositely charged species.

Ø Understanding Working Principle of Ion-Exchange Method:-

Ion-exchange is typically used to every extent. A device called Softener is used; it contains Ion-Exchange Resins (IERs). This is a simple technique in which Sodium (Na⁺¹) ions are physically exchanged through unwanted Calcium and Magnesium ions. This exchange process continues until the solution becomes saturated with Calcium and Magnesium lowering the concentration of Sodium ions. Now regeneration is done by flushing the exchanger bed with water. Again the process is started.

 

Reverse Osmosis (RO) Method:-

Overview:-

Reverse osmosis (RO), also regarded as ultra-filtration, is the modern water purification method. Reverse osmosis was developed under the supervision and funding of the U.S Government in the later 1950s to desalinate the seawater for the household uses of a citizen living besides coastal areas. Nowadays, it is considered the most convenient and cost-effective technology to filter water from unneeded elements. Filtered can be used in the home or in an industry that requires ultra-purified water.

How do the Reverse Osmosis (RO) Plant works?

To understand Reverse Osmosis, it would be more convenient to revise “Osmosis” first. Osmosis is the movement of a solvent through the semi-permeable membrane from the region of higher concentration to lower concentration naturally. This is done to establish on both sides of the membrane. Roots transport the water to the other organs of a plant through Osmosis. The most familiar example of a semi-permeable membrane is GORE-TEX fibre that contains tiny pores which permit only water vapours, not the liquid water molecules to pass. The kidney drains water from the blood through Osmosis.

Have you ever thought if you drink seawater to survive in the sea stormed what will happen to you? It will kill you but why? You will be thinking so here is the answer.

The phenomenon that can be used to illustrate is Osmosis. When you will put in seawater it will create osmotic pressure due to the concentration difference between your body’s water and enriched in minerals seawater. The seawater will drain all the water molecules present in your body by trying to dilute the salt in your stomach. Eventually, you will dehydrate and die.

Now we come to the hotspot, our aim was to understand Reverse Osmosis. Reverse Osmosis is reciprocal of Osmosis. The movement of water through a semi-permeable membrane to balance concentration difference on both sides of the membrane under the influence of external pressure is called Reverse Osmosis.

How Reverse Osmosis (RO) plant works? What stages are involved?

 When Contaminated Feed-Water enters the RO plant definitely it would be saturated with salts. A semi-permeable membrane is installed which only allow water molecules to pass through it. So it will cause a difference in the saturation on both sides. Pressure is applied externally to induce and move water through the membrane which will pass through the membrane keeping the impurities behind.

There might be 3,4 or 5 stages in the filtration of water through reverse osmosis but the following are the common stages involved in the RO water purification method:-

1.      Pre-filtration it tries to remove all the dust, dirt and rust particles by using Sediment Filter.

2.      The semi-permeable membrane removes up to 99% Total Dissolved Solids (TDS).

3.      Post- filtration this step involves the removal of unpleasant odour and taste by using a Carbon Filter.

4.      Storage Filtered and rejected both types of water is stored in different storages. Filtered water is brought into use while the rejected water is used to increase and maintain the concentration of in-going Feed-water of treatment. In the end, it is drained to lakes, rivers or seas.

 

What Contaminations will RO Plant removes and How?

Reverse osmosis has the capability of removing 99%+ contaminants (undesirable bacteria, ions, organic solvents and pyrogens). You cannot rely on RO Plant for 100% pure water. The filtration is based on two properties: Size and Charge; any molecules having a molecular weight above 200 will not pass through the membrane (Notice that molecular weight of water is 18). Ions having a multivalent charge like that of Calcium (Ca⁺²) and Magnesium (Mg⁺²) are not allowed to pass. Here is the question for you; would Sodium ions be allowed to go through the membrane? Give reasons to justify your answers.

 

 

Is there any relationship between Ion-Exchange Method and RO Plants? If yes then how they support each other?

Both the techniques have some drawbacks but they are made to interact, then believe that results will be amazing. Softener cannot filter the contaminants like bacteria, fungi and unpleasant odour rather it simply softens the water by removing the hardness causing factors like the presence of Calcium and Magnesium ions. Similarly, if the water is hard (having above 7 grains) will reduce the life of Semi-Permeable membrane causing the decline in the efficiency of RO Plant. So in most industries, both methods are used together.

Affects on Environment:-

Ro Plant drained water or wastewater doesn’t have any hazards to the environment. Because the chemicals are already removed, it is only saturated with minerals which the land on river, lakes or sea beds will absorb. So we can say that RO Plant is environmentally friendly.

Advantages of RO Plant:-

·         Very high rejection rates over a wide range of impurities

·         Cost-effective means of producing high purity water

·         Friendly to the environment

·         Does not use or produce and harmful chemicals

·         Requires no electricity to operate (unless the system incorporates a booster pump)

·         Requires minimal maintenance

References:-

1.      Franzmann, C., Löwenberg, J., Wintgens, T., & Melin, T. (2007). State-of-the-art of reverse osmosis desalination. Desalination, 216(1-3), 1-76.

2.      https://puretecwater.com/reverse-osmosis/what-is-reverse-osmosis

3.      https://www.freshwatersystems.com/blogs/blog/what-is-reverse-osmosis