Lesson: Wastewater Story

Question: 1

Fill in the blanks:

(a)            Cleaning of water is a process of removing ____________.

(b)            Wastewater released by houses is called ____________.

(c)            Dried ____________ is used as manure.

(d)            Drains get blocked by ____________ and ____________.


(a)            Pollutants

(b)            Sewage

(c)            Sludge

(d)            Oils, Fats

Question: 2

What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.


Sewage is a liquid waste that causes pollution in water and soil. It includes water released by homes, industries, hospitals, offices and other users. It also includes rainwater that has run down the street during a storm or heavy rain. Most of it is water, which has dissolved with waste matter and contains suspended impurities. These impurities are called contaminants. Discharging untreated sewage into rivers or seas will pollute the water resources. Contaminated water is dangerous for aquatic plants and animals. It also spread many diseases like cholera, typhoid, polio, meningitis, etc.

Question: 3

Why should oils and fats be not released in the drain? Explain.


Oils and fats should not be released in drains because they can harden and block the pipes. In an open drain, the fats clog the soil pores reducing the soil’s effectiveness in filtering water.

Question: 4

Describe the steps involved in getting clarified water from wastewater.


Treatment of wastewater involves physical, chemical, and biological processes that remove the substances that contaminate the wastewater.

(a)            Wastewater containing large objects such as plastics, cans, rags, etc. is passed through the bar screens or metal rods which separate the objects from the water.

(b)            After the objects are removed from the water by the bar screens, the liquid enters a large sand removal tank called a grit chamber. The incoming wastewater is kept still, so that if there are any heavy solids like sand or gravel present in it, they will settle down at the bottom.

(c)            From the grit chamber, the water enters another large tank called a Clarifier. It is a circular sedimentation basin which separates the remaining solid objects, such as faeces, from the water. The solid objects which settle down at the bottom is called sludge. The sludge is removed with a scraper and transferred to a separate tank it is decomposed by anaerobic bacteria.

(d)            The sludge passes through a separate tank where it is decomposed by the anaerobic bacteria which produce biogas.

(e)            After the physical impurities are removed from the wastewater, the liquid enters an aeration basin. Air is pumped into the clarified water which allows microorganisms to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in the clarified water.

(f)             The microorganisms consume human waste, food waste and other unwanted matter and settle down at the bottom of the tank as activated sludge. The water is then removed from the top.

(g)            The final step in the treatment of wastewater is the use of a disinfectant such as chlorine to kill harmful bacteria still in the treated water. Sometimes ultraviolet light is used instead of chemicals. The treated water is then discharged into the sea, a river or into the ground.

Question: 5

What is sludge? Explain how it is treated.


Solids like faeces that settle at the bottom during waste water treatment are called sludge. The sludge is used for biogas production by the action of anaerobic bacteria which can be further used as fuels or to produce electricity.

Treatment of sludge: Sludge is collected by a scrapper. It is transferred to a separate tank where it is decomposed by the anaerobic bacteria. The biogas produced in the process can be used as fuel. After the aerator tank, microbes and human waste settle down and form activated sludge. The activated sludge is about 97% water. The water is removed by sand drying beds or machines. Dried sludge is used as manure, returning organic matter and nutrients to the soil.

Question: 6

Untreated human excreta is a health hazard. Explain.


The untreated human excreta are a health hazard because it may cause water pollution and soil pollution. Both the surface water and groundwater get polluted through it. Groundwater is a source of water for tube wells, springs wells, and many rivers. Thus, it becomes the most common route for water borne diseases such as, cholera, typhoid, polio, meningitis, hepatitis and dysentery.

Question: 7

Name two chemicals used to disinfect water.


Chlorine and ozone

Question: 8

Explain the function of bar screens in a wastewater treatment plant.


Bar screen plays an important role in waste water treatment. Wastewater is passed through bar screens to remove large objects like rags, sticks, cans, plastic packets, napkins etc.

Question: 9

Explain the relationship between sanitation and disease.


Sanitation is a known problem; a very large fraction of people defecate in the open, on dry riverbeds, on railway tracks, near fields and many a time directly in water. Untreated human excreta are a health hazard. Many diseases are caused due to poor sanitation and contaminated drinking water. Poor sanitation leads to growth of harmful microbes, flies and mosquitoes which are the source of many diseases like cholera, typhoid, polio, meningitis, hepatitis and dysentery.

Question: 10

Outline your role as an active citizen in relation to sanitation.


(a)            Do not scatter litter anywhere. It should be thrown in the dustbin.

(b)            Do not throw cooking oil and fats down the drain. They should be thrown in the dustbins.

(c)            Do not throw the chemicals like paints, solvents, insecticides, motor oil, and medicine in the drain because some microbes which help in the purification of water may get killed by these.

(d)            Throw the used tealeaves, solid food remains, soft toys, cotton, sanitary towels, etc. in the dustbin.

(e)            Make people aware and encourage community practices to keep our environment clean.

(f)             Separate trash as recycled waste and non-recycled that will help in proper disposal of waste.

Question: 11

Here is a crossword puzzle: Good luck!


3. Liquid waste products

4. Solid waste extracted in sewage treatment

6. A word related to hygiene

8. Waste matter discharged from human body


1. Used water

2. A pipe carrying sewage

5. Micro-organisms which causes cholera

7. A chemical to disinfect water


Question: 12

Study the following statements about ozone:

(a)               It is essential for breathing of living organisms.

(b)               It is used to disinfect water.

(c)               It absorbs ultraviolet rays.

(d)               Its proportion in air is about 3%.

Which of these statements are correct?

(i)                 (a), (b) and (c)

(ii)              (b) and (c)

(iii)            (a) and (d)

(iv)             All four