Removal pathways and mechanism of NO by Tetradesmus obliquus PF3 culture-based DeNOx system

Microalgae-based DeNOx technology, as an emerging approach for flue gas denitrification, is suitable for the deep treatment of NOx at medium to low concentrations. To address the ambiguity surrounding the removal pathways and mechanisms in the development of microalgae DeNOx technology, the pathways and mechanisms of NO removal within a microalgae cultivation system was investigated. By investigating the gas-liquid and liquid-solid nitrogen transfer pathways facilitated by algal cells, algal cells were found to play a pivotal role in NO removal by the T. obliquus PF3 cultivation system. Microalgae cells enhance NO transfer across gas-liquid phases via extracellular substance secretion, exogenous iron reduction, NO adsorption, and NO molecular absorption. During this process, NO is transformed in the liquid phase into molecular NO, ionic nitrate, and nitrite, as well as organically complexed NO. The soluble extracellular substances of T. obliquus PF3 are primarily composed of humic-like acids and fulvic-like acids, while bound extracellular substances are dominated by tryptophan and tryptophan-like proteins, both of which possess reductive properties conducive to iron reduction and NO adsorption/complexation. By employing ATP hydrolysis inhibitor HgCl₂ and analyzing nitrogen balance in the system, It was revealed that the primary NO removal pathway involves NO dissolution and oxidation within the algal culture broth, with ionic nitrogen being the predominant form assimilated and utilized by algal cells from the solution. This study clarifies the NO removal pathways and mechanisms within the microalgae cultivation system, thereby providing a theoretical foundation for the advancement and process design of microalgae-based DeNOx technology.