Science STD 7 Chapter 13: Wastewater Story - Exercises

Sewage is the wastewater released from homes, industries, hospitals, and other sources. It is a complex mixture of suspended solids, organic and inorganic impurities, nutrients, and disease-causing microbes. Discharging untreated sewage into rivers or seas is harmful because it pollutes the water. The contaminants in the sewage can kill fish and other aquatic life, and the polluted water can become a source of waterborne diseases like cholera and typhoid, affecting humans and animals that use the water.

Oils and fats should not be released into drains because they can harden and block the pipes, making them less effective. In open drains, they clog the pores of the soil, which reduces its ability to filter water. This also hampers the degradation process of the wastewater, as it prevents the free flow of oxygen for the microorganisms to function.

The process of getting clarified water from wastewater involves several steps at a Wastewater Treatment Plant (WWTP):

1. First, the wastewater is passed through **bar screens** to remove large objects like rags, sticks, and plastic bags.
2. It then goes to a **grit and sand removal tank**, where the speed of the water is slowed down to allow sand, grit, and pebbles to settle at the bottom.
3. Next, the water is held in a large tank, where solid waste like faeces settles at the bottom as **sludge**. Floatable solids like oil and grease are removed with a skimmer. The water is now called clarified water.
4. Finally, the clarified water is aerated to allow aerobic bacteria to grow, which consume the remaining organic waste and other impurities.

Sludge is the solid waste, mainly faeces, that settles at the bottom of the clarification tank in a wastewater treatment plant. It is treated by transferring it to a separate tank where **anaerobic bacteria** decompose it. This process produces **biogas**, which can be used as fuel or to generate electricity. The dried sludge is then used as manure, returning nutrients and organic matter to the soil.

Untreated human excreta is a major health hazard because it contains disease-causing bacteria and other microbes. If left untreated, it can pollute both surface water and groundwater, which are sources for drinking water. This contamination can lead to waterborne diseases like cholera, typhoid, polio, and dysentery, causing widespread illness and even death.

Two chemicals used to disinfect water are chlorine and ozone.

Bar screens are the first stage of wastewater treatment. Their function is to physically remove large objects from the wastewater. This includes materials like rags, sticks, plastic packets, cans, and napkins. Removing these large solids protects the machinery at the treatment plant from damage and ensures a smoother flow of water for subsequent treatment stages.

There is a strong and direct relationship between sanitation and disease. Poor sanitation, such as open drains and improper disposal of human waste, leads to contaminated drinking water. This contaminated water becomes a breeding ground for disease-causing microbes like bacteria, flies, and mosquitoes. As a result, people are exposed to and suffer from a variety of waterborne diseases, including cholera, typhoid, and dysentery.

As an active citizen, my role in sanitation includes:

• Ensuring that my household's waste is properly disposed of and not thrown into drains or open areas.
• Avoiding the release of oils, fats, and chemicals like paint or solvents down the drain.
• Insisting that open drains in my neighbourhood are covered to prevent the breeding of flies and mosquitoes.
• Spreading awareness among friends and family about the importance of hygiene and safe sanitation practices.
• If I notice any sanitation issues in public places, I will use designated dustbins or inform the municipality or gram panchayat.

Across

3. Liquid waste products -> SEWAGE

4. Solid waste extracted in sewage treatment -> SLUDGE

6. A word related to hygiene -> SANITATION

8. Waste matter discharged from human body -> EXCRETA

Down

1. Used water -> WASTEWATER

2. A pipe carrying sewage -> SEWER

5. Micro-organisms which causes cholera -> BACTERIA

7. A chemical to disinfect water -> OZONE

1. (a), (b) and (c)
2. (b) and (c)
3. (a) and (d)
4. All four

Outline: This activity reinforces your understanding of the keywords from the chapter. You would create your own crossword puzzle using terms like Aeration, Biogas, Contaminant, Sanitation, etc., along with your own clues. This is a fun and interactive way to revise the chapter's vocabulary.

Outline: This project is a historical comparison of sanitation systems. You would interview elderly people to learn about older systems like pit latrines or open drains and compare them with modern systems like covered sewerage networks. The report would highlight the improvements in public health and hygiene due to advances in sanitation technology.

Outline: This is a field trip project to gain practical knowledge of a wastewater treatment plant. By visiting the plant, you would observe the various stages of wastewater treatment and ask questions to the officials there. The visit would give you a firsthand understanding of how wastewater is purified and the importance of this process for public health and the environment.