Resource 25

Building a better loo ¹

New toilets, where the sewage is turned into compost, are now available for unsewered areas. They are called 'composting toilets', with different sizes and varieties available for different tasks and places. They are especially recommended for environmentally sensitive areas, one of the best examples being at Uluru.

How does a composting loo work?

The composting loo comes with a tank to catch the sewage. The tank has about six sections and, as each fills, the tank is rotated.

Over several months, the liquid evaporates (a solar or mains heater can speed this process) while at the same time, microbes break up the solids.

Some varieties of composting loo need microbes to be added. This can be done by adding some apple peel or a handful of grass clippings.

At the end of the composting period, which is about 1 to 3 years, each compartment of the tank has a thin layer of sludge left over. This can be scraped out and buried quite safely 20-30 cm below the ground surface. It is a natural fertiliser for the soil.

The composting toilet
The composting toilet.

Questions

  1. Where is it illegal to use local sewage treatments like septic tanks or composting toilets?
  2. What is compost? How is it different to sewage?
  3. Why are composting loos used in environmentally sensitive areas?
  4. Ask much older members of your family if they had an outside loo when they were children. Did the nightman come to visit? How do composting loos differ from the nightman's cans?
  5. Choose one of the following tasks to help you explain why anyone would want to throw apple peel or grass clippings into the composting toilet. For the task you choose, record your observations or measurements in your science book and discuss it with your teacher and classmates and work out an answer.
    1. Leave some grass clippings in a plastic bag in a dark cupboard for a week.
    2. Leave some apple peel in a plastic bag in a dark cupboard for a week.
    3. Ask if you may measure the temperature of the inside of a compost heap at school or home, once a day for several days in a row.
    4. Put a mixture of grass clippings and apple peel into a vacuum flask and leave it overnight. Take the temperature of the grass and apple peel at the beginning and end of the experiment.

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