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Chapter Review:

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• Cleaning of water is a process of removing pollutants before it enters a water body or is reused.This treatment is commonly known as “Sewage Treatment”.
• Sewage is a liquid waste.Most of it is water, which has dissolved
  and suspended impurities.These impurities are called contaminants.
• Full Form of (WWTP) is WASTEWATER TREATMENT PLANT.
• Wastewater is generated in homes, industries, agricultural fields and in other human activities. This is called sewage.
• A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water.

Exercise

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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) Contaminants  (b) Sewage  (c) Sludge  (d) plastic, sludge.

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

Answer:

Sewage is wastewater released by homes, industries, hospitals, offices and other users. It also includes rainwater that has run down the streets during a storm or heavy rain.

The water that washes off roads and rooftops carries harmful substance with it. Sewage is a dissolved and suspended impurities which are called contminnts.

That is why, it is harmful to discharge untreated sewage into rivers to sea. 

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

Answer:

Oil does not mix with water. Being lighter, oil floats on water. This prevents mixing of water and air. This reduses oxygen supply for aqutic plants and animals.

Alongwith, in an open drain the fats clog the soil pores reducing its effectiveness in filtering water.   

4. Describe the steps involved in getting clarified water from wastewater.

Answer:

Treatment of wastewater involves physical, chemical, biological process, which remove physical, chemical, biological matter that contaminates the water.

Physical: 

(i) Waste water is passed through bar screens. Large objects like rags, cans, plastic, packets, napkins are removed.

(ii) Water 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.

Biological:

(i)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 removed with scaper. This is the sludge. skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water.

The sludge is transferred to a separate tank where it is decomposed by the anearobic bacteria.

(ii) Air pumped into the clerified water to help aerobic bacteria to grow.

Bacteria consume human waste, food waste, soap and other unwanted matter still remaining in clarified water.

After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top.

Chemical: 

Something it may be necessary to disinfected water with the chemicals like chlorine and ozone before releasing it into the distribution system.    

5. What is sludge? Explain how it is treated.

Answer:

During physical treatment, solids like feaces settle at the bottom of the the large tank. This is called sludge.

Treatment of sludge:

(i) Sludge are first removed from the bottom using a sraper.

(ii) Sludge is then transferred to a seprate tank. Where it is decomposed by the anearobic bacteria.

The biogas prodused in the process can be used as fuel.

6. Untreated human excreta is a health hazard. Explain.

Answer:

Untreated human excreta is a health hazard. it may cause water pollution and soil pollution. Both the surface water and groundwater is a source of water for wells, tubewells, springs and many rivers. Thus, it becomes the most common route for water-botne diseases. They include cholera, typhoid, polio, meningits, hepatitis and dysentery.  

7. Name two chemicals used to disinfect water.

Answer:

Ozone, chlorine.

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

Answer:

Wastewater is passed through bar screens to remove large objects like rags, sticks, cans, plastic packets, napkins.

9. Explain the relationship between sanitation and disease.

Answer:

Untreated human excreta is a health hazard. Improper sanitation may cause water pollution and soil pollution. Both the surface water and groundwater get polluted. Groundwater is a souce of water for wells, tube wells, springs and many rivers. Thus, it becomes the most common route for water- borne disease. They include cholera, typhoid, polio meningitis, hepatits and dysentery.

That is why, proper sanitation is must to avoid some of the deadliest disease.  

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

Answer:

We all have a role to play in keeping our enviorment clean and healthy. We must realise our responsiblty in maintaning the water source in a healthy state. Adopting good sanitation practices should be our way of life. As an agent of chance our individual intiative will make a great difference. We can influence others with our energy, ideas and optimies. A lot can be done if people work together. There is great power in collective action.

11. 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

Answer:

(ii) (b) and (c)

Additional Question with solution:

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Que: Wastewater is fit for human consumption or not. give reason to support your.

Ans: No, because it is dirty and has many diseases causing organisms like cholera, typhoid, etc.

Que: Name two chemicals used to disinfect wastewater.

Ans: Chlorine and ozone.

Que: Special type to toilets has been designed in aeroplanes, name it.

Ans: Vacuum toilets.

Que: Name the toilets used in areas with limited water supply.

Ans: Vermi - processing toilets.

Que: Name the type of toilets which are most suitable for holding an outdoor music festival in a park.

Ans: Chemical toilets.

Que: Name two things that can be made from sludge extracted during treatment of sewage.

Ans: Biogas and manure.

Que: Name two inorganic impurities present in sewage. 

Ans: Inorganic impurities present in sewage are nitrates and phosphates.

Que: Mention the use of dried sludge.

Ans: It is used manure, thus returning organic matter and nutrients to the soil.

Que: Mention the use of dried sludge.

Ans: It is used as manure, thus returning organic matter and nutrients to the soil.

Que: In which type of toilets, human excreta is treated by earthworm?

Ans: Vermi - processing toilets.

Que: Give some examples of onsite sewage disposal systems.

Ans: Chemical toilets, septic tanks, composting pits, etc.

 

Additional Question with solution:

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Que:  World water Day is celebrated on.

Ans:  22 March.

Que: Mention the period proclaimed as the International Decade for action on water for life.

Ans: 2005 - 2015 is the period proclaimed as the international Decade for action on water for life. 

Que: Name the three processes involved in treatment of wastewater.

Ans: Treatment of watewater involves physical, chemical and biological processes for removing different types of contaminants.

Que: Explain sewers and sewage.

Ans: Sewers are the pipes acting as a transport system that carries sewage from point of origin to the point of disposal. The wastewater released from homes, industries, hospitals, offices and other uses is called swewge.

Que: The used water should not be wasted. Do you agree? Justify.

Ans: The used water should not be wasted but it should be cleaned.

Que:  Bleaching powedr is mixed in water, why? Think and give appropriate reson for it.

Ans: Bleaching powder is mixed in water to make it safe for drinking because it kills the harmful germs present in water.

Que: Natural water is the purest from of water. Explain why or why not.

Ans: Natural water is not pure always. It is because all types of water except rainwater contain salts dissolved in it. Theses salts make the water impure. 

Que:  Mention the role of effluent treatment plants in cities.

Ans: The effluent treatment plants filter out undissolved materials from water.

Que: Protozoa is causative organism of which waterborne disease?

Ans:  Dysentry.

Que: Saniation can be improved. Explain, what step should be taken to improve it. 

Ans: Low cost onsite sewage disposal system must be encouraged to improve sanitation.

Que: Give the percentage of water being activated in sludge. 

Ans: About 97% of water is being activated in sludge.

Que: Wastewater is fit for human consumption or not. give reason to support your.

Ans: No, because it is dirty and has many diseases causing organisms like cholera, typhoid, etc.

Que: Name two chemicals used to disinfect wastewater.

Ans: Chlorine and ozone.

Que: Special type to toilets has been designed in aeroplanes, name it.

Ans: Vacuum toilets.

Que: Name the toilets used in areas with limited water supply.

Ans: Vermi - processing toilets.

Que: Open drain is big concern now - a - days. Justify.

Ans: Open drain is big concern for the society now - a days because they create unhygienic conditions. It provides favourable conditions to filies, mosquitoes and unhygienic conditions. It provides favourable conditions to filies, mosquitoes and other insects to breed and spread a number of diseases.

Que: Sewage also contains some nutrients Comment.

Ans: Sewage is a complex mixture which contains suspended solids, organic and inorganic impurities, nutrients, saprotrophic and disease causing bacteria and other microbes.

The nutrients present in sewage are phosphorus and nitrogen.

Que: The terms sewage, sewers and sewerage are interlinked with each other. Can you explain, how?

Ans: The terms like sewage, sewage and sewerage are interlinked with other because sewage is a mixture of watewater coming out of homes and other places. Sewers are pipes which carry sewage and sewerage is a network of sewage carrying pipes.