Impact of phenolic-formaldehyde resin microplastics on anaerobic granular sludge: EPS interaction mechanisms and impacts on reactor performance

This paper investigates the effects of phenolic-formaldehyde resin microplastics (PF-MPs) with different particle sizes on anaerobic granular sludge (AnGS) and reveals the complex interaction mechanisms between extracellular polymeric substances (EPS) and PF-MPs through the combination of molecular dynamics simulations and spectroscopy. PF-MPs provide a new ecological niche for microorganisms. Microorganisms and EPS can adhere and accumulate on the surface of PF-MPs, producing highly active floc sludge inside the reactor, thereby increasing the chemical oxygen demand (COD) removal rate and methane production of the reactor. However, the high metabolic activity of floc sludge consumes the biodegradable components in EPS, resulting in loose rupture of the sludge particles and reduced particle size. In addition, small particle size S-PF can adhere to the sludge surface，which caused mass transfer barriers and reduced the expression of genes and enzyme activities for the sludge acidification process and the main methanogenic processes. Insufficient internal nutrients lead to endogenous metabolism within the granules, causing internal hollowing, which affects the density and settling performance of the sludge. Monolayer physical adsorption plays a major role in the adsorption of EPS on PF-MPs. 2D-COS and FTIR spectroscopy were used to elucidate the preferential binding of polysaccharides to PF-MPs. This paper explores the fate of PF-MPs in anaerobic systems and demonstrates the important role of EPS in the capture of microplastics by granular sludge, providing a theoretical basis for understanding the migration of microplastics in wastewater treatment.