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Untreated human excreta contains many pathogens and disease causing microbe like cholera, diarrhea, typhoid, polio, meningitis, hepatitis etc. The germs of these diseases can easily reach human population through air, water or insects and through contaminated food and water. Thus, untreated human excreta are a health hazard.

Untreated human excreta is a health hazard. It contains various disease causing micro organisms. It causes pollution of soil and water including the underground water. Thus, it contaminate the sources of water from which people collect water for drinking and household purposes. When this contaminated water is used for drinking, it cause disease such as cholera, typhoid, hepatities, dysentery, etc., which may even lead to death.

Sludge is human waste (like faeces) in waste water left during sewage treatment. Since it is organic waste, it is used to produce bio gas and manure. 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.

Semi – solids such as faeces that settle down during wastewater treatment are called sludge. This sludge is removed using a skimmer and then transferred to a tank where it is decomposed by anaerobic bacreria to produce biogas. 

The biogas is used as a low – cost fuel for heating, cooking etc., It is also used to produce electricity.

Treatment of wastewater involves physical, chemical, and biological processes, which remove physical, chemical and biological matter that contaminates the wastewater.​

Following steps are involved:
1. Wastewater is passed through bar screens which remove large objects like rags, sticks, cans, plastic packets, napkins etc.
2. Water then goes through Grit and Sand removal tank, where sand, grit and pebbles settle down.
3. Water is then allowed to settle in a tank where solids like faeces (called sludge) settle at the bottom and are removed with a scraper. A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water. Sludge is used to produce biogas.
4. Clarified water is then passed through an aerator tank where air is pumped into the water. It helps aerobic bacteria to grow which decompose organic matter like human waste.
5. After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top. The dried activated sludge is used as manure.
6. Water is removed from the top and is stored in a tank. The treated water has low level of organic material and suspended matter. It is discharged into a sea, a river or into the ground. Sometimes it is disinfected through chemicals like Chlorine and ozone and then distributed to towns.

The steps involved in getting clarified water from wastewater are as follows : 

1. Use an aerator to bubble air through the wastewater. A mechanical stirrer or a mixer can also be used in place of the aerator. This helps in reducing bad odour of the Wastewater. 

2. Then, the water is filtered through the layers of sand, fine gravel and medium gravel, filtration makes the wastewater clean from varioustypes of pollutants. The water is filtered continuously until it becomes clear. 

3. Then any disinfectant such as chlorine tablet is added, to the filterate and stirred to obtain completely clear water.

Answer:

1. Answer : (a) Foul smell

Explanation: Foul smell is a quality of waste water.

2. Answer : (a) water for life

Explanation: Period 2005-2015 is being celebrated as the international decade for action on water for life.

3. Answer : (b) 50-60 m

Explanation: Manholes are located at every 50-60 m in the sewerage, at the junction of two or more sewers and at points where there is a change in direction.

4.  Answer : (b) aerobic bacteria

Explanation: 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.

5. Answer : (a) Earthworm

Explanation: In Vermi-processing toilets, humans excreta is treated by earthworms. In this process, human excreta is completely converted to vermi cakes by earthworms.

6. Answer : (a) liquid waste

Explanation: Sewage is defined as waste water due to which it is a liquid waste.

7. Answer : (c) Both Biogas and sludge

Explanation: Biogas and sludge are the products of wastewater treatment.

8. Answer : (d) All of these

Explanation: A Open drain systems are a breeding place for different flies, mosquitoes, and other disease causing organisms. The waste drainage system should be closed.

9. Answer : (a) Sewers

Explanation:The pipes through which the wastewater flows into the sewage are known as sewers, whereas, wastewater is collected into the sewage from homes, industries and hospitals. Hence, sewers is not a source of wastewater.

10. Answer : (d) Water coming out of a laundry

Explanation: This water is called as wastewater. Water coming out of the damaged tap, water coming out of shower and water flowing in a river are not dirty hence water coming out of a laundry.

11. Answer : (b) wastewater

Explanation: Wastewater is used water that has been affected by domestic, industrial and commercial use. Wastewater effluents are released to a variety of environments, such as lakes, ponds, streams, rivers, estuaries and oceans. Wastewater also includes storm runoff, as harmful substances wash off roads, parking lots and rooftops

12. Answer : (b) health hazard

Explanation: Untreated human excreta is a health hazard. It contains various disease-causing microorganisms. When this contaminated water is used for drinking, it causes diseases such as cholera, typhoid, hepatitis, dysentery, etc, which may even lead to death.

13. Answer : (d) Cow dung

Explanation: The gas produced from cow dung or other organic material is called biogas. Biogas is a gas produced from the fermentation process of organic materials. 

14. Answer : (d) sand and grit removal

Explanation: Grit removal is the process used to remove sand, silt and grit from water. Grit (and sand) removal is often found in the headworks of wastewater treatment plants.

15. Answer : (b) biogas plant

Explanation: In many villages, human excreta from the toilet seats in the homes flows directly into biogas plant through covered drains . The biogas produced is used as a fuel.

16. Answer : (a) Municipal corporation

Explanation: The urban poor suffer disproportionately from the lack of adequate sanitation. .Studies have shown that improved health outcomes are dependent on neighbours' access to adequate sanitation.

17. Answer : (a) cleaning of water

Explanation: Cleaning of water is a process of removing pollutants before it enters a water body or is reused. This process of wastewater treatment is commonly known as Sewage Treatment.

18. Answer : (c) energy

Explanation: Biogas is a mixture of gases, primarily consisting of methane and carbon dioxide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. It is a renewable energy source.

19. Answer : (c) Phosphates

Explanation: Phosphate or phosphorus is an inorganic component and hence, it is considered an inorganic impurity in sewage.Urea, pesticides, and vegetable waste all are organic.

20. Answer : (a) aerobic bacteria

Explanation: Aerator. Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in clarified water.

21. Answer : (b) Sewage

Explanation: Sewage is liquid waste containing dissolved impurities called as contaminants. Sewage comprises dissolved and suspended impurities.

22. Answer : (b) Waste Water Treatment Plant

Explanation: A wastewater treatment plant is a facility in which a combination of various processes (e.g., physical, chemical and biological) are used to treat industrial wastewater and remove pollutants.

23. Answer : (c) They harden and block the pipe 

Explanation: Cooking oil should not be thrown down the drain because it can block the drainage pipes. The fats clog the soil pores which reduces its effectiveness in filtering water and therefore blocks the drain pipes.

24. Answer : (d) Cholera

Explanation: Cholera, like other waterborne diseases, can spread if food and, in particular, water become contaminated with the stools of an infected person. 

25. Answer : (c) Organic

Explanation: It defines biodegradable waste as “any waste that is capable of undergoing anaerobic or aerobic decomposition, such as food and garden waste, and paper and cardboard.”

Click here for Practice MCQ Questions for Wastewater Story Class 7

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Practice MCQ Questions for Class 7 Science

1. Which one of the following is a quality of wastewater?

(a) Foul smell
(b) Sweet taste
(c) Sewage
(d) None of these

2. Period 2005-2015 is being celebrated as the international decade for action on

(a) water for life
(b) education for all
(c) global war
(d) terrorism

3. In sewerage manholes are located at every

(a) 20-25 m
(b) 50-60 m
(c) 90-100 m
(d) 100-110 m

4.  Sludge in separate tanks is decomposed to get biogas by

(a) yeasts
(b) aerobic bacteria
(c) anaerobic bacteria
(d) none of these

5. Which one of the following is used in vermi-processing toilet?

(a) Earthworm
(b) Cockroach
(c) Both of these
(d) None of these

6. Sewage is mainly a

(a) liquid waste
(b) Solid waste
(c) gaseous waste
(d) Mixture of solid and gas

7. Which of the following is/are products of wastewater treatment?

(a) Biogas
(b) Sludge
(c) Both Biogas and sludge
(d) Aerator

8. Open drain system is a breeding place for which of the following:

(a) Files
(b) Mosquitoes
(c) Organisms which cause diseases
(d) All of these

9. Which of the following is not a source of waste water?

(a) Sewers
(b) Homes
(c) Industries
(d) Hospital

10. Which of the following is wastewater?

(a) Water trickling from a damaged tap
(b) Water coming out of a shower
(c) Water flowing in a river
(d) Water coming out of a laundry

11. Water that is not fit for use is called

(a) clean water
(b) wastewater
(c) both (a) and (b)
(d) none of these

12. Untreated human excreta is a:

(a) waste water
(b) health hazard
(c) manure
(d) none of these

13. Which one is not a of household garbage

(a) Vegetable peels
(b) Dal packets
(c) Crockery pieces
(d) Cow dung

14. Which process removes the solids like foeces and other substances from the waste water:

(a) chlorination
(b) decomposition
(c) evaporation
(d) sand and grit removal

15. Excreta from the toilet seats flow through covered drains into a chemicals:

(a) chemicals
(b) biogas plant
(c) vermi-processing toilets
(d) none of these

16. Sanitation in the cities is the function of

(a) Municipal corporation
(b) Non-government organisation
(c) Individual person
(d) Societies of locality

17. The process of removing pollutants in water before it enter a water body is called

(a) cleaning of water
(b) refining
(c) filtering of water
(d) none of these

18.The biogas product is used as a source of:

(a) rains
(b) oils
(c) energy
(d) all of these

19. Which of the following is a part of inorganic impurities of the sewage?

(a) Pesticides
(b) Urea
(c) Phosphates
(d) Vegetable waste

20. What helps to clean the clarified water:

(a) aerobic bacteria
(b) anaerobic bacteria
(c) both (a) and (b)
(d) none of these

21. Liquid waste consisting of suspended impurities is called

(a) Contaminant
(b) Sewage 
(c) Aeration 
(d) Chlorination

22. WWTP stands for 

(a) Waste Water Therapy Plant
(b) Waste Water Treatment Plant
(c) Waste Water Travel Plant
(d) Waste Water Tremendous Plant

23. Cooking oil and fats should not be thrown down the drain because

(a) They flow through the drain freely
(b) It allows the particles to get filtered
(c) They harden and block the pipe 
(d) They break the pipe

24. Water borne disease is

(a) Diabetes 
(b) Cancer
(c) Appendicitis
(d) Cholera

25. Biodegradable wastes are generally

(a) Blended
(b) Synthetic
(c) Organic
(d) Inorganic

Answer is --(a) Sewers

Some points are given here, you can add more.
(i) Do not throw used tea leaves, solid food remains, etc. in the drain. Throw them in the dustbin.
(ii) Chemicals like medicines, paints, insecticides, etc. should not be thrown in the drain, as they increase the pollution load of the sewage

(a) liquid waste.

(c) Both biogas and sludge

Wastewater needs to be treated before it can be released into a water body. Wastewater has many impurities and these impurities should be removed by water treatment.
Wastewater from households is treated at the treatment plant to remove the physical, biological and chemical matter. In the physical process, wastewater is filtered to remove large impurities.
In water treatment plants, the layers are substituted by:
Bar screens are screens that prevent the flow of large objects in wastewater.  
The grit and sand removal tank may not remove some impurities, such as faeces.
A clarifier is a tank with its central part inclined downwards so as to allow faeces to settle down. This waste is termed as sludge. Sludge is transferred to a separate tank where it is decomposed using bacteria. Thus, if all the physical contaminants are separated from the sewage, then the sewage is termed to be clarified water.
Now this clarified water is passed into an aerator in waste water treatment. An aerator pumps air into the water. After many hours, the bacteria settle at the bottom of the tank as activated sludge. The water present in the top is 95% clean and is let out into a water source, while the activated sludge is dried in a sand bed and is used as manure.

In the chemical process, take a chlorine tablet and put it in a beaker full of water. Observe that water is clean when the tablet dissolves. That is why chlorine tablets or ozone is used to disinfect water in treatment plants.

Hint: See pages 223 and 224 of Chapter 18 of NCERT Science textbook for Class VII.

In a wastewater treatment plant bar screen removes large solid objects from water. The wastewater is allowed to pass through bar screen so that large solid objects such as rags, napkins, sticks, cans, plastic bags, polythene ec present in wastewater can be removed.

(b) sewerage. 

Sewage is nothing but waste waster. It is a complex mixture containing suspended solids, organic and inorganic impurities, nutrients, saprophytes and disease causing bacteria and other microbes.

(i) Sewage – mixture of wastewater coming out of homes and other places.
(ii) Sewers – pipes which carry sewage.
(iii) Sewerage – network of sewage carrying pipes.

The low – cost onsite sewage disposal systems are encouraged. The septic tanks. Chemical toilets, composting pits are the other alternate facilities. 

Some Organisations offer hygienic on – site human waste disposal technology. These toilets do not require scavenging. Excreta from the toilet seats flow through covered drains into a biogas plant. The bio-gas produced is used as a source of energy.

(ii) (b) and (c)

1. Open drains be covered and keep our surroundings clean. 

2. Should not litter anywhere adopt good sanitation practices. 

3. Chemicals like paints, insecticides, motor oil etc., should not be thrown in drain which may kill useful bacteria. 

4. Used tea leaves, solid food remains, soft toys, cotton, sanitary towels, etc should also be thrown in the dustbin. 

5. Make people aware and encourage community practices to keep our environment clean. 

6. Seperate trash as recycled waste and non – recycled.

Wastewater treatment plant requires costly infrastructure to build and to be maintained. So, we should be an active citizen and limit the type of waste. Try to follow the following:
1. Open drains be covered and keep our surroundings clean.
2. Should not litter anywhere adopt good sanitation practices e.g. oil and fats should not be thrown in drains.
3. Chemicals like paints, insecticides, motor oil etc. should not be thrown in drain which may kill useful bacteria.
4. Used tealeaves, solid food remains, soft toys, cotton, sanitary towels, etc. should also be thrown in the dustbin.
5. Make people aware and encourage community practices to keep our environment clean.
6. Separate trash as recycled waste and non-recycled.

Sewage is a liquid waste which has water as its largest component along with various types of impurities like waste water from houses, offices, factories, hospitals etc., is called sewage. It has a complex and inorganic impurities, nutrients, saprotrophic and disease causing bacteria and other microbes. 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, malaria, dengue etc.