Biodegradable Plastics in Anaerobic Digestion Systems: Compatibility and Engineering Strategies for Circular Agriculture

Abstract

Anaerobic digestion (AD) offers a potential route for integrating biodegradable plastics (BDPs) into circular agricultural waste management, but suitability depends on conversion of the complete material under practical digestion conditions. This review evaluates BDP compatibility with AD and engineering strategies to improve treatment. BDP conversion in AD generally requires depolymerization and hydrolysis to soluble products, initiated by surface microbial or enzymatic attack for some polymers, followed by microbial conversion to methane. The rate and extent of conversion depend on polymer chemistry and structure, crystallinity, chain mobility, hydrophilicity, material form and formulation, digestion temperature, and anaerobic microbial activity. Poly(hydroxybutyrate) (PHB) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) show high compatibility, while thermoplastic starch (TPS) and accessible cellulose-based materials undergo substantial conversion. Poly(lactic acid) (PLA) is strongly hydrolysis-limited under mesophilic conditions, whereas poly(caprolactone) (PCL) shows pronounced temperature-dependent conversion, with thermophilic conditions generally improving degradation. Poly(butylene succinate-co-adipate) (PBSA) converts more readily than poly(butylene succinate) (PBS) but remains incomplete without pretreatment. PBS and poly(butylene adipate-co-terephthalate) (PBAT) are poorly compatible. Polymer blends are often limited by their least-degradable major fractions. Fragmentation or mass loss does not indicate complete conversion, and polymer persistence does not necessarily indicate process instability. Reactor configuration and treatment should therefore target polymer-specific limitations through controlled co-digestion and loading, optimized particle size, targeted pretreatment, microbial acclimation or enrichment, appropriate temperature and staging, and AD-oriented material formulation.