Question

Describe the steps involved in getting clarified water from wastewater. [5 marks]

Answer 1

The steps involved in getting clarified water from wastewater are-

1. Wastewater first passes through bar screens to remove large objects such as rags, sticks, cans, plastic packets, napkins etc. from it. [1 mark]
2. Wastewater then moves at a reduced speed, to a grit and sand removal tank where sands, grits and pebbles settle down by sedimentation. [1 mark]
3. Wastewater is then subjected to primary treatment in which, water is allowed to settle in a large tank that is sloped towards the middle. Solids such as faeces, settle at the bottom of these large tanks and are removed with a scraper. These solids are called sludge. Floatable solids, such as oil and grease are removed using a skimmer. The water obtained after this step is called 'clarified water'. [1 mark]
4. Air is pumped into this clarified water to help in the growth of aerobic bacteria. These bacteria decompose human wastes, food wastes, soaps and other unwanted matter that are still present in the clarified water. [1 mark]
5. As a final treatment, disinfectants such as, chlorine and ozone are added to the water before releasing it to the distribution system. [1 mark]