Alum is a chemical added to raw water to act as coagulant. Alum is a name given to the aluminium sulphate with its chemical formula as Al2(SO4)318H2O. The alum when added to water reacts with bicarbonates alkalinities, which are generally present in raw supplies, so as to form gelatinous precipitation (floc) of aluminium hydroxide. This floc attracts other fine particles and suspended matter, and thus grows in size, and finally settles down to the bottom of tank.
