Introduction to Potable Water Treatment Processes
A. Bhatia, B.E.
Water suppliers use a variety of treatment processes to make water fit for consumption and remove materials that may cause damage to the utility equipment or that cause problems in the major treatment process. Because no single treatment process can be expected to remove all of the different types of contaminants that can be found in water (under all conditions), multiple barriers are desirable. The number of treatment processes required is influenced by the quality of the source water.
This 4-hour course
provides an overview of current water treatment practices and their application
in both potable and utility use. This course is based entirely on "Joint
Departments of the Army and Air Force, USA, Technical Manual TM 5-813-3/AFM
88-10, Volume 3, Water Supply, Water Treatment."
The course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of course materials.
At the conclusion of this course, the reader will learn:
This course is aimed at students, engineers, designers, facility managers, energy auditors, environmentalists, H &S professionals, technical and sales representatives.
The U.S. possesses abundant water resources and has developed and used those resources extensively. In order to meet the needs of existing and future populations, the nation's water supply must be sustainable and renewable. Sound water resource management, which emphasizes the efficient use of existing water supplies, coupled with the development of new water sources, is essential in order to meet these objectives.
Water treatment plants are those facilities that treat water, ground water or surface water, and produce potable water for public consumption or provide primary treatment and produce "industrial water."
This course illustrates the link between raw water quality and treatment process selection and performance. Individual topics concentrate on specific water treatment processes, detailing the chemical and engineering principles behind the process.
After reading this
course, you should have the basic information required to begin on-site investigations
of water treatment processes. You should be able to define and discuss coagulation,
flocculation, sedimentation, filtration, chemical treatment, disinfecting and
softening processes as applied to the physical treatment of surface waters.
The course content is in a PDF file Introduction to Potable Water Treatment Processes. You need to open or download this document to study this course.
You may need to download Acrobat Reader to view and print the document.
Safe drinking water is the result of careful evaluation of source water quality and variation and adequate, reliable treatment processes combined with performance monitoring to assure that treatment is within operating parameters. Ground waters that are protected from surface influence are usually of relatively good quality and so traditionally few, if any treatment processes are required. Lowland surface water sources are usually of much poorer quality and more treatment processes are needed to provide an acceptable level of safety. In general, the raw water goes through the following steps prior to entering the main distribution network:
1) Screening -
This step removes any large debris floating down the river from entering the
pumping station and causing equipment damage.
2) The partially treated river water enters the water treatment plant through a flow meter. This provides the plant operations personnel with the total amount of water being treated daily.
3) Then the major water treatment process begins. The following is a description of the steps used in the process of clarifying and disinfection water for public use.
4) Aeration - Water is sprayed into the air to release any trapped gases and to absorb oxygen for better taste.
5) Coagulation - Aluminum Sulfate is added to the water entering the plant. The water is mixed, rapidly at first, and then more slowly as the water continues through this step. The reaction of the chemically treated water to the mixing causes the small, light-weight particles to clump together (coagulate) into much larger particles. The most frequently used chemical coagulant is aluminum sulfate (Al2 (SO4)3 14H2O). This aluminum coagulant is also called "alum" or "filter alum," and dissociates in water for form S04, Al3+ ions and various aluminum hydroxide complexes.
6) Flocculation - The larger particles continue to combine (flocculate) into much larger and heavier particles. These particles become too heavy to float and begin to sink (settle).
7) Sedimentation - The water flows slowly through a basin or tank where the floc settles to the bottom.
8) Filtration - The clear water is filtered through coal, sand, and gravel to remove small, light particles. Particles not removed in the previous step will be removed here.
9) Chemical Pretreatment- This step destroys (oxidizes) algae and other.comanisms that cause taste and odor, or color. It also reduces the amount of Iron and Manganese that naturally occurs in surface-waters.
10) Disinfection - Small amounts of chlorine or other chemicals are added to kill remaining germs to keep the water pure as it travels through pipelines.
11) Fluoridation - To help strengthen tooth enamel and aid in the fight against tooth decay a small amount of fluoride is added to the water. The fluoride added is in the amount of one part fluoride per million parts of water.
12) Ion Exchange - Ion exchange processes are used to remove i.comanic contaminants if they cannot be removed adequately by filtration or sedimentation. Ion exchange can be used to treat hard water.
13) Stabilization - This step aids in the reduction of pipe corrosion and scale build up problems in the water service piping system. The pH of the water is adjusted upward to just above
neutral by the
addition of lime. Also, a corrosion control agent is added to reduce the corrosive
tendency of the water.
When the above steps are performed correctly the process of producing safe, high quality potable water is complete.
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.