Chemical Process
Zeolite removes both temporary as well as permanent hardness of water by precipitating calcium and magnesium present in water as insoluble zeolites. Used zeolite is regenerated by flushing with the solution of

Magnesium chloride
Sodium sulphate
Calcium sulphate
Sodium chloride

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Chemical Process
Presence of carbonaceous matter in the sewage

Reduces sulphate ions to sulphides causing obnoxious smell
Increases the quantity of chlorine used for its purification
Causes reduction in its dissolved oxygen content thereby endangering the life of aquatic creatures
All of these

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