*2.1. Physicochemical Properties of Sorbents and Sediment*

The physical properties of AC, SAC, and FeS were determined by using a physisorption analyzer (Micromeritics ASAP 2420, Norcross, GA, USA) based on the N2 adsorption-desorption isotherm at 77K. The Brunauer-Emmett-Teller (BET) equation was used to determine the specific surface area based on ASTM D6556-10 [30], and the micropore surface area and volume were calculated by using the *<sup>t</sup>*-plot method by using the Jura–Harkins equation: *<sup>t</sup>* <sup>=</sup> [13.99/(0.034 <sup>−</sup> log(p/p0)]0.5 [31].

Elemental analyses were conducted to measure the contents of elements including N, C, S, H (Elementar Vario EL cube, Langenselbold, Germany), and O (Thermo Fisher Flash 2000, Waltham, MA, USA) for AC and SAC. The water content of air-dried sediment was measured by the weight method based on the Taiwan Environmental Protection Administration (TEPA) standard method (NIEA S280.62C). Sediment pH value with 1:1 sediment to H2O ratio was measured by pH meter (Suntex SP-2300, New Taipei City, Taiwan) based on TEPA standard method (NIEA S410.62C). Sediment texture was measured by using the bouyoucos hydrometer method [32]. Sediment organic carbon (OC) content was measured by Walkley-Black wet oxidation [33]. Sediment cation exchange capacity (CEC) was measured by the ammonium acetate method based on the TEPA standard method (NIEA S201.61C). Detailed descriptions pertaining to characterizing the physical and chemical properties of sampled sediment can be found in Supplementary Material.
