Chromium ion removal from raw water by magnetic iron composites and Shewanella oneidensis MR-1

In this study, nanoiron active carbon composites (NZVI/GAC) were used to remove chromium ions from raw water. The composites were synthesized from a novel formula of biological activated carbon and characterized by various techniques. The adsorption test data were fit by a pseudo-second-order kinetic model and Langmuir model. The q_e and R² values were 187 mg Cr/g and 0.9960, respectively, with 0.2 g/L NZVI/GAC at an initial concentration of 118 mg/L Cr according to the Langmuir isotherm model. Moreover, a Cr⁶⁺ detoxification reactor was constructed with the magnetic iron composite. The results indicated that the synthesized magnetic iron composite was a significant adsorbent for Cr⁶⁺ removal from aqueous solutions. The detoxification reactor was able to remove Cr⁶⁺ from raw water at an initial concentration of 26.5 mg/L within a short time period (3-5 min), with a removal efficiency of up to 99.90% and a treatment capacity of 45.0 mg Cr⁶⁺/g of adsorbent; the Cr⁶⁺ concentrations in the outflow met the GB5749-2006 requirements for drinking water. A synergistic effect between NZVI/GAC and a suspension of the bacterium Shewanella oneidensis MR-1 was found, showing that this bacterium can be used as a regeneration agent for iron-depleted activated carbon materials.