Insight into complexation of Cu(II) to hyperthermophilic compost-derived humic acids by EEM-PARAFAC combined with heterospectral two dimensional correlation analyses.

Hyperthermophilic composting has been demonstrated to overcome the disadvantages of conventional composting in products with better quality. However, the complexation of heavy metals to hyperthermophilic compost (HTC)-derived HA remains unclear. In the present work, using Cu(II) as the representative heavy metal, we investigated the binding process of Cu(II) to HAs derived from HTC, thermophilic compost (TC), and sewage sludge (SS). The complexation ability of three HAs was analyzed by the method of parallel factor (PARAFAC) coupled with hetero two-dimensional correlation spectroscopy (hetero-2DCOS) analyses. Results showed that HTC-derived HA has the greater complexation ability (log KM = 5.68, CCM = 1.21) than both TC-derived HA (log KM = 5.27, CCM = 0.94) and SS-derived HA (log KM = 5.19, CCM = 0.586), likely due to the higher humification degree, as well as the faster response of carboxyl and phenols to Cu(II) binding with HTC-derived HA. This study demonstrated that the utilization of HTC might provide an effective approach for remediation of Cu(II)-polluted soils. Moreover, PARAFAC analysis integrated with hetero-2DCOS offers a unique insight into understanding the correlation between HAs fractions and functional groups during the Cu(II) binding process.