South Africa: This South African River Has a Bacteria Count Off the Charts - a Natural Filter Is Cleaning It for Watering Food Gardens

Every day, vast amounts of polluted water flow into South African rivers, eventually finding their way to the sea. In Franschhoek, South Africa, the Stiebeuel River in the Langrug informal settlement is severely contaminated due to inadequate sanitation and drainage systems for the 26,000 residents. Water researcher Annabelle van der Walt from the University of Cape Town's Future Water Institute explains how her team is using nature to treat and reuse water.

Van der Walt and her colleagues set up a natural water filtering system in an old wastewater treatment plant. They transformed drying beds into filter beds filled with stones, biochar, and coarse sand. The polluted water from the Stiebeuel River slowly passes through these filters, removing bacteria and nutrients. After five days, the water becomes safe for irrigation.

The naturally treated water contains no E. coli bacteria, indicating it's no longer contaminated. It also removes 85% to 95% of ammonia and phosphorus from the river, which are trapped in the filter beds. Plants absorb excess nutrients, further cleaning the water before it returns to the river or is used for irrigation.

This nature-based water treatment system is effective in removing pollutants and providing a safe water source for irrigation. However, it cannot replace traditional wastewater treatment plants due to the volume of water from towns and cities. Yet, the benefits of nature-based systems are evident. They can help municipalities facing rising electricity costs, deteriorating infrastructure, and limited technical skills.

The Stiebeuel River, once a bathing spot, now serves as a dumping ground for solid waste and carries high levels of E. coli bacteria, excessive ammonia, and phosphorus. Microplastics and traces of medicines have also been detected. These pollutants lead to declining water quality, increased treatment costs, and greater pressure on limited freshwater supplies.

The biofiltration system built by Van der Walt's team treats 50,000 litres of contaminated water daily, with 3,000 litres used for irrigating vegetable gardens managed by young women from the informal settlement. These gardens offer skills development, food production experience, and small-scale business opportunities. The remaining water is discharged back into the river, contributing to its cleaning and supporting plant life that further purifies the water downstream.

By decentralising water treatment, communities can improve water quality in areas where municipal service delivery is collapsing. Nature-based systems like the one at the Water Hub are cost-effective to set up and maintain with minimal skills required for daily operations. However, regular water quality monitoring and adjustments are necessary for optimal performance.