Key Laboratory of Three Gorges Reservoir Region's Eco-Environment, Ministry of Education, Chongqing University, Chongqing, 400045, China; College of Environment and Ecology, Chongqing University, Chongqing, 400045, China.
Key Laboratory of Three Gorges Reservoir Region's Eco-Environment, Ministry of Education, Chongqing University, Chongqing, 400045, China; College of Environment and Ecology, Chongqing University, Chongqing, 400045, China.
J Environ Manage. 2022 Aug 1;315:115109. doi: 10.1016/j.jenvman.2022.115109. Epub 2022 Apr 29.
A recent study found that the nitrogen cycle in marine sediments can occur under oxygen-limited conditions, and this is associated with a reduction of Mn (IV). However, the effect of MnO mediated anoxic ammonia oxidation in different sediments field test results are controversial. In this study, based on the fact that the crystal form and morphology of MnO in marine sediments are affected by geochemistry, α-, β-, γ-MnO and amorphous MnO were prepared to explore the effect of the different MnO crystals on nitrogen removal under oxygen-limited conditions. The experimental results showed that the anoxic ammonia oxidation process was mediated by microorganisms, and the reaction was affected by pH and temperature. The optimal pH was 7 in the range of pH 4-9 and the optimal temperature was 25 °C in the range of 10 °C-40 °C. When the initial concentration of NH-N was 50 mg/L, the removal amounts of NH-N under an anoxic condition by α-, β-, γ-MnO and amorphous MnO were 18.97 mg/L/d, 6.12 mg/L/d, 10.68 mg/L/d and 24.89 mg/L/d, respectively. During the anoxic oxidation between MnO and NH-N, the adsorption process occurred. In addition, the oxidation process produced both NO-N (nitrification reaction) and gaseous nitrogen (ammonia oxidation reaction). The kinetic study showed that the NH-N removal process conformed to the pseudo-second-order rate model, and the removal rates were ranked as amorphous MnO > α- > γ- > β-MnO. Together, these results showed that the amorphous MnO crystal structure was conducive to improve anoxic ammonia oxidation and nitrogen removal under oxygen-limited conditions.
最近的一项研究发现，海洋沉积物中的氮循环可以在缺氧条件下发生，这与 Mn（IV）的还原有关。然而，MnO 介导的不同沉积物现场测试中缺氧氨氧化的效果存在争议。在这项研究中，基于海洋沉积物中 MnO 的晶体形态和形貌受地球化学影响的事实，制备了 α-、β-、γ-MnO 和无定形 MnO，以探讨不同 MnO 晶体在缺氧条件下对氮去除的影响。实验结果表明，缺氧氨氧化过程是由微生物介导的，反应受 pH 值和温度的影响。在 pH4-9 的范围内，最佳 pH 值为 7，在 10-40°C 的范围内，最佳温度为 25°C。当 NH-N 的初始浓度为 50mg/L 时，α-、β-、γ-MnO 和无定形 MnO 在缺氧条件下对 NH-N 的去除量分别为 18.97mg/L/d、6.12mg/L/d、10.68mg/L/d 和 24.89mg/L/d。在 MnO 和 NH-N 之间的缺氧氧化过程中，发生了吸附过程。此外，氧化过程产生了 NO-N（硝化反应）和气态氮（氨氧化反应）。动力学研究表明，NH-N 去除过程符合拟二级速率模型，去除速率的顺序为无定形 MnO>α->γ->β-MnO。总之，这些结果表明，无定形 MnO 晶体结构有利于提高缺氧条件下的氨氧化和氮去除。
