A preliminary design of a ground water treatment plant for the production of
drinking water
WATER TREATMENT PROCESS
A Water Treatment Plant aims to ensure that water is:
Safe for human consumption
Pleasant to consumers
Provided at a reasonable cost
Water Treatment Plants have many processes and steps before a household turns on their
tap and receives water. From the dam to the tap there is a vigorous process with many steps
that are all essential in assuring high quality water for drinking.
This activity looks at two of these processes; it will help you understand the processes of
coagulation, flocculation and filtration which are all steps in water treatment.
COAGULATION AND FLOCCULATION
When particles are slow to settle or are non-settling, chemicals (coagulants), such as alum
(Aluminum Sulfate), are added to the water. These react with the unwanted suspended
particles to form larger particles, called floc. The larger size and weight of the flocs then
causes them to settle rapidly.
Jar testing determines how much alum to add to the water in a treatment plant to
economically settle out the particles. Jar testing is widely used in industry.
FILTRATION
Filtration is also another important element of the treatment process.
This process involves the water passing through a bed of fine particles, usually sand. This
process is called sand filtration. Other materials are also used in the filtration process.
Generally they are layered.
Originally filtration was a slow process, however because the sand filtration processes
become less effective at removing fine suspended particles at higher water flow rates.
The water must be pretreated– coagulated and flocculated – before passing through the
filter bed. Such high rate direct filtration processes are widely applied to raw water with low
levels of suspended matter.
The diagram below shows the complete water treatment plant processes. Note: where
coagulation, flocculation and...