Fate and Impacts of Microplastics in Sludge Anaerobic Digestion: Effects on Methanogenic and Acidogenic Pathways

Abstract Microplastics (MPs) in sludge and their impact on anaerobic digestion (AD) have become a critical environmental concern. This review examines the mechanisms by which MPs influence sludge AD, particularly methane and volatile fatty acid (VFA) production. First, we discuss the occurrence, sources, and physicochemical properties (e.g., size, shape, surface characteristics) of MPs in sludge, which govern their behavior. Next, we explore how MPs disrupt AD, potentially suppressing methane generation through physical obstruction, chemical toxicity, and biological interference. MPs also alter VFA composition and metabolic pathways, notably regulating short‐chain fatty acids like acetate and propionate. Furthermore, MPs may synergize with co‐pollutants (e.g., heavy metals, organic contaminants), amplifying environmental risks. These findings underscore the need for deeper mechanistic insights to assess ecological impacts and optimize sludge valorization strategies.