Chemical Process
Presence of carbonaceous matter in the sewage

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

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Chemical Process
One of the steps during refining of cane sugar consists of addition of hydrated lime to the sugar syrup followed by carbonation of the resulting solution. The purpose of this step is to

Improve the rate of crystallisation of sugar
Reduce the viscosity of the syrup
Adjust the pH of the syrup
Remove the coloring matter from the syrup

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