Australian Centre for Water and Environmental Biotechnology, The University of Queensland, St Lucia, QLD 4072, Australia.
Ecological Engineering of Mine Wastes, Sustainable Minerals Institute, The University of Queensland, Brisbane, QLD 4072, Australia.
Water Res. 2023 Sep 1;243:120370. doi: 10.1016/j.watres.2023.120370. Epub 2023 Jul 18.
Acidic partial nitritation (PN) has emerged to be a promisingly stable process in wastewater treatment, which can simultaneously achieve nitrite accumulation and about half of ammonium reduction. However, directly applying anaerobic ammonium oxidation (anammox) process to treat the acidic PN effluent (pH 4-5) is susceptible to the inhibition of anammox bacteria. Here, this study demonstrated the adaptation of anammox process to acidic pH in a moving bed biofilm reactor (MBBR). By feeding the laboratory-scale MBBR with acidic PN effluent (pH = 4.6 ± 0.2), the pH of an anammox reactor was self-sustained in the range of pH 5 - 6. Yet, a high total nitrogen removal efficiency of over 80% at a practical loading rate of up to 149.7 ± 3.9 mg N/L/d was achieved. Comprehensive microbial assessment, including amplicon sequencing, metagenomics, cryosection-FISH, and qPCR, identified that Candidatus Brocadia, close to known neutrophilic members, was the dominant anammox bacteria. Anammox bacteria were found present in the inner layer of thick biofilms but barely present in the surface layer of thick biofilms and in thin biofilms. Results from batch tests also showed that the activity of anammox biofilms could be maintained when subjected to pH 5 at a nitrite concentration of 10 mg N/L, whereas the activity was completely inhibited after disturbing the biofilm structure. These results collectively indicate that the anammox bacteria enriched in the present acidic MBBR could not be inherently acid-tolerant. Instead, the achieved stable anammox performance under the acidic condition is likely due to biofilm stratification and protection. This result highlights the biofilm configuration as a useful solution to address nitrogen removal from acidic PN effluent, and also suggests that biofilm may play a critical role in protecting anammox bacteria found in many acidic nature environments.
酸性短程硝化（PN）已成为一种稳定的废水处理工艺，可以同时实现亚硝酸盐积累和大约一半的氨氮还原。然而，直接将厌氧氨氧化（anammox）工艺应用于处理酸性 PN 出水（pH 4-5）时，容易受到 anammox 细菌的抑制。本研究在移动床生物膜反应器（MBBR）中展示了 anammox 工艺对酸性 pH 的适应性。通过向实验室规模的 MBBR 中供给酸性 PN 出水（pH = 4.6 ± 0.2），anammox 反应器的 pH 自维持在 pH 5-6 范围内。然而，在高达 149.7 ± 3.9 mg N/L/d 的实际负荷率下，实现了超过 80%的高总氮去除效率。综合微生物评估，包括扩增子测序、宏基因组学、冷冻切片-FISH 和 qPCR，确定了接近已知嗜中性成员的 Candidatus Brocadia 是优势 anammox 细菌。anammox 细菌存在于厚生物膜的内层，但在厚生物膜的表面层和薄生物膜中几乎不存在。批处理试验的结果还表明，当亚硝酸浓度为 10 mg N/L 时，anammox 生物膜的活性可以在 pH 5 下维持，而当破坏生物膜结构时，活性则完全受到抑制。这些结果共同表明，在本研究中富集的酸性 MBBR 中的 anammox 细菌并非固有耐酸。相反，在酸性条件下实现稳定的 anammox 性能可能是由于生物膜的分层和保护。这一结果突出了生物膜结构作为处理酸性 PN 出水脱氮的有效解决方案的重要性，同时也表明生物膜可能在保护许多酸性自然环境中发现的 anammox 细菌方面发挥着关键作用。
