Comparison of molecular transformation of dissolved organic matter in vermicomposting and thermophilic composting by ESI-FT-ICR-MS

The aim of this study was to investigate the effects of vermicomposting (VC) and thermophilic composting (TC) on the molecular transformation of dissolved organic matter (DOM). Here, the DOM after VC and TC (DOMv and DOMt, respectively) was characterized using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). The results indicated that VC could improve the preservation of nitrogen and the humification of DOM compared with TC. Concurrently, VC facilitated the formation of highly oxidized molecules (O/C = 0.4–0.9) by enhancing the oxidation. The aromatized molecules in each component were more easily generated during VC, especially N-containing aromatized molecules (39.4–58.0%), thereby improving the quality of compost products. Furthermore, this study found that VC could reduce the anaerobic microsites in pile, thus increasing nominal oxidation state of carbon (NOSC) of organic matter and promoting the decomposition of high-energy substrates (mainly lipids, NOSC = − 1.7~− 1.3). These findings provided new molecular insights that VC can significantly improve the oxidation of organic matter and the preservation of nitrogen.