Good Science Victorian Curriculum Year 7

CHAPTER 5: MIXTURES
2
Sewage is processed to reduce harm
to the environment
Sewage is semi-liquid human waste. When you flush the toilet, the
sewage goes into a sewerage system and is treated before it eventually
goes into the ocean.
Some countries do not have proper sewerage systems. Untreated
sewage is not good for human health and the natural environment,
so in economically developed countries like Australia it is processed
before release.
Figure 5.18 In some less economically
developed countries, human waste goes
into open sewers and is not treated.
CHECKPOINT 5.8
1 Explain why sewage treatment
is critical to a healthy
environment.
2 Identify the purpose of
flocculation in water
purification.
3 Describe what happens during
the sewage treatment phase
called screening.
4 Identify two different ways
of killing harmful bacteria.
5 Explain why the treatment and
purification of water are such
important processes.
6 What is the purpose of adding
fluoride to water?
7 Explain why air is blown into
tanks in a sewage treatment
plant.
8 Create a table of similarities
and differences between
water purification and sewage
treatment.
ETHICAL CAPABILITY
In Australia, there are six main steps in sewage treatment.
1 Sewerage: A network of pipes moves sewage from homes and
businesses to sewage treatment plants.
2 Screening: Screens at the plant act as a sieve and catch large objects,
which can be physically removed.
3 Aeration: Air is pumped into tanks that hold the sewage. This feeds
bacteria, which break down the sewage.
4 Settling: Other chemicals are added that cause the bacteria and
solids to settle to the bottom of the tank as thick sludge. This sludge
is removed and is used in soil and fertiliser products.
5 Filtration: The sewage passes through a filter made from pebbles.
This traps more solids, which are removed.
6 Disinfection: Special ultraviolet light or chlorine is used to kill harmful
bacteria in the sewage before it is released into the ocean.
What steps are involved in sewage processing?
9 In Victoria, special yellowtopped
recycling bins are
provided to every household.
Unfortunately, if people put any
non-recyclable items in these
bins, the whole load must go to
landfill. Should people caught
contaminating recycling be
fined? Your response should
include a discussion of ethical
considerations (what is wrong
and what is right).
SUCCESS CRITERIA
I can describe how water
is purified.
I can describe how sewage
is treated.
83