Unveiling the plastisphere in anammox process: Physicochemical evolution of microplastics and microbial succession...

Microplastics (MPs) and the plastisphere they form pose substantial ecological risks in aquatic environments and wastewater treatment processes. As a unique niche, the evolution of plastisphere in anaerobic ammonium oxidation (anammox) systems remains poorly understood. This study investigated the physicochemical evolution of polyethylene terephthalate (PET) MPs and microbial succession within the plastisphere during a 30-day incubation with anammox granular sludge. Results demonstrated that short-term exposure to 800 mg/L PET MPs exerted negligible impacts on nitrogen removal efficiency (>90 %) due to functional redundancy. During incubation, MPs exhibited increased surface roughness, reduced hydrophobicity, and attenuated zeta potential, attributed to the formation of biofilms containing hydrophilic functional groups (-OH, -NH₂). The plastisphere, initially colonized by heterotrophic denitrifiers, gradually converged with the anammox sludge community over time. Functional annotation indicated that early biofilm formation prioritized extracellular polymeric substance (EPS) synthesis pathways, while mature biofilms shifted toward resource conservation and inter-microbial signaling. These findings highlight the reciprocal influence between anammox consortia and plastispheres, providing insights into MP fate in anammox systems.