Abstract

For over two decades, sulfate reduction with ammonium oxidation (SRAO) had been reported from laboratory experiments. SRAO was considered an autotrophic process mediated by anammox bacteria, in which ammonium as electron donor was oxidized by the electron acceptor sulfate. This process had been attributed to observed transformations of nitrogenous and sulfurous compounds in natural environments. Results obtained differed largely for the conversion mole ratios (ammonium/sulfate), and even the intermediate and final products of sulfate reduction. Thus, the hypothesis of biological conversion pathways of ammonium and sulfate in anammox consortia is implausible. In this study, continuous reactor experiments (with working volume of 3.8L) and batch tests were conducted under normal anaerobic (0.2 ≤ DO > 0.5 mg/L) / strict anaerobic (DO > 0.2 mg/L) conditions with different biomass proportions to verify the SRAO phenomena and identify possible pathways behind substrate conversion. Key findings were that SRAO occurred only in cases of high amounts of inoculant biomass under normal anaerobic condition, while absent under strict anaerobic conditions for same anammox consortia. Mass balance and stoichiometry were checked based on experimental results and the thermodynamics proposed by previous studies were critically discussed. Thus anammox bacteria do not possess the ability to oxidize ammonium with sulfate as electron acceptor and the assumed SRAO could, in fact, be a combination of aerobic ammonium oxidation, anammox and heterotrophic sulfate reduction processes.

中文翻译：

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厌氧菌团中硫酸盐还原铵氧化的生物转化途径

摘要

在过去的二十多年中，实验室实验已经报道了用铵氧化还原硫酸盐（SRAO）的方法。SRAO被认为是由厌氧菌介导的自养过程，其中作为电子给体的铵被电子受体硫酸盐氧化。该过程归因于在自然环境中观察到的含氮和含硫化合物的转化。对于转化摩尔比（铵/硫酸盐），甚至硫酸盐还原的中间产物和最终产物，所得结果差异很大。因此，在厌氧氨氧化菌群中铵和硫酸盐生物转化途径的假设是不可信的。在这项研究中，在正常厌氧（0.2≤DO> 0.5 mg / L）/严格厌氧（DO> 0）下进行了连续反应器实验（工作量为3.8L）和分批测试。2 mg / L）条件下的生物量比例不同，以验证SRAO现象并确定底物转化背后的可能途径。关键发现是，SRAO仅在正常厌氧条件下有大量接种生物量的情况下发生，而在相同厌氧菌联盟的严格厌氧条件下则不存在。根据实验结果检查了质量平衡和化学计量，并严格讨论了先前研究提出的热力学。因此，厌氧氨氧化细菌不具有以硫酸盐为电子受体氧化铵的能力，并且假定的SRAO实际上可以是好氧铵氧化，厌氧氨氧化和异养硫酸盐还原过程的组合。