Free Wastewater Story Subjective Test 01 Practice Test - 7th grade 

Question 1

Define the term wastewater. [1 MARK]

SOLUTION

Solution :

Wastewater is any water that has been adversely affected in quality by external influence. Wastewater can originate from a combination of domestic, industrial, commercial or agricultural activities, surface runoff and from sewer inflow or infiltration.

Question 2

What is sewage? What are contaminants? [2 MARKS]

SOLUTION

Solution : Sewage: 1 Mark
Contaminants: 1 Mark

Sewage is a complex mixture containing suspended solids, organic and inorganic impurities, nutrients and other disease-causing bacteria and microbes. 

The impurities present in sewage are called contaminants.

Question 3

What are the various contaminants present in wastewater? Give examples. [2 MARKS]

SOLUTION

Solution :

Each point: 0.5 Mark

The various contaminants present in wastewater are:
i) Organic impurities: Human faeces, oils, animal wastes.
ii) Inorganic: Nitrates, phosphates, metals.
iii) Heavy metals: Mercury, lead.
iv) Microorganisms: Bacteria, viruses.

Question 4

Define the term sludge. Name two chemicals that are used to disinfect water? [2 MARKS]

SOLUTION

Solution :

Definition: 1 Mark
Each Disinfectant: 0.5 Marks

When wastewater is allowed to settle in a large tank, solids like faeces settle at the bottom of the tank. The solid waste at the bottom of the tank is known as sludge.

Two chemicals that are used to disinfect water are: 

  • Ozone
  • Chlorine

Question 5

Why is air pumped into the clarified water?  [2 MARKS]

SOLUTION

Solution : Explanation: 2 Marks

Air is pumped into the clarified water to help aerobic bacteria grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in the clarified water. After some time, the suspended microbes settle at the bottom of the tank as activated sludge. The pure water is then removed from the top.

Question 6

Why is open drainage system not preferred while planning a town or a city? Explain with an example. [3 MARKS]

SOLUTION

Solution :

Reason: 2 Marks
Example: 1 Mark

Open drain system serves as a breeding place for flies, mosquitoes, and organisms which cause diseases. Hence open drainage is never opted for when planning for a town.
Example:
Chandigarh being a planned city doesn't have any open drainage system. Instead, the city has a well planned underground network of pipes for disposal of sewerage. The system has been designed according to the natural slope of the city for sewage to flow under gravity.

Question 7

Give ways of better housekeeping practices. [3 MARKS]

SOLUTION

Solution :

Each point: 1 Mark.

The better housekeeping practices are as follows:-
1. Cooking oils and fats should not be thrown down the drain. They can harden and block the pipes.
2. Chemicals like paints, solvents, insecticides, motor oil and medicines may kill microbes that help purify water. So, efforts should be made to ensure that they are not disposed into the drain.
3. Used tea leaves, solid food remains, soft toys, cotton, sanitary towels etc should only be thrown into the dustbin. These solid food wastes choke the drain and do not allow the free flow of oxygen, thus hampering the degradation process.

Question 8

What is the purpose of chlorination in wastewater treatment? What are the various sources from which wastewater is generated? [3 MARKS]

SOLUTION

Solution :

Chlorination: 1 Mark
Sources: 2 Marks

Chlorine is used in wastewater treatment to disinfect the water.
The various sources from which wastewater is produced are:

  • Homes:  Water used in washing, cleaning, bathing, cooking etc.
  • Industries:  Water used in washing raw materials, cleaning machines, coolants.
  • Agricultural fields: Water used for irrigation washes off chemical fertilizers, insecticides, etc.
  • Other human activities: Water used for water sports, festivals etc.

Question 9

Untreated human excreta is a health hazard. Explain and give examples. [3 MARKS]
 

SOLUTION

Solution : Explanation: 2 Marks
Example: 1 Mark

Untreated human excreta is a health hazard. It may cause water pollution and soil pollution. Both the surface and groundwater get polluted.
Groundwater is a source of water for wells, tube wells, springs, and many rivers. Thus it becomes the most common route for waterborne diseases.

Poor sanitation and contaminated drinking water is the cause of a large number of diseases.
They include cholera, typhoid, polio, meningitis, hepatitis, and dysentery.

Question 10

What are some alternative arrangements for sewage disposal? What are the advantages of on-site human waste technology? [3 MARKS]

SOLUTION

Solution : Each arrangement: 0.5 Mark
Onsite human waste technology: 1.5 Marks

The various alternative arrangements for sewage disposal are:
i) Septic Tanks
ii) Chemical Tanks
iii) Composting Tanks

In case of on-site human waste technology, the toilets do not require scavenging. Excreta from the toilet seats flow through covered drains into a biogas plant. The biogas produced is used as a source of energy.

So, on-site human waste technology has a two-fold advantage:
i) It disposes off the wastes.
ii) The biogas produced from these can be used as an alternative source of energy.
 

Question 11

Name three organic impurities present in sewage. [3 MARKS]

SOLUTION

Solution :

Naming: 1 Mark each

Organic impurities in sewage include:
1) Human faeces
2) Herbicides
3) Fruit and vegetable wastes

Question 12

Match the following correctly. [3 MARKS]

a) Cleaning of water is a process ofi) sewage treatment plantb) Waste water released by houses is calledii) removing pollutantsc) Dried sludge is used asiii) low cost disposal systemsd) Drains get blocked byiv) manuree) Waste water is treated inv) sewagef) Septic tanks, chemical toilets, composting pits are examples ofvi) cooking oils and fats 

​

SOLUTION

Solution : Correct matching: 0.5 marks each

a) Cleaning of water is a process ofii) removing pollutantsb) Waste water released by houses is calledv) sewagec) Dried sludge is used asiv) manured) Drains get blocked byvi) cooking oils and fatse) Waste water is treated ini) sewage treatment plantf) Septic tanks, chemical toilets, composting pits are examples ofiii) low cost disposal systems

Question 13

Describe vermi-processing toilet. Why shouldn't we throw chemicals like paints, solvents, insecticides, motor oil, medicines down the drain? [5 MARKS]

SOLUTION

Solution :

Vermi-processing toilet: 4 Marks
Reason: 1 Mark

Vermi refers to small worms such as earthworms. Vermi-processing toilets are those toilets in which humans excreta is treated by earthworms. It has been found to be a novel, low water-use toilet for safe processing of human excreta without odour and fly problem. The operation of the toilet is very simple and hygienic. The human excreta is completely converted to vermi cakes - a resource much needed for enhancing the fertility of the soil.
We should not throw chemicals like paints, solvents, insecticides, motor oil, medicines down the drain as they may kill microbes that help purify water. It also leads to pollution of groundwater and may adversely affect the health of organisms.

Question 14

a) What is water pollution? Name any two sources of water pollution. [2 MARKS]
b) The terms sewage, sewers, and sewerage are interlinked with each other. Explain each of them. [3 MARKS]

SOLUTION

Solution :

a) 2 Marks
b) 3 Marks

a) Water pollution refers to the mixing of contaminants or pollutants into the water bodies (sea, lakes, rivers, oceans, groundwater, etc) through direct or indirect discharges which causes environmental degradation and affects whole biosphere.
Sources of water pollution are: domestic waste and sewage, hot water released from cooling power plants.

b) Sewage is a mixture of wastewater coming out of homes and other places.
    Sewers are pipes which carry sewage.
    Sewerage is a network of sewage carrying pipes.

Question 15

What are the reasons for the increase in the scarcity of freshwater? [5 MARKS]

SOLUTION

Solution : Each point: 1 Mark

i) Many cities have large and growing population resulting in greater demand for water resources. A large population means, not only more water is required for domestic use but also for higher foodgrain productivity. 
ii) Today the multinational companies and other industrial units consume large quantities of hydroelectric power and for the processing of which they put greater pressure on the existing freshwater resources.
iii) Pollution of water bodies due to the discharge of industrial effluents, use of pesticides, insecticides, and fertilizers used in agriculture, make the river water hazardous for human consumption.
iv) Inefficient use of water for agriculture is another reason for scarcity of freshwater. Traditional techniques of irrigation cause maximum water loss due to evaporation, drainage, percolation, water conveyance, and excess use of groundwater.
v) Reduction in traditional water recharging areas. Rapid construction is ignoring traditional water bodies that have also acted as groundwater recharging mechanism.
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