Fig. 10. Size distributions and necessary treatment processes for drinking water
Pure water used for decontarnination of effiuents by dilution consumes three times the volume of water required for other needs. Recently the problem of prevention of effiuent contamination by usmg recyctabte processes has attracted great attention. Introduction of highly effective methods of effluent purification in industrial plants is one of the promising trends in this field. Specific requirements are placed on water used for domestic purposes in every country.
New filters for the purification of drinking water and industrial ettiuenis are very important. Practically, water containing suspended particles is purified by percolation through quartz sand of 0.5-2 mm grain size. Quartz sand is however rather expensive and has a low fine-trapping capacity. Studies have shown that quartz sand can be successfully replaced by natural zeolites, which are superior in several ways. 
The advantages of using cimoptilotite based zeolite filter instead on quartz in physical filtration systems are:
· The high internal and external surface area of clinoptilolite exceeds that of quartz by more than 10 times
Zeolite pore space permeability for water transmission through the grains or fragments is 100% compared to non-permeable quartz grains.
• The amount or layer thickness of zeolite in the filtration systems can be much thinner (smaller volume) than quartz sand systems - because of the high "surface area and pore space".
• The density of zeolite is about half of quartz grains thus the volume of one ton of zeolite is twice that of quartz sand.
Zeolites also convert calcium and magnesium salts into sodium salts which do not cause hardness. This process uses zeolites which act as a medium for the exchange of the metal ion:
Calcium sulphate + sodium zeolite —»• calcium zeolite + sodium sulphate
The water is usually passed through a bed of the zeotites, which may be a processed sand or synthetic material. The zeolite is then regenerated by passing brine through the bed.
Calcium zeolite + sodium chloride —' sodium zeolite + calcium chloride
Fig.11. Water Filtration System