Enhanced decomplexation of Cu(II) complexes and Cu removal by the nFe3O4/persulfate coupled microbial system: Synergistic effect, validation, and mechanism

Abstract

The enhancement of decomplexation efficiency whilst minimizing subsequent microbial process impact is essential in the treatment of refractory heavy metal complexes. Herein, we developed the nano-Fe3O4 (nFe3O4)/peroxydisulfate (PDS) coupled microbial system for the removal of Cu(II)-citrate. Other Cu(II) complexes, such as tartrate, oxalate, and EDTA, were also selected to validate the effectiveness of the coupled system. In batch experiments, the coupled system facilitated the Cu(II)-citrate removal from 21.9 %, 18.9 % to 96.8 % within 120 min as compared to individual nFe3O4 + PDS or biosorption, respectively. Meanwhile, the coupled column was able to remove 86.9 % of copper after fifteen days under continuous flow operation. Impressively, microorganisms could promote the Fe(II)/Fe(III) cycling, thus reducing the usage of PDS. High-throughput sequencing analyses suggest that the coupled system has a higher microbial abundance, which played key roles in eliminating complexed Cu(II). The removal of Cu(II)-citrate in the coupled system involves de-complexation and biosorption, followed by precipitation of all remaining free metal ions. This work provides a feasible strategy potentially applied in efficient treatment of heavy metal complex wastewater.