Evaluation of the Long-Term Effect of Cr(III), Zn(II), Cd(II), Cu(II), Ni(II) and Pb(II) on the Anammox Process In A Continuous-Flow Anaerobic Membrane-Assisted Bioreactor (AnMBR)

The anaerobic ammonium oxidation (anammox) process, is widely applied for high nitrogen wastewater treatment, such as from reject water, landfill leachate, tannery wastewater, or coke-oven wastewater. However, the anammox process exhibits sensitivity to many substances that can be found in industrial wastewater, including heavy metals. In the present study, the long-term effect of a combination of heavy metals ions (Cr (III), Zn (II), Cd (II), Cu (II), Ni (II), and Pb (II)) on the nitrogen removal efficiency and biodiversity of the anammox bacteria in an anaerobic membrane bioreactor (AnMBR) was investigated. The findings indicated that even short-term exposure to low concentrations of these ions (Cr-0.25, Zn-1.6, Cd-0.004, Ni-0.18, Pb-0.1 and Cu-0.15 mg/L) significantly lowered the anammox bacteria’s activity, and the nitrogen removal rate decreased from 0.21 to 0.05 g N/L∙d. Moreover, the presence of these metals directly altered bacterial biodiversity. After eliminating heavy metals from the influent, recovery of the initial nitrogen removal rate took approximately 80 days. Concentrations of Cr-0.125, Zn-0, Cd-0.002, Ni-0.09, Pb-0.05, and Cu-0.075 mg/L were shown not to impact process performance negatively. Additionally, it was demonstrated that zinc was the least tolerated heavy metal in the reactor.