Monitor process state of batch anaerobic digestion in reliance on volatile and semi-volatile metabolome

It has been a challenge to recognize appropriate compounds as indicators for monitoring and early-warning of the anaerobic digestion process. A strategy was initiated to explore the evolution of the panorama profile of volatile and semi-volatile metabolites. Non-target analysis using high-resolution gas chromatography coupled with Orbitrap mass spectrometry was applied to construct a time-series molecular fingerprint of 218 metabolites classified in 14 categories. Alkanes accounted for the main part in early and late stages of methanization and aromatic compounds were the major in middle stage. Spearman correlation analysis and partial least squares analysis unwind that Trichococcus (1.49%-83.96%) was positively related to most of metabolites at early and middle stages, while Brevundimonas (0%-24.04%) was positively related to acylamide at late stage. This indicated that microbial volatile organic compounds were possible to serve as biochemical indicators for anaerobic digestion performance and to build nexus of "what" (metabolites), "who" (microorganism), and "how" (kinetics).