Engineered Anammox Biofilms for Low-Energy Wastewater Remediation and Environmental Protection

据英国环境署称，废水中NH4+和NO3-排放到环境中的问题持续存在，对水生生态、饮用水资源和人类健康造成危害。在城市污水处理中，通常采用硝化细菌和反硝化细菌的组合将NH4+转化为NO3-，然后再转化为N2气体。但是好氧NH4+氧化过程消耗了大量的能量（用于曝气），而且成本很高。一个有吸引力的替代方案是使用厌氧氨氧化（annamox）细菌，它通过将NH4+和NO2-直接转化为N2提供了一条“捷径”。一个关键的好处是厌氧氨氧化过程是厌氧的，这意味着不需要耗能的曝气。部分硝化/厌氧氨氧化过程估计需要0.3 g-O2/g-N，远低于常规硝化/硝化过程中使用的4.57 g-O2/g-N。此外，annamox不使用外部有机碳，从而减少了60%的能源消耗，并节省了外部化学品的成本。虽然厌氧氨氧化是解决严重环境问题的一个有前途的替代方案，但它的应用目前仅限于高NH4+浓度的废水（污泥消化池的侧流）。在主流污水处理和基于自然的解决方案（如人工湿地）中的应用提出了一些挑战，特别是如何固定厌氧氨氧化菌并保持其活性。天然存在的生物膜是厌氧氨氧化菌生长最合适的“栖息地”，因为它具有较长的滞留时间、保护性基质和种内/种间的相互作用。不幸的是，天然厌氧氨氧化生物膜生长缓慢。成熟的厌氧氨氧化生物膜容易分解并失去活性，特别是在英国的低温废水中。我们的突破性想法是开发一种“合成生物膜”，通过将厌氧氨氧化细菌包裹在水基聚合物中，制成一种工程“生物涂层”。我们假设我们的生物涂层可以机械地保护细菌，增加它们与生物反应器内载体的附着力，并在它们的表面上播下天然生物膜的种子。我们将加入导电纳米粒子（ECNP），如纳米线和碳纳米管，作为刺激细胞外电子转移（EET）的桥梁，以加速厌氧氨氧化过程中NH4+的氧化速率。我们推测ECNP将为外部电子受体（NO2-除外）提供传导途径，从而阻止有害温室气体N2O的产生。目前尚无厌氧氨氧化生物膜的相关报道，证实了该研究的新颖性。我们最近在生物涂层中有其他细菌种类的经验。

According to the UK Environment Agency, there are continuing problems with the discharge of NH4+ and NO3- from wastewater to the environment, causing harm to aquatic ecology, drinking water resources, and human health. In municipal wastewater treatment, combinations of nitrifying and denitrifying bacteria are commonly used to convert NH4+ to NO3- and then to N2 gas. But the aerobic NH4+ oxidation processes consume huge amounts of energy (for aeration) and are costly. An attractive alternative is to use anaerobic ammonia oxidation (annamox) bacteria, which provide a "shortcut" by converting NH4+ and NO2- directly to N2. A key benefit is that anammox processes are anaerobic, meaning no energy-consuming aeration is needed. A partial nitrification/anammox process is estimated to require 0.3 g-O2/g-N - much less than the 4.57 g-O2/g-N used in conventional nitrification/nitrification. Moreover, annamox uses no external organic carbon, thus reducing the energy consumption by 60% plus saving cost on external chemicals. Although anammox is a promising alternative to tackle an acute environmental problem, its application is currently limited to high NH4+ concentration wastewater (side-stream from sludge digestate). Applications to mainstream sewage treatment and nature-based solutions (e.g., constructed wetland) poses several challenges, especially how to immobilize the anammox bacteria and maintain their activity. Naturally-occurring biofilms are the most suitable "habitat" for anammox growth, due to long retention times, protective matrix, and intra-/inter-species interactions. Unfortunately, natural anammox biofilm growth is slow. Mature anammox biofilms easily disintegrate and lose their activity, especially in the UK's low temperature wastewater.Our breakthrough idea is to develop a type of "synthetic biofilm" by encapsulating anammox bacteria in a water-based polymer to make an engineered "biocoating." We hypothesise that our biocoatings will protect the bacteria mechanically, will increase their adhesion to carriers inside of bioreactors, and will seed natural biofilm growth on their surfaces. We will add electrically-conducting nanoparticles (ECNP), e.g. nanowires and C nanotubes, to provide bridges to stimulate extra-cellular electron transfer (EET) to accelerate the NH4+ oxidation rates in the anammox process. We speculate the ECNP will provide conducting pathways to external electron acceptors (other than NO2-), thereby halting the production of the harmful greenhouse gas, N2O. There are no prior reports of anammox biocoatings, which confirms the research novelty. We have recent experience with other bacterial species in biocoatings.