| Standards |
| WATER QUALITY PARAMETERS AND DRINKING WATER STANDARDS |
| IMPURITIES IN WATER |
| SOFTENING PLANT |
| BASICS OF REVERSE OSMOSIS SYSTEMS |
| SOFTENING PLANT |
| Hardness in water caused due to the presence of calcium and magnesium carbonates. These impurities cause scaling thereby reducing the life and effect of vessels in terms of heat transfer. Hence softening is an essential process during water treatment. Raw water is treated in softening plants, where lime in appropriate quantity is added to the water to reduce the hardness. |
| Softening Process: |
| The softening process consists of passing raw water containing hardness through a bed of cation resin in sodium form. The hardness ions Ca & Mg are taken up by resin and in exchange, the sodium ions are relinquished from the resin. This is called the service cycle. |
| Ca++ + 2A- + Na2R ® CaR + 2Na + 2A- Mg++ + 2A- + Na2R ® MgR+ 2Na +2A- |
| Where A- represents the relevant anions of bicarbonates, sulphates or chlorides and R represents the anionic part of the softener resin. |
| Regeneration of the softener: |
| Raw water will continue to get softened till the resin gets exhausted. Bringing back the resin to it original form is called regeneration. Softener resin is regenerated by sodium chloride of 10-15% concentration. Depending on the softener design, the regeneration may need to be done every day or every few days or every week. |
| CaR + 2NaCl ® Na2R + CaCl2 MgR + 2NaCl ® Na2R + MgCl2 |
| BASICS OF REVERSE OSMOSIS SYSTEMS |
| What is Reverse Osmosis? |
| Reverse Osmosis (RO) is the finest water purification technology in the world. It involves the passage of water from the section containing lower concentration of ionic substances to a higher concentration section when the two are separated by a semi-permeable membrane. In RO, sufficient pressure is applied to force water to flow through the membrane in a reverse direction. Thus, pure water is produced by screening out dissolved salts and other contaminants. It can improve the color, taste and other properties of feed water. |
| What is RO membrane? |
| The membrane is the heart of the reverse osmosis process. It is made of semi-permeable material which could be cellulose acetate, aromatic polyamides or polysulfonated polysulfone. The membrane can be cast as fine sheets, tubes and fine hollow fibres. It has the smallest pore structure, with pore diameter ranging from 0.5nm to 1.5nm. |
| What does RO remove? |
| All dissolved salts, sugars, viruses, pyrogens, proteins, dyes and other particles with a weight greater than 150-250 daltons can be removed by RO to the highest extent. Dissolved salts that carry a range are also more likely to be rejected by a membrane. |
| How is RO different from a water filter? |
| While ordinary filter can only remove suspended particles and sediments from water, RO can also remove high percentage of dissolved contaminants -molecule by molecule- from water. RO is a crossflow (also called tangential flow) filtration system with the feed water flowing parallel to the membrane instead of perpendicular to it. So the reject water sweeps the rejected salts away from the membrane surface ensuring that the pores do not get easily clogged. |
