Abstract
Microplastics (MPs), as a new type of pollutant, are widely detected in sewage treatment plants. Currently, research on MPs in traditional sewage treatment systems has mainly been focused on the pollution level and distribution characteristics, with a lack of studying the impact of MPs on the sludge granulation. In order to explore the effect of MPs on the granulation process, a microplastic exposure test was conducted by adding polyethylene terephthalate microplastics (PET-MPs), which are widespread in the environment. The operating performance of the system, extracellular polymeric substance (EPS) composition, and flora enrichment were analyzed on the sludge granulation. The results showed that the exposure of PET-MPs significantly accelerated the sludge granulation process, whereas the increase in EPS content dominated by PN enhanced the sludge surface hydrophobicity; the granulation rate and EPS secretion were proportional to the exposed particle size. Microplastics and EPS secretions synergistically promoted the formation of granular sludge. However, continuous microplastic exposure led to deterioration of the system decontamination performance and inhibited the degradation process of pollutants, with the most negative effect of nitrite nitrogen accumulation under 250 μm PET-MPs exposure, as high as (5.08±0.24) mg·L-1. The high-throughput sequencing revealed that the microbial community diversity fell in the experimental group. The dominant bacteria at the phylum level were Proteobacteria and Bacteroidota on the sludge granulation. Rhodocyclaceae, Sphingomonadaceae, Flavobacteriaceae, and Rhodanobacteraceae promoted flocculation by increasing EPS secretion. The decrease in Comamonadaceae and Chitinophagaceae weakened the ammonia and nitrite oxidation capacity of the system, whereas the decrease in Rhodobacteraceae, Hyphomonadaceae, and Xanthomonadaceae inhibited the removal of nitrate nitrogen.
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