Isolation and nitrogen removal characteristics of two heavy metal-tolerant heterotrophic nitrifying-aerobic denitrifying strains of Providencia

Abstract:

[Background] In recent years, with the expansion of the animal farming scale, a large amount of breeding sewage rich in heavy metal ions is produced. The conventional nitrogen removal technologies have limitations in treating such sewage, demonstrating reduced nitrogen removal efficiency. [Objective] To isolate and screen heavy metal-tolerant heterotrophic nitrifying-aerobic denitrifying bacteria from sewage and sludge of a sewage treatment plant and study the nitrogen removal efficiency of the isolates. [Methods] We identified the strains by observing the morphological characteristics of colonies and cells and analyzing the 16S rRNA gene sequences. With NH₄⁺-N, NO₃⁻-N, and NO₂⁻-N as the only nitrogen sources, the nitrification and denitrification performance of the strains, as well as the removal capacity of ammonia nitrogen in the presence of heavy metals (Cu, Zn, Cd, Cr, and Pb), was investigated. [Results] Two strains of heterotrophic nitrifying-aerobic denitrifying bacteria were isolated from sewage and sludge, identified as Providencia sp., and named WS-A and WH-K. Both WS-A and WH-K could grow in the media with (NH₄)₂SO₄, NaNO₃, or NaNO₂ as the only nitrogen source, with the NH₄⁺-N removal rates of 84.93% and 84.48% within 48 h, the NO₃⁻-N removal rates of 82.5% and 86.7%, and the NO₂⁻-N removal rates of 93.60% and 93.84%, respectively. WS-A and WH-K showcased the ammonia nitrogen removal rate more than 80% in the presence of 100 mg/L Zn²⁺ and the ammonia nitrogen removal rate within the range of 56% to 77% in the presence of 1 000 mg/L Cu²⁺ or 80 mg/L Cr³⁺, Cd²⁺,and Pb²⁺. [Conclusion] We screened out two strains of heterotrophic nitrifying-aerobic denitrifying bacteria showing good nitrogen removal performance under the stress of five heavy metal ions and examined their heavy metal tolerance. The findings provide technical guidance for practical application.