Resource 30

Water recycling

About the activity

To complete this activity, you will need to be able to watch the video Recycled Water and have access to a computer simulation Western Treatment Plant Explorer. You will find the video in the 'videos' tab in 'Outlets'.

Where to find the video on the Western Treatment Plant Explorer
Where to find the video on the Western Treatment Plant Explorer

You can also find some useful information in the fact sheet 'Water recycling in Melbourne' available from Melbourne Water.

Background

In most modern cities, sewage from homes and industry flows into the sewerage system, is treated at a treatment plant and discharged into the oceans. Yet it could be reused to water parks and gardens.

Melbourne Water is taking a great interest in different ways of recycling and reusing treated sewage to help conserve and maximise the use of our water resources.

The recycling plant

One initiative was the trialling of an on-site water recycling plant and irrigation system in the King's Domain gardens in Melbourne during 2002. The aim was to demonstrate that water from sewers could be successfully recycled and used to irrigate parks and gardens.

The recycling plant is housed in a portable shipping container and uses the latest membrane technology to deliver 30,000 litres of high quality, recycled water each day. The plant uses 1.4 W of energy for each litre of recycled water at a cost of 1.4 cents per litre.

How does it work?

Raw sewage is pumped from the sewer, screened and fine screened. Particulates larger than 3 mm are returned to the sewer. During the first stage of the process, the membrane bioreactor reduces organics and removes particles in the product water down to 0.04 micron using an aerobic biological treatment process coupled with an ultrafiltration separation membrane.

During the second stage, the water is treated by reverse osmosis to reduce nutrients, pathogens and salts to acceptable levels. Before passing through the reverse osmosis unit, the water is preconditioned through filtering, UV (ultra violet) disinfection and descaling to avoid fouling the reverse osmosis membranes.

A rigorous testing program will be carried out during the trial to ensure that recycled water meets EPA and Department of Human Services health requirements. The purpose of it is to demonstrate the technology to the public. Make them comfortable with the fact that you can actually use sewage as a resource rather than a waste.

Tasks

After reading the background notes above, watching the video and reading 'Water recycling in Melbourne', answer the following questions:

  1. Why recycle water from sewage? After all, isn't there plenty of tap water.
  2. How much effluent is discharged from Melbourne's sewage treatment plants?
  3. Melbourne Water aims to recycle 20 per cent of the city's effluent by 2010. How could this be done?
  4. If we recycle and reuse treated effluent, what other benefits are there besides saving our water resources?
  5. Recycling is only one way of conserving our water resources. Make a list of other ways of saving water.
  6. Draw up a flowchart showing how to convert sewage to clean water.
  7. Dream up some creative ways of recycling water by completing the following sentence: We could recycle water by...