Decipherment of dissolved organic matters compositions on waste activated sludge under multi-enzyme pretreatment: novel bioavailability-oriented evaluation framework

This study systematically elucidated the dissolved organic matters (DOM) molecular conversion and biological response mechanisms during anaerobic digestion (AD) of waste activated sludge under different multi-enzyme pretreatment durations. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) analysis revealed that biodegradable protein-like and amino sugar-like substances were converted into recalcitrant aromatic nitrogen-containing compounds via hydrolysis, condensation, and cyclization, significantly reducing DOM bioavailability. Metagenomic sequencing further indicated that this deterioration inhibited the enrichment of hydrolytic and acidogenic bacteria, thereby suppressing acetotrophic methanogenesis. Based on these insights, a novel DOM bioavailability-oriented evaluation framework was proposed for pretreatment optimization, focusing on three key metrics: the relative abundance of biodegradable substrates, key microorganisms and functions, and methanogenic pathways. This study provides theoretical and data support for the precise design of enzymatic hydrolysis and high-efficiency AD of WAS.