Microplastic Fibers Deteriorate Dewaterability of Waste Activated Sludge through Alteration of Extracellular Proteome and Extracellular Polymeric Substance Structures

Microplastic fiber (MF) is a prevalent microplastic type in wastewater. However, its potential impact on waste-activated sludge (WAS) dewaterability remains unclear, posing challenges for sustainable wastewater management. This study revealed that MFs significantly deteriorate the sludge dewaterability, as evidenced by an increase in capillary suction time by 48.8% and a decrease in the total solids of the dewatered sludge cake by 14.1%. Proteomic analysis revealed that MFs altered extracellular protein profiles, notably reducing cation-binding proteins' abundance, leading to decreased organic binding metals content and increased hydrophilicity of extracellular polymeric substances (EPS). Meanwhile, the regulation of extracellular proteins by MFs also altered the spatial distribution of EPS, promoting a transformation from tightly bound EPS to loosely bound EPS, facilitating the retention of bound water. Further, XDLVO analysis indicated that MFs-induced changes in EPS compositions and structure enhanced the interparticle energy barrier so that sludge floc became more stable and more resistant to water release. The adverse effect of MFs on sludge dewaterability highlighted the importance of adjusting sludge conditioning strategies and controlling MFs' entry into wastewater/sludge to mitigate their impact. It also unveiled a previously overlooked mechanism that microplastics could regulate extracellular proteins and consequently reshape the structure and function of aquatic bioflocs.