畜禽沼液磷回收鸟粪石结晶驱动四环素类抗生素迁移机理研究

Recovering phosphorus from the livestock and poultry biogas slurry is an important means of relieving the shortage of phosphorus ore resources worldwide. However, the high-strength antibiotic residues seriously restrict the utilization of the recovered products, and the relevant mechanisms concerning antibiotic transport in the phosphorus recovery process are not systematically studied. In this research project, tetracylines (TCs) will selected as the target veterinary antibiotics for phosphorus recovery from biogas slurry by struvite crystallization, and the status of TCs complexation will be adopted as the key clue for analyzing the TCs transport behavior. The mechanisms from the molecular level concerning struvite crystallite adsorbing TCs will be investigated through characterizing the morphology and FTIR peaks of struvite crystals before and after struvite crystals adsorbing TCs. The combination of FTIR, three dimensional fluorescence parallel factor and “exclusion chromatography+TOC+TON” analyses will be employed to evaluate the property and component variation of dissolved organic matters (DOM) during struvite crystallization. In addition, strict experiments concerning dialysis and adsorption will be conducted to analyze the scientific connection between the transformation of TCs complexing status and DOM evolution process (aggregation, hydrolysis and struvite adsorption), so as to reveal the influencing mechanism of DOM evoluton on TCs migration behavior. On these bases, a TCs transport model integrating struvite crystallizing adsorption and DOM evolution processes will be established. The performance of this project will provide scientific bases for identifying the antibiotic risk of phosphorus recovery from wastewater and developing safe phosphorus recovery technology in wastewater.

畜禽沼液磷回收是缓解磷资源短缺的重要方式之一，然而高强度的抗生素残留严重制约了磷回收产物的资源化利用，而与磷回收相关的抗生素迁移过程和作用机理缺乏系统深入的研究。本项目拟以四环素类抗生素TCs为代表性抗生素，以沼液磷回收时鸟粪石结晶反应驱动TCs结合形态转化为核心线索，通过表征鸟粪石结晶吸附TCs前后的晶形和特征峰变化，从分子水平上阐明鸟粪石结晶原位吸附TCs的作用机制；应用FTIR、三维荧光平行因子和“排阻色谱-有机碳-有机氮”分析，探明鸟粪石结晶反应时溶解性有机质DOM性质与组分的演化规律；通过严格控制条件的渗析和吸附实验研究，获取DOM凝聚、水解和鸟粪石吸附等DOM演化过程与TCs结合形态转化的科学关联，揭示DOM演化对TCs迁移的影响机制；在此基础上，建立基于鸟粪石结晶吸附与DOM演化过程协同的TCs迁移模型，为识别废水磷回收的抗生素安全风险和发展安全的废水磷回收技术提供科学依据。

采用鸟粪石（MgNH4PO4•6H2O）回收法从畜禽养殖废水中回收磷有利于缓解世界磷资源短缺的问题。然而，畜禽养殖废水广泛残留着兽用抗生素，在废水磷资源回收时易引发抗生素抗性在环境中的扩散和传播。本项目选取四环素类抗生素（Tetracyclines, TCs）为典型污染物，首先揭示了TCs在畜禽沼液鸟粪石产物中明显残留（TC、OTC、CTC、DXC分别为6.5-53.4、6.4-79.5、4.9-31.1、6.2-30.6 mg/kg）。明确碱性条件下，鸟粪石晶体主要通过静电作用吸附TCs，且鸟粪石结晶对TCs的吸附经历了快速增加、波动和稳定三个阶段；在此基础上，揭示了在不同pH值、不同P浓度条件下，不同形貌鸟粪石晶体具有不同TCs吸附能力，且鸟粪石晶体晶面上的Mg离子强度对TCs的吸附起到了关键作用。此外，溶解性有机物（Dissolved organic matters, DOM）是废水中的重要介质，对TCs的迁移行为有重要的影响。研究表明，DOM是推动鸟粪石回收时抗生素由废水向回收产物迁移的重要影响因素，实际废水中回收的鸟粪石TCs含量（360-742 μg/g），显著高于模拟废水（1.49-2.16 μg/g TCs）。根据分子量将DOM分成5级：100 kDa-0.45 μm (FDOM1)、30-100 kDa (FDOM2)、5-30 kDa (FDOM3)、1-5 kDa (FDOM4)和<1 kDa (FDOM5)。进一步分析表明大分子量DOM（如类腐殖酸、类溶解性微生物代谢产物以及类富里酸）的失稳和凝聚是驱动TCs由水相向固体产物转移的主要因素。此外，碱性条件下大分子量DOM（FDOM1和FDOM2）水解，促进TCs从大分子量DOM重新分布到小分子量DOM；之后，厘清了纯鸟粪石晶体吸附、DOM-TCs络合物吸附和DOM凝聚的贡献分别占TCs迁移总量的2.29-6.53%、23.53-34.66%和59.09-74.19%，并构建了废水鸟粪石回收时TCs在不同相的分配模型。本项目研究成果有助于认识影响抗生素迁移的关键因素和关键作用机制，为识别废水磷回收的抗生素安全风险和发展相应的控制技术开发提供了理论支撑。