Waste Materials and Their Effective Management
Senior 1 · Chemistry
Waste Materials and Their Effective Management
Lesson 2 of 5
25 min
Every day, lorries carry hundreds of tonnes of waste out of Kigali to the Nduba landfill (Lesson 3). It comes from homes, markets, hotels, factories, building sites, hospitals and schools. Before a school can manage its waste well, it needs to know how much it produces and what kind. The tool for that is a waste audit, and in this lesson you plan and analyse one.
Table 2.1: Sources of waste and typical wastes
| Source | Examples | Typical wastes |
|---|---|---|
| Domestic (homes) | houses and flats | food scraps and peelings, packaging, old clothes, ash, grey water, sewage |
| Commercial | markets, shops, restaurants, hotels | rotten fruit and vegetables, cardboard, bottles, cooking oil |
| Industrial | tea and coffee factories, breweries, cement and food factories | husks and pulp, waste water, dust, chemicals, packaging |
| Agricultural | farms and cattle sheds | crop residues, dung, pesticide and fertiliser containers |
| Institutional | schools, hospitals, offices | paper, food waste, medical waste such as needles and bandages, e-waste |
| Construction and demolition | building and road sites | rubble, broken bricks, cement bags, scrap metal |
| Mining | quarries and mines | waste rock, soil and muddy water |
Definition
Waste audit: a survey in which the waste produced by a place over a set time is collected, sorted into categories and weighed, to find out how much of each kind there is. Example: sorting and weighing all the waste from a school's classrooms and kitchen for one day.
A school is a small town. The kitchen produces peelings, leftovers and ash from the stoves; classrooms and offices produce paper, pens, chalk dust and, sometimes, old computers and printer cartridges; the laboratory produces used chemicals and broken glass; dormitories produce packaging, old shoes and soap wrappers; the toilets produce sewage; and the grounds produce leaves and grass cuttings. Good management starts with separating these at the source: one bin for food and garden waste (for compost), one for paper, one for plastic, glass and metal, and a closed box, kept by a teacher, for hazardous waste and e-waste.
Aim: to find out how much waste your school produces in one day, and what it is made of.
You need: gloves, a large plastic sheet or tarpaulin, labelled buckets or sacks, a bathroom scale or spring balance, a notebook.
Warning
Safety. Wear gloves throughout and never pick up broken glass, needles or razor blades by hand: tell the teacher. Put batteries, chemical containers and broken bulbs in a separate closed box. Work outside, keep your hands away from your face, and wash your hands with soap when you finish.
A class did the audit and obtained the results below. These figures are illustrative, invented to show how the analysis works; your own school's figures will be different.
Table 2.2: One day's waste at a school (illustrative)
| Category | Mass in kg | Percentage of total |
|---|---|---|
| Food and kitchen waste | 38.5 | 64.2% |
| Paper and cardboard | 9.2 | 15.3% |
| Plastic | 6.4 | 10.7% |
| Other (sweepings, chalk) | 3.7 | 6.2% |
| Glass | 1.1 | 1.8% |
| Metal | 0.8 | 1.3% |
| Hazardous and e-waste | 0.3 | 0.5% |
| Total | 60.0 | 100% |
Figure 2.1: One day's waste at a school, by category (illustrative figures).
Worked example
Problem. Use Table 2.2. (a) Show how the percentage for food waste was calculated. (b) What percentage of the waste is biodegradable (food plus paper)? (c) The school has 800 students. What mass of waste is produced per student per day, in grams?
Solution.
Answer: 64.2%; 79.5% biodegradable; 75 g per student per day.
Worked example
Problem. The school wants to cut the waste it sends to the landfill as much as possible. It can afford one project this year: a compost pit for food waste, or a collection point for recyclable paper, plastic, glass and metal. Use the data to decide.
Solution.
Answer: start with the compost pit; add recycling later. With both, only (6.7%) would be left.
Tip
Sort, weigh, calculate, act. An audit is only useful if its numbers lead to a decision.
Rumbalara Environmental Education Centre: How to conduct a waste audit in a school (5 min). Compare their categories with those in Table 2.2.
Practice
Sources and credits
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
