GO, SiO ₂ , and SnO ₂ nanomaterials as highly efficient adsorbents for Zn ²⁺ from industrial wastewater—A second stage treatment to electrically enhanced membrane bioreactor

The aim of this work was to investigate the efficiency of adsorption process, as a post-treatment to the electrically-enhanced membrane bioreactor (eMBR) effluent, for the removal of Zn ²⁺ . Three nanomaterials were tested, namely, graphene oxide (GO), silica (SiO ₂ ), and tin oxide (SnO ₂ ). pH and adsorbent dosage were optimized, and the maximum Zn ²⁺ removal efficiency was reported to be 93.1 ± 2.1% (0.027 ± 0.008 mg/L), 99.1 ± 0.3% (0.004 ± 0.001 mg/L), and 83.2 ± 3.5% (0.067 ± 0.001 mg/L) for GO, SiO ₂ , and SnO ₂ , respectively. The maximum Zn ²⁺ adsorption capacity was also reported to be 243, 9.1, and 102 mg/g for GO, SiO ₂ , and SnO ₂ , respectively. Adsorption isotherms verified a mechanism of monolayer adsorption for the three nanomaterials. Moreover, adsorption kinetic studies revealed that chemisorption is the predominant removal mechanism for the three nanomaterials. Inner sphere surface complex mechanism was predominant in the case of Zn ²⁺ adsorption on SnO ₂ ; however, adsorption on GO and SiO ₂ was governed by outer-sphere surface mechanism at low pH values, and inner-sphere surface mechanism at high pH values. Thus, the proposed two-stage treatment of industrial wastewater was found to be efficient in removing Zn ²⁺ from wastewater. This finding can open the doors to introducing a novel integrated technology for industrial wastewater treatment.