Denitrification performance of the nitrate-dependent manganese redox strain Dechloromonas sp. YZ8 under copper ion (Cu(Ⅱ)) stress: Promotion mechanism and immobilization efficacy.

A novel nitrate-dependent manganese (Mn) redox strain was isolated and identified as Dechloromonas sp.YZ8 in this study. The growth conditions of strain YZ8 were optimized by kinetic experiments. The nitrate (NO-N) removal efficiency was 100.0 % at 16 h at C/N of 2.0, pH of 7.0, and Mn(II) or Mn(IV) addition of 10.0 or 500.0 mg L, along with an excellent Mn redox capacity. Transmission electron microscopy supported the Mn redox process inside and outside the cells of strain YZ8. When strain YZ8 was exposed to different concentrations of copper ion (Cu(II)), it turned out that moderate amounts of Cu(II) increased microbial activity and metabolic activities. Moreover, it was discovered that the appropriate amount of Cu(II) promoted the conversion of Mn(IV) and Mn(II) to Mn(III) and improved electron transfer capacity in the Mn redox system, especially the Mn redox process dominated by Mn(IV) reduction. Then, δ-MnO and bio-manganese oxides (BMO) produced during the reaction process have strong adsorption of Cu(II). The surface valence changes of δ-MnO before and after the reaction and the production of BMO, Mn(III)-rich intermediate black manganese ore (MnO), and Mn secondary minerals together confirmed the Mn redox pathway. The study provided new insights into the promotion mechanism and immobilization effects of redox-coupled denitrification of Mn in groundwater under Cu(II) stress.