ENVIRONMENT and ENERGY
25
National water strategy:
water reuse case studies
By Extract from the NWRS 2 by the Department of Water and Sanitation
The cost of reusing water relative to other alternatives is one of the
most important factors that will determine water reuse decisions. It
is therefore important to understand the key factors that will affect
costs, how these vary between different applications of reuse, and
how they are likely to change over time, relative to other water
supply alternatives.
An understanding of how these costs might be reduced
to make water reuse more economically attractive is
also required. The key determinants of cost are location,
water quality, treatment technology, and volume (scale).
Because the possible applications of water reuse (and hence
the appropriate treatment technologies to be used) are very
extensive, it is not feasible to discuss these exhaustively or
in any detail here. Instead, five main applications of water
reuse are discussed in the form of ‘case studies’, with the
understanding that the approaches and principles emerging
from these cases can be applied to other similar water reuse
applications. The five ‘case studies’ are:
• The use of treated municipal wastewater for urban uses
• The use of treated municipal wastewater for industrial use
• Rethinking household sanitation and grey water
• The direct reuse of treated municipal wastewater for
potable use purposes
• The treatment of acid mine drainage.
Using treated municipal wastewater
for urban uses
The reuse of treated wastewater for urban applications,
such as public parks, sports fields, and golf courses, could
replace the use of freshwater. The construction and operation
of a separate recycled water reticulation system is relatively
expensive and has been an impediment to implementation.
Water reuse systems (‘purple pipes’) have, however, been
successfully implemented in many countries with appropriate
controls and safeguards. The concept of small scavenging
wastewater treatment plants, taking wastewater from the
sewers and producing a water fit for reuse at the local point of
the water requirement, may be more cost-effective. Municipal
by-laws would have to be adapted to encourage and better
regulate such reuse of water.
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Use of treated municipal wastewater
for industrial uses
Several successful projects to reuse treated municipal
wastewater for industrial processes are in operation in
South Africa (refer to Appendix A of the original document).
These projects typically involve a large wet industry,
such as a steel mill or pulp/paper mill, linked to a source
of treated wastewater. The concept is well established
and the project drivers are a combination of the factors
listed in section 3.1 of this document. Some innovative
implementation models involving private sector financing,
operation, and maintenance are available. Since an
industry is involved, private sector resources can be readily
deployed to implement such water reuse projects.
Rethinking household sanitation
and grey water
Conventional waterborne sanitation uses potable standard
water to wash away human faeces, in the process
combining good quality water with potentially valuable
resources (faeces and urine) to create polluted water
that needs to be treated. This is not an efficient system
in a context where fresh water is scarce and precious
and where fertilizer inputs for agriculture productivity are
limiting. As resource scarcity and prices change over time,
it may make increasing sense to rethink our conventional
sanitation solutions and to invest in more environmentally
friendly and sustainable alternatives. Similarly, the
implications of current practices of adding phosphates to
detergents and soaps used in washing processes, and then
combining this water (grey water) with domestic sewage
will need to be carefully considered. These practices are
likely to need to change in future as fresh water becomes
more valuable and the cost of treating polluted water
resources becomes higher.
July 2017 Volume 23 I Number 5