Effect of single and hybrid microplastic exposures on anaerobic sludge in microbial electrochemical technology (MET)

Microplastics (MPs) in wastewater treatment pose significant environmental risks. While microbial electrochemical technology (MET) is effective in removing refractory pollutants, most studies focus on single MP types, despite real-world wastewater often containing mixtures. This study examines the effects of single and hybrid MPs (HD-MPs) on wastewater treatment performance and microbial communities in MET systems. Results show that MPs significantly impair methanogenesis, reducing methane production by 25.27-36.46 %, decreasing COD removal efficiency by 26.82-33.33 %, and increasing volatile fatty acid accumulation by 17.23-26.79 %, with PVC exhibiting the strongest inhibition. Electrical stimulation (0.7 V) exacerbates oxidative stress, elevating reactive oxygen species (ROS) and lactate dehydrogenase (LDH) release in biofilm sludge (BFS) compared to anaerobic granular sludge (AGS). Extracellular polymeric substances (EPS) shift from protein-dominant (65-77 % under PVC-MPs and HD-MPs) to polysaccharide-rich (52-55 % under PE-MPs), reflecting type-specific microbial responses. High-throughput 16S rRNA sequencing reveals that applied voltage selectively enriches fermentative bacteria (Firmicutes and Bacteroidota), creating distinct microbial profiles between AGS and BFS. Metatranscriptomic analyses show that HD-MPs under electrical stimulation induce structural reorganization of key functional microorganisms, including a 144 % increase in fermentation bacteria, 61.7 % rise in acetogens, and 3.89-fold enhancement of electrogenic bacteria at the BFS anode compared to AGS. Transcriptional upregulation of genes in glycolysis, TCA cycle, and methane metabolism confirms the dominance of the acetoclastic methanogenic pathway (79.18-86.97 % of total methanogenesis). This study enhances understanding of electrostimulated microbial consortia in complex pollutant environments and proposes practical MET configurations for real-world applications.