Microplastic-Intervened Anaerobic Fermentation: Discrepancies in Hydrolysis and Acidification of Acidic/Alkaline Treatment

Microplastics (MPs) are widely present in waste-activated sludge (WAS), and their effects on different stages of WAS acidic/alkaline anaerobic fermentation (AF) remain unclear. To fill this knowledge gap, poly(ethylene terephthalate) (PET), a representative MP, was selected to evaluate the influence of MPs on the WAS AF performance. By analyzing the release patterns of organics and the formation of volatile fatty acids (VFAs), it was determined that acidic AF hydrolysis was inhibited more than alkaline one, while alkaline AF acidification was inhibited more than the acidic one. An in-depth investigation of the microbial mechanism further confirmed these ideas. After adding PET, the abundance of Soehngenia and genes pta, aceE, and aceF associated with acidification was reduced only in an alkaline environment, while genes involved in glycolysis, such as pgk, eno, and TPI, were almost suppressed in an acidic environment. This research is expected to provide a theoretical foundation for comprehending and unveiling the mechanisms by which the PET influences pH-regulated AF.