UNIT 3: Water Pollution
7 MarksComplete handwritten-style notes in very simple English
Index / Contents
- Meaning of Water Pollution
- Surface Water Pollution: Sources and Effects
- Groundwater Pollution: Sources and Effects
- Eutrophication
- Biomagnification
- Marine Pollution
- Water Pollution Control
- Sewage Treatment Plant
- Primary Treatment
- Secondary Treatment
- Tertiary Treatment
- Treatment Comparison Table
- Quick Revision Sheet
- Board Exam Questions with Answers
- Practice Questions
1. Meaning of Water Pollution
Easy explanation
Water is needed for drinking, cooking, farming, industries and the survival of plants and animals. When sewage, chemicals, plastics, oil or other harmful materials enter water, the water becomes polluted.
Types of water pollution
- Surface water pollution: Pollution of rivers, lakes, ponds, streams and reservoirs.
- Groundwater pollution: Pollution of water stored below the Earth's surface.
- Marine pollution: Pollution of seas and oceans.
Major pollutants
| Pollutant | Examples | Possible effect |
|---|---|---|
| Organic waste | Sewage, food waste | Decreases dissolved oxygen |
| Chemicals | Pesticides, detergents, acids | Toxic effects on organisms |
| Heavy metals | Lead, mercury, cadmium | Damage to organs and food chains |
| Pathogens | Bacteria, viruses, parasites | Water-borne diseases |
| Solid waste | Plastic, bags, bottles | Blockage and harm to aquatic life |
2. Surface Water Pollution: Sources and Effects
Surface water is water present on the Earth's surface, such as rivers, lakes, ponds, streams and reservoirs.
Sources of surface water pollution
- Domestic sewage: Wastewater from houses contains soaps, detergents, food waste and human waste.
- Industrial discharge: Factories may release chemicals, dyes, acids, hot water and heavy metals.
- Agricultural runoff: Rainwater carries fertilizers, pesticides, soil and animal waste into rivers and lakes.
- Urban runoff: Water flowing over roads carries oil, dust, plastics and other waste.
- Solid waste dumping: People may throw plastic, bottles, religious waste and garbage into water bodies.
- Mining activities: Mining can release metals, sediments and acidic water.
- Thermal pollution: Hot water released by industries increases water temperature.
Effects of surface water pollution
Human health
- Cholera, typhoid and diarrhoea.
- Skin and stomach problems.
- Poisoning due to chemicals and metals.
Aquatic life
- Fish death due to low oxygen.
- Damage to eggs and aquatic plants.
- Loss of biodiversity.
Water quality
- Bad smell, colour and taste.
- Increase in turbidity.
- Decrease in dissolved oxygen.
Environment
- Algal blooms.
- Food-chain contamination.
- Reduced usefulness of water.
3. Groundwater Pollution: Sources and Effects
How groundwater becomes polluted
Sources
- Leaking septic tanks and sewage pipelines.
- Excessive use of fertilizers and pesticides.
- Leachate from landfills and garbage dumps.
- Industrial chemicals and leaking storage tanks.
- Mining and improper disposal of hazardous waste.
- Seawater intrusion in coastal areas due to over-pumping.
- Natural minerals such as arsenic or fluoride in some areas.
Effects
- Groundwater may become unsafe for drinking and cooking.
- Nitrates in drinking water can create health risks, especially for infants.
- Arsenic, fluoride and heavy metals may cause long-term health problems at harmful levels.
- Polluted groundwater is difficult and costly to clean.
- Pollution may spread slowly and remain underground for many years.
- Contaminated groundwater can affect wells, crops and nearby surface water.
4. Concept of Eutrophication
Easy explanation
Fertilizers and sewage add extra nutrients to lakes and ponds. These nutrients act like food for algae. Algae grow rapidly and form an algal bloom. When algae die, microorganisms decompose them and use dissolved oxygen. Oxygen becomes low, and fish and other aquatic organisms may die.
Causes
- Excess fertilizers from agricultural fields.
- Untreated sewage and detergents.
- Industrial nutrient discharge.
- Soil erosion and surface runoff.
Effects
- Algal blooms cover the water surface.
- Sunlight cannot reach deeper water.
- Underwater plants may die.
- Decomposition decreases dissolved oxygen.
- Fish and other aquatic organisms may die.
- Some algal blooms may produce harmful toxins.
Control of eutrophication
- Reduce excessive use of fertilizers.
- Treat sewage before discharge.
- Use buffer strips and vegetation near water bodies.
- Control soil erosion and runoff.
- Reduce phosphorus-rich detergents where applicable.
5. Concept of Biomagnification
Easy explanation
Some pollutants, such as mercury and certain pesticides, do not break down easily. Small organisms absorb them. Small fish eat these organisms, bigger fish eat small fish, and birds or humans eat bigger fish. The concentration of the pollutant increases at each higher trophic level.
Important features
- Usually involves persistent and non-biodegradable pollutants.
- Pollutants accumulate in body tissues.
- Concentration becomes higher at higher trophic levels.
- Top consumers are often at greater risk.
Examples
- Mercury in aquatic food chains.
- DDT and other persistent pesticides.
- Some industrial chemicals that accumulate in fatty tissues.
| Term | Meaning |
|---|---|
| Bioaccumulation | Pollutant builds up inside one organism. |
| Biomagnification | Pollutant concentration increases from one trophic level to the next. |
6. Marine Pollution
Sources of marine pollution
- Plastic waste: Bags, bottles, fishing nets and microplastics enter oceans.
- Oil spills: Oil from ships, tankers and offshore activities covers the water surface.
- Sewage: Untreated sewage adds pathogens and nutrients.
- Industrial chemicals: Toxic chemicals and heavy metals reach coastal waters.
- Agricultural runoff: Fertilizers and pesticides flow through rivers to the sea.
- Noise pollution: Ships and underwater activities disturb marine animals.
- Thermal pollution: Hot water changes marine water temperature.
Effects of marine pollution
Marine animals
Animals may swallow plastic, become trapped in fishing nets or suffer from toxic chemicals.
Coral reefs
Pollution and temperature changes can damage coral reefs and reduce biodiversity.
Food chain
Heavy metals and persistent pollutants may enter seafood and biomagnify.
Human activities
Pollution affects fishing, tourism, public health and coastal livelihoods.
Control of marine pollution
- Reduce single-use plastics.
- Treat sewage and industrial wastewater.
- Prevent and quickly control oil spills.
- Use safe fishing practices and collect lost fishing gear.
- Control agricultural runoff.
- Protect mangroves, coral reefs and coastal wetlands.
- Spread awareness and enforce marine protection laws.
7. Water Pollution Control
Water pollution control means preventing pollutants from entering water and treating polluted water before it is released or reused.
A. Prevention at source
- Reduce waste generation and use water carefully.
- Do not throw plastics, chemicals or garbage into water bodies.
- Use fertilizers and pesticides according to need.
- Maintain sewage pipelines and septic tanks.
- Use cleaner production methods in industries.
B. Treatment of wastewater
- Domestic sewage should be treated in sewage treatment plants.
- Industrial wastewater should be treated according to its pollutants.
- Reuse treated water for gardening, industry or other suitable purposes.
C. Natural and community measures
- Plant vegetation along riverbanks to reduce runoff.
- Protect wetlands because they can filter some pollutants.
- Harvest rainwater and protect groundwater recharge areas.
- Conduct regular water-quality testing.
D. Government and public measures
- Follow water pollution control standards.
- Monitor industries and sewage discharge.
- Promote public awareness and cleanliness drives.
- Apply the principle of “reduce, reuse and recycle”.
8. Sewage Treatment Plant (STP)
What is sewage?
Sewage is wastewater produced from homes, schools, hospitals, offices and other human activities. It contains water, human waste, food particles, soaps, detergents, microorganisms and other impurities.
Main stages of an STP
Primary: Mainly physical removal of floating and settleable solids.
Secondary: Biological removal of dissolved and fine organic matter.
Tertiary: Advanced polishing to remove nutrients, remaining particles, specific pollutants and pathogens.
9. Primary Treatment
Steps of primary treatment
- Screening: Bar screens remove large objects such as plastics, cloth, sticks and paper.
- Grit removal: Grit chambers remove sand, small stones and heavy inorganic particles.
- Primary sedimentation: Sewage is kept in a settling tank. Heavy solids settle as primary sludge, while oil and grease float and are removed.
What does primary treatment remove?
- Large floating materials.
- Sand and grit.
- Settleable suspended solids.
- Some oil, grease and organic matter.
10. Secondary Treatment
Activated sludge process
In the activated sludge process, sewage is mixed with microorganisms in an aeration tank. Air or oxygen is supplied so that microorganisms can use organic matter as food. The mixture then moves to a secondary settling tank.
Steps
- Aeration: Air is supplied to support aerobic microorganisms.
- Biological decomposition: Microorganisms consume organic pollutants and convert them into simpler substances, new cells and gases.
- Secondary clarification: Microbial flocs settle at the bottom.
- Sludge return: Some settled activated sludge is returned to the aeration tank, while excess sludge is removed for further treatment.
Importance
- Reduces biochemical oxygen demand (BOD).
- Removes a large amount of biodegradable organic matter.
- Improves water clarity and quality.
- Reduces oxygen depletion in receiving water bodies.
11. Tertiary Treatment
What can tertiary treatment remove?
- Nitrogen and phosphorus nutrients.
- Fine suspended particles.
- Remaining microorganisms.
- Some toxic chemicals, salts and specific pollutants, depending on the technology.
Common methods
| Method | Purpose |
|---|---|
| Filtration | Removes fine suspended particles. |
| Disinfection | Uses chlorine, ultraviolet light or other approved methods to reduce pathogens. |
| Nutrient removal | Reduces nitrogen and phosphorus to prevent eutrophication. |
| Activated carbon | Can remove some dissolved organic chemicals, taste and odour compounds. |
| Membrane treatment | Can remove very small particles and selected dissolved substances. |
Importance
- Produces higher-quality treated water.
- Helps prevent eutrophication.
- Supports safe reuse where standards are met.
- Provides additional protection against disease-causing organisms.
12. Comparison of Primary, Secondary and Tertiary Treatment
| Point | Primary | Secondary | Tertiary |
|---|---|---|---|
| Main nature | Physical | Biological | Advanced physical, chemical or biological |
| Main target | Large and settleable solids | Biodegradable organic matter | Nutrients, fine particles, pathogens and specific pollutants |
| Examples | Screening, grit removal, sedimentation | Aeration tank, activated sludge, biological filters | Filtration, nutrient removal, disinfection, membranes |
| Main result | Reduces suspended solids | Reduces BOD and organic pollution | Produces higher-quality effluent |
Sludge management
Sludge is the solid material collected during treatment. It may be thickened, digested, dewatered and safely managed. Proper sludge management prevents secondary pollution.
13. Quick Revision Sheet
- Water pollution: Change in water quality due to harmful substances.
- Surface water: Rivers, lakes, ponds and reservoirs.
- Groundwater: Water stored below the Earth's surface.
- Eutrophication: Excess nutrients cause algal blooms and oxygen depletion.
- Biomagnification: Pollutant concentration increases at higher food-chain levels.
- Marine pollution: Pollution of seas and oceans.
- Primary treatment: Physical removal of solids.
- Secondary treatment: Biological breakdown of organic matter.
- Tertiary treatment: Advanced removal of nutrients, pathogens and specific pollutants.
- BOD: Oxygen required by microorganisms to break down biodegradable organic matter.
- Best principle: Prevent pollution at its source and treat wastewater before discharge.
14. Board Exam Questions with Answers
Very Short Answer Questions
Q1. Define water pollution.
Answer: Water pollution is the contamination of water by harmful substances that reduce its quality and make it unsafe.
Q2. What is eutrophication?
Answer: Eutrophication is excessive nutrient enrichment of water that causes algal growth and oxygen depletion.
Q3. Define biomagnification.
Answer: Biomagnification is the increase in concentration of persistent toxic pollutants at successive food-chain levels.
Q4. What is sewage?
Answer: Sewage is wastewater produced from homes and other human activities.
Q5. Name the three main stages of sewage treatment.
Answer: Primary, secondary and tertiary treatment.
Q6. What is BOD?
Answer: BOD is the amount of dissolved oxygen required by microorganisms to decompose biodegradable organic matter.
Short Answer Questions
Q1. Write four sources of surface water pollution.
Answer: Domestic sewage, industrial discharge, agricultural runoff and dumping of solid waste.
Q2. Write four effects of groundwater pollution.
Answer: It makes drinking water unsafe, causes health risks, contaminates crops and remains difficult to clean.
Q3. Explain eutrophication in simple words.
Answer: Extra nitrogen and phosphorus enter a water body through fertilizers and sewage. Algae grow rapidly. When algae die, decomposition uses oxygen, causing oxygen depletion and fish death.
Q4. Differentiate between bioaccumulation and biomagnification.
Answer: Bioaccumulation is pollutant build-up inside one organism. Biomagnification is the increase of pollutant concentration at successive food-chain levels.
Q5. What is primary treatment?
Answer: Primary treatment is the physical stage of sewage treatment in which screening, grit removal and sedimentation remove large and settleable solids.
Long Answer Questions
Q1. Explain the sources and effects of surface and groundwater pollution.
Answer: Surface water is polluted by sewage, industries, agricultural runoff, plastics, mining and urban waste. It causes diseases, oxygen depletion, fish death and eutrophication. Groundwater is polluted by leaking septic tanks, fertilizers, pesticides, landfills, industrial chemicals and mining. It can make drinking water unsafe and is difficult to clean because pollutants remain underground for long periods.
Q2. Explain eutrophication and biomagnification.
Answer: Eutrophication occurs when excess nitrogen and phosphorus enter water and cause algal blooms. Decomposition of dead algae uses dissolved oxygen and may kill fish. Biomagnification is the increase of persistent toxic pollutants at higher food-chain levels. Pollutants such as mercury and certain pesticides may become highly concentrated in top consumers.
Q3. Describe marine pollution and its control.
Answer: Marine pollution is caused by plastics, oil spills, sewage, industrial chemicals, agricultural runoff and lost fishing gear. It harms marine animals, coral reefs, food chains, fisheries and human health. It can be controlled through plastic reduction, sewage treatment, oil-spill prevention, safe fishing, control of runoff and protection of coastal ecosystems.
Q4. Explain primary, secondary and tertiary sewage treatment.
Answer: Primary treatment uses physical methods such as screening, grit removal and sedimentation to remove solids. Secondary treatment uses microorganisms in processes such as activated sludge to break down organic matter and reduce BOD. Tertiary treatment is advanced treatment that removes nutrients, fine particles, pathogens and selected pollutants through filtration, disinfection and other methods.
15. Practice Questions
- Define water pollution and name its three major types.
- Write five sources of surface water pollution.
- Explain the effects of surface water pollution.
- Write the sources and effects of groundwater pollution.
- Define eutrophication and explain its process with a flow chart.
- Write five methods to control eutrophication.
- Define biomagnification with a suitable food-chain example.
- Differentiate between bioaccumulation and biomagnification.
- What is marine pollution? Explain its sources.
- Write five effects of marine pollution.
- Explain water pollution control measures.
- Define sewage treatment plant.
- Explain primary treatment with its steps.
- Explain secondary treatment and activated sludge process.
- Explain tertiary treatment and its importance.
- Differentiate between primary, secondary and tertiary treatment.
Exam Writing Tips ✍️
- Start every answer with a clear definition.
- Write sources, effects and control under separate headings.
- Draw the eutrophication flow chart for better presentation.
- Remember the order: Primary → Secondary → Tertiary.
- Use key terms such as nutrients, algal bloom, dissolved oxygen, BOD and biomagnification.
- Underline important words in the board examination.
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