Used water does not disappear. Although some of it is used for food and drinks, some of it evaporates, or we use it for watering plants, we return a large share of water to nature as polluted or used water. This is a different type of wastewater.
Advertisments for cleaning products and detergents tell us that they are “biodegradable”, but not at the moment that they drain away from washing machines. The biodegradation occurs in biological procedures in the water treatment plants or in rivers, as much as they still have their self-purification ability.
- Have a debate in small groups about how much is too much pollution in various situations and then report to the whole class and continue with a debate:
- How much is too much pollution for rivers and streams?
- Can be wastewater too polluted for a wastewater treatment plant?
- Find out together with pupils (you can plan a trip to a wastewater treatment plant):
- Is sewage from your school cleaned in a water treatment plant, before it is discharged into a river?
- Is the wastewater treatment plant in your town capable of cleaning all the wastewater that flows through it?
- Must all factories have their own wastewater treatment plants? (No. It depends on what they produce. If wastewater or water that is used in technological processes (e.g. cooling water in a factory, etc.) are not polluted with specific substances, such a factory can be attached to a public sewage network and a wastewater treatment plant. If the public utility cannot purify the type of wastewater produced by the factory, the factory must have its own industrial water treatment plant.)