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

根据英国环境局的说法，废水中的NH4+和NO3-排放到环境中的问题持续存在，对水生态、饮用水资源和人类健康造成了危害。在城市污水处理中，硝化细菌和反硝化细菌的组合常用于将NH4+转化为NO3-，然后再转化为氮气。但好氧NH4+氧化过程消耗大量能量(用于曝气)，而且成本高昂。一种有吸引力的替代方案是使用厌氧氨氧化(Annamox)细菌，这种细菌通过将NH4+和NO2-直接转化为氮气提供了一条“捷径”。一个关键的好处是厌氧氨氧化工艺是厌氧的，这意味着不需要耗能的曝气。据估计，部分硝化/厌氧氨氧化工艺需要0.3g-O2/g-N，远低于传统硝化/硝化所需的4.57g-O2/g-N。此外，Annamox不使用外部有机碳，因此降低了60%的能源消耗，并节省了外部化学品的成本。虽然Anammox是一种很有前途的解决严重环境问题的替代方案，但目前它的应用仅限于高NH4+浓度的废水(来自污泥填埋场的侧流)。应用于主流污水处理和基于自然的解决方案(例如人工湿地)带来了几个挑战，特别是如何固定化厌氧氨氧化细菌并保持其活性。自然形成的生物膜是最适合厌氧氨氧化生长的“栖息地”，因为它具有较长的保留时间、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很容易解体和失去活性，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”，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将从机械上保护细菌，增加它们与生物反应器内载体的粘附性，并在它们的表面种植自然的生物膜。我们将添加导电纳米颗粒(ECNP)，例如纳米线和碳纳米管，以提供桥梁来刺激细胞外电子转移(EET)，以加快Anammox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。之前没有关于厌氧氨氧化生物涂料的报道，这证实了研究的新颖性。我们最近在生物涂料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.