Applications, challenges and prospects on efficient and reliable bacterial-algal symbiosis system for wastewater treatment: A systematic review

Human activities have increased pollutant emissions and damaged ecosystems. The use of microalgae-bacteria symbiosis systems in dealing with the adverse effects of pollutants has gradually attracted people's attention. Compared with single bacteria or algae, the synergistic effect between bacteria and algae could enhance the removal ability of pollutants and the adapt to the environment. However, high environmental requirements and challenges such as maintaining stable algal symbiotic system activity under fluctuating wastewater composition have potentially limited their widespread application. Therefore, this review focused mainly on the bacterial-algal system and summarized its role in urban, industrial and aquaculture wastewater, as well as its outstanding advantages in biomass energy production. The main influencing factors were explored, and the advantages and disadvantages of different types of reactors were compared. Moreover, this paper highlighted the system's superior sustainability, efficient removal of emerging pollutants and heavy metals, and the dual benefits of carbon emission reduction and resource recovery, thereby solving these problems. Comprehensive analysis showed that the use of bacteria and algae systems to treat wastewater was significantly better than the traditional activated sludge method. The bacterial and algal system exhibited strong adaptability to different water qualities and could produce mainstream biomass energy such as biohydrogen, biodiesel and bioethanol. In addition, environmental factors played important roles in the efficient operation of bacterial and algal systems. This review was dedicated to accelerating the mature application of bacterial-algal systems in industry.