Wastewater is generated in homes, industries, hospitals, agricultural fields, etc. due to human activities. It contains a lot of impurities and is unfit for human consumption.
The steps involved in getting clarified water from wastewater are:
1. Wastewater is passed through bar screens. Large objects like rags, sticks, cans, plastic packets, etc. are removed.
2. Water then goes to a grit and sand removal tank. The speed of the incoming wastewater is decreased to allow sand, grit and pebbles to settle down.
3. The water is then allowed to settle in a large tank which is sloped towards the middle. Solids like faeces settle at the bottom and are removed with a scraper. This is the sludge. A skimmer removes the floating impurities like oil and grease. The water so obtained is called clarified water.
4. Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria decompose human waste, food waste, soaps and other unwanted organic matter still remaining in clarified water.
5. Clarified water is treated with chemicals like ozone and chlorine to disinfect it.