Chemical Treatment of Municipal Water Supplies Commonly Entails Use of CaO

Chemical treatment of municipal water supplies commonly entails use of CaO, Al₂(SO₄) ₃, and Cl₂. The purpose of adding CaO is to _ .

A) remove all SO₄^2- as solid CaSO₄
B) selectively kill anaerobic (but not aerobic) bacteria
C) remove all HCO₃^- as solid CaCO₃
D) remove all Cl^- as solid CaCl₂
E) make the water slightly basic so that addition of Al₂(SO₄) ₃ will afford a gelatinous precipitate of Al(OH) ₃