NCERT Solutions for Class 6 Science Chapter 16 — Garbage In, Garbage Out

Key Concepts

Intext Questions (Page-by-Page)

Non-biodegradable waste such as plastics, metals, glass, aluminium foil, and synthetic fibres cannot be composted because microorganisms cannot decompose them. These materials remain in the environment for hundreds of years. They need to be handled differently — some can be recycled (like metals, glass, and paper), while others like certain plastics are difficult to recycle and end up in landfills or cause pollution.

So, while composting is an excellent way to handle biodegradable waste, it cannot process all types of garbage. Proper waste management requires segregation of waste into biodegradable and non-biodegradable categories, followed by appropriate processing of each type.

1. Different processing methods: Biodegradable waste can be converted into compost or vermicompost, while non-biodegradable waste needs to be recycled, reused, or sent to landfills. If they are mixed, it becomes impossible to process either type effectively.

2. Prevents pollution: If non-biodegradable waste (especially plastics) is mixed with biodegradable waste and sent to composting, the compost will be contaminated with harmful substances. If plastic waste reaches landfills mixed with organic waste, it prevents proper decomposition.

3. Enables recycling: Non-biodegradable items like paper, glass, metals, and some plastics can be recycled into new products. But if they are mixed with wet, organic waste, they become dirty and difficult to recycle.

4. Reduces landfill burden: When biodegradable waste is composted separately, only non-biodegradable waste goes to landfills. This significantly reduces the amount of waste in landfills.

5. Health and hygiene: Mixed garbage decomposes and produces foul smells, attracts flies and mosquitoes, and can spread diseases. Segregated waste is easier to manage and less harmful.

6. Value recovery: Separated waste has economic value — compost from biodegradable waste is a good fertiliser, and recycled materials can be sold.

1. Collection: Sanitation workers or garbage collectors gather waste from homes, offices, and public places using garbage trucks or carts.

2. Segregation: At waste processing centres, the garbage is sorted into biodegradable and non-biodegradable categories. Some cities have systems for segregation at the source (home level).

3. Processing of biodegradable waste: The biodegradable waste is sent for composting or vermicomposting. In composting, it is placed in pits and allowed to decompose naturally. In vermicomposting, earthworms are used to convert it into compost.

4. Processing of non-biodegradable waste: Items that can be recycled (paper, glass, metals, some plastics) are sent to recycling units. Items that cannot be recycled are sent to landfills.

5. Landfilling: The remaining waste that cannot be composted or recycled is dumped in low-lying areas called landfills. The waste is spread in layers and covered with soil. Over time, the landfills become full and new sites need to be found.

6. Open dumping: In some places, especially in smaller towns and villages, garbage is dumped in open areas without proper processing. This causes pollution and health problems.

A banana peel is made of organic compounds (carbohydrates, proteins, etc.) that microorganisms can feed on and decompose within a few days to weeks. A plastic bag, on the other hand, is made of synthetic polymers (long chains of carbon-based molecules) that are chemically very stable and resistant to microbial attack.

Plastics can take hundreds of years to break down — some estimates suggest 500 to 1000 years for a plastic bag to decompose. Even when they do break down, they don't fully decompose but instead break into smaller and smaller pieces called microplastics, which continue to pollute the environment.

This is why it is extremely important to reduce, reuse, and recycle plastic items and avoid using single-use plastics.

Differences between vermicomposting and regular composting:

How to set up vermicomposting: 1. Take a pit or a large container. 2. Add a layer of coarse material (small stones or twigs) at the bottom for drainage. 3. Add a layer of sand on top. 4. Add kitchen waste (vegetable peels, fruit waste, tea leaves, etc.) mixed with some soil. 5. Introduce redworms into the pit. 6. Keep the pit moist (not wet) by sprinkling water. 7. Cover with a wire mesh or grass to prevent flies and maintain moisture. 8. After 3-4 weeks, the worms will have processed the waste into vermicompost.

Exercise Questions (NCERT Textbook)

(b) Waste that can be decomposed by microorganisms is called ________ waste.

(c) Waste that cannot be decomposed by microorganisms is called ________ waste.

(d) A low-lying open area used to dump garbage is called a ________.

(b) Plastics are biodegradable.

(c) Composting is done only for biodegradable waste.

(d) Recycling reduces the amount of waste.

Summary:

• Biodegradable: Paper, cotton cloth, vegetable peels, leather shoes, wood, banana peel
• Non-biodegradable: Plastic bottle, aluminium foil, glass, metal can

1. Reduce: This means using less and creating less waste in the first place. By reducing our consumption, we produce less garbage.

Examples:

• Carry your own cloth bag instead of taking a plastic bag from the shop.
• Use both sides of a paper for writing or drawing.
• Buy products with less packaging.
• Avoid single-use items like disposable cups, plates, and cutlery.
• Serve only as much food as you can eat to reduce food waste.
• Use a refillable water bottle instead of buying bottled water every time.

2. Reuse: This means using an item again, either for the same purpose or a different purpose, instead of throwing it away.

Examples:

• Use old jam bottles or containers for storing spices, pulses, or other items.
• Use the back side of printed paper for rough work or drawing.
• Donate old clothes, books, and toys to people who can use them.
• Use old envelopes for making lists or notes.
• Turn old t-shirts into cleaning rags.
• Use old tyre tubes as planters or swings.

3. Recycle: This means converting waste materials into new products through processing, so that the material is used again instead of being thrown away.

Examples:

• Paper waste is recycled to make new paper, cardboard, and paper products.
• Plastic bottles are recycled to make polyester fibre for clothing, carpets, and furniture.
• Glass bottles and jars are melted and reshaped into new glass products.
• Aluminium cans are melted and made into new aluminium products.
• Metal scrap is recycled to make new metal products.

Following the three Rs helps reduce the burden on landfills, conserves natural resources, saves energy, and reduces pollution.

How a landfill works:

1. Site selection: A low-lying area or a specially dug pit is chosen for the landfill. The site is usually away from residential areas and water sources.

2. Lining the bottom: The bottom of the landfill is lined with clay and plastic sheets to prevent the leachate (contaminated liquid from decomposing waste) from seeping into the ground and polluting groundwater.

3. Dumping garbage: Garbage is brought to the landfill site by trucks. The waste is spread in thin layers over the area.

4. Covering with soil: Each layer of garbage is covered with a layer of soil. This helps reduce bad odour, prevents flies and mosquitoes from breeding, and keeps the waste from being scattered by wind or animals.

5. Compaction: Heavy machinery like bulldozers and compactors are used to compress the waste, reducing its volume and creating more space.

6. Final covering: When the landfill is full, a thick layer of soil is spread over the top. Grass and trees may be planted on the surface.

Problems with landfills:

• They take up valuable land space.
• They produce harmful gases like methane, which contributes to global warming.
• Leachate from landfills can contaminate groundwater.
• They attract pests and can spread diseases.
• Once full, new landfill sites must be found, which is increasingly difficult.

1. Health: Improperly disposed garbage becomes a breeding ground for flies, mosquitoes, and other pests that spread diseases like malaria, dengue, cholera, and typhoid.

2. Environment: Garbage dumped in open areas pollutes the soil, air, and water. Harmful chemicals from waste can seep into groundwater, making it unsafe for drinking.

3. Aesthetics: Piles of garbage look ugly and give off foul smells, making the surroundings unpleasant and unhygienic.

4. Drainage: Garbage thrown in drains and gutters blocks the flow of water, causing waterlogging and flooding during rains.

5. Animals: Stray animals like cows and dogs eat plastic waste from garbage dumps, which can cause serious health problems and even death.

6. Soil pollution: Non-biodegradable waste like plastics and chemicals pollute the soil and make it infertile.

Problems caused by improper garbage disposal:

1. Spread of diseases: Garbage attracts disease-carrying organisms like flies, mosquitoes, rats, and cockroaches. 2. Water pollution: Waste dumped near water bodies contaminates the water, making it unsafe for drinking and harming aquatic life. 3. Air pollution: Decomposing waste produces foul-smelling gases. Burning garbage releases toxic smoke and harmful chemicals into the air. 4. Soil pollution: Chemical waste and plastics contaminate the soil, affecting plant growth. 5. Blockage of drains: Plastic bags and other waste clog drainage systems, causing flooding. 6. Harm to wildlife: Animals can choke on or get entangled in plastic waste. 7. Global warming: Decomposition of organic waste in landfills produces methane, a greenhouse gas that contributes to climate change.

How compost is prepared:

Method 1 — Pit composting: 1. Dig a pit: Dig a pit about 2-3 feet deep in a corner of the garden or backyard. 2. Spread a layer: At the bottom, spread a layer of coarse material like small twigs or dried leaves for drainage. 3. Add waste: Put biodegradable waste like vegetable peels, fruit waste, leftover food, tea leaves, garden leaves, and grass clippings into the pit. 4. Add soil: Sprinkle a layer of soil or cow dung over the waste. This introduces microorganisms that help decomposition. 5. Add water: Sprinkle some water to keep the pit moist (not wet). Microorganisms need moisture to function. 6. Repeat layers: Continue adding layers of waste, soil, and water until the pit is full. 7. Cover the pit: Cover the top with a layer of soil to prevent flies and bad odour. 8. Wait: Leave the pit for 2-3 months. Microorganisms (bacteria and fungi) will decompose the waste. 9. Harvest compost: After 2-3 months, the waste will have decomposed into dark, crumbly, earthy-smelling compost. This can be mixed with soil to enrich it.

Things to remember:

• Only biodegradable waste should be used for composting.
• Non-biodegradable items like plastics, glass, and metals should not be put in the compost pit.
• The pit should be kept moist but not waterlogged.
• Turning the compost occasionally speeds up the process by adding air.

1. Non-biodegradable: Plastics do not decompose naturally. They remain in the environment for hundreds of years, causing long-term pollution.

2. Soil pollution: When plastic bags are thrown on land, they prevent rainwater from seeping into the soil, reducing groundwater recharge. They also make the soil infertile.

3. Water pollution: Plastic bags thrown into rivers, lakes, and oceans pollute water bodies. They harm aquatic animals that may mistake them for food or get entangled in them.

4. Harm to animals: Stray animals like cows often eat plastic bags along with food waste from garbage dumps. The plastic gets stuck in their digestive system and can cause serious health problems and even death.

5. Blockage of drains: Plastic bags clog drainage systems and sewers, causing waterlogging and flooding during rains.

6. Air pollution: When plastic is burned, it releases toxic gases and chemicals into the air, which can cause respiratory problems and other health issues.

7. Microplastics: Over time, large plastic items break down into tiny pieces called microplastics, which contaminate soil, water, and food chains.

8. Visual pollution: Plastic bags scattered in the environment look ugly and spoil the beauty of natural landscapes.

Alternatives to plastic bags:

• Use cloth or jute bags for shopping.
• Use paper bags or biodegradable bags.
• Carry your own reusable bags.
• Avoid asking for plastic bags at shops.

1. Non-biodegradable nature: Plastics are synthetic polymers that cannot be broken down by natural processes or microorganisms. A plastic bag can take 500-1000 years to decompose, meaning every piece of plastic ever made still exists somewhere on Earth.

2. Soil contamination: Plastic waste dumped on land prevents rainwater from seeping into the ground, reducing groundwater levels. It also blocks the flow of nutrients in the soil and makes agricultural land less productive.

3. Water body pollution: Millions of tonnes of plastic waste enter oceans, rivers, and lakes every year. Marine animals like turtles, fish, and birds mistake plastic for food and die from ingestion or entanglement.

4. Threat to animal life: On land, stray animals (especially cattle) eat plastic bags while foraging for food in garbage. The plastic accumulates in their stomachs, causing blockages, infections, and death.

5. Drainage blockage: Plastic bags are a major cause of clogged drains and sewers in cities, leading to waterlogging, flooding, and unhygienic conditions during monsoons.

6. Toxic emissions: When plastics are burned (a common waste disposal method), they release harmful gases like dioxins, furans, and other toxic chemicals that cause respiratory diseases, cancer, and other health problems.

7. Microplastics: Large plastic items gradually break into tiny fragments called microplastics (less than 5mm). These enter the food chain through water and soil, eventually reaching humans, and may cause health problems.

8. Depletion of resources: Plastics are made from petroleum, a non-renewable resource. Manufacturing plastics consumes fossil fuels and contributes to carbon emissions.

9. Difficult to recycle: Not all plastics can be recycled. Mixed plastics, contaminated plastics, and multi-layered plastics are hard to process. Most plastic waste ends up in landfills or the environment.

This is why there is a global push to reduce plastic usage, ban single-use plastics, and find eco-friendly alternatives.

Multiple Choice Questions (MCQs)

Common Mistakes

1. Confusing biodegradable and non-biodegradable: Students sometimes classify items incorrectly. Remember: biodegradable waste comes from natural sources and can decompose (vegetable peels, paper, cotton, wood, leather). Non-biodegradable waste is synthetic or processed and does not decompose (plastics, metals, glass, aluminium foil, thermocol). When in doubt, ask: "Can bacteria and fungi break this down naturally?"

2. Thinking all plastics can be recycled: Not all plastics can be recycled. Multi-layered plastics (like chip packets), thermocol, and mixed plastics are very difficult to recycle. Only certain types of plastics (PET bottles, HDPE containers) are commonly recycled. Students should not assume that all plastic waste can be processed through recycling.

3. Confusing composting and vermicomposting: Composting uses bacteria and fungi to decompose waste, while vermicomposting specifically uses earthworms (redworms). Vermicomposting is faster and produces more nutrient-rich compost, but it requires specific conditions (moisture, temperature) and cannot handle all types of organic waste (e.g., avoid putting dairy, meat, or oily food in a vermicompost bin).

4. Forgetting that Reduce and Reuse come before Recycle: The three Rs are listed in order of priority — Reduce first, then Reuse, then Recycle. Many students focus only on recycling, but reducing waste at the source and reusing items are more effective than recycling because they prevent waste from being created in the first place.

5. Thinking landfills are a good solution: Landfills are not a sustainable long-term solution for waste disposal. They take up land, produce methane (a greenhouse gas), contaminate groundwater through leachate, and create health hazards. The best approach is to reduce waste generation and maximise composting and recycling.

Exam Checklist

• [ ] I can classify waste as biodegradable or non-biodegradable with at least 5 examples of each.
• [ ] I can define composting and describe the steps to prepare compost in a pit.
• [ ] I can explain vermicomposting, including the organism used and the process, and differentiate it from regular composting.
• [ ] I can describe what a landfill is, how it works, and the problems associated with landfills.
• [ ] I can explain the three Rs (Reduce, Reuse, Recycle) with at least 3 examples for each.
• [ ] I can list the harmful effects of plastics on the environment and suggest alternatives to plastic bags.
• [ ] I can explain why it is important to segregate biodegradable and non-biodegradable waste before disposal.
• [ ] I can list at least 5 things we can do at home to reduce garbage production.