Classical Greek ideas about beauty and personal hygiene laid early groundwork for urban wastewater systems. The drive to keep water clean goes back to ancient Rome, where the Cloaca Maxima played a pivotal role in removing waste from one of the era’s largest cities.
Those advances faded during the Middle Ages. Few cities preserved Roman sewer structures, and overflowing blind wells became common. In a way that seems strange today, some people threw feces out their windows and shouted that the water would take care of itself. This practice brought pests, disease, and neighborhood conflicts in its wake.
Today, in developed countries, street-level wastewater is no longer visible. Yet the truth remains: wastewater still exists. To glimpse it, one only needs to visit a treatment facility located just beyond urban boundaries.
In this painting you can see the Cloaca Maxima of Rome. Christoffer Wilhelm Eckersberg / National Gallery of Art
These facilities remove contaminants from wastewater, enabling safe disposal or reuse. They mark significant progress and authority in public health. However, the contaminants removed are not recovered by these processes, and the operations require substantial energy and investment.
Microalgae: efficient and sustainable purifiers
Amid climate change, regenerating wastewater becomes essential for sustainable development. A common saying persists: water is not scarce until the well runs dry. The well may not be dry yet, but the pressure on it is growing. The situation is urgent: about one in three people lack access to safe drinking water, and roughly four billion people lack basic sanitation. Dirty water remains a leading cause of death worldwide.
Against this backdrop, the United Nations prioritizes universal, equitable water access. Microalgae are highlighted as a key element in integrated water resource management. They enable wastewater treatment with lower energy input while boosting process sustainability, largely because they rely on photosynthesis fueled by sunlight.
microalgae reactor Ana Sanchez
Another major advantage is that these microorganisms consume carbon dioxide, helping address one of the major drivers of climate change. They can produce and accumulate compounds of interest, including agricultural biostimulants, turning costs into benefits and opening new supply chains for sustainable agriculture.
The dual role of microalgae in wastewater purification and biomass production stands out. In algae-based systems, the concept of recovery is central. While conventional methods remove nutrients and pollutants, microalgae can restore them and transform them into useful products.
These tiny organisms sequester carbon, nitrogen, and phosphorus from wastewater to grow biomass, which can be used as eco-friendly fertilizer or a sustainable ingredient in animal feed. Algae-based biostimulants offer a clear path to sustainability and can reduce reliance on fossil fuels and imported feed ingredients.
Algal biostimulants support greener crops with less fertilizer and water, while feed uses help cut imports of crops like soy. This adds resilience to farming systems and supports local economies.
Challenges of large-scale implementation
Wastewater purification with microalgae is a relatively new field that continues to develop. Algae can struggle with intense color, and light exposure requires shallow water to keep cells illuminated for growth.
Researchers aim to boost the efficiency of these processes so that larger volumes can be treated with smaller reactors. They also seek to understand how environmental and operating parameters affect the quality of the produced algae, a factor that directly influences the final product quality and performance.
Research with microalgae in the laboratory A. Sánchez
Great effort is also going into understanding how microalgae interact with bacteria. Bacteria thrive in wastewater and the surrounding environment, and their collaboration with microalgae can enhance purification. A deeper grasp of this relationship will guide the design of more efficient, sustainable systems.
While wastewater was once thought of as mere waste, today it can become a valuable resource in the hands of modern science. The progress is real, and the gains are meaningful. Cities like Chiclana in Andalusia have begun using microalgae purifiers, and the H2020 SABANA project is funding one of Europe’s largest microalgae treatment plants in Mérida. As researchers and engineers continue to explore these solutions, the benefits of these small, remarkable organisms become clearer.
Ana Sánchez Zurano is a researcher in Biotechnology at the University of Almería. Tomás Lafarga is a researcher in Chemical Engineering at the University of Almería. The article was originally published in The Conversation.
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Contact details for the environmental department were previously provided for outreach. The content here focuses on the science and strategy behind wastewater purification with microalgae, offering a current view of the field and its potential for practical application in diverse settings.
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