Processes, technology and equipment employed to purify the water
There are various processes employed to purify the water and various combinations of the processes mentioned below are incorporated to ensure that final composition of the product confirms to latest BIS norms.
Desalination
Desalination is defined as the removal of dissolved salts from various waters – brackish, sea, etc. Desalination can be performed by several processes including two-membrane process, namely reverse osmosis and electrodialysis. The other membrane process, which can be employed for partial desalination, include ultrafiltration and nanofiltration.
Reverse Osmosis
RO membranes are effective in removing constituents and are efficient in removing TDS in any feedwater up to 40,000 ppm (i.e. sea water.)
Osmosis is natural bio-chemical process that affects the movement or diffusion of water molecules through a semi-permeable membrane towards a solution that has high TDS, and it is induced by osmotic pressure. RO is accomplished by forcing water molecules under pressure through a semi-permeable membrane out of solution that has high TDS. The feedwater on the inlet side becomes brine and water that passes through – permeates, becomes the product water.
RO membrane can be distinguished from other membranes based on pore size, which is around 0.0005 microns. The pore size of RO membrane is small, that it functions primarily by diffusion instead of filtration or adsorption.
Nanofiltration (NF)
NF is effective in removing divalent ions (i.e. calcium and magnesium), larger monovalent ions (i.e. sulphate), high molecular weight organic molecules, and colour. NF membranes are efficient in softening feedwater below 1,000 mg/l TDS. These membranes provide significant rejection of hardness caused by dissolved calcium and magnesium. The pore size of NF membranes range between 0.0007 to 0.01 microns. (Taylor, 1989, 18)
Ultrafiltlration (UF)
UF is effective in removing high molecular weight proteins, bacteria and viruses. Rejection of monovalent and divalent ions are considerably less than RO and NF. UF membrane pores are smaller than MF but greater than NF, and range between 0.001 to 0.1 microns. The primary mechanism of constituent removal is filtration, however, some salts are transported across the semi-permeable membranes by diffusion.
Microfiltration (MF)
MF is effective in removing suspended solids of all types and larger colloids. These generally filter out suspended constituents in feedwater.
Ultra Violet Unit (UV)
Thorough research in last few years have given lot of confidence to water treatment professionals in terms of its effectiveness in microbiological treatment.
UV is a band of invisible light in the electromagnetic spectrum, in the range of 200-400 nm wavelengths, having germicidal effectiveness, which penetrates the microbial cell membrane to destroy the DNA molecule thus preventing cell replication.
UV is used to provide Bacterial Disinfection in water. As UV does not change the Physical or Chemical characteristics in water & does not have any residual properties left in treated water, it is widely used to disinfect the water for micro biological contamination.
The U.S. Public Health Service requires that UV disinfection equipment have a minimum UV dosage of 16000 uW sec/cm2 (microwatt seconds per square centimeter).
Recommended maximum concentration levels in Ultra Violet unit
Turbidity : 5 NTU [ Nephelometric turbidity unit ]
Suspended Solids : 10mg/Litre
Colour : None
pH : 6.5 to 8.5
Ozonation through Ozonator
What is Ozone?
Ozone, triatomic Oxygen is colourless, unstable & reactive gas with a acrid odour. It is strongest available sanitizer and decomposes back to oxygen without leaving any tresses and makes preferred choice for disinfection. Since it is a very reactive Disinfecting agent, & 3000 times more effective than any other known disinfectents, It destroys any Bacteria, Viruses, Cysts and Pathogens in a shortest possible time when it comes into contact with water .
Ozone Production
Ozone generation involves splitting of an Oxygen molecule into two highly unstable Oxygen atoms. These unstable Oxygen atoms combine with other Oxygen molecule to ultimately produce Ozone.
Dry air or Oxygen is passed through the Ozone cell consisting of two electrodes kept at a high potential with a dielectrics in between them. The Corona discharge formed in the gap energizes the Oxygen molecules, thereby converting a portion of Oxygen into Ozone. As Ozone is highly unstable & cannot be stored is produced at site where it is required.
