Outdoor microalgae‐based urban wastewater treatment: Recent advances, applications, and future perspectives

Abstract

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. This article is categorized under: Engineering Water > Engineering Water

A Review on the Reliability and the Readiness Level of Microalgae-Based Nutrient Recovery Technologies for Secondary Treated Effluent in Municipal Wastewater Treatment Plants

“…Depending on the environmental conditions, the effluent requirements and the specifics of the existing or newly designed WWTP, the studied algae-based wastewater treatment systems varied across a broad range of technological designs. Тhe treatment systems can generally be divided into three main groups-suspended, algal bead (active immobiliza-tion), and attached (passive immobilization) growth [39][40][41]. Each of these groups has specific reactor design variations (Figure 2).…”

“…The open suspended algal growth reactors include natural or artificial ponds. Perhaps the most investigated reactor configuration is the High Rate Algal Ponds (HRAP) that are usually formed into Raceway ponds [31,40]. These reactor designs consist of artificially constructed water beds that function in a continuous or batch mode [39,42,43].…”

A Review about Microalgae Wastewater Treatment for Bioremediation and Biomass Production—A New Challenge for Europe

“…These limits lead to low biological activity and odor problems, especially when climatic conditions are not optimal [35]. Finally, these systems have very long retention times and involve a lot of land availability, and for this reason they are used in rural areas due to the high availability of land [37].…”

“…Unlike HRAPs, closed systems such as PBRs have higher installation and operating costs but operate in controlled environments and result into better photosynthetic efficiency, which allows greater nutrient removal and more efficient biomass production [41]. However, the high operational cost of these systems make them unlikely to be used for sustainable wastewater treatment [37]. There are different types of PBRs, which exploit different types of technologies and are generally divided into horizontal and vertical.…”

Integration of Algal Biofuels With Bioremediation Coupled Industrial Commodities Towards Cost-Effectiveness

“…The nutrient removal efficiency of different microalgal strains and their productivities varied in different cultivation systems and wastewater types as illustrated in Table 2. The treatment efficiency of algae-based system and biomass productivity can be improved by operating parameters such as mode of cultivation (batch or continuous), aeration, changing water chemistry (pH, adding require nutrients) (González-Camejo et al, 2021). Further, different stresses like pH, temperature, salinity changes or nutrients reduction in growth media have been suggested to increase lipid yield for biofuel production (Bélanger-Lépine et al, 2018).…”