Coagulation and Flocculation
In this lesson we will answer the following questions:
* How do coagulation and flocculation fit into the water treatment process?
* Which chemical principles influence coagulation and flocculation?
* Which chemicals are used in coagulation?
* What factors influence coagulation and flocculation?
Along with the online lesson, read Chapter 4: Coagulation and Flocculation, in your textbook Operation of Water Treatment Plants Volume I .
Overview of the Process
Location in the Treatment Plant
After the source water has been screened and has passed through the optional steps of pre-chlorination and aeration, it is ready for coagulation and flocculation.
In theory and at the chemical level, coagulation and flocculation is a three step process, consisting of flash mixing, coagulation, and flocculation. However, in practice in the treatment plant, there are only two steps in the coagulation/flocculation process - the water first flows into the flash mix chamber, and then enters the flocculation basin.
In this lesson, we will primarily be concerned with the theory behind coagulation/flocculation. In later lessons, we will consider the practice in more detail.
The primary purpose of the coagulation/flocculation process is the removal of turbidity from the water. Turbidity is a cloudy appearance of water caused by small particles suspended therein. Water with little or no turbidity will be clear.
Turbidity is not only an aesthetic problem in water. Water with a high turbidity can be very difficult or impossible to properly disinfect. As a result, the maximum allowable level of turbidity in water is 0.5 NTU, while the recommended level is about 0.1 NTU. (NTU, or TU, stands for nephelometric turbidity units, a measurement of the turbidity of water.)
In addition to removing turbidity from the water, coagulation and flocculation is...