Lime, also known as calcium oxide, is used for pH adjustment, softening, and corrosion control. After the raw water has been treated with polyelectrolyte, ferric sulfate, and lime, it is gently mixed by large mechanical paddles in two flocculation basins where the suspended particles gather together into larger particles. The settled particles form a sludge layer on the bottom of each primary settling basin. This sludge is pushed into sumps by traveling mechanical rakes, and is then removed from the basins through a series of valves and pumps. The clarified water then exits the settling basins, and is disinfected by the addition of free chlorine.
Anhydrous ammonia is added shortly thereafter, producing chloramine.
Chloramine is a compound produced by reacting free chlorine with ammonia, and is used for residual disinfection. Chloraminated water then enters large secondary settling basins, allowing additional settling time for suspended particles and disinfection contact time. After the water exits the secondary settling basins, it is treated with sodium hexametaphosphate and fluorosilicic acid. The sodium hexametaphosphate is used as a sequestrant, which holds the lime in solution keeping it from depositing on the filter or the media. The fluorosilicic acid is used to add fluoride to the drinking water to aid in the prevention of dental cavities.