Microalgae Shed Light on Interconnected Nitrogen Transformation in Microalgal-Bacterial Consortia

Nitrogen is a component of many fundamental biomolecules and also participates in environmental redox chemistry. Nitrogen pollution is a serious environmental problem. Biological nitrogen removal is one of the most significant issues in wastewater treatment. Microbial-driven nitrogen transformations are carried out through metabolic pathways. Wastewater treatment systems using microalgal-bacterial cocultures can improve nutrient removal efficiency through interspecies synergistic interactions. However, relevant studies on the nitrogen metabolism and microbial characteristics of microalgal-bacterial systems have not been systematically reviewed and discussed. This Review comprehensively analyzes nitrogen contaminants in various biological nitrogen removal microalgal-bacterial composite systems and summarizes the microbial characteristics and nitrogen-metabolizing enzymes present. Nitrogen metabolism regulation methods involving quorum sensing and genetic regulation are described, and methods of enhancing microbial nitrogen removal through microbial community interactions, enhancing enzyme activity, and promoting electron transfer are introduced in detail. This Review provides a perspective on the improvement and optimization of microalgal-bacterial wastewater treatment technology through analyzing the nitrogen metabolism and increasing process performance.