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Microplastics enhance the denitrification of glycogen-accumulating organisms by regulating electronic transport in carbon-nitrogen coupling
Summary
Researchers investigated how different sizes of PVC microplastics affect the denitrification process carried out by glycogen-accumulating organisms in wastewater treatment systems. They found that larger 100-micrometer particles enhanced denitrification efficiency by 14.6% by promoting carbon metabolism and electron transport, while smaller 100-nanometer particles inhibited the process by 8.4%. The study reveals a novel mechanism by which microplastic particle size regulates carbon-nitrogen coupling in activated sludge.
The increasing presence of microplastics (MPs) in wastewater treatment systems profoundly impacts microbial metabolism and process performance. However, the effects of MPs on the denitrification process of glycogen-accumulating organisms (GAOs) remain unclear. Herein, various types and concentrations of MPs were introduced into the activate sludge of GAOs to assess their impact on denitrification processes and to investigate the underlying mechanisms. Our findings revealed that adding 100 μm PVC increased the denitrification efficiency of GAOs by 14.6 %, whereas adding 100 nm PVC decreased efficiency by 8.4 %. Additionally, 100 nm PVC inhibited polyhydroxybutyrate (PHB) degradation, while 100 μm PVC promoted it. Furthermore, 100 nm and 100 μm PVC differently influenced metabolic functions, including reactive oxygen species (ROS) levels, electron transport chain (ETC) activity, and intracellular nicotinamide adenine dinucleotide (NADH) content. Metatranscriptome analyses revealed differential expression of genes such as phaC, CS, nuoL, CYC1, and nisK, which are involved in carbon-nitrogen metabolism and oxidative phosphorylation. Consequently, 100 μm PVC enhanced the denitrification rate in GAOs by promoting PHB decomposition, increasing NADH electron-donating capacity, and ultimately enhancing the denitrification rate of GAOs. Our findings reveal a novel mechanism on regulating the carbon-nitrogen coupling in activated sludge under the different particle size of MPs.