UCT cleans river water for Langrug food
A University of Cape Town project uses a natural, off-grid filtration system of stones, biochar, and sand to clean 36,000 litres of polluted river water
Researchers from the University of Cape Town are cleaning 36,000 litres of polluted water every day without chemicals. They use a system of stones, heat-treated wood, and sand to make the water usable for growing food in the Langrug informal settlement near Stellenbosch. The water, polluted by sewage, chemicals, and traces of drugs, is treated using renewable energy.
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. He stated that one would be very hard pressed to know the difference between it and municipal treated water. The project, established in 2018, only succeeded this year in reducing bacteria and pathogens to a level safe for irrigation, though not for drinking.
The Filtration Process
The system was built 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 Stiebeuel River into the cells where it filters slowly 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. Smaller stones and sand absorb the remaining toxins and pollutants.
Winter says the system now removes about 99% of the toxins before most of the 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.
Project Development and Impact
Winter has worked in the area since 2006. He has seen Langrug's population grow from 3,000 to more than 26,000 people, driven by seasonal farm work and jobs in nearby Franschhoek. This unplanned growth left residents without clean water or sewage facilities. Local water plants were stretched beyond their capacity, so Winter's team took on the task.
Context of Water Scarcity and Future Model
The Western Cape faced a severe water crisis in 2018 when reservoirs nearly ran dry after an extended drought. Households rationed water and about 31,000 farm workers lost their jobs. Winter argues this natural system is a crucial climate-change strategy for food security. He says climate in the next 30 years, particularly in our region here, is going to look very, very different, with prolonged periods of drought when food and access to water is scarce.
He notes the filtration system is not designed to replace conventional plants cleaning industrial-levels of water for towns and cities, but that it does provide clean water for rural communities. The scientists behind the project think it could be a model for ensuring food security in the climate crisis worldwide. Winter says making water available for food, and for food security, as a climate-change strategy is absolutely crucial worldwide and we have got to learn to be able to do that more and more.
