Towards understanding the stabilization process in vermicomposting of excess sludge under copper oxide nanoparticles stress using PARAFAC analysis of fluorescence spectra

In this study, fluorescence excitation-emission matrix (EEM) combined with parallel factor analysis (PARAFAC) was employed to trace the behaviour of dissolved organic matter during vermicomposting of excess sludge under four dosages (0, 400, 800, 1600 mg/kg-TSS) of copper oxide nanoparticles (CuO NPs) stress. Determination of dissolved organic carbon (DOC) and total content of organic carbon (TOC), available nitrogen and available phosphorous indicated the presence of CuO NPs decrease the sludge stabilization by vermicomposting, but the organics degradation efficiency was not significantly inhibited with the increase of CuO NPs concentration. Fluorescence spectra results of dissolved organic matter (DOM) during the four groups of vermicomposting indicated CuO NPs led to the reduce of humic acid-like materials in vermicomposting. The positive relationship of protein-like component 1 and negative relationship of humic-like component 2 with CuO NPs concentrations in the substrates reflected by PARAFAC analysis suggested CuO NPs inhibit transformation of humic-like maters during the vermicomposting.