Class 7 Chapter 18 - Wastewater Story - Detailed Notes - CBSE Class Notes Online

Definition of Wastewater

Wastewater is the water that has been used and contaminated. It includes a wide range of water from various sources that have been affected by human activities. This water is no longer suitable for direct use without treatment due to the presence of pollutants.

Types of Wastewater

Household Wastewater- This type comes from residential areas. It includes water from sinks, showers, toilets, washing machines, and dishwashers. It often contains soap, food particles, human waste, and detergents.
Industrial Wastewater- Generated from industrial activities, this wastewater can contain a variety of chemicals and pollutants, depending on the industry. For instance, a factory may discharge water contaminated with heavy metals, oils, or toxic substances.
Agricultural Wastewater- This type of wastewater is predominantly from agricultural activities. It includes runoff from fields that may contain fertilisers, pesticides, and animal waste. This runoff can lead to high levels of nutrients and organic matter in the water, which can be harmful to aquatic ecosystems.

Contaminants in Wastewater

Organic Impurities

Wastewater often contains various organic impurities, which significantly impact its quality. These include-

Animal Waste- This is a common organic pollutant in wastewater, especially in areas near livestock rearing facilities. It includes animal manure and urine, which can carry harmful microorganisms.
Oil- Oil contamination in wastewater primarily comes from industrial sources, kitchens, and sometimes from runoff from roads and parking lots.
Vegetable and Fruit Waste– This type of organic waste is predominantly from household kitchens and food processing industries. It decomposes and contributes to the biological oxygen demand of the water.
Pesticides and Herbicides- These chemicals, used in agricultural fields, can runoff into water bodies, contaminating them. They pose a threat to aquatic life and can accumulate in the food chain.

Inorganic Impurities

In addition to organic matter, wastewater also contains various inorganic impurities-

Phosphates- These often come from detergents and fertilisers. High levels of phosphates in water can lead to eutrophication, causing excessive growth of algae.
Nitrates- Similar to phosphates, nitrates are primarily from agricultural runoff. They can contaminate drinking water and lead to health issues like methemoglobinemia or “blue baby syndrome.”
Metals- Heavy metals such as lead, mercury, and cadmium can be found in industrial wastewater. These are toxic even at low concentrations and can accumulate in living organisms.

Pathogenic Bacteria

Wastewater can be a breeding ground for various pathogenic bacteria, causing serious diseases-

Cholera- Caused by Vibrio cholerae, this disease is transmitted through contaminated water and causes severe diarrhoea and dehydration.
Typhoid- Salmonella typhi, the bacterium causing typhoid, spreads through contaminated water. It leads to high fever, weakness, and stomach pains.
Pneumonia- Certain bacteria in contaminated water can cause pneumonia, a lung infection, though it’s more commonly spread through air droplets.

The presence of these contaminants in wastewater necessitates effective treatment processes to remove them, ensuring the water is safe for reuse or discharge into the environment. This is crucial to prevent health hazards and environmental degradation

Sewage and Its Treatment

Definition and Components of Sewage

Sewage refers to the wastewater that is released by various sources such as homes, industries, hospitals, and other establishments. It is carried away through sewers or drains for treatment or disposal. The composition of sewage includes-

Suspended Solids- These are particles that float in the water and can include a wide range of materials like soil, organic matter, and microorganisms.
Organic and Inorganic Impurities- Organic impurities include human waste, animal waste, oil, and plant materials. Inorganic impurities comprise substances like phosphates, nitrates, and metals.
Nutrients- Essential for plant growth, nutrients like nitrogen and phosphorus are also found in sewage.
Bacteria and Microbes- Both saprophytic (decomposing) and pathogenic (disease-causing) bacteria are present in sewage.

Wastewater Management

In wastewater management, the focus is on efficiently treating and handling wastewater to minimise environmental impact and ensure public health. This process involves several key stages-

Treatment Processes in Wastewater Management

1. Screening-

Purpose- Screening is the initial step in wastewater treatment, aiming to remove large and potentially harmful objects from the wastewater.
Process- The wastewater flows through screens that capture large items such as rags, sticks, plastic wrappers, and other sizable debris.
Significance- This step is crucial to prevent damage to pumps, pipes, and other equipment in the treatment facility. By removing these large items, the subsequent treatment processes can operate more efficiently and effectively.

2. Primary Treatment-

Objective- The goal of primary treatment is to separate solid organic matter from the wastewater.
Process- Wastewater is poured into large sedimentation tanks. Here, gravity helps heavier solids to settle at the bottom of the tanks, forming a mass known as sludge. Meanwhile, lighter materials like oils and fats float to the top.
Outcome- This stage effectively removes a significant portion of the suspended solids and organic material. The resulting semi-clear liquid is then ready for secondary treatment.

3. Secondary Treatment-

Purpose- Secondary treatment is a biological process aimed at further reducing the organic content in the wastewater.
Process- The partially treated water from primary treatment is introduced into aeration tanks. In these tanks, air is pumped through the water to encourage the growth of aerobic bacteria. These bacteria consume the remaining organic matter in the water.
Settling Tanks- After aeration, the water is moved to settling tanks. Here, the bacterial floc (small particles of sludge) settles out, leaving clearer water. This settled mass, also known as activated sludge, is partially recycled back into the aeration tanks to maintain an optimal level of bacterial activity.

4. Final Treatment-

Filtration- In this stage, the water undergoes further purification. It is often passed through filters, such as sand filters, to remove any remaining particles.
Disinfection- Sometimes, to ensure the elimination of harmful microorganisms, the water is disinfected using chlorine or ultraviolet light.
Release- The treated water, now significantly cleaner and safer, is discharged into local waterways, used for irrigation, or in some cases, further treated for use as drinking water.

Each of these steps plays a vital role in transforming wastewater from a potential health hazard into a resource that can safely re-enter the environment or be reused. The treatment process is designed to tackle both the visible and invisible contaminants, ensuring the protection of public health and the environment.

Sludge Treatment and Biogas Utilisation

Sludge Treatment-

Nature of Sludge- Sludge is the semi-solid by-product from the sedimentation process during wastewater treatment. It contains organic material, nutrients, and microbes.
Treatment Process- Sludge treatment primarily involves anaerobic digestion. In this process, the sludge is broken down by microorganisms in the absence of oxygen. This breakdown results in the reduction of the sludge volume and makes it less hazardous.
Benefits- Post-treatment, the sludge can be used as a soil conditioner in agriculture, enhancing soil nutrient levels. It also becomes less odorous and easier to handle or dispose of.

Also Check – First study on Indian sludge finds ‘high potential’ for use as fertilizer

Biogas Production-

Production Process- During the anaerobic digestion of sludge, biogas is produced. This gas primarily consists of methane (CH4) and carbon dioxide (CO2), along with traces of other gases.
Utilisation of Biogas- Biogas is a valuable renewable energy source. It can be used for various purposes-
- Heating- Biogas can be used directly for heating purposes in industries or domestic settings.
- Electricity Generation- Biogas can be utilised to run generators, producing electricity. This electricity can be used to power the wastewater treatment plants themselves, making them more energy-efficient and sustainable.
- Vehicle Fuel- After purification, biogas can be used as a fuel for vehicles. It is a cleaner alternative to fossil fuels.

Environmental and Economic Benefits-

Reduction in Greenhouse Gases- By capturing methane from sludge, biogas production helps reduce greenhouse gas emissions, as methane is a potent greenhouse gas.
Cost-Effective- Utilising biogas as an energy source can significantly reduce operational costs of wastewater treatment plants.
Sustainability- The process contributes to the sustainable management of wastewater by turning waste into a resource.

Sewage Systems

Infrastructure of Sewage Systems-

Composition- Sewage systems consist of a complex network of pipes, called sewers, which are designed to transport wastewater from residential, industrial, and commercial areas to wastewater treatment facilities.
Components-
- Household Drains- These collect wastewater from individual homes and buildings.
- Sewers- Underground pipes that carry this wastewater. They can vary in size, from small pipes just a few inches in diameter to large tunnels.
- Pumping Stations- These are used in areas where gravity alone is insufficient to move wastewater through the pipes. They help in transporting sewage to higher elevations.
- Manholes- These provide access to the sewer system for maintenance and inspection. They are strategically placed at regular intervals and at points where the sewer changes direction or joins another sewer.

Importance of Proper Sewage Systems-

Public Health- A well-maintained sewage system is essential for public health. It safely transports potentially harmful waste away from populated areas to treatment facilities.
Environmental Protection- Properly functioning sewage systems prevent the contamination of water bodies, thereby protecting aquatic life and maintaining the overall health of ecosystems.
Urban Development- Efficient sewage systems are crucial for urban areas, supporting residential and commercial growth by effectively managing waste.
Prevention of Disease- By properly transporting and treating wastewater, sewage systems play a key role in preventing diseases that can be caused by exposure to untreated sewage, such as cholera and typhoid.
Sustainability- Modern sewage systems are designed to be sustainable, often incorporating energy-efficient processes and methods for recovering resources like water and energy from wastewater.

Sanitation and Health

Link Between Poor Sanitation, Diseases, and the Importance of Clean Water-

Impact of Poor Sanitation-

Spread of Diseases- Poor sanitation is directly linked to the spread of numerous infectious diseases. Inadequate sanitation facilities lead to the contamination of water sources with human waste.
Health Hazards- Open defecation and improper disposal of waste contribute to the presence of harmful microbes in the environment, leading to waterborne diseases.

Common Diseases Due to Poor Sanitation-

Waterborne Diseases- Diseases such as cholera, typhoid, hepatitis, polio, and diarrhoea are primarily caused by the ingestion of water contaminated with human faeces.
Vector-Borne Diseases- Poor sanitation can lead to increased breeding of disease-carrying vectors like mosquitoes, resulting in diseases like malaria and dengue.

Importance of Clean Water-

Prevention of Diseases- Access to clean water is essential for preventing a range of waterborne diseases. It is a fundamental requirement for maintaining good health.
Hygiene and Sanitation- Clean water is crucial not just for drinking but also for personal hygiene, cooking, and cleaning purposes. It plays a significant role in ensuring overall community health and sanitation.

Role of Sanitation Facilities-

Reducing Exposure to Pathogens- Proper sanitation facilities such as toilets and sewage systems reduce the exposure of communities to harmful pathogens found in human waste.
Improving Public Health- Investments in sanitation infrastructure and public awareness are key to improving health outcomes, particularly in areas with limited access to clean water and sanitation facilities.

Community and Individual Responsibility-

Community Initiatives- Community-led initiatives focusing on improving sanitation can have a significant impact on public health.
Personal Hygiene Practices- Individual practices like hand washing, safe disposal of waste, and using clean water for domestic purposes are essential for maintaining hygiene and preventing disease spread.

Alternative Sewage Disposal Systems

Septic Tanks-

Definition and Structure- A septic tank is an underground, watertight container, usually made of concrete, fibreglass, or plastic. It is used for basic onsite sewage treatment.
Functioning- Wastewater enters the septic tank from the house. The solid waste settles at the bottom, forming sludge, while grease and oils float to the top as scum. The liquid waste or effluent resides in the middle.
Process- Anaerobic bacteria in the tank decompose the solid waste. The partially treated water then flows out of the tank into a drain field where further natural filtration occurs in the soil.

Vermi-processing Toilets-

Concept- These toilets use earthworms to treat sewage slurry. They are an eco-friendly and effective method of treating organic waste.
Mechanism- The worms feed on organic waste material in the sewage, breaking it down into simpler compounds. This process reduces the volume of waste and transforms it into vermicompost, which is a nutrient-rich soil conditioner.
Advantages- These toilets are hygienic, low-cost, consume less water, and do not produce foul odours or attract flies.

Composting Toilets-

Principle- Composting toilets use the natural process of composting to decompose human excreta into compost.
Functionality- These toilets separate liquid and solid waste. The solid waste is decomposed aerobically by microorganisms into compost, which can be used as fertiliser.
Benefits- They are water-efficient, reduce the need for conventional sewage treatment, and are ideal for areas without sewer systems.

Each of these systems offers a sustainable and efficient method of managing sewage, especially in areas without access to centralised sewage treatment plants. They not only help in reducing pollution but also contribute to resource recovery and recycling of waste products.

Housekeeping Practices for Wastewater Management

Proper Disposal Methods for Household Waste-

Cooking Oil and Fats- Should not be poured down drains as they can solidify and clog pipes. Instead, dispose of them in the garbage.
Solid Food Remains- Leftover food, tea leaves, and other solid kitchen waste should be thrown in the trash, not down the sink, to prevent drain blockages.
Chemicals- Household chemicals, including cleaning agents, paints, and medicines, should never be disposed of in drains as they can harm the water treatment process and the environment.
Personal Hygiene Products- Items like cotton swabs, sanitary products, and diapers should be disposed of properly in the trash, not flushed down toilets.

Role of Citizens and Sanitation at Public Places-

Community Participation- Active community involvement is crucial in maintaining local sanitation. This includes reporting open drains, insisting on covered sewage systems, and participating in community cleanliness drives.
Personal Responsibility- Individuals should avoid littering in public places and use trash bins for waste disposal to maintain cleanliness.
Public Awareness- Educating the public about the importance of sanitation and the impact of littering on the environment is key to fostering a culture of responsibility towards public spaces.

Planting Eucalyptus Trees for Natural Wastewater Treatment-

Absorption of Wastewater- Eucalyptus trees are known for their ability to absorb water rapidly. Planting them near sewage ponds can help in naturally treating wastewater.
Environmental Benefits- These trees can release pure water vapour into the atmosphere, contributing to the purification process.
Sustainable Practice- Using plants for wastewater treatment is a sustainable practice, reducing reliance on mechanical treatment methods and promoting ecological balance.

Water Pollution and its Effects

Impact of Water Pollution on Ecosystems and Human Health-

Ecosystems- Water pollution severely impacts aquatic ecosystems. Contaminants like chemicals, heavy metals, and plastic waste harm aquatic life, disrupting food chains and leading to the loss of biodiversity.
Human Health- Contaminated water can cause numerous health issues in humans. Drinking or using polluted water leads to diseases like cholera, typhoid, and hepatitis. Long-term exposure to polluted water can also cause chronic health problems, including kidney damage and cancer.

Major Water Pollutants and Their Sources-

Industrial Waste-

Sources- Factories, power plants, and industrial sites.
Pollutants- Heavy metals, toxic chemicals, and radioactive waste.
Effects- Toxic to aquatic life, can contaminate drinking water sources.

Agricultural Runoff-

Sources- Farms, orchards, and agricultural fields.
Pollutants- Pesticides, herbicides, and fertilisers.
Effects- Causes eutrophication in water bodies, leading to oxygen depletion and harming aquatic organisms.

Sewage and Organic Waste-

Sources- Household sewage, untreated wastewater.
Pollutants- Nutrients, bacteria, and organic matter.
Effects- Can cause waterborne diseases and oxygen depletion in water bodies.

Plastics and Microplastics-

Sources- Urban runoff, improper waste disposal.
Pollutants- Plastic bags, bottles, and microbeads from personal care products.
Effects- Harmful to marine life, can enter the food chain.

Oil Spills-

Sources- Oil tankers, offshore oil rigs, and industrial leaks.
Pollutants- Crude oil and petroleum products.
Effects- Devastating for marine life, difficult to clean up, can pollute beaches and coastal areas.

Urban Runoff-

Sources- Cities and urban areas.
Pollutants- Trash, oil, heavy metals from vehicles, and chemicals.
Effects- Contaminates rivers, lakes, and oceans, harms aquatic life.

Water pollution is a pressing environmental issue that requires immediate action. Mitigating these pollutants involves a combination of stricter regulations, improved waste management practices, and public awareness campaigns. Ensuring clean water for all life forms is essential for maintaining a healthy and sustainable planet.