Long-term effect of heavy metals Cr(III), Zn(II), Cd(II), Cu(II), Ni(II), Pb(II) on the anammox process performance

The process of the anaerobic ammonia oxidation (anammox) has been successfully used to remove nitrogen from reject water after dewatering of the digested sewage sludge. However, it is also used on other types of wastewater, including industrial wastewater, which may contain substances that inhibit this process. Examples of such substances include heavy metals which may be found in tanning wastewater, landfill leachate, or coke oven wastewater. The study presented shows the influence of two different mixtures of heavy metals on the anammox process in a long-term test. In SBR1, a mixture of nickel (Ni²⁺), copper (Cu²⁺), and zinc (Zn²⁺) was tested, while in SBR3 a mixture of chromium (Cr³⁺), cadmium (Cd²⁺), and lead (Pb²⁺) was checked, whereas the SBR2 reactor was a control reactor. The study demonstrated that even the highest levels of chromium, cadmium, and lead tested did not inhibit the process. However, in the case of the second metal mixture, strong inhibition of the nitrogen removal efficiency was observed. It was shown that zinc is the metal that was predominantly responsible for the inhibition, and its elimination from the incoming sewage allowed to restore the initial efficiency of the process.