CORDIO Status Report 1999.pdf

WASTEWATER
Wastewater problems are becoming acute in many parts
of the world and, for the future of cities, wastewater
treatment is one of the most critical areas of development.
The discharge of sewage into coastal waters can have
a destructive impact on coral reefs and coastal ecosystems.
The population in coastal areas grows rapidly, and
the use of freshwater and discharge of sewage will increase.
As this has destructive effects on coastal environments,
in particular coral reefs, it is essential that especially
cities and tourist resorts aim to reduce the amount
of freshwater used and discharged as sewage. This can
be achieved by implementing alternative ways of use,
and treatment of the sewage.
Biological treatment of organic wastes has been used
for centuries. Composting, for example, is a natural way
to enhance nutrient cycling. Nature sees sewage as a resource,
while modern society sees sewage as a problem,
and often thinks the solution is to transport it to rivers
or directly to the sea.
We need to seriously change our way of thinking.
Instead of discharging treated or untreated sewage into
the sea, it should be kept inland for some productive
uses. Several demonstration projects shows that complete
use of wastewater for aquaculture and agriculture
is possible.
The Chinese developed aquaculture systems several
thousand years ago. These systems use the sewage/nutrients
and produce fish. Today China is the world’s leading
producer of farmed fish (Figure 1).
Another way of doing it is to separate the sewage at
source. Today, most sanitation systems mix faeces and
urine. In the human body, urine is separated from faeces.
If we keep it that way, we will get two valuable resources.
The faeces can be composted to produce biogas,
which in turn can be used for cooking or to generate
electricity. The urine can be used as fertiliser on farmland
or in greenhouses.
Table 1. Toilet water content
Urine
Faeces
Nitrogen (N) 5,6 kg 0,09 kg
Phosphorus (P) 0,4 kg 0,19 kg
Potassium (K) 1,0 kg 0,17 kg
Million tons
16
12
8
4
China
Developing countries
(without China)
Industrial countries
0
1984 1988 1996 2000
Figure 1. Aquaculture production by region 1984–1995.
Source: FAO
By implementing modern technology, a community
can be self-sufficient on energy and by using
existing resources, pollution of coastal waters can
be avoided and instead sewage can be used to
supply the community with food products. This
will strengthen the economy of the community,
as well as increase the quality of life. A better
environment will also strengthen the tourism. By
re-using the nutrients for food production and
fertilising plants, communities can support the
tourist resorts and thereby create a source of
income.
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