Resource 24

Sludge ¹

What good could possibly come from wastewater?

Many households are not able to connect up to sewerage networks or to have their wastes collected for delivery to sewage treatment plants. They must arrange for safe local treatment - septic tanks are allowed in many places and composting toilets are becoming more common.

There is no better way to dispose of waste than through the sewerage system. It is illegal to use any of the local treatments for sewage if connection to a system is possible.

Even after thorough sewage treatment, there is always some material left over. Sludge is the safe 'leftover' of sewage treatment. The same word is used for the leftovers of local and system treatment.

Is there a use for sludge?

CSIRO stands for the Commonwealth Scientific and Industrial Research Organisation, a Federal Government organisation which investigates problems and ideas in agriculture, pollution, manufacturing, conservation and many other areas.

The CSIRO Division of Soils has been studying the fertiliser value of sewage sludge. Human sewage is widely used in many countries of the world as a fertiliser. It helps crops to grow by returning to the soil nutrients which have been removed in the farming process.

The use of sludge could also improve the structures of soils which have been damaged by the use of artificial fertiliser over a long time.

Questions

  1. Why is sludge rich in nutrients? Go to the library and find out what nutrients would be found in human wastes.
  2. After a class brainstorm, write a letter to the Victorian Department of Agriculture explaining why farmers should be encouraged to use sludge for fertilising their crops rather than artificial fertilisers.
  3. Why is it necessary to test each batch of sludge to find out if it is safe to use?

¹ Based on an activity from: Keith McTaggart and Paul Saddler 1993, Flushing Dunnies, Melbourne Water and Science Teachers Association of Victoria.