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Q1. What is sludge?

Solution

Solid faecal matter which is generated after the water treatment plant is known as sludge.

Q2. Why it is that cooking oil and fats should not be thrown down the drain? Where should they be thrown?

Solution

Cooking oil and fats should not be thrown down the drain as it can harden and block the pipes. In an open drain, the fats clog the soil pores reducing its effectiveness in filtering water. We should throw cooking oil and fats in the dustbin.

Q3. Which trees should we plant near sewage ponds? Why?

Solution

We should plant eucalyptus trees all along sewage ponds. These trees absorb all surplus wastewater rapidly and release pure water vapour into the atmosphere.

Q4. In waste water treatment plant, discuss the first step of treatment?

Solution

In the first step, wastewater is passed through bar screens. Large objects like rags, sticks, cans, plastic packets, napkins are removed.

Q5. During waste water treatment,(a) How the sludge obtained is further treated?(b) What are the uses of biogas produced in this process?

Solution

(a)The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria.(b) The biogas produced in the process can be used as fuel or can be used to produce electricity.

Q6. Name two disinfectants used to treat water before releasing it into the distribution system.

Solution

Chlorine and ozone.

Q7. Why should not chemicals be released in the drain?

Solution

Chemicals like paints, solvents, insecticides should not be thrown down the drain as it may kill the useful microbes that help to decompose the wastes present in the sewage and purify water.

Q8. Name any four water borne diseases.

Solution

Cholera, typhoid, polio, meningitis, hepatitis and dysentery. (Any 4)

Q9. As an active citizen, write two ways how can you maintain sanitation at public places?

Solution

Ways of maintaining sanitation at public places are:(i) We should not scatter litter anywhere.(ii) If there is no dustbin in sight, we should carry the litter home and throw it in the dustbin.(iii)We should not defecate out in the open.(Any two)

Q10. Write any two examples of low cost onsite sewage disposal systems.

Solution

Examples are septic tanks, chemical toilets and composting pits. (Any two)

Q11. Name any three water borne diseases

Solution

Water-borne diseases include cholera, typhoid, polio, meningitis, hepatitis etc. (Any three)

Q12. What happens when people do not have access to safe drinking water?

Solution

Lack of safe drinking water leads to a large number of water-related diseases and even deaths in humans.

Q13. Manu's mother tells him not to throw the left over paints, motor oil and medicines down the drain. Why?

Solution

Throwing paints, motor oil and medicines down the drain may kill microbes that help purify water. So, it should be avoided.

Q14. What are the various causes of water pollution?

Solution

Water is polluted by various factors like: 1. Bathing of cattle in river bodies 2. Washing of clothes and utensils by people in rivers 3. Discharging wastes form factories, industries in nearby river bodies and ponds

Q15. Name some places where large amount of waste is generated due to visit by many people. What will happen if this waste is not disposed off properly?

Solution

Railway stations, bus depots, airports, hospitals etc. are places visisted by many people everyday. Large amount of waste is generated here must be disposed of properly otherwise epidemics could break out.

Q16. What do you understand by sewage?

Solution

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

Q17. During waste water treatment, the waste water has been treated in a grit and sand removal tank. Discuss the step that needs to be done after this?

Solution

After the grit and sand removal tank, the waste water is then allowed to settle in a large tank which is sloped towards the middle. Solids like faeces settle at the bottom and are removed with a scraper. This is the sludge. A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water.

Q18. How is sludge treated?

Solution

The sludge is transferred to a separate tank where it is decomposed by anaerobic bacteria. The biogas produced can be used as a fuel and the dried sludge is used as a manure for replenishing the nutrients of the soil.

Q19. Name the following components found in sewage:(i) Any four organic impurities(ii) Any two inorganic impurities(iii)Any two nutrients

Solution

(i) Organic impurities -Human faeces, animal waste, oil, urea (urine), pesticides, herbicides, fruit and vegetable waste. (Any 4) (ii) Inorganic impurities - Nitrates, Phosphates, metals. (Any 2) (iii) Nutrients - Phosphorus and Nitrogen

Q20. Discuss the technique of hygienic on-site human waste disposal technology offered by certain organisations.

Solution

In on-site human waste disposal 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.

Q21. What is sewarage? Write its function.

Solution

A network of big and small pipes passing through the ground called sewers for bringing clean water and taking away waste water forms the sewerage. It carries sewage from the point of being produced to the point of disposal, i.e. treatment plant.

Q22. How does defecating in the open cause spread of several water borne diseases?

Solution

A large fraction of our people defecates in the open. Untreated human excreta is a health hazard and may cause water pollution and soil pollution. Both the surface water and groundwater get polluted. Groundwater is a source of water for wells, tubewells, springs and many rivers. Thus, it becomes the most common route for water borne diseases.

Q23. What is the function of bar screens in waste water treatment plant?

Solution

The bar screens remove the large objects like rags, sticks, cans, etc from the sewage

Q24. What are the harmful effects of sewerage?

Solution

Accumulation of sewerage leads to: 1. Spread of various diseases 2. Water pollution 3. Discharge of sewerage in water bodies leads to excessive growth of algae

Q25. (a) What did the General Assembly of the United Nations announced the period 2005 - 2015 as? What was its aim in doing so?(b) What is sewage treatment?

Solution

(a) On 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. (b) Sewage treatment is a process of removing pollutants from waste water before it enters a water body or is reused.

Q26. Why is sewage said to be a complex mixture?

Solution

Sewage contains many substances in it like suspended solids, organic and inorganic impurities, nutrients, saprotrophic and disease causing bacteria and other microbes. Hence it is said to be a complex mixture.

Q27. Name two alternative arrangements for sewage disposal where there is no sewerage system.

Solution

Septic tanks and chemical toilets can be set up as an alternative arrangement for sewage disposal.

Q28. Why should used tea leaves, solid food remains, etc not be released in the drains?

Solution

Used tea leaves, solid food remains, etc should not be thrown down the drain as they may choke the drain.

Q29. Name two inorganic impurities present in sewage.

Solution

Two inorganic impurities present in sewage are nitrates and phosphates.

Q30. How can we maintain sanitation in public places?

Solution

Sanitation in public places can be maintained by: 1. Use of dustbins for throwing litters 2. Use of public toilets for urination and defecation. Example- Sulabh 3. Use of handkerchief or tissue paper while sneezing or coughing in order to prevent air-borne diseases

Q31. What is the percentage of water in activated sludge? How is this water removed? What is the use of resultant dried sludge?

Solution

The activated sludge is about 97% water. The water is removed by sand drying beds or machines. The resultant dried sludge is used as manure, returning organic matter and nutrients to the soil.

Q32. What do you mean by sewage treatment?

Solution

Sewage treatment is a process of removing pollutants before it enters a water body.

Q33. Why are bacteria used in sewage treatment plants?

Solution

The bacteria decompose the suspended waste that include domestic wastes and other undesirable organic substances present in the clarified water. The activity of bacteria produces decomposed organic material from which solid waste is separated. This solid waste s used as manure.

Q34. What problems are encountered during rainy seasons due to open drains? What can we as responsible citizens, do in this case?

Solution

During rainy season, the open drains start overflowing. People have to wade through the mud pools on the roads. Most unhygienic and unsanitary conditions prevail. Flies, mosquitoes and other insects breed in it. As responsible citizens, we can approach the municipality or the gram panchayat and insist that the open drains should be covered.

Q35. Explain why is it harmful to discharge untreated sewage into water bodies.

Solution

It is harmful to discharge the untreated sewage into the water bodies as it contains harmful substances. Most of it is water which has dissolved and suspended impurities which may pollute the water bodies and also harm the aquatic plants and animals.

Q36. (a) What is the point of origin of sullage water and foul waste?(b) What is the point of origin of trade waste?

Solution

(a) Kitchen and toilets.(b) Industrial and commercial organisations.

Q37. What is a vermiprocessing toilet?

Solution

Vermiprocessing toilet is a type of toilet in which human excreta is treated through earthworms. The earthworms convert human excreta into vermi cake which can be used as a manure

Q38. Write any six ways in which we use clean water at home.

Solution

(i) Drinking (ii) Bathing (iii) Washing utensils (iv) Brushing (v) Washing clothes (vi) Mopping floor

Q39. Name any four factors causing increased scarcity of fresh water.

Solution

(i) Population growth.(ii) Increase in pollution.(iii) Industrial development. (iv) Increase in agriculture.(v) Water wastage and mismanagement.(Any 4)

Q40. What are septic tanks? Give two examples of places where they are used.

Solution

Septic tanks are low cost onsite sewage disposal systems suitable for places where there is no sewerage system. It can be used for hospitals, isolated buildings or a cluster of 4 to 5 houses.