The response mechanism and dynamic succession of microbial community in activated sludge system under dexamethasone stress

The mass production and widespread use of dexamethasone (DEX) during the COVID-19 pandemic inevitably led to the increase of residue concentrations in wastewater treatment plants. In this study, the effects of DEX at different concentrations on the activated sludge system were investigated. The results indicated that organic matter removal and ammonia nitrogen oxidation were inhibited. The effluent COD and TN gradually increased with increasing DEX concentration. The extracellular polymeric substance was secreted as a protective barrier against DEX stress, ensuring the integrity of the cell membrane. According to assembly mechanism analysis, the relative importance of homogeneous selection in deterministic processes gradually increased under DEX stress, which acts as the main driving force to alter the distribution of abundance and rare taxa, causing the decrease of rare taxa and community diversity, thus forming more homogeneous and similar community structure. These negative consequences, coupled with the inhibition in autotrophic nitrifiers such as Nitrosomonas and Ellin6067, and the decrease in gene abundance of nitrification metabolism including AmoCAB and Hao , were directly responsible for the obvious deterioration of NH 4 + -N oxidation capacity. This study provided reliable experimental data about the effects of DEX on activated sludge systems, which is conducive to reducing the environmental risk of DEX and maintaining the stable operation of the activated sludge system.