Access to the AP 7th Class Science Study Material 13th Lesson Wastewater Story Questions and Answers are aligned with the curriculum standards.
AP 7th Class Science 13th Lesson Wastewater Story Questions and Answers
AP Board Solutions Class 7 Science Chapter 13 Wastewater Story
Exercises
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 …………
Answer:
a) Pollutants
b) Sewage
c) Sludge
d) Cooking oil and fat
Question 2.
What is sewage ? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Answer:
Water containing liquid waste disposal from domestic household activities, industrial activities and agriculture activities is termed as sewage. The untreated sewage can harm the rivers and seas as the contaminated water pollutes the whole source of water. As the sewage water may contain harmful substances and disease causing organisms, it is dangerous to release the untreated sewage into the water bodies.
Question 3.
Why should oils and fats not be released in the drain ? Explain.
Answer:
Oils and fats are not soluble in water and they block the drains. In an open drain, they clog the soil pores, making the filtration process difficult. So, oils and fats should not be released in the drain.
Question 4.
Describe the steps involved in getting clarifled water from waste – water.
Answer:
Treatment of wastewater involves physical, chemical and biological processes. The steps involved in getting clarified water from the waste water are as follows:
- In the first step, all the plastic bags, stones, cans etc., are removed by passing the water through bar screens.
- Now, water is subjected to sedimentation where impurities are removed by the force of gravity.
- Solids settled at the bottom of the sedimentation tank are removed. This is called sludge.
- An aerator cleanses the water from other impurities.
- Chlorination is done to remove all disease causing bacteria.
Question 5.
What is sludge? Explain how it is treated.
Answer:
Sludge is a solid like faeces which settle down and removed with a scraper. For the treatment of sludge, it is transferred in a separate tank where it is decomposed by anaerobic bacteria. The biogas is produced in this process and it can be used as a fuel.
Question 6.
Untreated human excreta is a health hazard. Explain.
Answer:
Untreated human excreta contains many microbes, which can cause deadly diseases like cholera, diarrhoea, jaundice and typhoid. The germs of these diseases can easily reach human population through insects and through contaminated food and water. Thus, untreated human excreta is a health hazard.
Question 7.
Name two chemicals used to disinfect water.
Answer:
Chlorine and zone are used to disinfect water.
Question 8.
Explain the function of bar screens in a wastewater treatment plant.
Answer:
Bar screens are large filters which are used in wastewater treatment plants to remove large solids like plastic bottles, pebbles, cans, etc., from wastewater.
Question 9.
Explain the relationship between sanitation and disease.
Answer:
Sanitation and diseases are related to each other as lack of sanitation can cause diseases. By sanitation, proper disposal of sewage and refuse from households and public places is carried out. Implementation of proper sanitation results in a state where we are free from any disease. Lack of it may lead to various diseases.
Question 10.
Outline your role as an active citizen in relation to sanitation.
Answer:
Good sanitation can only be maintained if every citizen contributes to it. The roles as an active citizen in relation to sanitation are as follows:
- Throwing wastes in dustbin.
- Reporting to municipality if any problem in sewage system.
- By optimum utilisation of water.
- Keep the surrounding clean.
- Always keep the sewerage closed and ensuring there is no leakage or any other problem.
- To aware the neighbours about sanitation if it is lacking.
Question 11.
Here is a crossword puzzle : Good luck !
Across
3. Liquid waste products
4. Solid waste extracted in sewage treatment
6. A word related to hygiene
8. Waste matter discharged from human body
Answer:
Down
1. Used water
2. A pipe carrying sewage
5. Micro – organisms which causes cholera 7. A chemical to disinfect water
A. Across:
3. Sewage
4. Sludge
6. Sanitation
8. Excreta
Down :
1. Wastewater
2. Sewer
5. Bacteria
7. Ozone
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 of these
Answer:
ii) (b) and (c)
Questions given in the lesson
Page No. 158
Question 1.
The water in a river is cleaned naturally by processes that are similar to those adopted in a wastewater treatment plant.
Answer:
Air passes through the water flowing in the rivers, it works as an aeration process. It helps aerobic bacteria to grow which consumes the organic impurity of wastewater. Soils and rocks present on riverbeds help in sedimentation. Plants and trees provide nutrients. Evaporation of water helps in forming clouds and pure water comes back in the river in the form of rain.
Page No. 160
Question 2.
Don’t add to the load of WWTP. Paheli wonders how!
Answer:
Normal awareness of every citizen can reduce the load of WWTP. We should not throw the oil, fats, paints, insecticides, medicines, tea leaves, food wastes, cotton into the drain. It can block the sewerage and can hamper the degradation process.
Page No. 162
Question 3.
Bhoojo wants to know how sewage is disposed of in an aeroplane.
Answer:
The sewerage is collected in a large holding tank through plane’s sewer lines. After landing off the plane, these tanks are transported to the WWTP for treatment of wastewater.
Extended Learning – Activities and Projects
Question 1.
Construct across word puzzle of your own using the key words.
Across :
1. A gas prepared by decomposition
3. Bacteria which air
5. Solid waste which settles at the bottom Down :
2. Network of sewers
4. Micro organisms which cause choler
6. Bubbling of air through polluted water
Answer:
Across:
1. BIOGAS
3. AEROBIC
5. SLUDGE
Down :
2. SEWAGE
4. BACTERIA
6. AERATION
Question 2.
Then and now: Talk to your grand parents and other elderly people in the neighbourhood? Find out the sewage disposal systems available to them. You can also write letters to people living in far off places to get more information. Prepare a brief report on the information you collected?
Answer:
Student Activity
Question 3.
Visit a sewage treatment plant.
It could be as exciting and enriching as a visit to a zoo, a museum, or a park. To guide your observation here are a few suggestions.
Record in your notepad:
Place ………… Date ………… Time …………
Name of the official at the plant ………… Guide/Teacher
a) The location of the sewage plant.
b) Treatment capacity.
c) The purpose of screening as the initial process.
d) How is air bubbled through the aeration tank.
e) How safe is the water at the end of the treatment? How is it tested?
f) Where is the water discharged after treatment?
g) What happens to the plant during heavy rains?
h) Is bio gas consumed within the plant or sold to other consumers?
i) What happens to the treated sludge?
D) Is there any special effort to protect nearby houses from the plant?
k) Other observations.
Answer:
Student activity.
Activities
Acitivity 13.1 Page No:150
Question 1.
We have given one example of the use of clean water. You can add many more?
Answer:
Activity 13.2 Page No: 152
Question 2.
Locate an open drain near your home, school or on the roadside and inspect water flowing through it.
Record colour, odour and any other observation. Discuss with your friends and your teacher and fill up the following Table.
Answer:
Aim : To locate an open area near your home, school or on the roadside and inspect water flowing through it.
Procedure:
Visit the nearby drain and observe it carefully.
Observations: Contaminant survey
| S.No. | Type of sewage | Point of origin | Contaminants | Any other remark |
| 1) | Sullage water | Kitchen | Fruits and vegetable waste, oil etc. | Not so polluteds. |
| 2) | Foul waste | Toilets | Human faeces, urine etc. | Cause diseases like dysentery, cholera, etc. |
| 3) | Trade waste | Industrial and commercial organisations | Nitrates, phosphates of metals. | Causes water & soil pollution. |
Activity 13.3 Page No : 154
Question 3.
Study the sewage route in your home? school/building. Do the following:
i) Make a line diagram of the sewage route.
ii) Walk down the street or survey the campus to find the number of manholes.
iii) If possible, observe open drain and record which living organisms are found in and around it.
In case you do not have a sewerage system In your locality, find out how sewage is being disposed off.
Answer:
When I study the sewage route in my locality,
i) Line diagram of the sewage route.
ii) There are S man holes in our streets. They are located at every 50 to 60 metres.
iii) An open-drain system is a breeding place for flies, mosquitoes, and organisms which cause disease.
Activity 13.4 Page No: 154
Question 4.
Divide yourself Into groups to perform the activity. Record observations at each stage:
1) Fill a large glass jar 3/4 full of water. Add some dirty organic matter such as grass pieces or orange peels, a small amount of detergent, and a few drops of an ink or any colour.
2) Cap the jar, shake it well and let the mixture stand in the sun for two days.
3) After two days, shake the mixture and pour a small sample into test tube. Label this test tube “Before treatment; Sample 1”. How does it smell?
4) Use an aerator from an aquarium to bubble air through the sample in the glass jar. Allow several hours for aeration; leave the aerator attached overnight. If you do not have an aerator, use a mechanical stirrer or a mixer: You may have to stir it several times.
5) The next day when aeration is complete, pour another sample into a second test tube. Label it as “After aeration; Sample 2”.
6) Fold a piece of filter paper to form a cone. Wet the paper with tap water and then insert the cone in a funnel. Mount the funnel on a support (as you have learnt in Class VI).
7) Place layers of sand, fine gravel and finally medium gravel in the funnel (Figure). (An actual filtration plant does not use filter paper, but the sand filter is several metres deep).
8) Pour the remaining aerated liquid through the filter into the beakers. Do not allow the liquid to spill over the filter. If the filtered liquid is not clear, filter it a few times till you get clear water.
9) Pour a sample of the filtered water into a third test tube labelled “Filtered; Sample 3″.
10) Pour another sample of the filtered water into a fourth test tube. Add a small piece of a chlorine tablet. Mix well until the water is clear. Label the test tube ” Chlorinated; Sample 4″.
11. Observe carefully the samples in all the test tubes. Do not taste! Just smell them!
Answer:
Aim : To treat a sample of polluted water and make it clean.
Materials required : Funnel, a glass jar, filter paper, flannel stand, soil, grass pieces, orange peels, detergent, ink, strainer, and beaker.
Procedure:
1. Fill a large glass jar 3/4 full of water. Add some dirty organic matter such as grass pieces or orange peels, a small amount of detergent, and a few drops of an ink or any colour. Cap the jar, shake it well and let the mixture stand in the sun for two days.
2. Shake the contents of the class are well and pour the content over a strainer kept over a beaker. The large pieces of grass and orange peels will not pass through the holes of strainer and hence get removed. The remaining parts of the polluted water will collect in the beaker kept below the strainer.
3. Allow the polluted water to stand in the beaker for sometime. The solid fine soil present in the polluted water will settle down at the bottom of the beaker.
4. Transfer the polluted water from this beaker into the another beaker by decantation. Pass air into this polluted water for several hours by using an aerator.
5. When the aeration is complete, we will find that the foul smell from polluted water has almost disappeared. Filter the aerated water through the layer of sand, fine gravel and medium gravel arranged on the filter paper in a funnel. Collect the clean water as a filtrate in a beaker kept below the funnel.
6. Add a small piece of chlorine tablets to the clean water collected in the beaker. Mix well until the water is clean and colourless. This is the cleaner clear safe water obtained by the treatment of polluted water.
Observation :
| S.No. | State | Colour | Transparency | Smell |
| 1) | Raw sample (before treatment) | Greyish | Almost opaque | Foul smell |
| 2) | After aeration | Greyish | Almost opaque | Unpleasant smell |
| 3) | After filtration | Almost colourless | Almost transparent | No smell |
| 4) | After chlorination | Colourless | Transparent | Odourless |
Conclusion: From the above activity, we can conclude that with this treatment we can clean polluted water. This treated water does not give foul smell and it is safe to use.
Now answer the following questions:
a) What changes did you observe in the appearance of the liquid after aeration ?
Answer: Aerated water contains some suspended impurities.
b) Did aeration change the odour?
Answer: The foul odour of the polluted water disappears completely after aeration.
c) What is removed by the sand filter?
Answer: Sand filter removes tiny suspended impurities.
d) Does chlorine change the colour of treated water ?
Answer: Chlorine makes the water clear and colourless.
e) Do chlorine have an odour ?
Answer: Yes, chlorine have a peculiar odour which is not worse than wastewater.