Decipherment of dissolved organic matter compositions on waste activated sludge under in situ 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 (WAS) under different multi-enzyme pretreatment durations. Fourier transform ion cyclotron resonance mass spectrometry analysis revealed that the biodegradable protein-like and amino sugar-like substances were converted into recalcitrant aromatic nitrogen-containing compounds via hydrolysis, condensation, and cyclization processes as extended pretreatment duration, significantly reducing DOM bioavailability. Metagenomic sequencing further indicated that the DOM deterioration inhibited the enrichment of hydrolytic and acidogenic bacteria, thereby suppressed the acetotrophic methanogenesis and methane production. Based on these insights, a novel DOM bioavailability-oriented evaluation framework was proposed for WAS pretreatment optimization, focusing on three key metrics, including the relative abundance of biodegradable substrates, key microorganisms and functions, and methanogenic pathways. Expectantly this study may provide theoretical and data support for future precise design of enzymatic pretreatment process and high-efficiency AD of WAS.