The microbial response to biodegradable polylactic acid microplastics during anaerobic fermentation of waste activated sludge

The global accumulation of microplastics (MPs) in natural environments has raised significant ecological concerns, with wastewater treatment plants serving as major accumulation points. This study investigated the impact of polylactic acid (PLA) MPs on volatile fatty acid (VFA) production from waste activated sludge (WAS). Under different PLA MPs levels (0-200 particles/g-TS), the VFA production, extracellular polymeric substances (EPS) structure, and the microbial community responses were systematically examined. Results demonstrated a clear inhibition on acidogenic efficiency by PLA MPs, with VFA yields decreased by 5.14-18.18% compared to the control. Although PLA MPs enhanced sludge solubilization (increased by 2.3-11.91%), they significantly inhibited subsequent hydrolysis and acidification processes through: (1) inhibition of key enzymatic activities, (2) increase of oxidative stress (39.9% increase in lactate dehydrogenase (LDH) leakage), and (3) alteration of microbial community structure (reduced Bacteroidota and key functional genera). These findings provide novel insights into the complex interactions between biodegradable MPs and anaerobic fermentation processes, highlighting the need for mitigation strategies in WAS treatment systems confronted with increasing biodegradable microplastic contamination.