When the PDOM was added, the maximum adsorption capacity of three sediments of FT, RB, and RF reached 1056.176 mg/kg, 549.200 mg/kg, and 1350.031 mg/kg, respectively, at 318 K, which is increased by 0.876, 0.913, and 0.960 times compared to that at 298 K, respectively.
In addition, the values of [DELTA]G for the sorption process followed the order: the process of MDOM > without DOMs > PDOM, indicating that the spontaneous degree of the adsorption was PDOM > without DOMs > MDOM, which also means that the adsorption of OTC could be promoted by adding PDOM, whereas the addition of MDOM could inhibit the adsorption.
The results showed that the presence of PDOM enhanced the adsorption of OTC to sediments in all examined concentrations, and the concentration ranging from 100 to 200 mg TOC/L related to a more obvious enhancement (Figure 5), indicating that the appropriate concentration of PDOM promoted a better effect; Jia et al.
The PDOM can promote the adsorption of OTC to sediments, because it has a high-intensity H3 peak at Ex/Em = 340/430, which was assigned to a large number of humus-like substances.
Compared with the MDOM, the PDOM has the higher C, H contents, whereas the content of N is low, which is consistent with the source of this kind of DOM.
Considering that the H/C value of the PDOM is smaller, its high aromaticity leads to an easier combination with the sediment, so as to increase the number of adsorption sites and promote the adsorption of OTC.
(2) Comparing the adsorption mechanism of the two kinds of DOM, it was found that the PDOM has high aromaticity, low hydrophilicity, and polarity because it consists of humus-like substances, leading to an easier combination with the sediment, so as to increase the number of adsorption sites and promote the adsorption of OTC.
FT-PDOM, RF-PDOM, and RB-PDOM refers to the sorption with the presence of corrupt plant derived DOM (PDOM).
Caption: Figure 6: The 3D fluorescence spectra of (a) corrupt plant derived DOM (PDOM); (b) chicken manure derived DOM (MDOM).