Characterisation of dissolved organic matter extracted from the bio-oxidative phase of co-composting of biogas residues and livestock manure using spectroscopic techniques

• The effect of biogas residue content of initial composting mixture on the composting efficiency was evaluated by HCA.
• The humified and stabilised degree of compost was optimal when the weight fraction of biogas residues was 40–50%.
• Describe the relationship between bacterial community structure and organic matter transformation during composting.

The composition of composting substrate significantly influences the composting process. To evaluate the effect of biogas residue content of initial composting mixture on the composting efficiency, co-composting processes of biogas residues and livestock manure (BRLM) were performed in terms of weight fractions of biogas residues (T1: 30%, T2: 40%, T3: 50% and T4: 60%). The dissolved organic matter (DOM) transformation was characterised. Fractionation of DOM, FTIR, UV–vis and fluorescence spectra indicated that the degradation efficiency of alcohols, ether and polysaccharides, and molecular weight, aromaticity and polycondensation degree of composts were in the order T3 > T2 > T1 > T4. Parallel factor analysis also showed that the content of humic-like substances was in the same order. Hierarchical cluster analysis showed that humified and stabilised degree of compost was optimal when the weight fraction of biogas residues was 40–50%. Bacterial profiles implied that biogas residue content of composting substrate significantly influenced bacterial dynamics. Bacteria were mainly active in the degradation of easily biodegradable organic matter and lignin. The abundance of bacteria involved in the degradation of easily biodegradable organic matter and lignin in the course of composting was closely related to composting efficiency and humification degree of compost.