Interactions among low-molecular-weight organics, heavy metals, and Fe(Ⅲ) during coagulation of landfill leachate nanofiltration concentrate

摘要

The generation of landfill leachate nanofiltration concentrate (LLNC) has been a dilemma for leachate treatment plants because it contains large amounts of refractory organics with low molecular weight (LMWO), as well as heavy metals (HMs), and is difficult to handle. The coagulation removal of LMWOs is a significant challenge, as is the removal of HMs bonded to LMWOs. In this study, coagulation through the dosing of FeCl_3 was used to remove LMWOs and HMs from LLNC. The results interestingly demon-strated that the removal rates of dissolved organic carbon (DOC), Cr, Ni, and As reached up to 84.1% ± 3.9%, 91.0 ± 1.1%, 73.1 ± 2.2%, and 96.9 ± 1.5%, respectively. The partition of LMWO components, as well as the interactions among the LMWOs, HMs, and Fe(Ⅲ) were investigated to determine the mechanism behind the LMWO and HM removal. LMWOs with a high degree of humification, including humic and ful-vic acid-like components, were preferentially removed through aggregation and electrostatic attraction originating from the specialistic adsorption of Fe_2(OH)_2~(4+) and Fe_3(OH)_4~(5+). In addition to being removed, a portion of these two components was dissociated into aromatic protein I, aromatic protein Ⅱ, and sol-uble microbial by-product-like materials due to an acid effect and the formation of inner-sphere com-plexes. A redundancy analysis revealed that As, Cr, and Ni are mainly removed through the electrostatic attraction of Fe(Ⅲ), bonding to humic substances and hydrophilic organics, respectively. The outcomes provide a new understanding on the coagulation removal of LMWOs and HMs.