This South African river has a bacteria count off the charts: A natural filter is cleaning it for watering food gardens

South Africa's Stiebeuel River in Franschhoek, about 47 miles east of Cape Town, suffers from severe pollution due to inadequate sanitation and drainage systems. About 26,000 residents in the nearby informal settlement of Langrug generate significant sewage and polluted rainwater runoff. A team of water researchers at the University of Cape Town's Future Water Institute and the Water Hub in Franschhoek developed a natural water-filtering system to clean the river water for irrigation purposes.

The researchers repurposed old drying beds from a former wastewater treatment plant as filtration beds, filling them with small stones, biochar, and coarse sand. These natural filter systems effectively removed pollutants such as bacteria and nutrients from the contaminated river water. After five days, the water was clean enough for irrigation, with E. coli bacteria levels consistently at zero, meaning it was no longer contaminated by human or animal waste.

Additionally, the system removed up to 95% of ammonia and phosphorus, essential nutrients that contribute to river and dam pollution.

While nature-based systems cannot fully replace conventional wastewater treatment plants due to the large volume of water from towns and cities, they offer a cost-effective and sustainable solution for municipalities facing rising electricity costs, deteriorating infrastructure, and limited technical skills. This decentralized approach can help communities better manage limited water supplies, particularly in areas affected by drought and climate change.

In the Stiebeuel River, local residents cannot use the water due to extremely high E. coli levels (above 400,000 colony-forming units per 100 mL) and high concentrations of ammonia and phosphorus. These pollutants, primarily from household cleaning agents, can trigger harmful algal blooms, depleting oxygen levels in rivers and lakes.

The research demonstrates that a biofiltration system, mimicking the natural purification processes of wetlands, can effectively clean water without relying on energy-intensive treatments like chemical disinfection.

The treated water supports the irrigation of vegetable gardens managed by young women from the informal settlement, providing valuable opportunities for skills development and small-scale enterprises. The remaining treated water is discharged back into the river, playing a crucial role in maintaining water quality and supporting the health of the ecosystem.

Decentralized water treatment systems like this can be replicated in other communities, enabling local water quality improvements and strengthening water security while fostering food production, livelihoods, and resilience.