Determinants of microbial colonization on microplastics through wastewater treatment processes: The role of polymer type and sequential treatment

This study examines the microbial colonization characteristics of microplastics (MPs) in wastewater treatment plants (WWTPs), focusing on polymer types (High-Density Polyethylene (HDPE) and Polyethylene Terephthalate (PET)) and various stages of wastewater treatments. Through individual and sequential deployment approaches, the research aimed to identify the determinants of bacterial colonization on MPs, whether they were introduced at each stage of treatment individually or in sequence from primary to tertiary stages. The study revealed that the stage of wastewater treatment profoundly influenced bacterial colonization on the polymer types MPs, with bacterial attachment being largely niche-specific. HDPE showed increased sensitivity to wastewater composition, leading to selective biofilm formation. For instance, in HDPE, Firmicutes accounted for 25.1 ± 0.04 % during primary treatment, while Alphaproteobacteria increased significantly in the tertiary treatment to 19.8 ± 0.1 %. Conversely, PET exhibited a stochastic pattern of bacterial colonization due to differences in surface hydrophilicity. Additionally, in sequential deployments, a notable shift towards stochastic bacterial attachment on MPs, particularly with HDPE was observed. The Shannon diversity values for MP biofilms were consistently higher than those for wastewater across all stages, with PET showing an increase in diversity in sequential deployments (Shannon diversity: 5.01 ± 0.03 for tertiary stage). These findings highlight the critical role of MPs as carriers of diverse bacteria, emphasizing the necessity for strategies to mitigate their impact in WWTPs. This study presents a significant advancement in our understanding of the interactions between MPs and microbial populations in WWTP environments.