Question

. Sketch the layout for a typical conventional surface water treatment plant. Label each process. Briefly describe the different water treatment processes and their basic functions.

Answer 1

1) Screening:Screening is the process in which surface water contains suspended matter such as branches, leaves, tree trunks etc., are removed.This is done with the help of units termed as screens.

Function:To remove heavy suspended solids from raw water.

2) Primary Sedimentation: Sedimentation is the process in which raw water containing suspended solids such as soil, debris etc. are removed. When water flows at a very slow speed, then suspended solids settle under their own weight by the action of gravity.

Function: To remove small suspended solids from water.

3) Coagulation: Coagulation is the process in which negative protective charge present over fine suspended impurities is neutralised and they are thus provided opportunity to come closer. This is done with the help of certain chemicals called coagulants and by fast mixing.

Function: To bring closer the fine suspended solids.

4) Flocculation: Flocculation is the process in which the neutralised particles are brought in intimate contact with each other to form flocs and their agglomeration. It is done by slow mixing.

Function: To remove fine suspended solids in the form of flocs.

5) Secondary Sedimentation: This is provided to give even more time for the flocs to settle down before water reaches  filtration process.

Function: To prevent the clogging of filter media.

6) Filtration: Filtration is the process in which even finer suspended matter and flocs are removed. The turbidity and colloidal matter of non settling type are also removed. It also removes organic matter, micro-organisms and dissolved minerals. This is all done with the help of filter medium such as garnet, anthracite, sand etc.

Function: To remove finer suspended solids, flocs, organic matter, micro-organisms and dissolved minerals.

7) Disinfection: Disinfection is the process of killing disease causing micro-organisms from water with the help of physical methods or by using chemicals before water is supplied. Physical methods include boiling and UV treatment. Chemicals such as potassium permanganate, ozone, chlorine etc.

Function: To kill disease causing micro-organisms.