Outdoor Microalgae-Based Urban Wastewater Treatment: Recent Advances, Applications, And Future Perspectives

Although microalgae-based wastewater treatment has been traditionally carried out in extensive waste stabilization ponds, recent trends focus on the use of microalgae to apply the circular economy principles in the wastewater treatment sector due to the capacity of algae to absorb carbon dioxide while recovering nutrients from sewage. To this aim, the development of new intensive microalgae-based systems with higher efficiency and level of process control is required. Results obtained for these systems at lab scale are generally promising. However, upscaling to outdoor conditions is often uncertain. Some advances have been made in terms of applying open systems at large scale. However, there are still some issues related to land requirements and the economic feasibility and robustness of the process that have to be overcome to widely implement these systems. This article aims at describing the main design and operating factors regarding outdoor microalgae cultivation. It will also explain some microalgae cultivation technologies to treat wastewater, showing their advantages, disadvantages, and the possibility to treat different wastewater streams with microalgae cultures. Future perspectives of this biotechnology will be commented as well.