Chen Hong, Zheng Xiong, Chen Yinguang, Li Mu, Liu Kun, Li Xiang
State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, Shanghai, China.
PLoS One. 2014 Mar 24;9(3):e92871. doi: 10.1371/journal.pone.0092871. eCollection 2014.
The physical-chemical properties of activated sludge, such as flocculating ability, hydrophobicity, surface charge, settleability, dewaterability and bacteria extracellular polymer substances (EPS), play vital roles in the normal operation of wastewater treatment plants (WWTPs). The nanoparticles released from commercial products will enter WWTPs and can induce potential adverse effects on activated sludge. This paper focused on the effects of copper nanoparticles (CuNPs) on these specific physical-chemical properties of activated sludge. It was found that most of these properties were unaffected by the exposure to lower CuNPs concentration (5 ppm), but different observation were made at higher CuNPs concentrations (30 and 50 ppm). At the higher CuNPs concentrations, the sludge surface charge increased and the hydrophobicity decreased, which were attributed to more Cu2+ ions released from the CuNPs. The carbohydrate content of EPS was enhanced to defense the toxicity of CuNPs. The flocculating ability was found to be deteriorated due to the increased cell surface charge, the decreased hydrophobicity, and the damaged cell membrane. The worsened flocculating ability made the sludge flocs more dispersed, which further increased the toxicity of the CuNPs by increasing the availability of the CuNPs to the bacteria present in the sludge. Further investigation indicated that the phosphorus removal efficiency decreased at higher CuNPs concentrations, which was consistent with the deteriorated physical-chemical properties of activated sludge. It seems that the physical-chemical properties can be used as an indicator for determining CuNPs toxicity to the bacteria in activated sludge. This work is important because bacteria toxicity effects to the activated sludge caused by nanoparticles may lead to the deteriorated treatment efficiency of wastewater treatment, and it is therefore necessary to find an easy way to indicate this toxicity.
活性污泥的物理化学性质，如絮凝能力、疏水性、表面电荷、沉降性、脱水性能以及细菌胞外聚合物（EPS），在污水处理厂（WWTPs）的正常运行中起着至关重要的作用。商业产品释放的纳米颗粒会进入污水处理厂，并可能对活性污泥产生潜在的不利影响。本文重点研究了铜纳米颗粒（CuNPs）对活性污泥这些特定物理化学性质的影响。研究发现，在较低的CuNPs浓度（5 ppm）下，这些性质大多未受影响，但在较高的CuNPs浓度（30和50 ppm）下则出现了不同的情况。在较高的CuNPs浓度下，污泥表面电荷增加而疏水性降低，这归因于CuNPs释放出更多的Cu2+离子。EPS的碳水化合物含量增加以抵御CuNPs的毒性。由于细胞表面电荷增加、疏水性降低以及细胞膜受损，絮凝能力被发现有所恶化。絮凝能力的恶化使污泥絮体更加分散，这通过增加CuNPs对污泥中细菌的可利用性进一步增加了CuNPs的毒性。进一步研究表明，在较高的CuNPs浓度下，除磷效率降低，这与活性污泥物理化学性质的恶化一致。物理化学性质似乎可以作为确定CuNPs对活性污泥中细菌毒性的指标。这项工作很重要，因为纳米颗粒对活性污泥的细菌毒性影响可能导致污水处理效率下降，因此有必要找到一种简便的方法来指示这种毒性。
