Response to microplastics exposure and changes in system performance: a stark contrast between domestic sewage and landfill leachate

Explored the evolution process of representative polyethylene (PE) and polystyrene (PS) in anaerobic/aerobic biological treatment of domestic sewage and landfill leachate, and their effects on system efficiency, sludge performance, and microbial community structure. The results showed that microplastics (MPs) promoted the degradation of COD and NH-N in domestic wastewater (approximately 99.00 % and 98.16 %), but this result was completely opposite to that in the leachate. The biofilm formation of MPs in leachate was relatively fast in the initial stage, with a biofilm amount (9.39) higher than that in domestic sewage (1.05), showing an "S"-shaped trend, but with large fluctuations over time. The amount of PE and PS biofilm in domestic sewage varied with different oxygen concentrations, but the amount of PS biofilm in leachate was generally higher than that in PE, and PS was more sensitive to biodegradation, while PE had stronger resistance to microbial attacks. Meanwhile, the presence of MPs significantly enhanced the synthesis of extracellular polymeric substances in the leachate (139.81 mg/g MLVSS, anaerobic condition on day 15), increased the concentration of heavy metals in the supernatant (842.91 μg/L, anaerobic condition on day 15), manifested as Mn and Zn. MPs stress led to varying degrees of changes in the structure of microbial communities, but the microbial abundance on the surfaces of PE and PS in the same reactor was similar. Ottowia, unclassifiedd_f_Rhizobiaceae, and Castellaniella were potential MPs degradation genera. The proportion of Thermomonas in the leachate system was about three times that of domestic sewage. The symbiotic mode between MPs and dominant bacteria in activated sludge confirmed the shaping of microbial community structure by MPs. This study contributes to improving the overall understanding of the environmental behavior and risks of MPs in domestic wastewater and leachate biological systems.