Waste Materials and Their Effective Management
Senior 1 · Chemistry
Waste Materials and Their Effective Management
Lesson 1 of 5
25 min
Empty a classroom bin at the end of the day and sort what you find: banana peels and maize cobs, sheets of exercise-book paper, a broken pen, a juice bottle, pencil shavings, perhaps a used battery from a calculator. In a few weeks the banana peel will have rotted away; the pen and the bottle will look almost the same in a hundred years; and the battery contains metals that can poison soil and water. Waste is not all alike, and how we deal with it depends on what kind it is.
Definition
Waste: any material that its owner no longer wants and throws away, whether it is a solid, a liquid or a gas. Example: vegetable peelings from the school kitchen, used water from washing the floors, and smoke from burning rubbish are all waste.
Bacteria and fungi in soil feed on materials that came from living things, such as food, paper, wood and cotton, and break them down into carbon dioxide, water and minerals. Most plastics, glass and metals are not broken down in this way.
Definition
Biodegradable waste: waste that is broken down into simpler, harmless substances by microorganisms such as bacteria and fungi. Example: banana peels, paper, cow dung. Non-biodegradable waste cannot be broken down in this way, or only over hundreds of years. Example: plastic bottles, glass, aluminium cans.
Weigh a piece of each material in Figure 1.1 and bury each in its own pot of damp soil. Label the pots and keep them warm and moist. After four weeks, dig each item up, rinse off the soil, let it dry, weigh it again and describe how it looks.
Figure 1.1: A burial test for biodegradability.
Warning
Safety. Wear gloves when you dig up the items and wash your hands afterwards: rotting material carries bacteria and fungi. Do not bury meat or fish, which smell and attract rats and flies.
Table 1.1: Results of a burial test (illustrative)
| Item | Mass before in g | Mass after in g | Appearance after 4 weeks |
|---|---|---|---|
| Banana peel | 20.0 | 4.0 | dark, soft, mostly gone |
| Paper | 5.0 | 3.2 | soft, torn, with holes |
| Cotton cloth | 5.0 | 4.1 | weak, stained |
| Plastic bottle piece | 5.0 | 5.0 | unchanged |
| Aluminium foil | 5.0 | 5.0 | unchanged, slightly dull |
Worked example
Problem. Use Table 1.1 to calculate the percentage of mass lost by the banana peel, the paper and the plastic, and decide which materials are biodegradable.
Solution. Percentage lost .
Answer: the banana peel, paper and cotton lost mass, so microorganisms were breaking them down: they are biodegradable. The plastic and aluminium lost nothing: non-biodegradable. The banana peel rotted fastest because it is soft and full of water and sugars.
Some waste is dangerous even in small amounts. Hazardous waste is poisonous, corrosive, flammable, explosive or infectious; its containers often carry the hazard symbols you learned in Unit 2. It includes batteries, used engine oil, pesticide containers, old paint, laboratory chemicals, medical waste such as used needles, and electrical and electronic waste.
E-waste is one of the fastest-growing kinds of waste. Old phones, computers, chargers, televisions and solar lamps contain valuable metals, such as gold, silver and copper, that can be recovered. They also contain poisonous heavy metals, such as lead, mercury and cadmium, that escape into soil, water and air if the equipment is dumped or burned.
Definition
Hazardous waste: waste that can harm people or the environment because it is toxic, corrosive, flammable, reactive or infectious. E-waste (electronic waste) is discarded electrical and electronic equipment and its parts. Example: a broken mobile phone and its battery.
Table 1.2: Types of waste with school examples
| Type of waste | What it is | Examples at school |
|---|---|---|
| Biodegradable solid | broken down by microorganisms | food leftovers, fruit peels, paper, cardboard, leaves and grass cuttings |
| Non-biodegradable solid | not broken down, or only very slowly | plastic bottles and pens, glass, metal cans, broken chairs with metal frames |
| Liquid | used water and other liquids | water from washing plates and floors, used laboratory solutions, toilet waste |
| Gaseous | gases and smoke released into the air | smoke from the kitchen stove or from burning rubbish |
| Hazardous | poisonous, corrosive, flammable or infectious | used batteries, laboratory chemicals, first-aid needles, broken fluorescent tubes |
| E-waste | discarded electrical and electronic equipment | old computers, projectors, phones, chargers and calculators |
Worked example
Problem. Classify each item as biodegradable, non-biodegradable or hazardous: (a) maize cobs, (b) a glass jar, (c) a dry-cell battery, (d) a cardboard box, (e) an empty pesticide bottle, (f) a plastic bucket.
Solution.
Answer: a hazardous item is often also non-biodegradable, but it must be kept apart from ordinary waste because of the harm it can do.
Warning
Handling e-waste and broken batteries. Never open, crush, burn or throw a battery into a fire: it can burst, and it releases corrosive and poisonous substances. Wear gloves to pick up a leaking battery, put it in a sealed bag, and wash your hands. Do not break fluorescent tubes or energy-saving bulbs, which contain mercury. Keep old phones and batteries in a box until they can be taken to an e-waste collection point.
Tip
"If microbes can eat it, it's biodegradable." Things that came from living things usually rot; plastics, glass and metals do not.
Khan Academy India: Biodegradable and non-biodegradable waste (6 min). Notice what the microorganisms do to the food waste.
Practice
Sources and credits
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
