1. Water And Waste Water -
ü Water is needed by all forms of life. Clean water is a basic need of human beings. Unfortunately, clean water is not available to a large segment of human populations.
ü The water which is unfit for human consumption becomes the source of many water-borne diseases which ultimately lead to loss ( of human life. It is estimated that one billion human beings do not get safe drinking water.
ü So, realizing the urgency we celebrate 22nd March as World Water Day to bring awareness amongst people for safe water, fit for human consumption.
ü Thus, the water is cleaned by removing pollutants before it enters a water body or is reused. This process of waste water treatment is commonly known as sewage treatment which takes place in several steps as discussed later.
ü On the World Water Day, i.e. 22 March 2005, the General Assembly of the United Nations proclaimed the period 2005-2015 as the International Decade for action on Water for Life. All efforts made during this decade aim to reduce by half the number of people who do not have access to safe drinking water.
2. Sewage -
ü It is waste water released by homes, industries agricultural fields and other human activities. It also includes rainwater that has run down the street during a storm or heavy rain and it is liquid waste.
ü Most of its water has dissolved and suspended impurities called contaminants.
ü Composition of Sewage-
n The organic impurities present in sewage are human faeces, animal wastes (like animal dung), urea (as urine), oil, fruits and vegetable wastes, pesticides, herbicides, etc.
n The inorganic impurities present in sewage are nitrates, phosphates and metals.
n The nutrients present in sewage are nitrogen and phosphorus.
n The bacteria present in sewage include those bacteria which cause water-borne diseases such as cholera and typhoid.
n The other microbes present in sewage are Protozoa which cause a water-borne disease called dysentery.
3. Sewerage System-
ü The pipes which carry away waste water or sewage from houses and other buildings are buried under the ground. An underground pipe which carries away dirty drainage water and waste matter is called sewer.
ü The provision of drainage at a place by laying sewers under the ground is called sewerage. Actually, sewerage is an underground network of interconnected pipes called sewers that carries the sewage from the place where it is produced to the sewage treatment plants, where it is processed.
ü Manholes - 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, cleaning, etc. Manholes are provided at every 50-60 m distance in the main sewer pipeline. Manholes are also provided at the junction of two or more sewers and at points where there is a change in the direction of the sewer line.
4. Water Treatment -
ü Waste water Treatment Plant - A place where waste water or sewage from houses and other buildings is brought for processing is called waste water treatment plant.
ü Treatment of waste water involves physical, biological and chemical processes depending on the nature of contaminants.
ü Physical Process (Screening)-
n The bar screens first remove the large rubbish objects like rags, sticks, cans, polybags, napkins, sanitary towels, etc., from the waste water.
n After passing through the bar screen, waste water is taken to a tank called grit and sand removal tanks.
n In this, sand and grit settle down slowly at the bottom of the tank as water passes slowly through this tank.
n The settled sand and impurities are removed from the tanks from time to time.
ü Biological Process-
n The first sedimentation tank is sloped towards the center. Solid like faeces settle at the bottom and is called sludge which is removed by a scraper.
n Oils and grease float at the surface of the water are removed by a skimmer. The biogas produced (by anaerobic bacteria) in the process can be used as fuel or can be used to produce electricity.
n Here, water gets cleared of rubbage, oil, grease, etc and we get clarified water which is sent to aeration tank now. In the aeration tank, the watery waste already contains bacteria (aerobic) in it.
n The compressed air bubbles are passed through this waste to provide 02 to the bacteria to increase bacterial activity which ultimately digests human waste, food waste, soaps and other unwanted and harmful matter still remaining in the waste water leaving behind fairly pure water.
ü Chemical Process-
n The water after aeration tank is allowed to stand in a second sedimentation tank. Here, the microbes present get settled at the bottom at the tank in the form of activated sludge which is about 97% water.
n At this stage, water has very low level of organic matter suspended matter and does not contain many harmful things.
n It is safe for human consumption but is disinfected by chlorine or ozone before distributing it.
5. Alternate Sewage Disposal -
ü Septic Tanks-
n Septic tank is a low-cost onsite sewage disposal system.
n Septic tanks are suitable where there is no sewerage made.
n These tanks need cleaning every four to six months.
n A septic tank usually consists of a big, covered underground tank made of concrete having an inlet pipe at one end and on outlet pipe at the other end.
n The toilet seat is connected to the inlet pipe of the septic tank. The human excreta from the toilet seat enters into the septic tank through the inlet pipe.
n The solid part of excreta keeps on collecting at the bottom of the septic tank in the form of a sludge whereas watery waste remains above it.
n The anaerobic bacteria breakdown most of the solid organic matter present in human excreta due to which the volume of solid waste is reduced too much.
n The digested solid waste keeps on depositing at the bottom of septic tank.
n The watery waste is also cleaned by anaerobic bacteria.
n The excess water goes out of the septic tank through the outlet pipe and get absorbed in soil.
ü Composting Pits-
n These are self-sustained human waste disposal units which is not connected to a sewer line or a septic tank.
n A composting toilet breaks down and dehydrates human waste to compost.
ü Chemical Toilets-
n These toilets have limited storage capacity for human waste and need to be emptied periodically.
n These are the toilets which use chemically treated reservoir located just below the toilet seats.
n The chemicals reduce the foul smell coming out of human excrete and carry out partial disinfection of human waste.
NCERT PRACTICE QUESTION
1. Fill in the blanks:
(a) Cleaning of water is a process of removing ____________.
(b) Waste water released by houses is called ____________.
(c) Dried ____________ is used as manure.
(d) Drains get blocked by ____________ and ____________.
Ans.- (a) pollutants. (b) sewage. (c) sludge (d) cooking oil and fats.
2. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Ans.- Waste water released by houses is called sewage. Untreated sewage should not be discharged untreated into the sea because sewage consists of pollutants and harmful microorganisms which will contaminate water causing disease in people using contaminated water.
3. Why should oils and fats be not released in the drain? Explain.
Ans.- Oils and fats should not be released in the drain because drains get blocked by cooking oil and fats.
4. Describe the steps involved in getting clarified water from waste water.
Ans.- 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. This reduces the foul smell of waste water. Then, the water is filtered through the layers of sand, fine gravel, and medium gravel. Filtration makes the waste water clean from various types of pollutants. The water is filtered continuously until it becomes clear. Water is disinfected by using a chlorine tablet.
5. What is sludge? Explain how it is treated.
Ans.- Solids like faeces settle at the bottom while treating sewage, and this material is called as sludge. Sludge can be treated as follows
Sludge is removed using a skimmer and then transferred to a tank where it is decomposed by anaerobic bacteria to produce biogas.
6. Untreated human excreta is a health hazard. Explain
Ans.- Untreated human excreta is a health hazard because it consists of various disease-causing microorganisms and pollutants that will contaminate the soil and water resource from where people draw water for drinking and domestic purposes. When people use water contaminated with human excreta, they get diseases like Cholera, Typhoid, Dysentery and Hepatitis.
7. Name two chemicals used to disinfect water
Ans.- Chlorine and Ozone are used to disinfect water.
8. Explain the function of bar screens in a wastewater treatment plant.
Ans.- Bar screen removes large objects like rags, sticks, cans, plastic packets and napkins.
9. Explain the relationship between sanitation and disease.
Ans.- Sanitation and disease are interrelated as lack of sanitation lead to illness and good sanitation practices prevent the diseases.
10. Outline your role as an active citizen in relation to sanitation.
Ans.-
ü Ensure that our surroundings are kept clean.
ü The sewage system in the house should be properly managed
ü Report to the concerned authority immediately in case of leakages in sewage pipes.
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
Down
1. Used water
2. A pipe carrying sewage
5. Micro-organisms which causes cholera
7. A chemical to disinfect water
Ans.- Across 3. Sewage 4. Sludge 6. Sanitation 8. Excreta
Down 1. Waste water 2. Sewer 5. Bacteria 7. Ozone
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 four
Ans.- (ii) (b) and (c)
Junior Science Topic - Waste Water Story. Chapter notes, video lectures, power point presentation and NCERT exercise solution. (Class 7, CBSE syllabus, chapter 18)
By - EduPorm India - The Educational Platform
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