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氨氮一般指水中以游离氨(
$ {\text{NH}}_{\text{3}} $ )和铵离子($ {\text{NH}}_{\text{4}}^{\text{+}} $ )形式存在的氮,是一种水体污染物,主要来源于城市地区人类活动和农业、工业生产过程[1]。氨在水中不完全硝化会产生亚硝酸盐,若被饮用会和蛋白质结合形成致癌的亚硝胺,严重影响人体健康[2-3]。高浓度的氨氮也会使水体富营养化,导致水华和赤潮等现象,直接影响水体生态环境[4]。废水脱氨主要方法有生物法、化学沉淀法、吹脱法、吸附法[5]。但是生物法流程长,反应器大,占地多,常需要额外投加碳源,能耗大,成本高;化学沉淀法成本高,再生难,有二次污染;吹脱法能耗大,有二次污染,出水氨氮浓度仍然偏高。吸附法具有除污效率高、操作便捷、适用范围广、吸附剂可重复使用等优点,在氨氮废水处理中逐渐得到了广泛关注。ALSHAMERI等[6]对比了高岭石、埃洛石、蒙脱石、海泡石等六种天然粘土矿物对
$ {\text{NH}}_{\text{4}}^{\text{+}} $ 的吸附性能,发现天然粘土矿物是经济、安全且有效的$ {\text{NH}}_{\text{4}}^{\text{+}} $ 吸附剂,具有良好的发展前景。尽管吸附法具有较高的氨氮去除效率,同时也为废水中氮回收提供了可能,但颗粒吸附材料在废水处理后的低碳回收问题尚未得到有效解决。目前,大部分吸附材料多以微纳米颗粒的形式存在,直接与废水混合能够充分利用其吸附性能,但也存在微纳米材料使用中流失和回收困难等问题。通过微滤或超滤膜辅助回收,将会增加额外能耗和成本,影响其进一步的推广应用。也有研究将吸附材料制备成毫米级微球,通过柱吸附实现污染物去除,但大颗粒吸附材料吸附容量低于微纳米颗粒[7]。因此,如何既能保证吸附容量,又能实现微尺度吸附材料的低碳回收,已经成为吸附法应用中的新困难。动态膜技术具有成本低、操作压力小、清洗简单、微颗粒分离效果好等优点,为微尺度颗粒材料回收提供了绿色低碳新方法[8]。但目前多数研究围绕在动态膜系统过滤特性和应用效能,沸石吸附脱氨效能和优化改性,鲜有对动态膜成膜材料吸附性能的拓展和深度耦合探索,及对动态膜系统和成膜材料作用的独立解析,考虑到沸石吸附脱氨和动态膜分离的优点和不足,本研究尝试构建吸附与动态膜耦合系统,同步实现废水中氨氮去除和颗粒吸附材料回收,从而为吸附法进一步走向工程应用提供新方案。
本研究围绕吸附脱氨和动态膜回收2个方面,通过静态吸附实验,系统探究沸石吸附脱氨效能和投加量、初始氨氮浓度对脱氨效能的影响,揭示沸石吸附氨氮的动力学特性,阐明吸附-动态膜系统的脱氨效果和成膜特征,为沸石吸附脱氨和沸石颗粒回收的进一步应用提供参考。
复合沸石动态膜系统的脱氨效能及其对沸石的同步回收
Simultaneous ammonia removal and zeolite recovery by a composite zeolite dynamic membrane system
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摘要: 为同步实现吸附脱氨和微尺寸沸石回收,将沸石与动态膜技术耦合联用,构建了一种复合沸石-动态膜系统,并考察其脱氨和沸石回收效果。在初始氨氮质量浓度为10 mg·L−1条件下,投加10 g·L−1沸石可有效实现氨氮的去除,去除率为67%。吸附动力学和等温模型分析结果表明,该过程符合准二级动力学模型,Langmuir吸附等温模型拟合得到的最大氨氮吸附量为4.12 mg·g −1。按照1:1的质量比投加沸石与硅藻土,在投加量均为1 g·L−1,流量为40 mL·min−1,支撑膜孔径38 μm下可快速形成动态膜,出水浊度稳定在1 NTU以下,氨氮去除率可达到56%,在脱氨的同时能够实现沸石的有效回收。该研究结果可为复合沸石动态膜系统同步吸附脱氨和吸附材料回收提供参考。Abstract: To achieve simultaneous ammonia adsorption and microscale zeolite recovery, zeolite was coupled with dynamic membrane technology to establish a composite zeolite-dynamic membrane system, and its ammonia removal rate and zeolite recovery efficiency were evaluated. At initial ammonia concentration of 10 mg·L−1, 67% ammonia could be removed effectively with 10 g·L−1 zeolite dosing. The adsorption kinetics and isothermal model indicated that the adsorption fitted well with the pseudo-second-order model, and the theoretical maximum adsorption capacity was 4.12 mg·g−1 predicted by Langmuir model. Zeolite and diatomite were mixed in the zeolite-dynamic membrane system at a mass ratio of 1:1, and the composite zeolite dynamic membrane could rapidly form under the conditions of 1 g·L−1 dosage, 40 mL·min−1 flow rate and 38 μm supporting membrane. After the formation of DM layer, the effluent turbidity remained stably below 1 NTU, and ammonia removal rate was 56%. Ammonia removal and zeolite recovery were achieved at the same time, which laid the foundation for simultaneous ammonia adsorption and adsorbents recovery for the composite zeolite dynamic membrane system in future.
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Key words:
- ammonia /
- adsorption /
- dynamic membrane /
- zeolite /
- recovery
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表 1 准一级与准二级动力学方程拟合参数及相关系数
Table 1. Fitting parameters and correlation coefficients of pseudo-first order kinetics and pseudo second order kinetics
qe,exp /(mg·g−1) 准一级动力学 准二级动力学 qe,celc/(mg·g−1) k1/min−1 R2 qe,celc/(mg·g−1) k2/(g·(mg·min)−1) R2 1.30 1.22 0.21 0.969 1.24 0.34 0.982 表 2 Langmuir与Freundlich吸附等温模型拟合参数及相关系数
Table 2. Fitting parameters and correlation coefficients of adsorption isotherm models of Langmuir and Freundlich
温度/ ℃ Langmuir Freundlich qm/(mg·g−1) b/(L·mg−1) R2 Kf/(mg(1−1/n) g−1 L1/n) 1/n R2 25 4.12 0.33 0.995 0.69 0.40 0.960 -
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