Main idea

Flowing water can clean itself. Physical, chemical and biological processes are all parts of the self-purification ability of water. Dilution, sedimentation, filtering, and aeration are physical processes. The most important chemical processes are oxidation and reduction; other accompanying processes help (e.g. adsorption, absorption, coagulation, complexation, etc.). The biological processes are primarily mineralization (the decomposition of dead organic substances to basic elements) and assimilation (uptake of substances in food chains).

Goal

To make sure that the students understand all the influences the self-purification ability of water in rivers and streams. They have to realize that biological processes of self-purification mean that organisms, through their food chains, include waste substances in a natural cycle called the biological cycle. Furthermore, they will realize what the functions of riparian zone richly overgrown with vegetation are and the form of a river itself. They will also learn that there is a limit to self-purification of natural systems, and that we exceed this limit in many rivers, so the consequences are that natural systems cannot handle the pollution. We have to clean our wastewater before we return it to the natural environment!

Concepts

water purification → biological processes (biological cycle), physical processes (filtration, etc.), chemical processes (oxidation, etc.) → wastewater treatment plant

Introduction: Can a River Clean Itself?

Let students find out through conversation by themselves that there are different self-purification processes in nature. However, if there is too much pollution or the pollution is man-made, water in nature cannot always purify itself. We need to purify water in treatment plants before it is discharged in natural streams.

Activities in this lesson

When Waste Water Enter a River (dilution)
6.1.1
Subject: Biology, Chemistry, Health care and recreation, Math, Physics
Age group: All, 4 - 6, 7 - 9, 10 - 12, 13 and up
Type of activity: Experiment
Number of participants: Team
When a River Passes Seven Stones…
6.1.2
Subject: Art and craft, Biology, Chemistry, Geography, Physics, Social skills
Age group: 10 - 12, 13 and up
Type of activity: Debate, Experiment
Number of participants: Paired, Team
Who eats what? Who is food for whom?
6.1.3
Subject: Biology, Chemistry
Age group: 13 and up
Type of activity: Debate, Project
Number of participants: Individual, Team
A Visit to a Wastewater Treatment Plant
6.1.4
Subject: Art and craft, Biology, Geography
Age group: All, 4 - 6, 7 - 9, 10 - 12, 13 and up
Type of activity: Debate, Field activity, Project
Number of participants: Team
Wetland – nature’s purification (filtering)
6.1.5
Subject: Art and craft, Biology, Chemistry, Geography, Physics
Age group: All, 4 - 6, 7 - 9, 10 - 12, 13 and up
Type of activity: Experiment
Number of participants: Team
Wetland – Nature’s Purification (absorption)
6.1.6
Subject: Biology, Chemistry, Geography, Physics
Age group: 10 - 12, 13 and up
Type of activity: Experiment
Number of participants: Team
Purification Functions of a River
6.1.7
Subject: Art and craft, Biology, Geography
Age group: All, 4 - 6, 7 - 9, 10 - 12, 13 and up
Type of activity: Debate, Project
Number of participants: Individual, Paired, Team

Discussion: Too Much Pollution / How to Increase Self-purification Capacity

When the level of pollution is high, there are two things that should be considered: to decrease the pollution intake and to increase the self-purification capacity of a water system.

  • How can the self-purification capacity be increased (The riparian zone could be restored and enlarged. Wetlands could be restored. Wastewater treatment plans should be built. Smarter use of fertilizers in agriculture should be practised, etc.).