National water strategy: water reuse case studies

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.

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.

A limited number of countries in the world have implemented urine separation and collection systems, with the aim of nutrient (nitrogen, phosphorous and potassium) recycle to agriculture.

Changing household practices at this fundamental level may have significant implications for water use and the availability of wastewater for reuse in the long term. A water reuse strategy that is forward thinking over ten to twenty years needs to take these possible changes into account. The economic tipping point for the implementation of alternative household sanitation approaches will dictate the speed of change.

Direct reuse of treated municipal wastewater for potable purposes

The direct reuse of treated municipal wastewater for potable purposes is practised at a limited number of locations in the world. The knowledge of municipal wastewater composition and sophisticated treatment technologies has advanced to the point where this can be considered as an option in the spectrum of water supply alternatives. Specific opportunities exist in the coastal communities and cities where treated municipal wastewaters are discharged to the ocean, effectively losing an opportunity for water reuse. The implementation of such direct reuse projects will, however, have to overcome perceptions and risks related to public acceptance, trust in scientific knowledge and engineered systems, trust in water supply authorities, social justice, and fairness. Direct reuse of treated municipal wastewater for potable purposes would only be practical where sophisticated technology, competent operational and management systems, and safeguards are in place to protect the public health.

Treatment of acid mine drainage

Acid mine decant or drainage is a potentially important source of water for reuse. This water must be treated to limit current and future environmental damage to water resources, and can be treated for reuse for industrial and even potable water use purposes. Several AMD treatment and reuse projects have now been implemented in South Africa, demonstrating the technical feasibility, financial viability, and stakeholder acceptance of such projects. Challenges remain to address the issues of appropriate and long-term (post mine closure) operation and maintenance of such AMD reuse schemes. AMD treatment and reuse projects could utilise the large storage available in mining workings, do not have to contend with evaporation loss of water, and can deliver reclaimed water in proximity to several large urban areas, such as the Witwatersrand and Mpumalanga Highveld.

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