Key Laboratory of Water and Sediment Sciences of Ministry of Education, State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, PR China.
Department of Civil and Environmental Engineering, Rice University, 6100 Main Street, Houston, TX 77005, United States.
Water Res. 2014 Jul 1;58:62-70. doi: 10.1016/j.watres.2014.03.028. Epub 2014 Mar 21.
The growing production and application of silver nanoparticles (Ag NPs) increases the chance of these particles entering wastewater treatment plants and interacting with activated sludge. In this paper, the removal of Ag NPs by flocculent and granular sludge was studied, and the short- and long-term inhibitory impacts of Ag NPs on the sludge were compared. Results showed that both forms of sludge contributed to removal of Ag NPs with 30-58% and 2.5-9.4% removal by the flocculent sludge and the granular sludge, respectively, at Ag NP dosage of 1-8 mg/L. Exposure to Ag NPs had greater inhibitive effects on the flocculent sludge than the granular sludge. Short-term (12 h) exposure to Ag NPs at 1, 10, 50 and 100 mg/L reduced the ammonia oxidizing rate of the flocculent sludge by 21.0-24.9%, while no inhibition was found for the granular sludge; the oxygen uptake rate of the flocculent sludge was inhibited at Ag NP concentrations as low as 1 mg/L, while that of the granular sludge was only affected at much higher Ag NP concentrations (50 and 100 mg/L). The denitrification rate, however, was not inhibited for either sludge. After long-term (22 day) exposure to 5 and 50 mg/L of Ag NPs, flocculent sludge was significantly inhibited on ammonia oxidizing rate, denitrification rate and oxygen uptake rate, but the microbial activity of granular sludge was not inhibited. Exposure to Ag NPs resulted in oxidative stress and damage of bacterial cell integrity for both flocculent and granular sludge as was determined by generation of reactive oxygen species and release of lactate dehydrogenase (LDH). The toxic effect of Ag NPs on sludge was mediated via both ROS-dependent and ROS-independent pathways, and both small (<10 nm) and large (>10 nm) Ag NPs contributed to it. Overall, granular sludge demonstrated stronger resistance to the toxicity of Ag NPs than flocculent sludge, while flocculent sludge was more efficient in removing Ag NPs.
纳米银（Ag NPs）的产量和应用不断增加，这增加了这些颗粒进入废水处理厂并与活性污泥相互作用的机会。本文研究了絮状和颗粒状污泥对 Ag NPs 的去除效果，并比较了 Ag NPs 对污泥的短期和长期抑制影响。结果表明，Ag NPs 剂量为 1-8mg/L 时，两种污泥都有助于去除 Ag NPs，絮状污泥的去除率为 30-58%，颗粒状污泥的去除率为 2.5-9.4%。Ag NPs 对絮状污泥的抑制作用大于颗粒状污泥。在 1、10、50 和 100mg/L 的 Ag NPs 短期（12h）暴露下，絮状污泥的氨氧化速率降低了 21.0-24.9%，而颗粒状污泥没有受到抑制；絮状污泥的耗氧速率在 Ag NPs 浓度低至 1mg/L 时受到抑制，而颗粒状污泥仅在更高的 Ag NPs 浓度（50 和 100mg/L）下受到影响。然而，两种污泥的反硝化速率都没有受到抑制。在长期（22 天）暴露于 5 和 50mg/L 的 Ag NPs 后，絮状污泥的氨氧化速率、反硝化速率和耗氧速率受到显著抑制，但颗粒状污泥的微生物活性没有受到抑制。Ag NPs 的暴露导致了絮状和颗粒状污泥的氧化应激和细菌细胞完整性的损伤，这是通过活性氧（ROS）的产生和乳酸脱氢酶（LDH）的释放来确定的。Ag NPs 对污泥的毒性作用是通过 ROS 依赖和非 ROS 依赖途径介导的，小（<10nm）和大（>10nm）Ag NPs 都起到了作用。总的来说，颗粒状污泥对 Ag NPs 的毒性比絮状污泥具有更强的抵抗力，而絮状污泥在去除 Ag NPs 方面更有效。
