UCT project cleans river with stones and
A University of Cape Town project uses a natural, off-grid filtration system to clean 36,000 litres of polluted river water daily for irrigation in
Researchers from the University of Cape Town are cleaning 36,000 litres of polluted water every day using stones, heat-treated wood and sand. Without chemicals and using renewable energy, they treat water polluted by sewage, chemicals, and traces of drugs and medication from the Stiebeuel River. This makes the water usable for growing food in the fast-expanding Langrug informal settlement.
Kevin Winter, a researcher behind the Water Hub project, says the treated water is now used for growing vegetables to feed hungry children and residents. "You'd be very hard pressed to know the difference between it and your municipal treated water, which has been through a treatment plant and been chlorinated," he stated.
A Nature-Based Filtration System
The project built its system in an abandoned wastewater site, turning old drying beds into a network of filtration cells. It is off-grid, using solar power to pump water from the river into the cells. The water slowly filters through these cells over five days.
Large stones trap particles and chemicals first. A layer of biochar, wood burned at 800C (1,470F), filters out traces of drugs, pharmaceutical waste and ammonia. Final layers of smaller stones and sand absorb remaining toxins and pollutants.
From Pollution to Irrigation
Established in 2018, the project succeeded this year in reducing bacteria and pathogens to a level safe for irrigation, though not for drinking. Winter says the system removes about 99% of toxins before most water is released back into the river, where it feeds surrounding ecosystems.
About 3,000 litres is held back daily to irrigate food-producing gardens at the Water Hub. This provides a resource for a settlement whose population has grown from 3,000 to more than 26,000 people since 2006, mostly driven by seasonal work on farms and in the nearby town of Franschhoek.
Addressing Water Scarcity and Food Security
Winter links the project directly to climate adaptation. He argues that making water available for food security is a crucial climate-change strategy worldwide. The Western Cape faced an almost catastrophic water crisis in 2018, when reservoirs came close to running dry after an extended drought.
For months, households rationed water and about 31,000 farm workers lost their jobs. Winter warns the region will face prolonged periods of drought when food and access to water is scarce, alongside wildfires and flooding. The natural system is not designed to replace conventional treatment plants cleaning industrial-levels of water for towns and cities. It aims to provide clean water for rural communities.
The team took on the task after local water plants were stretched beyond capacity by Langrug's unplanned growth, which left residents without access to clean water or sewage facilities. Scientists behind the project think it could be a model for ensuring food security in the climate crisis, using treated water to feed ecosystems and irrigate community gardens.
