In the rural South African town of Motetema, untreated sewage once overwhelmed outdated wastewater ponds and flowed directly into nearby rivers, threatening both public health and fragile ecosystems. But after a year-long experiment led by a team of scientists, that same sewage is now being cleaned naturally and safely using nothing more than sunlight, water, and algae.
The groundbreaking project used phycoremediation—the application of photosynthetic microalgae to clean domestic wastewater without the use of electricity or chemicals. In doing so, it offers a sustainable and replicable blueprint for communities across Africa that are grappling with a growing sanitation crisis and limited infrastructure.
“Across Africa, many rural communities face a growing sanitation crisis. Wastewater treatment systems, where they exist, are often old, overloaded, or broken. In some towns, untreated sewage flows directly into rivers, contaminating water sources and harming both ecosystems and public health,” wrote Yolandi Schoeman, an ecological engineer and post-doctoral fellow at University of the Free State.
Conventional wastewater treatment relies on complex mechanical plants that require electricity, skilled operators, and costly chemical inputs—resources often in short supply in rural areas. In response, researchers led by environmental management professor Paul Oberholster turned to nature for a simpler and more resilient solution.
The team traveled to Limpopo province and worked with the Motetema Wastewater Treatment Works, a system designed for far fewer households than it currently serves. The researchers introduced two fast-growing microalgae species, Chlorella vulgaris and Chlorella protothecoides, into the treatment ponds. These algae were carefully selected after testing dozens of strains for their ability to absorb nutrients like nitrogen and phosphorus from wastewater.
To ensure a reliable algae supply, the team cultivated large amounts in photobioreactors—transparent tanks that provide optimal light and conditions for growth. After insertion into Motetema’s ponds, the algae began photosynthesizing, producing oxygen that enabled aerobic bacteria to break down organic matter such as human waste and food residue.
The results were dramatic. Within a year, the system achieved a 99 percent reduction in ammonia, an 83 percent reduction in orthophosphate, and a 73 percent reduction in total nitrogen. Before this intervention, the ponds often released effluent directly into the environment. Now, the treated water met environmental safety standards and could be safely discharged.
“This is a sustainable, low-cost approach to wastewater treatment that can improve public health and the environment in small towns, especially those with limited infrastructure and unreliable electricity. And it’s especially important to find ways of cleaning wastewater that don’t cost much or use electricity because climate change increases water stress and energy costs across the continent,” Schoeman wrote.
Motetema, a town of roughly 11,000 people, has twelve wastewater treatment ponds. Six operate while the others undergo cleaning. The system treats around 4.5 million liters (1.19 million gallons) of sewage per day—nearly double its intended capacity. Like many towns in South Africa, Motetema faces a wastewater system that is underfunded, outdated, and stressed by a rising population.
“Across South Africa, wastewater treatment plants are outdated, underfunded and rarely enlarged to cope with population increases. Many towns already use pond systems for wastewater treatment,” Schoeman noted. “These systems often underperform because of electricity cuts, poor maintenance and limited budgets for the necessary chemicals. There is also a lack of skilled operators. But algae don’t need salaries or power. With the right strains, simple culturing, and periodic injection into the ponds, these can become effective wastewater systems.”
Phycoremediation is not a new concept—algae-based systems have been used in parts of the U.S., Europe, India, and Central Asia for decades. What makes the Motetema pilot distinct is its tailoring to local conditions, strategic algae selection, and its execution in a real-world, overburdened setting.
Still, the process is not without challenges. In Motetema, the project encountered duckweed overgrowth that blocked sunlight, seasonal wildfires that damaged piping, peak-hour sewage surges, and sludge accumulation that slowed purification. These issues are manageable, but they underscore the need for regular maintenance and reinjections of healthy algae.
Phycoremediation systems require space and time. Each treatment pond covers nearly 40,000 square meters (430,556 square feet), and the algae need two to three weeks to clean the wastewater. These parameters make the method especially viable for rural regions with available land but limited budgets.
Beyond sanitation, this model offers broader environmental benefits. Phycoremediation helps prevent the creation of “dead zones”—areas in rivers or lakes where oxygen is so depleted that aquatic life cannot survive. It also recasts wastewater as a resource that, once treated, could be reused for agriculture, fish farming, or even groundwater recharge.
“Phycoremediation also challenges how we think about wastewater. Rather than treating it as a burden, it becomes a resource, something that can be cleaned and reused to support agriculture, fish farming, or even to recharge groundwater,” Schoeman wrote.
The study, titled Is Africa Ready to Use Phycoremediation to Treat Domestic Wastewater as an Alternative Natural Base Solution? A Case Study, was published in the journal Phycology. With the right support from governments and municipalities, its findings could serve as a catalyst for a new generation of nature-based sanitation systems across Africa—ones that are not only affordable and effective, but resilient in the face of climate change.
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