All questions of Wastewater story for Class 7 Exam

Cleaning of water involves removing contaminants, which include pollutants, chemicals, and other harmful substances that can affect water quality and safety.

Wastewater treatment, also called sewage treatment, the removal of impurities from wastewater, or sewage, before they reach aquifers or natural bodies of water such as rivers, lakes, estuaries, and oceans. Since pure water is not found in nature (i.e., outside chemical laboratories), any distinction between clean water and polluted water depends on the type and concentration of impurities found in the water as well as on its intended use. In broad terms, water is said to be polluted when it contains enough impurities to make it unfit for a particular use, such as drinking, swimming, or fishing.

The process of clarifying wastewater involves sedimentation to remove solids, aeration to promote bacterial decomposition of waste, and chlorination to disinfect the water, making it safe for use.

Sludge, when dried, is rich in nutrients and organic matter, making it a valuable manure for agriculture. It helps improve soil fertility and plant growth.

A scraper is used to remove sludge that settles at the bottom of treatment tanks. This sludge is then transferred for further treatment, such as anaerobic digestion, to produce biogas and manure.

Biogas produced from sludge is a renewable source of energy. It can be used for heating, cooking, and generating electricity, providing a sustainable energy option and reducing dependence on fossil fuels.

Introduction to Water Disinfection
Water disinfection is a critical process that removes or inactivates harmful microorganisms in water, making it safe for consumption and use. Two commonly used chemicals for this purpose are chlorine and ozone.
Chlorine
- Effectiveness: Chlorine is one of the most widely used disinfectants due to its effectiveness against a broad range of pathogens, including bacteria, viruses, and protozoa.
- Application: It can be applied in various forms, such as chlorine gas, sodium hypochlorite, or calcium hypochlorite.
- Residual Protection: Chlorine provides residual disinfection, meaning it continues to disinfect as water travels through pipes, preventing recontamination.
Ozone
- Strong Oxidant: Ozone is a powerful oxidizing agent that effectively kills microorganisms.
- No Residual Taste: Unlike chlorine, ozone leaves no residual taste or odor in the water.
- Decomposition: Ozone decomposes quickly after use, making it less suitable for long-term water treatment but excellent for immediate disinfection.
Comparison with Other Options
- Fluoride and Bromine: While fluoride is primarily used for dental health and bromine has some disinfecting properties, they are not commonly used for water disinfection.
- Iodine and Hydrogen Peroxide: Iodine is effective but generally used for smaller-scale disinfection (like in camping). Hydrogen peroxide is not as commonly used for large-scale water treatment.
- Ammonia and Nitrate: Ammonia can help in chlorination processes but is not a disinfectant on its own, and nitrate is not used for disinfection.
Conclusion
In summary, chlorine and ozone are preferred due to their effectiveness in killing pathogens and ensuring safe drinking water. Their unique properties allow for versatile application in various water treatment scenarios.

Understanding Wastewater Treatment
Wastewater treatment is a crucial process that ensures the safe disposal and recycling of used water. It helps protect the environment and public health.
Processes Involved
Wastewater treatment utilizes three main types of processes:

• Physical Processes: These involve the removal of solids and large particles from wastewater. Techniques include screening, sedimentation, and filtration. Physical methods help to separate contaminants without altering their chemical state.
• Chemical Processes: In this stage, chemicals are added to the wastewater to facilitate the removal of pollutants. Common methods include coagulation, flocculation, and disinfection (like chlorination). These processes help to break down harmful substances chemically.
• Biological Processes: This involves the use of microorganisms to break down organic matter in wastewater. Bacteria and other microbes consume pollutants, converting them into harmless byproducts. Biological treatment is effective in reducing the organic load of wastewater.

Conclusion
In summary, wastewater treatment is an integrated approach that incorporates physical, chemical, and biological methods to ensure that water is cleaned effectively before being released back into the environment or reused. Therefore, the statement "Wastewater treatment involves physical, chemical, and biological processes" is indeed true.

Chlorination involves adding chlorine to water to kill harmful microorganisms, making the water safe to drink. It is a crucial step in ensuring water quality and preventing waterborne diseases.

Understanding Drain Blockages
Drains can become blocked for various reasons, but the most common culprits are cooking oil and fats. Here’s why these substances lead to drain issues:
Why Cooking Oil and Fats Cause Blockages
- Sticky Nature: Cooking oils and fats are sticky substances. When poured down the drain, they can cling to the sides of pipes.
- Solidification: As the oil cools, it can solidify and form clumps. Over time, these clumps can gather more debris, leading to complete blockages.
- Accumulation: Regularly disposing of oil and fats down the drain leads to gradual accumulation, which eventually narrows the pipe and restricts water flow.
Other Common Blockage Causes
While stones and pebbles can block drains, they are not as common as cooking oils and fats in household scenarios. Other materials that can cause blockages include:
- Food Waste: Small food particles can combine with grease and form larger clogs.
- Hair: Hair can tangle with soap and other debris, creating stubborn blockages.
Preventing Drain Blockages
- Dispose Properly: Always dispose of cooking oils and fats in a container rather than pouring them down the drain.
- Regular Maintenance: Regularly check and clean drains to prevent buildup.
- Use Strainers: Install strainers in sinks to catch food particles and prevent them from entering the drain.
In conclusion, while stones and pebbles can block drains, cooking oil and fats are the primary offenders, making it crucial to manage their disposal effectively.

Oils and fats can solidify in pipes and drains, leading to blockages and clogs. These substances do not easily break down and can cause severe plumbing issues.