ENVIRONMENTAL SCIENCE 5.4 The Waterworks

At the Waterworks When reservoirs or rivers are the source of drinking water, the water must be treated to remove certain substances Intake  Water enters the treatment plant through an intake pipe, which contains a screen to remove large objects Primary Disinfection  Chlorine is usually added  Ozone may also be used  Better disinfectant for all microorganisms  May reduce need for future filtration  Reduces THMs

Chemical Treatment and Mixing  Alum is added to cause suspended particles to floc  Sodium hydroxide is added to raise pH and reduce corrosion  Orthophosphate is added to reduce corrosion and prevent leaching of lead and copper  Activated carbon is used to remove chemicals that cause taste, odor, or color Flocculation  Water flows to large tank that contains a series of baffles  Water moves over one baffle and under the next  More particles stick together (flocculation)

Sedimentation  Floc is heavy and sinks to bottom of settling tank Filtration  Graded sand filter is used to filter out any remaining particles  Filters must be backwashed more frequently in summer b/c heavier algae growth Final Chlorination  Small amount of chlorine is added to kill an bacteria that have survived the processes  Ozone not used b/c it leaves no residual  Fluoride is added to help prevent tooth decay