Microplastics Reduce Nitrogen Removal Efficiency in Wastewater Treatment Facilities

Basic Science Support Institute Research Team

Gyeonggi-do Ilsan Public Sewage Treatment Facility. Archive photo. Not related to the article.

[Asia Economy Reporter Kim Bong-su] It has been found that microplastics degrade the nitrogen removal capacity of wastewater treatment facilities.

The Korea Basic Science Institute (KBSI) announced on the 12th that Dr. Jeong Seul-gi's research team at the Seoul Center, in collaboration with the University of British Columbia research team, successfully confirmed the effects of microplastics on the nitrification process efficiency of wastewater treatment facilities and the expression of functional genes in microorganisms.

In conventional wastewater treatment facilities, nitrogen components in sewage and wastewater cause various water pollution issues such as eutrophication of aquatic ecosystems, so processes using microorganisms to remove nitrogen are essential.

The research team used a spinning disk confocal microscope to observe the interaction between microplastics and nitrifying microorganisms. To verify differences according to the size of the plastic, they exposed nitrifying microorganisms cultured in a bioreactor to two sizes of polystyrene (PS), 50nm and 500nm. They observed the oxidation process from ammonium (NH4+) to nitrite (NO2-) and then to nitrate (NO3-), as well as the expression level of the specific ammonia oxidation gene amoA possessed by nitrifying microorganisms.

Observation of interactions between microorganisms and microplastics (green) through confocal microscopy

The white arrows indicate the interior of the microorganisms, showing that the microplastics (green) are not absorbed inside the microorganisms and remain empty. (a) 50nm polystyrene, (b) 500nm polystyrene

Microorganisms exposed to 500nm PS did not affect the nitrification process efficiency, but those exposed to the finer 50nm PS showed reduced production of nitrite (NO2-) and nitrate (NO3-), which influence nitrification efficiency, compared to the 500nm PS exposure group. This suggests that microplastics could significantly impact the removal of nutrients such as nitrogen, which is one of the most difficult and important processes in sewage and wastewater treatment.

However, microplastics were observed not to interfere with the expression of the specific ammonia oxidation gene amoA. Confocal microscopy experiments confirmed that most microplastic particles did not enter the microorganisms but were distributed separately around them. Since microplastics vary greatly in size, material, and shape, experiments conducted with only a few characteristics cannot represent all potential hazards. Nevertheless, the research team explained that they were able to confirm the biological risks of microplastic particle size in sewage and wastewater treatment processes.

Dr. Jeong stated, "This study confirmed that microplastics can affect nitrification efficiency even without being absorbed by nitrifying microorganisms," adding, "To understand the exact mechanism, it is necessary to examine how various conditions such as particle characteristics like charge, size, type, and contained harmful substances influence the process."

The results of this study were recently published online in the international environmental science journal 'Journal of Hazardous Materials.'

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