Understanding Cape Town’s wastewater system
Being able to meet the city’s water and sanitation demands requires a sound and efficient wastewater management system. Wastewater is defined as any water that enters the sewerage system that then passes to a wastewater treatment plant to be processed. This water includes wastewater that is produced by bathing, showering, washing clothes and dishes, flushing toilets, and industrial and commercial effluent. Processing this water is required by the National Water Act (NWA) of 1998 and is essential to maintain human and environmental health as the quality of wastewater discharges can drastically affect ecosystems, human well-being, and the economy. Therefore, the City follows national standards for sanitation and performs wastewater treatment in an environmentally sound and hygienic manner.
Treated effluent and treatment by-products can be highly valuable resources, and can be recycled and reused in various ways. However, wastewater management can also be challenging. Wastewater management is linked to the entire water system of the city which has a total of 20 000 kms of pipes and sewer reticulation network. The treatment and reuse of wastewater is recognised as a vital component in adapting to Cape Town’s limited water supply in the face of drought, rapid urbanisation, and population growth.
Wastewater is treated in various ways due to it containing multiple different pollutants and contaminants, such as bacteria and other pathogens, organic compounds and organic matter, synthetic chemicals, nutrients and heavy metals. Regulation of what pollutants or contaminants enter the water system is vital as some substances can adversely affect treatment processes. Furthermore, wastewater can contain high levels of nutrients such as nitrates and phosphates. High concentrations of these compounds can lead to excessive growth of algae and water plants, creating an imbalance in aquatic ecosystems known as eutrophication. If left untreated, wastewater also contains high levels of bacteria, viruses, and helminths (worms) that can cause the spread of disease.
Cape Town’s wastewater treatment works
There are 26 wastewater treatment works (WWTWs) in Cape Town, which are also commonly called sewage works. The treatment of wastewater is as follows:
- Preliminary treatment: Screening to remove all materials that can be easily collected from raw sewage. Non-biodegradables are removed through processes of screening and grit removal.
- Primary treatment: A physical process that may involve maceration and sedimentation.
- Secondary treatment: A biological process, through solar and other energy, bacteria, algae and a variety of aquatic biota, to remove organic matter.
- Tertiary treatment: Remove remaining bacteria and viruses through disinfection techniques.
The outputs of this treatment process are as follows:
- The majority of treated effluent is released into rivers, canals, vleis or the ocean, and is absorbed into the environment.
- A portion is reused by industry and for watering golf courses and sports fields, as it is much cheaper and more environmentally sustainable than using potable water.
- Sludge or bio-solids left over from the purification process, depending on its composition, are either used or disposed of. ‘Activated’ sludge is dewatered and applied to agricultural land and ‘primary’ sludge is sent to landfill.