Class 7 Science Chapter 18 Wastewater Story

Last updated on March 19th, 2023 at 12:35 pm

Class 7 Science Chapter 18 Wastewater Story


Q.2. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Ans. Sewage is a liquid waste generated from households, industries, and agriculture. Discharging untreated sewage into rivers and seas can lead to environmental pollution and harm. Sewage comprises harmful substances and disease-causing organisms that make it dangerous to release into water sources. The unprocessed waste can cause the death of aquatic life due to oxygen depletion, contamination, and harmful bacterial growth. Waterborne diseases, ranging from minor skin infections to severe illnesses, are common among people who use such water sources. Proper sewage treatment through primary and secondary processes is vital to ensure environmental safety and human health.


Q.3. Why should oils and fats be not released in the drain? Explain.
Ans. When oils and fats are poured down the drain, they often mix with other substances like soap and detergent, and the resulting mixture can create a thick, sticky mass that can harden and clog pipes over time. The fats and oils can also adhere to the inner lining of the pipes, reducing the diameter of the pipes and causing water to back up. This can lead to unpleasant smells, unsanitary conditions, and expensive repairs. It is important to properly dispose of oils and fats by storing them in containers and disposing of them in the garbage or recycling where possible.


Q.4. Describe the steps involved in getting clarified water from wastewater.
Ans. Water purification involves several steps. Firstly, physical impurities such as stones, cans and plastic bags are removed by passing the water through bar screens. The water is then taken to a grit and sand removal tank where impurities are removed by sedimentation, and sludge is collected from the bottom. Next, clarified water is cleaned of other impurities through aeration, and all disease-causing bacteria are eliminated through chlorination.


Q.5. What is sludge? Explain how it is treated.
Ans. Sludge is the solid waste produced during the treatment of wastewater in a water treatment plant. It is broken down by anaerobic bacteria in a separate tank. The resulting product, known as activated sludge, can be used as a type of fertilizer.


Q.6. Untreated human excreta is a health hazard. Explain.
Ans. Untreated human excreta can lead to health problems as it can contaminate water, air and soil. The bacteria found in polluted water can cause diseases such as cholera and meningitis, which can easily spread and cause epidemics.


Q.7. Name two chemicals used to disinfect water.
Ans. Two chemicals commonly used to disinfect water are chlorine and ozone.


Q.8. Explain the Junction of bar screens in a wastewater treatment plant.
Ans. Bar screens are used to remove physical impurities from wastewater. They are effective in removing larger items such as napkins, plastics, and cans from the wastewater before it continues on for further treatment.


Q.9. Explain the relationship between sanitation and disease.
Ans. Sanitation and disease are closely related, as proper disposal of sewage and refuse from homes and public places is crucial in preventing the spread of disease. When sanitation is present, the occurrence of diseases is minimized, but when sanitation is lacking, various types of diseases can occur and spread easily. Therefore, it is important to maintain good sanitation practices to avoid disease outbreaks.


Q.10. Outline your role as an active citizen in relation to sanitation.
Ans. As active citizens, we have a responsibility to maintain personal environmental sanitation and raise awareness about its benefits. This includes taking action to help municipal corporations cover open drains and remove disease-causing substances that are often thrown in open areas. By doing so, we can help prevent the spread of diseases and create a healthier environment for ourselves and others.


Important points from the chapter

  • There are three types of waste water: domestic, industrial, and agricultural.
  • Water from toilets, sinks, and bathtubs is considered domestic wastewater.
  • The term industrial wastewater refers to wastewater generated by industry and includes water used in the manufacturing process.
  • Water used for irrigation and animal husbandry is included in agricultural wastewater.
  • The treatment of wastewater involves the removal of impurities from wastewater so that it can be reused or released into the environment safely.
  • By using physical processes such as screening and sedimentation, wastewater is first treated by removing large solids.
  • The secondary treatment of wastewater involves biological processes such as the use of bacteria to breakdown organic matter.
  • Chemical and physical processes are used to remove dissolved solids and nutrients from wastewater during tertiary treatment.
  • There are a number of ways to reuse wastewater, including irrigation, industrial processes, and recharging groundwater.
  • Using wastewater for a variety of purposes can conserve water resources, reduce pollution, and provide a sustainable source of water.
  • Reusing wastewater, however, requires proper treatment and management to ensure that it is safe for use and does not cause harm to human health or the environment.
Updated: 19 Mar 2023 — 12:35 pm

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