基于沼液膜浓缩的重金属和抗生素阻控作用机制研究

For solving the problems such as large output, high storage and transportation cost and low nutrient content of biogas slurry, membrane concentration technology has provided feasibility for the utilization of biogas slurry, but the risk factors including heavy metals and antibiotics should be effectively removed before membrane concentration. As the pretreatment of reverse osmosis, ceramic membrane ultrafiltration will be applied so as to remove trace heavy metals and antibiotics in biogas slurry simultaneously. Firstly, the retention efficiency of heavy metals and antibiotics in biogas slurry by ceramic membrane will be investigated, and the effect of water quality and membrane process parameters on the removal of the pollutants will be studied. The adsorption behavior of antibiotics by suspended solid (SS) in biogas slurry will be studied by a variety of instruments under the condition of changing the water quality parameters. The semi-equilibrium dialysis combined with 3D fluorescence spectrum will be employed to investigate the interaction between antibiotics and dissolved organic matter (DOM) in biogas slurry. Dynamic light scattering will be applied for measuring particle size distribution of SS and DOM colloid. The microstructure, morphology, surface functional groups and the element composition of ceramic membrane will be characterized by several spectroscopic and spectral methods such as atomic force microscopy, FT-IR, Raman spectroscopy. On the basis the retention mechanism of heavy metals and antibiotics by ceramic membrane will be revealed. The study will be of theoretical and practical significance to realize harmlessness, reduction and resource utilization of biogas slurry.

针对沼液产量大、储存运输费用高和营养物质含量偏低等问题，膜浓缩技术为当前沼液资源化利用提供了可行性，但沼液中的重金属和抗生素等风险因子需在膜浓缩前进行有效去除。本项目拟采用陶瓷膜超滤用于反渗透膜浓缩的前处理，实现对沼液复杂水质背景下重金属和抗生素的同步去除。首先考察陶瓷膜对沼液中重金属和抗生素的截留效能，研究关键水质因子和膜滤工艺参数对目标物去除的影响。然后通过改变水质条件、结合多种仪器分析沼液中颗粒物组分对抗生素的吸附行为；采用平衡透析法结合三维荧光猝灭光谱重点研究抗生素与沼液中溶解性有机物之间的相互作用；通过动态光散射测定膜滤沼液过程中颗粒物及胶体的粒径分布；应用原子力显微镜、傅里叶红外、拉曼光谱等多种光谱和波谱手段，观测受污染陶瓷膜的微结构、形态、表面官能团和元素组成。通过上述研究阐明陶瓷膜对沼液中重金属和抗生素的阻控作用机制。本研究对于推进沼液无害化减量化资源化具有理论和现实意义。

沼液作为沼气工程的主要副产物，在资源化利用过程中面临诸多问题：沼液的连续产生与作物的季节性需肥存在矛盾、而远距离运输成本过高；与化肥或商品有机肥相比, 沼液中各项营养元素浓度偏低；沼液含有大量悬浮颗粒物，使其在水肥一体化喷滴灌的应用受到阻碍；沼液中残留的重金属、抗生素、致病菌和病毒等污染物使其长期还田利用存在较大的生态环境风险。因此沼液需要进行减量化和无害化处理方能进行资源化利用，本项目利用具有高效过滤及抗污染性能的陶瓷超滤膜，用于沼液反渗透膜浓缩的前处理，在探明陶瓷超滤膜对沼液中重金属和抗生素的截留特征，并阐明其阻控作用机制的基础上，通过工艺参数优化和水质因子调控，实现对残留重金属和抗生素的高效稳定同步去除。研究证明7种不同孔径陶瓷膜中10～50 nm超滤陶瓷膜通量较高，20 nm陶瓷膜通量随温度升高呈指数型增长；较适宜的膜面流速为3.0 m/s，对应的膜通量可达175 L/(m2•h)；经济性较高的变频器运行频率范围为40～45 Hz；20 nm陶瓷膜的极限浓缩倍数大于10倍，优于100 nm膜。20 nm陶瓷膜对沼液中微量抗生素-磺胺二甲嘧啶的截留效率有限，不同水质条件下截留效率有所差别：随着沼液初始pH的升高，陶瓷膜超滤对SMZ的去除率呈现先降低后上升的趋势；加入Na+后，SMZ的去除率略有下降，而加入Ca2+后，陶瓷膜超滤对SMZ的去除率有较大提升；沼液中的腐殖质类有机物和悬浮颗粒物可提高陶瓷膜超滤对SMZ的去除率；絮凝预处理有助于陶瓷膜超滤对SMZ的截留。平衡透析实验结果表明沼液中粒径200-450nm组分对SMZ的结合力最强。实验还发现20nm陶瓷膜可完全截留猪瘟、蓝耳、伪狂犬等病毒。综上所述，20 nm陶瓷膜可完全去除沼液中浊度，并对沼液中多种重金属、病毒等具有良好的阻控效果，同时较好的保留溶解性有机质和氮磷钾等无机营养。本研究对于深入理解沼液复杂水质背景下重金属和抗生素的环境化学行为具有科学意义，对于通过膜技术实现沼液无害化、减量化和资源化具有现实意义。