Question 1 What is sewage? State the various ways in which we produce sewage in our homes?
Question 2 Explain why, it is harmful to discharge untreated sewage into rivers, lakes or ground?
Question 3 What is meant by treatment of sewage?
Question 4 What is meant by sewage and sewerage?
Question 5 Name the organic and inorganic impurities present in sewage?
Question 6 Name diseases caused by micro-organism in sewage?
Question 7 What is the composition of sewage?
We use clean water everyday for drinking, bathing, washing clothes, cooking food, washing utensils, and flushing toilets. When we use water for various purposes, we make the water dirty.
The black-brown water containing lather and mixed with dirt and grease, which comes from the sink of a kitchen, a washing machine, a bathroom shower or a bath tub, and goes down the drain in our house is dirty water. This used water is called wastewater.
When we flush the toilet, then faeces and urine go down the drain with water. So, the filthy water which comes out from the toilet and goes into drain is also dirty water. Thus, the wastewater may also contain faeces (or human excreta).
Used water or wastewater could be re-used after cleaning it. The cleaning of water is a process of removing pollutants from it before it is re-used or released into the environment (such as rivers, lakes, sea or ground).
The wastewater and faeces (human excreta) from homes and other buildings which is carried away in sewers, is called sewage. Sewage includes
(1) household wastewater from kitchen sink, washing machine, washbasin, bathroom shower, bath tub and faeces (human excreta) from the toilet.
(2) Sewage is also produced and released by shops, offices, schools, hospitals, factories, industries, and all other places where humans work or lives.
(3) Sewage also includes rainwater that has run down the streets and roads during rains carrying harmful substances with it, and flows into sewer pipes.
Sewage is a liquid waste and is dirty water having dissolved and suspended impurities in it. The impurities present in sewage are called contaminants’ or ‘pollutants.
Composition of Sewage
Sewage is a complex liquid mixture containing water, dissolved and suspended solids, organic and inorganic impurities, nutrients, saprotrophic and disease-causing bacteria, and other microbes.
(1) The organic impurities present in sewage are: Human faeces, Animal waste (like Animal dung), Urea (as Urine), Oil, Fruit and Vegetable wastes, Pesticides, and Herbicides, etc.
(2) The inorganic impurities present in sewage are: Nitrates, Phosphates and Metals.
(3) The nutrients present in sewage are : Nitrogen and Phosphorus.
(4) The bacteria present in sewage include those bacteria which cause water-borne diseases such as cholera and typhoid.
(5) The other microbes present in sewage are protozoa which cause a water-borne disease called dysentery.
(6) Sewage that reaches sewage treatment plants may also contain rubbish such as rags, wooden sticks, cans, plastic bags (polythene bags), napkins, sanitary towels grit and sand.
In a house (or a public building) generally there are two sets of pipes : one set of pipes brings clean drinking water into the house and the other set of pipes takes away wastewater (or sewage) produced in the house.
The clean water supply pipes are narrow whereas the wastewater carrying pipes are much wide.
An underground pipe which carries away dirty drainage water and waste matter is called a sewer. The provision of drainage at a place by laying sewers under the ground is called sewerage.
Sewerage is an underground network of interconnected pipes (called sewers) that transports or carries the sewage from the place where it is produced (homes and other buildings), to the sewage treatment plant (or wastewater treatment plant) where it is processed.
A manhole is a covered vertical hole in the ground, pavement or road, above the underground sewer pipeline through which a worker can go down up to the sewer pipes for inspection and cleaning.
Manholes are also provided at the junction of two or more sewers, and at points where there is a change in the direction of sewer line.
Sewage is Harmful
The sewage (or wastewater) released by houses and other buildings contains a large number of harmful substances and disease-causing micro-organisms.
If this untreated sewage is discharged into rivers, lakes or ground, it will contaminate our freshwater sources (like rivers, lakes and groundwater).
Drinking of water contaminated with sewage will spread diseases in people which can even lead to deaths.
The discharge of untreated sewage into rivers (and sea) can also kill fish and other aquatic animals.
Untreated sewage should not be allowed to run into rivers, lakes, sea or underground. Sewage water should be treated suitably (or processed) before releasing it back to the environment.
The processing of sewage to remove pollutants and make it harmless so that it may be disposed of safely in the rivers, etc., is called sewage treatment (or wastewater treatment).
The main purpose of sewage treatment is to reduce the pollutants (or harmful substances) present in it to such a low level that it may not remain a health hazard for any one.
Sewage is carried from houses and other places by underground pipes called sewers to sewage treatment plant. A sewage treatment plant removes solid and liquid wastes, as well as most of the disease causing micro-organism from the sewage so that the water leaving the sewage treatment plant is fit to use.