Grades 3–5 · Systems
How do recycling systems sort and reuse materials?
A used paper sheet and a steel can need different preparation before becoming useful material again. Recycling connects collection with sorting, processing and manufacturing. Putting an item in a collection route starts that journey; it does not finish it.
The invented program in the illustration accepts paper and steel only when its clean condition is met. A clean steel item passes both parts of that rule. The rule keeps unsuitable inputs out of this program's route; another program with different equipment may accept a different set.
Recovered paper can be mixed with water to separate its fibers. After unwanted material is removed, the fibers can be drained, pressed and dried into a new sheet. Steel scrap takes a different route: it can be melted, its composition adjusted, and the metal shaped into new products. Sorting helps each process receive material it can use.
The Steel can passes the pictured Listed AND clean? rule because it meets both conditions in this invented program. Collection → processing → new products shows the further steps still needed.
In the diagramOne classification step in a longer systemSteel canClean flag: yesListedANDclean?Listed + cleanOther routeExample list · clean items onlyPaper + steelCollection → processing → new productsThis rule: accept · real local rules vary
Manufacturers can combine recovered material with new material to make products. The pictured clean steel item has only entered a possible route: its acceptance does not instantly make a new can. Recycling works when collection rules, processing equipment and manufacturing uses fit together.
About this explanation
Starting knowledge: Classify objects and apply an AND rule from a supplied list.
Sources
- US Environmental Protection Agency — Recycling Basics and Benefits
- US Environmental Protection Agency — The U.S. Recycling System
- US Environmental Protection Agency — Recycle City: Materials Recovery Facility
- American Iron and Steel Institute — Steel Production