Particulate-to-molecule multiscale determinants of dewaterability of anaerobically digested biowaste

Dewatering is a critical step in biomass resource recovery. Existing studies have primarily focused on macroscopic physical parameters and bulk chemical analyses, remaining fragmented and lacking panoramic coverage of all substance categories. In this study, three distinct yet representative biowaste substrates were used to monitor the evolution of particulates and affinity-fractionated dissolved organic matter (DOM) molecules throughout the anaerobic digestion process. This approach enables continuum-scale material characterization spanning from particles to molecules, helping establish the structure-performance relationship with dewatering behavior. Carbonyl-amine condensation reactions (termed Maillard-like reactions) were highly likely to occur in the polysaccharide-rich system. This occurrence, evidenced by molecular characteristics, functional group evolution, and mismatched acidogenic and methanogenic potentials, was considered to be associated with limited dewaterability and biodegradability. Specifically, the DBE of the UCFW group increased by 32.41%-46.56%, yielding a much higher acidogenic output than the CFW group, while its methanogenic potential remained below 30% of the CFW level. The network between lignin-like substances and extracellular polymer substances (EPS) hindered the dewatering performance of the lignin-rich system. ‌Long-chain fatty acids (LCFAs) generated from lipid hydrolysis represented a class of compounds capable of mitigating dewatering deterioration, whereas lipid-derived oil films severely impeded solid-liquid separation, thereby conferring a dual functional role on lipids in the lipid-rich system. These findings suggest that dewatering performance can be improved by regulating substrate particle size and compositional ratios, providing guidance for the rational design and optimization of sustainable treatment processes.