Influence of nanoplastic type on the short-cut nitrification-denitrification in a sequencing batch reactor: Elucidating the metabolic relationship of nitrogen, extracellular polymeric substances, and oxidative stress

Nanoplastics (NPs), an emergent pollutant in wastewater treatment plants, include both biodegradable and non-biodegradable types, and their impact on the metabolism relationship of bacteria in activated sludge is a valuable investigation. This study explored the impacts of biodegradable polybutylene adipate-co-terephthalate NPs (PBAT-NPs) and non-biodegradable polyethylene NPs (PE-NPs) (0-1.5 mg/L) on the short-cut nitrification-denitrification (SCND) performance of a sequencing batch reactor (SBR), focusing on metabolic links among reactive oxygen species (ROS), extracellular polymeric substances (EPS), and SCND performance. Results showed that alterations in EPS synthesis, oxidative stress, and metabolic intermediate and electron supply in the tricarboxylic acid (TCA) cycle were closely associated with disrupted nitrogen metabolism, accompanied by severe deterioration of SCND performance at different NPs stresses, and PE-NPs induced a stronger inhibition on the SCND performance than PBAT-NPs. Compared to the control without PBAT- and PE-NPs, PE-NPs increased the ROS production by up to 194.17 %, whereas PBAT-NPs induced an increase in the ROS level of 129.28 %. PE-NPs primarily elicited a greater number and more important ROS-generating genes and enzymes than PBAT-NPs. Compared to PE-NPs, PBAT-NPs strongly reduced the protein (PN) level of LB/TB-EPS by affecting a greater number of enzymes, while comparably suppressed polysaccharides (PS) of LB/TB-EPS by disturbing the same number of enzymes. The TCA cycle could join the metabolic associations between ROS and EPS. This study reveals the metabolic correlation by which biodegradable and non-biodegradable NPs induce toxicity in the SCND system, providing a scientific basis for implementing targeted risk mitigation.