Analysis of the complexation behaviors of Cu(II) with DOM from sludge-based biochars and agricultural soil: Effect of pyrolysis temperature.

Pyrolysis temperature is one of the important factors that affect the structure and composition of biochar-derived dissolved organic matter (DOM), which may impact interaction between biochar-derived DOM and Cu(II). Moreover, soil application of biochars pyrolyzed at different temperatures is supposed to cause different complexation behaviors between soils-derived DOM and Cu(II). However, little is known about these aspects. Here, incubation experiments and quenching titration experiments were conducted to explore such pyrolysis temperatures-dependent changes in sludge and sludge-based biochars (SSBA). Two-dimension correlation spectroscopy (2D-COS) indicated humic-like fraction had stronger affinities with Cu(II) in DOM from both sewage sludge (SS) and 500 °C sludge-based biochars (SSB5) while protein-like fraction showed the fastest response to Cu(II) binding in DOM from 300 °C sludge-based biochars (SSB3). One protein-like substance (Component 1) and two humic-like substances (Component 2 and 3) were identified in the DOM derived from SSBA through excitation-emission matrix-parallel factor (EEM-PARAFAC) analysis. Moreover, the Cu(II) complexation affinities of component 1, 2 and 3 decreased from 4.43, 4.53 and 4.86 to 3.26, 3.50 and 3.39 with increasing pyrolysis temperatures, respectively. The addition of 10% SS evidently increased the complexation affinities of humic-like substances in soil-derived DOM from 4.43 to 4.68 to 4.60-6.86, while the complexation affinities of humic-like substances decreased from 4.52 to 4.78 to 3.82-4.50 at a 10% amendment of sludge-based biochars. Compared with sewage sludge, agricultural soil amended with 10% sludge-based biochars had better performance in the aspect of Cu(II) mobility, but had weaker detoxication effect on Cu(II).