An evaluation of the effects of nanoplastics on the removal of activated-sludge nutrients and production of short chain fatty acid

Abstract Nanoplastics in the environment and their effect on the ecosystem has aroused wide concern. This study investigated the effect of polystyrene nanoplastics on activated sludge properties, including nutrient removal, dewaterability, and short chain fatty acid (SCFA) production potential. The results indicated that the nanoplastics inhibited the ammonia oxidation rate and nitrate generation rate during nitrification. The denitrification rate was also inhibited in the presence of nanoplastics, while the percentage of total inorganic nitrogen removed was not affected. The phosphorus absorption rates during the aerobic stage were 75.52%, 76.19%, 60.69%, 71.58%, and 49.48% for nanoplastics concentrations of 0, 10, 50, 100, and 1,000 μg/L. The phosphorus release was inhibited in the reactors where nanoplastics were added during denitrification. These results indicate that bacteria, including nitrifiers, denitrifiers, and phosphorus-accumulating bacteria are affected by the nanoplastics. This probably attributed to the nanosize of the polystyrene effect on bacterial cells or overproduction of reactive oxygen species that caused dysfunction of microbial metabolism. SCFA production was inhibited by adding nanoplastics, particularly at a concentration of 10 μg/L, suggesting that the hydrolysis and acidification processes were affected by the nanosized polystyrene. The dewaterability of the activated sludge was improved after adding nanoplastics, this probably attributed to the aggregation of polystyrene and its function as a sludge skeleton builder. The results of this study reveal that nanoplastics have a negative effect on activated sludge properties, which should be considered for practical applications.