Improvement in humus synthesis by the humus precursors derived from nitrobenzene degradation during co-composting of nitrobenzene-polluted soil and cow manure

Nitrobenzene (NB) mineralization problem exists during co-composting of NB-polluted soil and cow manure (CM). Regulating the conversion of NB degradation into humus (HS) synthesis offers a new way to circumvent the aforementioned problem. To explore the influence of the presence of NB on humification process during co-composting, co-composting of NB-polluted soil and cow manure was conducted with composting of clean soil and CM, serving as the control. Results showed that a 54.66% of NB-degradation rate was achieved after 47 d of composting. Simultaneously, compared to CK, not only HS content increased by 18.75%, but also the proportion of fluorescent component with the highest complexity of humic and fulvic acid increased by 21.92% and 44.44%, respectively. NB intermediate metabolites substantially contributed to HS formation. Meanwhile, a markedly strong interaction between bacteria and environmental factors may be crucial for enhancing the humification process in the NB group. It was verified that the addition of NB increased the content of polyphenols (λ=0.912, p＜0.001) and further improved the synthesis of humic acid (λ=0.420, p＜0.05) by strengthening the Maillard reaction. Simultaneously, the inhibitory effects of NB and polyphenols on bacterial growth prevented excessive depletion of ammonia nitrogen, favoring humic acid synthesis. These results illustrated that NB intermediate metabolites promoted HS synthesis, which was the prerequisite for subsequent establishment of targeted regulation technology of NB degradation-HS synthesis during co-composting.