They save energy, absorb CO2 and produce sustainable fertilizers

This is how this innovative ecological sewage purification system works

The cult of beauty and personal hygiene of Classical Greece gave rise to one of the first wastewater treatment systems. This interest in removing waste and enjoying clean water extended to ancient Rome. The famous Cloaca Maxima It allowed waste to be eliminated from one of the most populated cities in the ancient world.

These advances were cut short during the Middle Ages. Very few cities preserved Roman sewer structures. The blind wells soon overflowed. And, although it seems crazy now, throwing the excrement out the window shouting “water goes!” It became a common practice. As you can imagine, in addition to conflicts between neighbors, this practice attracted countless pests and diseases.

Nowadays, in developed countries you no longer see wastewater flowing through the streets. But, as believers know, this does not mean that they do not exist. To see them, you only need to drive a few kilometers to any treatment plant operating on the outskirts of cities.

These facilities are responsible for removing contaminants from wastewater., allowing them to be poured or reused safely. They have been a great advance and are essential. However, the removed contaminants are not recovered and are expensive processes that demand a large amount of energy.

Microalgae: efficient and sustainable purifiers

In the era of climate change, wastewater regeneration is of vital importance for sustainable development. An old saying goes that you don’t miss the water until the well is dry. The truth is that the well is not dry yet, but little by little we are drying it out. The situation is already dramatic. One in three people does not have access to safe drinking water. About 4 billion people lack basic sanitation services. Besides, Polluted water is the leading cause of death worldwide.

In this situation, one of the main goals of the United Nations is to achieve universal and equitable access to water. Microalgae are called to be one of the keys to the integrated management of water resources. They allow us to purify wastewater with lower energy consumption and increase the sustainability of the process at the same time. They consume less energy because they carry out photosynthesis and, therefore, are nourished by sunlight.

Another enormous advantage of these microorganisms is that they consume carbon dioxide to produce and accumulate compounds of interest. Let us not forget that carbon dioxide is one of the main causes of climate change. These products of interest, for example agricultural biostimulants, allow benefits to be obtained where previously only costs were generated.

Their ability to purify wastewater gives them a dual role: allow to recover contaminants from wastewater and produce valuable compounds simultaneously. This is one of his greatest virtues. In processes based on microalgae, the word recover is the key. While nutrients and contaminants from wastewater are removed in conventional processes, microalgae have the ability to recover them.

These microorganisms They recover carbon, nitrogen and phosphorus from wastewater to reproduce and produce more individuals, or what is the same, biomass. We can use the biomass produced as an ecological and sustainable fertilizer or as an ingredient for animal feed.

Biostimulants based on microalgae are a guarantee of sustainability. They consume carbon dioxide during their production and They allow quality fruits and vegetables to be obtained with less consumption of fossil fertilizers and water.. Its use in feed is also sustainable. Not only do they improve animal health, they also minimize the need to import products such as soybeans.

Challenges for large-scale application

Wastewater purification using microalgae is a novel technology. It is still in development and faces a number of challenges.. Having an intense color, the microalgae shadow each other. Due to its need for light, it must be worked with shallow waters.

One of the main objectives of studies in this area is to increase the efficiency of these processes, allowing greater volumes of water to be purified in smaller reactors. Furthermore, very little is known about how environmental and working parameters affect the quality of the microalgae produced. This is vitally important, as it directly affects the quality of the final product.

Great efforts are also being made to understand how these organisms interact with bacteria. Bacteria are naturally present in wastewater and the environment. They collaborate with microalgae in water purification. Knowing this process in more detail will allow us to design more efficient and sustainable systems.

Wastewater has gone from being black water in the Middle Ages to black gold in the 21st century. Although there is still a long way to go, the results obtained to date are promising. There are already cities like Chiclana, in Andalusia, that use microalgae purifiers. One of the largest microalgae treatment plants in Europe is being built in Mérida thanks to the project H2020 SABANA. Little by little we will learn to take advantage of the great advantages that these small and valuable living beings offer us.

Ana Sánchez Zurano is a researcher in Biotechnology, University of Almería

Tomás Lafarga is a researcher in the area of ​​Chemical Engineering, University of Almería Article originally published in

The Conversation

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