Abstract
AbstractTo investigate the characteristics of humic acids (HAs) and the combined effects of HAs on heavy metals, three HAs derived from kitchen waste compost (KW), pig manure compost (PM), and green waste compost (GW) were exposed to Cd(II) and Zn(II). The elemental contents and functional groups of HAs were different due to different raw materials. Fulvic-, humic-like content C1, humic-like content C4, and two protein-like contents C2 and C3 were identified in three HAs by EEM-PARAFAC analysis. The effects of HAs on heavy metals were associated with the metal species and HA source. Our results reveal that titrating Cd(II) caused stronger fluorescence quenching compared to titrating Zn(II) for all HAs. C1 and C4 of KW-HAs and PM-HAs showed fluorescence quenching after Cd(II) was added, whereas negligible fluorescence quenching was found when Zn(II) was added. In addition, C1 and C4 in the GW-HAs did not show obvious fluorescence quenching regardless of whether Cd(II) or Zn(II) was added. C3 in all HAs caused significant fluorescence quenching, suggesting that C3 plays an important role affecting the mobility of heavy metals. Consequently, these results suggest that HAs from KW and PM have greater potential for Cd-contaminated soil remediation than those from GW.
Highlights
Vast amounts of organic solid wastes, such as kitchen waste, pig manure, and green waste, are generated in China and continue to increase annually [1,2,3]
The H/C ratios of the pig manure compost (PM)- and green waste compost (GW)-derived humic acids (HAs) were similar, but a slightly higher H/C ratio was observed for the kitchen waste compost (KW)-derived HAs, suggesting a higher content of aromatic groups [40]
The sequences of the O/C and O/H atomic ratios of the HAs were in the order of GW > KW > PM
Summary
Vast amounts of organic solid wastes, such as kitchen waste, pig manure, and green waste, are generated in China and continue to increase annually [1,2,3]. Utilization of these wastes in an environmentally friendly manner has received much attention [4,5,6]. Composting is an effective and acceptable biological process to convert organic solid wastes into fertilizer or soil conditioner for agricultural use, as composting improves soil fertility, reduces greenhouse gas emissions, and remediates soil heavy metal pollution [7,8,9,10,11]. The compositions of HAs differ because they are formed from different raw materials [17], so it is necessary to compare the binding capacity of different HAs to heavy metals
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