Drinking Water Treatment Facility
A public drinking water system consists of several parts: securing raw water, storing it when necessary, and treating it chemically for flocculation and sedimentation; the water treatment plant itself which contains units for coagulation, sedimentation, filtration, disinfection, and storage; a distribution system; another storage system of potable water if necessary; and final end use by people, businesses, industry, etc. Water systems and water distribution systems have the same types of problems as sewage treatment systems and sewage collection systems. The treatment facilities have aged and the pipes have deteriorated with the potential for inflow of water or sewage or other contaminants into the potable water supply.
The chemicals used in processing and treating the water and the chemical byproducts may become hazardous to people and the environment. Chemicals are used for coagulation, removal of phosphorus, removal of bad taste, odors, and color, reducing inorganic compounds, reducing organic chemicals, reducing hardness, and final treatment to destroy microorganisms with chlorine, bromine, iodine, ozone, and other chemicals.
Filtration systems may include:
- • Conventional filtration for drinking water treatment utilizing rapidly mixed alum and a polymer in the raw water (used to help precipitate dissolved solids), followed by actual filtration with a slow sand filter and then disinfection;
- • Direct filtration, where the water source is much better and cleaner and therefore the water can go straight to filtration and disinfection;
• Lime softening, where the raw water has high concentrations of calcium and magnesium and the lime helps remove them as well as other toxic minerals, followed by a final step that neutralizes the access alkalinity.
In all cases, filters become dirty and need to be properly maintained and cleaned. (See discussion on sewage treatment plant in chapter 11, pages 411-412.)
Special problems for water treatment plants include Cryptosporidium, cyanotoxins, and turbidity. (See endnotes 16, 17, 18, 19, 20.)