The influence of flue gas desulphurization gypsum additive on characteristics and evolution of humic substance during co-composting of dairy manure and sugarcane pressmud

[Display omitted] •Characteristics and evolution of HS during composting with FGDG was studied.•Particle size of HS was below 600nm and represented a bimodal distribution.•Adding FGDG increased the unsaturated degree and aromatization of composting HS.•FGDG increased the nitrogen compounds in HS from compost.•The decrease of alkane and increase of benzene and nitrogen compounds in HS occurred. For the purpose of evaluating the effect of flue gas desulphurization gypsum (FGDG) additive on characteristics and evolution of humic substance (HS) during composting, HS from composts with FGDG (CPG) and without FGDG (CP) were extracted and assessed with respect to their particle size, elemental analysis, FTIR and UV–vis spectroscopy, and the molecular composition of HS was characterized via pyrolysis-GC/MS as well. The particle size of HS ranged between 300 and 600nm, representing a bimodal distribution. As composting proceeded, the C/H of HS increased, and C/N decreased. The FTIR and UV–vis spectroscopy indicated that the aromatization of HS was promoted over the composting process. Adding FGDG increased the unsaturated degree and aromatization of HS. Pyrolysis-GC/MS showed the level of alkane decreased, and the level of benzene and nitrogen compounds increased upon the addition of FGDG. The nitrogen compounds of HS in CPG was significantly higher than that in CP.