Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.
Water Res. 2013 Aug 1;47(12):3866-77. doi: 10.1016/j.watres.2012.11.060. Epub 2013 Mar 26.
Discharge of silver nanoparticles (Ag-NP) from textiles and cosmetics, todays major application areas for metallic Ag-NP, into wastewater is inevitable. Transformation and removal processes in sewers and wastewater treatment plants (WWTP) will determine the impact of Ag-NP on aquatic and terrestrial environments, via the effluents of the WWTP and via the use of digested sludge as fertilizer. We thus conducted experiments addressing the behavior of Ag-NP in sewers and in WWTP. We spiked Ag-NP to a 5 km long main trunk sewer and collected 40 wastewater samples after 500 m, 2400 m and 5000 m each according to the expected travel times of the Ag-NP. Excellent mass closure of the Ag derived by multiplying the measured Ag concentrations times the volumetric flow rates indicate an efficient transport of the Ag-NP without substantial losses to the sewer biofilm. Ag-NP reacted with raw wastewater in batch experiments were sulfidized to roughly 15% after 5 h reaction time as revealed by X-ray absorption spectroscopy (XAS). However, acid volatile sulfide (AVS) concentrations were substantially higher in the sewer channel (100 μM) compared to the batch experiments (3 μM; still sufficient to sulfidize spiked 2 μM Ag) possibly resulting in a higher degree of sulfidation in the sewer channel. We further investigated the removal efficiency of 10 nm and 100 nm Ag- and gold (Au)-NP coated with citrate or polyvinylpyrrolidone in activated sludge batch experiments. We obtained very high removal efficiencies (≈ 99%) irrespective of size and coating for Ag- and Au-NP, the latter confirming that the particle type was of minor importance with respect to the degree of NP removal. We observed a strong size dependence of the sulfidation kinetics. We conclude that Ag-NP discharged to the wastewater stream will become sulfidized to various degrees in the sewer system and are efficiently transported to the WWTP. The sulfidation of the Ag-NP will continue in the WWTP, but primarily depending on the size the Ag-NP, may not be complete. Very high removal efficiencies in the WWTP will divert most of the Ag-NP mass flow to the digester and only a small fraction of the Ag will be released to surface waters.
从纺织品和化妆品中释放出的银纳米粒子（Ag-NP），是当今金属 Ag-NP 的主要应用领域，不可避免地会进入废水。污水管道和废水处理厂（WWTP）中的转化和去除过程，将通过 WWTP 的废水以及使用消化污泥作为肥料，来决定 Ag-NP 对水生和陆地环境的影响。因此，我们进行了实验，以研究 Ag-NP 在污水管道和 WWTP 中的行为。我们向一条 5 公里长的主污水管中注入 Ag-NP，并在预计 Ag-NP 的迁移时间后，在 500 米、2400 米和 5000 米处分别采集了 40 个废水样本。Ag 的质量封闭性非常好，通过将测量的 Ag 浓度乘以体积流量相乘得出，这表明 Ag-NP 的传输效率很高，没有大量损失到污水生物膜中。在批处理实验中，Ag-NP 与原废水反应，5 小时后硫化反应约为 15%，这一结果通过 X 射线吸收光谱（XAS）揭示。然而，与批处理实验（3 μM；仍足以硫化注入的 2 μM Ag）相比，污水管道中的酸可挥发硫化物（AVS）浓度要高得多（100 μM），这可能导致污水管道中硫化程度更高。我们进一步研究了在活性污泥批处理实验中，用柠檬酸或聚乙烯吡咯烷酮涂覆的 10nm 和 100nm 的 Ag 和金（Au）-NP 的去除效率。对于 Ag 和 Au-NP，我们获得了非常高的去除效率（≈99%），无论尺寸和涂层如何，后者证实了与 NP 去除程度相比，颗粒类型的重要性较小。我们观察到硫化动力学的强烈尺寸依赖性。我们得出的结论是，排入废水的 Ag-NP 将在污水系统中被硫化到不同程度，并有效地输送到 WWTP。Ag-NP 的硫化将在 WWTP 中继续，但主要取决于 Ag-NP 的尺寸，可能不完全。在 WWTP 中非常高的去除效率将使大部分 Ag-NP 质量流转移到消化器中，只有一小部分 Ag 将释放到地表水中。
