Chapter Notes - Wastewater story Class 7 Notes | EduRev

Science Class 7

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Class 7 : Chapter Notes - Wastewater story Class 7 Notes | EduRev

The document Chapter Notes - Wastewater story Class 7 Notes | EduRev is a part of the Class 7 Course Science Class 7.
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We use water every day for various purposes. Water should be filtered before it is used for drinking as it contains many impurities that cannot be easily seen with the naked eye. In order to have safe drinking water, it should be boiled.Chapter Notes - Wastewater story Class 7 Notes | EduRevFig: Water treatment plantWater gets contaminated by humans and it is not safe for drinking. Drinking contaminated water results in diseases such as cholera, typhoid and diarrhoea. Polluted water can also prove fatal. Water gets contaminated and scarcity of clean water is due to the following reasons:

  • People take baths and wash clothes in rivers and lakes.
  • Many people bathe their animals in rivers and lakes.
  • Increase in the population, industries and improper disposal of waste.

Water has become so scarce that many people have to travel several kilometres to get drinking water. March 22nd is celebrated as World Water Day. It was on March 22, 2005, that the United Nations declared 2005-2015 as the International Decade for the Action "Water for Life". Clean water is needed not only for drinking, but also for cooking, washing and bathing. A lot of waste water is produced at homes, which should be cleaned before it drains into rivers or lakes and also before it is reused.

Process of Cleaning Water
Pollutants in waste water can be removed in several stages, and this process is called "sewage treatment". Waste water released from homes, industries, hospitals and offices, and water collected during rains from roof tops or streets, is collectively termed Sewage. This sewage is liquid waste containing dissolved impurities, and the impurities are called contaminants, which contain many harmful substances.

Sewage contains:

Organic and inorganic impurities
Organic impurities in sewage include animal waste, urine, oil, vegetable and fruit waste, faeces, pesticides and herbicides. Inorganic impurities include phosphates, nitrates and metals.

Disease-causing bacteria
There are disease-causing bacteria in sewage.

Saprotrophic bacteria
These are bacteria that feed on dead organisms.

Nutrients
Sewage contains some useful nutrients, such as phosphorus and nitrogen.

Other microbes
Microbes that cause typhoid, cholera, diarrhoea and dysentery are present in sewage.

Types of Sewages
There are various types of sewage, depending upon its colour and odour. Some sewage is black and has a very bad odour.
Sullage water
Waste water released from the kitchen is called sullage water. The contaminants in sullage water are mild detergents, oils and food particles. Moreover, it contains lots of water released when utensils are washed.

Foul waste
Waste water released from toilets is termed as foul waste. It consists of human waste and a lot of bacteria that release gases and bad odour. It is highly infectious.

Trade waste
Waste released from industries and commercial organisations is called trade waste. It consists of acids and strong chemicals that are toxic in nature.


Sewerage
The network of small and big pipes that carry wastewater is called sewers, and all sewers together form the sewerage. Wastewater is carried from home to the point of disposal, that is, the wastewater or sewage treatment plant.
After treatment of wastewater, the clean water is released into nearby water bodies. Sewerage has manholes that can be used to clear blockages. Manholes are located every 50 to 60 metres in the sewerage. If there is no sewage facility, then waste water is directly drained into nearby streams and lakes, which results in water contamination.
Water Treatment
Waste water needs to be treated before it can be reused, or released into a water body.
Waste water needs to be treated before it can be reused, or released into a water body. Wastewater has many impurities and these impurities should be removed by water treatment.Chapter Notes - Wastewater story Class 7 Notes | EduRevFig: Water cleaning processWaste water from households is treated at a treatment plant to remove the physical, biological and chemical matter. In the physical process, waste water is filtered to remove large impurities.
For example: Take a funnel. Place a filter paper in the funnel and wet it with water. Then add some sand, fine gravel and medium gravel into the funnel. These are layers for the filtration of water. Now pour wastewater into the funnel and collect clean water. Repeat the same process several times till the collected water looks clean.


In water treatment plants, the layers are substituted by:

Bar Screens
Bar screens are screens that prevent the flow of large objects in wastewater. These screens help to remove large objects like rags, plastic bags, cans, napkins and sticks from sewage. These bar screens are cleaned regularly either manually or with the help of the machines.

Grit and sand removal tank
The grit and sand removal tank may not remove some impurities, such as faeces.
Clarifier
A clarifier is a tank with its central part inclined downwards so as to allow faeces to settle down. The inclined waste is then removed using a scraper. This waste is termed as sludge.
Sludge is transferred to a separate tank where it is decomposed using bacteria. The gas produced is burned in an apparatus such as micro-turbine to generate electricity. Finally, a skimmer is used to remove the oils and grease.
Thus, if all the physical contaminates are separated from the sewage, then the sewage is termed to be clarified water.Chapter Notes - Wastewater story Class 7 Notes | EduRevFig: Primary waste water purifierBiological contaminates such as bacteria and microbes consume human waste, food waste, soaps and other wastes, and still remain in the 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 settles 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.Different mechanisms were used to treat water, even in the olden days. The ancient Greek and Indian writings dating back to as early as 2000 BC recommended water treatment methods. People knew about water treatment procedures back in 2000 BC.
The Egyptians discovered the process of coagulation for water treatment. Eucalyptus trees are planted along the sewage ponds in which water is released after water treatment processes.
Eucalyptus trees absorb wastewater from the pond and release pure water vapour into the atmosphere. Oils and fats can harden and block water pipes. Fats clog the soil pores in an open drain, reducing the effectiveness of filtration of water.
So avoid throwing tea leaves, solid food remains and napkins into the drain. These block the flow of oxygen to the microbes that help in water treatment. Chemicals like paints, medicines, motor oil and solvents kill the microbes that help in water treatment.
People need to be made aware of the ill effects of throwing pollutants into the drain.

IMPORTANCE OF SANITATION
Everyone must know about the adverse effects of poor sanitation.

Effects of poor sanitation
Everyone must know about the adverse effects of poor sanitation. The problem is at its worst in villages, where proper sanitation is not available. Villagers defecate in the open, on dry river beds, railway tracks, fields and even directly in water.
This causes water and soil pollution. Moreover, it contaminates and affects ground water as well as surface water, resulting in diseases such as cholera, typhoid, polio, meningitis, hepatitis and dysentery.
Sanitation is a major problem in developing countries such as India and China. The government is unable to provide proper sanitation through underground drainages. Also, lack of knowledge and of money, illiteracy, large population and lack of social awareness results in improper sanitation.
To avoid these problems, low-cost onsite sewage disposal systems should be used. These systems collect human excreta and store it in a hole or a pipe, and later direct it to a sewage treatment plant.
In the absence of a proper sanitation network, people can use some other mechanism for sewage disposal. The other mechanisms are septic tanks, chemical toilets, composting pits and vermi-processing toilets.

Septic Tanks
Septic tanks are suitable for places such as hospitals, isolated buildings and clusters of houses where there is no sewage. Local governments or private corporations usually provide septic tanks in areas that have no
direct connection to main sewage pipes. The septic tank system consists of a small sewage treatment system.

Chemical Toilets
Aeroplanes and trains usually have chemical toilets. A chemical toilet uses chemicals to disinfect human waste and remove its bad odour. That is why trains and aeroplanes do not have elaborate plumbs and sewage.

Composting Toilets
Another method of clearing human waste is by the process of composting pits. A composting toilet is a system that converts human waste into organic compost and usable soil.
This happens when micro-organisms, such as bacteria and fungi, and macro-organisms, such as earthworms, oxidise organic waste to break it down into essential minerals.

Vermi-Composting Toilets
A vermi-composting toilet is a process that involves earthworms, which treat human excreta. This process is low cost. Moreover, the entire human waste is converted into of vermi-compost.

Sulabh Toilets
Organisations such as Sulabh International have developed a twin-pit pour flush toilet system that is being used by ten million people every day. The waste from these toilets flows through covered drains into a biogas plant for the generation of biogas and bio-fertilisers.
Biogas plants offer safe and hygienic disposal of wastes. Biogas has great advantage, i.e. it is used as a source of low-cost fuel. It can be used for heating, cooking running heat engines, generating mechanical or electrical power.

Litter and Waste
Litter and waste cause sanitation havoc at public places. This becomes common when exhibitions and fares are conducted.
Public places such as railway stations, bus depots, airports and hospitals generate a lot of waste, which leads to diseases. To prevent disease, certain measures should be taken and awareness among people should be created.

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