Question

What are the five stages of water treatment?

Answer 1

We know that the cleaning of polluted water by removing the pollutant before it is discharged to water bodies. This process of wastewater treatment is known as sewage treatment. The water treatment is carried into two steps: Primary and Secondary Treatment.

Complete answer:
Large quantities of wastewater are generated every day. A major part of the component of wastewater is human excreta. The municipal wastewater is called sewage. Wastewater can also be generated from industries and other commercial areas. The following are the five stages of water treatment:
-Screening
-Coagulation
-Sedimentation
-Filtration
-Disinfection
This step involves the removal of physical particles from the sewage by filtration and sedimentation. First, all the floating debris is removed by filtration which is followed by the sedimentation where all the soil, stone and pebble are removed. The solid particles which are sediment at the bottom form the primary sludge and the supernatant form the effluent. The effluent from the primary settling tank is transferred for the secondary treatment. The effluent from primary treatment is passed into a large aeration tank where it is continually agitated mechanically and the air is pumped into it. This will lead to the growth of aerobic microbes.
These microbes consume most of the organic matter from the effluent. This step will reduce the BOD of the effluent. After the BOD is reduced, the bacterial flock is transferred into a settling tank for sediment. These sediments are called activated sludge. The sludge is divided into two parts the smaller part is pumped into the aeration tank where it serves as an inoculum, while the remaining larger part is again transferred into anaerobic sludge digesters. In these digesters, other kinds of bacteria will grow aerobically and digest all the fungi and bacteria in the sludge. During this process, bacteria produce the mixtures of gases like hydrogen sulphide, methane and carbon dioxide and form biogas. Finally, the effluent from the secondary treatment plant is released into the water bodies.

Note:
Remember that the filter can be made out of paper, cloth, cotton, slag or glass or any other suitable material. There are certain drawbacks of using chlorine as well because it forms compounds with certain organic compounds present in water, mainly trihalomethanes. It also impacts the colour and taste of water.