Anthropogenic enrichment of phosphorus (P) in water environment can cause eutrophication, harmful algal blooms, and water quality deterioration. Adsorbents are often used for the removal and recovery of P from water, however, P is highly susceptible to re-release in anoxic benthic environments. As a response, this study prepared oxygen-carrying iron-rich biochar (O-Fe-BC) as an effective oxygen micro-nanobubble carrier (Q = 8.7024 cm³/g STP at 1.5 MPa) and P adsorbent (qm = 16.7097 mg P/g, q0.1 = 3.1974 mg P/g). Over the 90-day experimental period with O-Fe-BC, dissolved oxygen (DO) levels in the overlying water could maintain at ∼4 mg/L (peaking at ∼9.5 mg/L), and total phosphorus (TP) and soluble reactive phosphorus (SRP) levels decreased by over 96 %. The higher inorganic phosphorus content in the surface sediment-biochar mixture, along with the lower labile P and Fe concentration in the sediment pore water in the O-Fe-BC group compared to other groups, suggested the enhanced P immobilization. Further mechanism exploration revealed the combined roles of adsorption and microbial response, in which O-Fe-BC achieved efficient phosphate adsorption primarily through inner-sphere complexation via ligand exchange and keystone taxa (particularly Candidatus Electronema) played a crucial role in driving water chemistry divergence. Specially, these cable bacteria could provide large pools of Fe oxides in the surface sediment, binding with P to prevent its release, as supported by significant correlations between Ca. Electronema abundance and oxidation–reduction potential (ORP), TP, SRP, and sediment Fe-P variations. Additionally, a pot experiment with mung bean seedlings showed that the recovered O-Fe-BC significantly promoted the seed germination and growth, indicating its potential as a novel material for removing and recovering P from eutrophic waters. Taken together, our work provided a promising strategy for sustainable anoxia and P pollution mitigation, and also highlighted the indispensable roles of inner-sphere adsorption in P recovery and microbial keystone taxa in P cycling regulation.

中文翻译：

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使用携氧富铁生物炭增强缺氧水中的磷去除能力：吸附和关键分类群的综合作用


水环境中磷 （P） 的人为富集会导致富营养化、有害藻华和水质恶化。吸附剂通常用于从水中去除和回收 P，但是，P 在缺氧底栖环境中极易重新释放。作为回应，本研究制备了携氧富铁生物炭 （O-Fe-BC） 作为有效的氧微纳米气泡载体 （Q = 8.7024 cm³/g STP，1.5 MPa） 和 P 吸附剂 （qm = 16.7097 mg P/g，q0.1 = 3.1974 mg P/g）。在使用 O-Fe-BC 的 90 天实验期间，上覆水中的溶解氧 （DO） 水平可以保持在 ∼4 mg/L（峰值约为 ∼9.5 mg/L），总磷 （TP） 和可溶性活性磷 （SRP） 水平下降了 96% 以上。与其他组相比，O-Fe-BC 组表面沉积物-生物炭混合物中较高的无机磷含量，以及沉积物孔隙水中不稳定的 P 和 Fe 浓度较低，表明 P 固定化增强。进一步的机制探索揭示了吸附和微生物反应的综合作用，其中 O-Fe-BC 主要通过配体交换的球内络合实现高效的磷酸盐吸附，而关键分类群（特别是 Candidatus Electronema）在驱动水化学分歧中起着至关重要的作用。特别是，这些电缆细菌可以在表面沉积物中提供大量 Fe 氧化物，与 P 结合以防止其释放，这得到了 Ca. Electronema 丰度与氧化还原电位 （ORP）、TP、SRP 和沉积物 Fe-P 变化之间的显着相关性的支持。 此外，绿豆幼苗的盆栽试验表明，回收的 O-Fe-BC 显著促进了种子的发芽和生长，表明其作为从富营养化水域中去除和回收 P 的新材料的潜力。综上所述，我们的工作为可持续缺氧和 P 污染缓解提供了一种有前途的策略，并且还强调了球内吸附在 P 恢复中不可或缺的作用和微生物关键分类群在 P 循环调节中的作用。