1) What are the various types of impurities generally found in drinking water?
Given below are the two categories of impurities generally found in drinking water-
PROPERTIES WISE: Physical, Chemical and Bacteriological.
SIZE WISE: Suspended (larger than 0.45 micron), dissolved (smaller than 0.45 micron-mostly referred as TDS
2) .What does TDS stand for?
TDS is 'Total Dissolved Solids’. Its unit is PPM (parts per million).
3) What is the TDS range fit for drinking water?
The upper limit (desirable) of TDS for drinking water is 500 ppm. IS 10500,'DRINKING WATER-SPECIFICATION' of BIS may be referred for the TDS as well as many other impurities. Note: There is no lower limit of TDS specified.Drinking water of 100-150 ppm TDS or lower is better.
4) Why filtration/purification needed for drinking water at all?
To improve aesthetic and hygienic value and to make water free from disease causing impurities.
5) What are the basics of water filtration/purification?
Generally in any type of systems following main stages are used for converting dirty water into drinkable water.
a) SEDIMENT FILTRATION: Suspended impurities up to micron level, such as dust, dirt, silt, fibers etc are trapped by sediment filters made of mostly PP cloth, fiber or yarn. (pp = poly propylene)
b) CARBON FILTRATION: Granular Activated Carbon (GAC) adsorbs Colour, odour, gases and other organic impurities.
c) DISINFECTION:Removal of pathogens, mostly bacteria and viruses, is done in this stage. Various methods are:BOILING, CHLORINATION, OZONISATION, UV, UF and RO.
d) TASTE ENHANCING/POLISHING: A cartridge containing GAC, some times impregnated with silver put prior to final output restores the natural taste of water and also act as bacteriostatic filter.
6) What is advantage of RO over other methods?
In case of RO, in addition of removing bacteria and viruses, it also removes about 95% of TDS impurities, which can not be removed by any other process.
7) WHAT IS RO, THEN?
RO means Reverse Osmosis.
8) Please explain RO briefly.
In an RO system there is a semi-permeable membrane having billions of pores of size in 0.0001 micron range which allow only pure water molecules to enter when a stream of water is forced through it by an external pump and does not allow rest of water along with all dissolved metallic or any other type of impurities including bacteria and viruses to pass through it.
9) What is the size of bacterium, virus and metal ions?
Bacteria: The least size of any bacterium is 0.45 micron and that of virus is 0.02 micron. And most of the Metal ions are found in the range of 0.0009 micron.
10) What is a micron by the way?
Micron is unit of length, which is one millionth of a meter. Practically, human hairs are in the range of 60 -100 micron.
11) Have heard of UF filter. What is it? And how UV/UF/RO differs?
UF is Ultra Filtration, works more or less in similar manner as RO does. But the pore size of UF membrane (0.004MICRON RANGE) is much larger. Therefore external pump is not required to force the water. The difference can be tabulated as below.
TECHNOLOGY USED
REMOVAL OF BACTERIA/VIRUSES
REMOVAL OF HARDNESS (PART OF TDS)
REMOVAL OF TDS (METALLIC IMPURITIES)
REMARKS
UV
No Removal (deactivates only)
No Removal
No Removal
Dead or alive bacteria /viruses remain in driking water
UF
Removed
No Removal
No Removal
UF good for low tds water
RO
Removed
Removed
Removed
RO best for 1000-1500 ppm tds
RO+UF
REMOVED
REMOVED
REMOVED
RO WITH RICH MINERALS
12) Is there any other technology? Heard something about Nano filtration?
Yes,Nano Filtration (NF) is in between UF and RO having pore size in the range of 0.001 micron and can remove the bi (and trivalent) metal ions such as Calcium and Magnesium,thus reduces Hardness and hence it is called as SOFTENING MEMBRANE.But it is not popularly being used in water purification industry.
13) What is life of RO Membrane?
Usually three-four years, provided pre-filtration system is adequate and regular.
14) What is GPD?
GPD means gallon per day ,the capacity of membrane yielding permeate (pure) water in gallons per day and 1 GPD=12 LPH (approx).
