Decentralised wastewater treatment system in eThekwini (South Africa)

Circular and resilient water management in urban areas

agosto 2025

ICLEI-Local Governments for Sustainability

The eThekwini Metropolitan Municipality, situated on the east coast of South Africa, is the country’s third-largest city, with a population of 4.24 million (2022). Its steep, flood-prone coastal terrain is exposed to increasing hydrological risks, including drought and storm damage. During the 2014–2016 drought, flow restrictors were installed on more than half a million water connections to manage demand. In 2022, severe flooding damaged roads and wastewater treatment infrastructure, causing sewage discharges into the Umbilo River and the prolonged closure of beaches due to dangerous levels of E. coli. These repeated crises, combined with rapid urbanisation and the expansion of informal settlements, prompted eThekwini’s water and sanitation department to explore more resilient and decentralised approaches to wastewater management.

The DEWATS (Decentralised Wastewater Treatment Systems) programme was developed to address these challenges by deploying modular, gravity-fed, decentralised wastewater treatment plants in Durban’s informal settlements. This system, developed in partnership with BORDA (Bremen Overseas Research & Development Association) and the University of KwaZulu-Natal (UKZN), aims to enhance water resilience, protect public health and watercourses, whilst recovering water, energy and nutrients for sustainable management. The Newlands-Mashu pilot site, operational since 2014, treats up to 41,000 litres of domestic wastewater per day for 84 households (750 users).

Solutions implemented

• Modular DEWATS system : Comprises a two-chamber settling tank, three parallel baffled anaerobic reactors, two anaerobic filters and a hybrid wetland system (vertical flow to remove ammonia and horizontal flow to refine treatment).

• Gravity-fed operation : No electricity is required, ensuring continuity of service even in the event of a power cut – a major advantage in areas prone to frequent power cuts.

• Biogas capture : The methane-rich biogas produced during anaerobic digestion is captured and used for cooking or heating, thereby creating a local source of renewable energy.

• Reuse of effluent : Treated wastewater is used in automated drip irrigation systems for food crops such as bananas and taro, thereby reducing the demand for fresh water and commercial fertilisers.

• Sludge composting : Scum and sludge are composted in drying beds, producing nutrient-rich compost that is reused in local agriculture and landscaping.

Key findings

• Wastewater treatment and recycling : up to 41,000 litres of domestic wastewater are treated daily and reused for non-potable purposes, such as agricultural irrigation.

• Improved water quality and environmental health  : compared with untreated effluent, the water discharged by the DEWATS contains 85 per cent fewer organic pollutants and 75 per cent fewer suspended solids, thereby reducing the risk of eutrophication and improving aquatic biodiversity in adjacent watercourses, such as the Umgeni River.

• Improvement in public health : the reduction in discharges of raw sewage during floods has led to a reduction in the number of cases of E. coli contamination. Long-term monitoring of the Newlands-Mashu DEWATS demonstration site shows a 98.4 per cent reduction in the presence of E. coli between raw effluent and treated effluent.

• Food security : the use of treated wastewater for irrigation boosts agricultural productivity, thereby contributing to the community’s food security.

• Enhancing water resilience : at other sites, DEWATS improve water resilience during droughts and crises by enabling the reuse of treated wastewater for non-potable purposes, such as flushing toilets, thereby ensuring a reliable and safe water supply for essential needs.

Climate and environmental impacts

• Climate change mitigation : DEWATS systems capture methane from wastewater for cooking or heating, thereby reducing dependence on fossil fuels. They operate without electricity, which reduces demand on the electricity grid and lowers greenhouse gas (GHG) emissions. Compared with conventional centralised wastewater treatment plants, DEWATS generate significantly fewer GHG emissions thanks to their low energy consumption and simpler biological treatment processes.

• Climate adaptation and resilience : DEWATS operate entirely by gravity, without pumps or an external power supply, ensuring uninterrupted treatment in the event of power cuts, flooding or other disruptions.

Their decentralised design allows wastewater to be treated locally, thereby reducing pressure on centralised infrastructure and preventing sewer overflows during extreme weather events, such as floods.

• Biodiversity : The Newlands-Mashu DEWATS system removes 95 per cent of organic pollutants and 75 per cent of suspended solids from wastewater, thereby reducing the nutrient and sediment loads discharged into neighbouring watercourses, such as the Umgeni River. This creates healthier ecosystems and increases the diversity of aquatic, animal and plant species.

Success factors

• Values :

  - Recognising domestic wastewater as a source of water, energy and nutrients, rather than simply as waste to be disposed of.

  - Awareness of the benefits of decentralised, human-scale systems for building climate resilience and reducing vulnerability to disruptions.

• Connections :

  - Physical connections : DEWATS offer a modular, off-grid solution integrating wastewater treatment, reuse and resource recovery.

  - Social connections : The success of the initiative relies on knowledge-sharing and active community participation :

  Training and collaboration with local residents enable community-led management and maintenance of the system, fostering a sense of ownership.

  Regular communication through workshops and educational materials helps to promote a culture of wastewater reuse and resource recovery.

  A global network of researchers and practitioners, coordinated by BORDA, supports the implementation of DEWATS through forums, academic publications and technical exchanges.

• Investment : Low investment and operating costs, combined with community-managed operation and maintenance, create a viable economic model that can be replicated on a large scale.

Referencias

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