A review: Biological technologies for nitrogen monoxide abatement

Nitrogen oxides (NO_x), including nitrogen monoxide (NO) and nitrogen dioxide (NO₂), are among the most important global atmospheric pollutants because they have a negative impact on human respiratory health, animals, and the environment through the greenhouse effect and ozone layer destruction. NO_x compounds are predominantly generated by anthropogenic activities, which involve combustion processes such as energy production, transportation, and industrial activities. The most widely used alternatives for NO_x abatement on an industrial scale are selective catalytic and non-catalytic reductions; however, these alternatives have high costs when treating large air flows with low pollutant concentrations, and most of these methods generate residues that require further treatment. Therefore, biotechnologies that are normally used for wastewater treatment (based on nitrification, denitrification, anammox, microalgae, and combinations of these) are being investigated for flue gas treatment. Most of such investigations have focused on chemical absorption and biological reduction (CABR) systems using different equipment configurations, such as biofilters, rotating reactors, or membrane reactors. This review summarizes the current state of these biotechnologies available for NO_x treatment, discusses and compares the use of different microorganisms, and analyzes the experimental performance of bioreactors used for NO_x emission control, both at the laboratory scale and in industrial settings, to provide an overview of proven technical solutions and biotechnologies for NO_x treatment. Additionally, a comparative assessment of the advantages and disadvantages is performed, and special challenges for biological technologies for NO abatement are presented.