Quick answer: Biodegradable wastes (fruit and vegetable peels, leftover food, paper, cotton) can be broken down by bacteria and fungi into simple substances. Non-biodegradable wastes (plastics, glass, metals, many pesticides such as DDT) cannot, because the decomposers' enzymes are specific and cannot act on these materials. Such wastes persist, harm the environment, and are best reduced, reused, recycled or sent to properly managed landfills.
Biodegradable and non-biodegradable wastes
| Type | Meaning | Examples |
|---|---|---|
| Biodegradable | Broken down by biological processes (bacteria, fungi) | Peels, leftover food, paper, cotton cloth, cow dung, leaves |
| Non-biodegradable | Not broken down by biological processes | Polythene bags, plastic bottles, glass, metal cans, DDT |
Why decomposers cannot break down plastics
- Bacteria and fungi break down materials using enzymes.
- Enzymes are specific: each one acts only on particular substances (for example, starch or cellulose).
- Plastics and many man-made chemicals are not natural materials, and decomposers do not have enzymes that can break them down.
- So these substances remain in the environment for a very long time.
NCERT point: Substances are non-biodegradable because the enzymes of decomposers are specific in their action, so they cannot break down every substance.
Harmful effects of non-biodegradable wastes
- Blocked drains: plastic bags clog drains and sewers, causing waterlogging and breeding places for mosquitoes.
- Harm to animals: cattle and other animals that eat plastic bags can be seriously harmed or killed.
- Biological magnification: some chemicals, such as DDT, are not broken down and build up at each level of a food chain, reaching the highest concentrations in top consumers, including humans.
- Soil damage: plastics in soil can stop water from soaking in and affect plant growth.
Managing waste
| Method | Suitable for | How it works |
|---|---|---|
| Composting | Kitchen and garden waste | Microbes break it down into manure |
| Recycling | Paper, plastics, glass, metals | Materials are processed and used again |
| Sanitary landfill | Waste that cannot be recycled | Waste is buried in lined pits and covered with soil daily |
| Incineration | Hazardous waste, such as medical waste | Burnt at high temperature in special furnaces |
Landfills: open dumping vs sanitary landfill
- Open dumping attracts flies and rats, smells bad, and lets polluted liquid (leachate) seep into groundwater.
- A sanitary landfill is a pit lined with clay or plastic sheets. Waste is spread in layers, pressed down and covered with soil to reduce pollution.
Separating waste at home
In many Indian cities, households are asked to separate waste:
- Green bin – wet waste: kitchen and garden waste, which can be composted.
- Blue bin – dry waste: paper, cardboard, plastic, glass and metal, which can be sent for recycling.
Note: Paper and cardboard are biodegradable, but they go in the dry-waste bin because they are better recycled than composted.
The 5 Rs
Reduce, reuse, recycle, repurpose and refuse (for example, refuse plastic bags and carry a cloth bag). Reducing and reusing are better than recycling, because they avoid making waste in the first place.
Summary table
| Feature | Biodegradable | Non-biodegradable |
|---|---|---|
| Broken down by microbes | Yes | No |
| Time to break down | Days to months | Very long; many persist for decades or more |
| Origin | Mostly natural (plant and animal) | Mostly man-made |
| Main problem | Smell and disease if left to rot openly | Long-term pollution, biomagnification |
| Best handling | Composting, biogas | Reduce, reuse, recycle; landfill as a last option |
Exam tips
- Use the word "specific" when explaining why enzymes cannot break down plastics.
- Give at least two examples of each type of waste.
- When asked about harmful effects, include biological magnification for non-biodegradable chemicals.
- Suggest practical steps, such as separating waste and using cloth bags.
Common mistakes
- Calling paper non-biodegradable. Paper is biodegradable.
- Saying all non-biodegradable wastes are poisonous. Many, like glass, are harmful mainly because they persist.
- Thinking that burning plastics is a safe way to get rid of them. Open burning releases harmful gases.
- Mixing up biodegradable and recyclable. Some biodegradable items (paper) are recycled, and some non-biodegradable items (glass, metal) can also be recycled.
Frequently Asked Questions
What are biodegradable wastes?
They are wastes that can be broken down by bacteria and fungi into simpler substances, such as vegetable peels, leftover food and paper.
What are non-biodegradable wastes?
They are wastes that cannot be broken down by biological processes, such as plastic bags, glass and many pesticides.
Why can't plastics be broken down by decomposers?
Decomposers use enzymes that are specific in their action. They do not have enzymes that can act on plastics, so plastics remain unchanged for a long time.
How do non-biodegradable wastes harm the environment?
They block drains, harm animals that swallow them, pollute soil and water, and some chemicals build up in food chains by biological magnification.
What is the difference between open dumping and a sanitary landfill?
Open dumping leaves waste uncovered, causing smell, pests and groundwater pollution. A sanitary landfill uses a lined pit and covers the waste with soil to reduce these problems.