Effects of combined polystyrene nanoplastics and ibuprofen on the activated sludge processes: Short-term exposure in pure cultures versus long-term stress in mixed communities

Abstract

Given their large production and widespread application, polystyrene nanoplastic (Nano-PS) and ibuprofen (IBU), as particularly relevant compounds, are found to coexist in wastewater treatment plants. In this study, the effect of combined Nano-PS and IBU on the activated sludge processes was investigated through short-term exposure in pure cultures and long-term stress in mixed communities. This study found that the inhibition of SO42− removal by sulfate-reducing bacteria was more pronounced for small-sized Nano-plastics in motion state. Compared to individual pollutants, the toxicity of Nano-PS + IBU mixture showed antagonistic effects at low dosage and synergistic effect at high dosage. In mixed communities, COD and TN removal of sequencing batch reactor decreased from 93.3 % and 90.7 % to 80.1 % and 64.5 % with increasing Nano-PS/IBU. The membrane integrity was destroyed by excess reactive oxygen species, further reducing the protein of extracellular polymeric substances. Furthermore, Nano-PS/IBU altered the community structure, decreased microbial diversity and affected the distribution of abundance and rare taxa. These adverse effects, accompanied by a decline in the relative abundance of nitrifiers (e.g., Nitrosomonas and Ellin6067) and genes (e.g., AmoCAB and Hao), directly accounted for the strong deterioration observed in ammonia oxidation. This study provided important information on the effects of nanoplastic and pharmaceutical compounds on activated sludge system, which is a hidden danger to nitrogen removal in biological treatment and should give more attention.