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How we treat wastewater

About this lesson

Students carry out an experiment on how to treat wastewater and demonstrate their understanding by writing a procedure.


Year level: 8

Theme: Wastewater


Learning objectives

Students can:
  • work in a team to conduct an experiment
  • record observations and draw conclusions
  • draft, edit and publish a procedure on how to carry out a treating wastewater experiment
  • order paragraphs to organise and convey information clearly.

Curriculum links

English

  • Experiment with text structures and language features to refine and clarify ideas to improve the effectiveness of students’ own texts ACELY1810

Science

  • Summarise data, from students’ own investigations and secondary sources, and use scientific understanding to identify relationships and draw conclusions ACSIS145
  • Measure and control variables, select equipment appropriate to the task and collect data with accuracy ACSIS141
  • Use scientific knowledge and findings from investigations to evaluate claims based on evidence ACSIS234

Sustainability

  • OI.3 – Sustainable patterns of living rely on the interdependence of healthy social, economic and ecological systems.

Things you will need

  • Water 
  • Ice-cream containers
  • Cooking oil, detergent, sand, food scraps, sugar,
  • Scrap paper, pieces of plastic, matches, cotton buds, combs
  • Strainers
  • Blotting paper/kitchen towel or other absorbent paper
  • Fine mesh material
  • Science journal (or somewhere to record observations and findings)

Lesson description

Discuss

  • Explain to students what wastewater is.
  • Conduct a brainstorm about what goes into the wastewater system and what wastewater looks like when it arrives at a treatment plant.

Experiment

  • In groups of four, fill an ice cream container two-thirds full with water.
  • Add a tablespoon of cooking oil, a tablespoon of detergent, some sand, food scraps, sugar, small pieces of torn paper, plastic, matches and cotton buds.
  • Stir and leave to stand for a few minutes.
  • Have students record their observations during the experiment.
  • Come together and discuss what would have to be done to this mixture before it could be released back into the environment?
  • Have each group work out a way of removing the solid ingredients and trial tools to help remove certain items.
  • Once items have been removed, get students to review the quality of the water and discuss in their group whether the water is now clean?
  • Have students’ suggest ways the water could be further cleaned?

Activity

  • Get students to draft, edit and publish a procedure on how to carry out the experiment.
  • Students are to order paragraphs to organise and convey information clearly.

Reflect & summarise

Select groups to share their work and discuss their conclusions. Possible questions to follow up with include:

  • What worked best to remove the paper, cotton buds and matchsticks. How did you remove the sand?
  • How did you remove the cooking oil?
  • What problems did you encounter? How did you overcome these?
  • What do you think happens to the items that are removed?
  • What did this experiment make you think about?

Extension activities

Teacher background information

Wastewater  is a hidden part of everyday life. It is collected every day from households, commercial businesses and industries. Wastewater is directed to treatment plants and treated to an environmentally acceptable standard before being reused or safely discharged back into the environment.

Our treatment plants

In WA, Water Corporation is responsible for the treatment and disposal of wastewater. It operates more than 113 wastewater treatment facilities around the state. The three large metropolitan plants at Beenyup, Subiaco and Woodman Point treat approximately 80% of the state's wastewater.

What is wastewater?

Wastewater is the spent or used water from a community. It comes from domestic, commercial and industrial sources. The collection, treatment and disposal of wastewater are an integral part of the water cycle that maintains the balance of water in nature.

Surprisingly, wastewater is 99.97% water because by far the greatest volume comes from showers, baths and washing machines. The rest is dissolved and suspended matter. Wastewater also comes from industrial processes.

Wastewater treatment

Wastewater treatment is a series of processes that remove the pollutant materials from wastewater such as solids, oil and greases, detergents, nutrients, heavy metals and bacteria. These processes are carried out at wastewater treatment plants. The treatment involves speeding up the natural processes of bacterial breakdown and removing solids by filtration and settling. The treated wastewater then:

  • returns to the marine environment via ocean outfalls
  • is re-used in horticulture or to irrigate recreational areas
  • infiltrates back into the ground
  • evaporates.

Treatment processes

There are 3 stages of wastewater treatment:

  • Preliminary treatment
    • Raw wastewater enters the plant from wastewater pipes and flows through a screening process to remove large items (called screenings).
    • After screening, the wastewater flows through grit removal tanks to allow grit to settle while the organic material remains suspended.
    • The grit is removed and sent to an approved landfill site together with the screenings.
  • Primary treatment
    • The wastewater is pumped into the primary sedimentation tanks to let the solids settle to the floor of the tanks while oil and grease floats to the top.
    • Mechanical scrapers remove the settled solids and the oil and grease is removed.
    • The settled solids are further treated and become bio solids.
  • Secondary treatment
    • In aeration tanks the wastewater is treated with a natural bacterial process and air, which breaks down the remaining organic compounds in the water.
    • The water then flows into the secondary sedimentation tanks. Here the biologically active sludge settles and is removed.
    • The treated wastewater is then suitable for ocean discharge.

Did you know?

In Perth around 370 million litres of wastewater, the equivalent of 185 Olympic-sized swimming pools, is collected every day.

Key vocabulary

  • Biosolids: Stabilised, nutrient-rich, organic residues generated from the wastewater treatment process
  • Discharge: The pouring of a substance from an area where it was confined
  • Dispose: To cast something away
  • Dissolve: To pass into a solution
  • Recycle: To use again after processing
  • Stormwater: Rainwater which has run off roads, roofs, paved areas etc. and is conveyed by constructed drains to waterways
  • Wastewater: Water that has been used inside a home, business or industry that travels to a wastewater treatment plant