Nitrite-oxidizing bacteria (NOB) can be inhibited by high concentrations of heavy metals; however, trace elements (TE) are critical for their growth and sustained activity. In this first time report, the long-term impacts of limiting Ni(II), Co(II), and Zn(II) on nitrite oxidation were separately evaluated using a continuous test system, wherein NOB was immobilized on polyvinyl alcohol gel carriers. Even under Ni(II)- and Co(II)-limited conditions, a high nitrite oxidation rate (NOR) of 1.2 kg-N m⁻3 d⁻1 was maintained for three months without these TE supplementation, suggesting that continuous addition of Ni(II) or Co(II) is not strictly necessary. In contrast, Zn(II) limitation suppressed NOR to 0.8 kg-N m-3 d⁻1. Supplementation with 1 µg L⁻1 Zn(II) initiated NOR recovery, and 2 µg L⁻1 fully restored activity. Under all limitation conditions and during Zn(II) recovery, microbial community analysis focusing on NOB revealed that Nitrospira consistently accounted for only a few percent, whereas Nitrobacter showed a relatively high abundance of approximately 20%. These findings highlight the essential role of Zn(II) in maintaining optimal nitrite oxidation and demonstrate that minimal TE supplementation can be crucial for stable nitrification performance in nitrogen wastewater treatment systems, particularly where background TE concentrations are inadequate.
Hamabe et al. (Thu,) studied this question.