Author: Fabio Magrassi
Microalgae can remove nutrients from wastewater, such as phosphorous (P) and nitrogen (N), which are major contributors to eutrophication. Eutrophication is a process in which bodies of water become overloaded with nutrients, leading to excessive growth of algae and other aquatic plants. This can cause several negative impacts, including reduced oxygen levels in the water, changes in the species composition of aquatic communities, and even fish kills. Microalgae are a diverse group of photosynthetic microorganisms that can remove pollutants from wastewater through a process known as biofiltration. This process involves the growth of microalgae in a treatment system where they can remove pollutants such as nutrients, heavy metals, and organic compounds, through uptake and metabolism from the wastewater. Several different technologies can be used to grow microalgae for wastewater treatment, each with its advantages and disadvantages. Some of the most common technologies include:
Open ponds: Open ponds are the simplest and most common technology used to grow microalgae. They consist of large tanks or lagoons that contain microalgae and wastewater. Open ponds are relatively inexpensive to construct and operate and can be easily scaled up to treat large volumes of wastewater. However, they also have some drawbacks, such as the need for large land areas, the potential for contamination with other microorganisms, and difficulty in controlling the growth conditions of the microalgae.
Photobioreactors (PBRs): Photobioreactors are closed systems that use light to enhance the growth of microalgae. They can be designed to suit different needs such as tubular, flat panel, vertical and horizontal configurations. PBRs can be used to control the growth conditions of the microalgae, such as light intensity, temperature, and nutrients, which can improve the efficiency of the treatment process. However, PBRs are also more complex and expensive to construct and operate compared to open ponds.
Hybrid systems: Hybrid systems are a combination of open ponds and photobioreactors. They use the advantages of both technologies to optimise the growth of microalgae. For example, microalgae can be initially grown in open ponds and then transferred to photobioreactors for further growth and treatment. This approach allows for the use of low-cost open ponds to grow the microalgae, while also using photobioreactors to control the growth conditions and improve the efficiency of the treatment process.
Biofilm systems: Biofilm systems use a thin film of microalgae attached to a solid support, such as a plastic sheet, to treat wastewater. These systems can be used to treat both liquid and gaseous wastewater and can be easily scaled up to treat large volumes of wastewater. They also have the advantage of being able to operate at high biomass concentrations and low hydraulic retention times, which can improve treatment efficiency.
Integrated systems: Integrated systems combine different technologies such as microalgae cultivation with other treatment methods like membrane filtration, ozonation, and advanced oxidation processes. These systems can be used to remove a wide range of pollutants from wastewater and are very flexible in terms of their application.
The choice of technology depends on the specific characteristics of the wastewater and the goals of the treatment process. Each technology has its advantages and disadvantages. In FRONTSH1P we will be treating wastewater of many different natures and we need to have a modular, and scalable system that can be moved to a different location to finalise different tests. The most appropriate technology is the Photobioreactors (PBRs) that will be built in a commercial container equipped with an artificial lighting system specifically studied and developed for this purpose.
Another advantage of using microalgae for wastewater treatment is that they can use CO2-rich gases as a source of carbon. These gases can be obtained from industrial sites, where they are often emitted as a by-product of various processes. Using CO2-rich gases as a source of carbon has several benefits:
Increased growth potential: CO2-rich gases can be used to increase the growth potential of microalgae, leading to improved treatment efficiency. By providing a source of CO2, the microalgae can photosynthesize more efficiently, resulting in higher biomass production and more effective pollutant removal.
Reduced costs: CO2-rich gases can be obtained from industrial sites, where they are often emitted as a by-product of various processes. Using these gases as a source of carbon can reduce the overall costs of the treatment process, as they are typically cheaper than other sources of carbon such as liquid carbon sources.
Reduced greenhouse gas emissions: CO2-rich gases are a major source of greenhouse gas emissions and using them as a source of carbon for microalgal treatment of wastewater can help to reduce these emissions. By capturing CO2 from industrial sources and using it for microalgal growth, it is possible to reduce the overall amount of CO2 released into the atmosphere.
Improved treatment efficiency: The use of CO2-rich gases can improve the efficiency of the treatment process by increasing the growth potential of microalgae, leading to more effective pollutant removal, and potentially reducing the size of the treatment system.
It is important to note that the use of industrial CO2-rich gases as a source of carbon in microalgal treatment of wastewater is still an emerging technology and one of the FRONTSH1P Circular Systemic Solution 3 aims is to fully understand its potential and limitations. In conclusion, the use of microalgae for wastewater treatment is a promising technology that can remove pollutants and reduce the eutrophication potential of wastewater. The use of CO2-rich gases as a source of carbon can increase the growth potential of microalgal biomass, making the process more efficient.