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纳米银具有独特的抗菌性能,广泛应用于家用电器[1]、纺织品[2]、食品容器、医疗用品、化妆品等领域[3],AgNPs已经成为全球应用最多的纳米材料之一。AgNPs产品在生产、运输和使用过程中不可避免地直接或间接释放到环境中[4],最终进入污水处理厂[5]。有研究结果[6-7]表明,纳米颗粒进入水体后,粒子本身性质(粒径、形状、溶解性、表面电位和包被材料等)、存在状态(离子态和络合态)和环境因素(pH、溶液离子强度、有机物等)均会显著影响其在水体中的行为。贾俊彩等[8]发现,AgNPs粒径越小,对斑马鱼的毒性越强,易导致斑马鱼胚胎发生多种畸形。BURCHARDT等[9]发现,AgNPs及其溶解释放的Ag+对藻类具有毒性效应。AgNPs的粒径、Ag+溶出强度、表面电位等理化性质均会直接影响其在水体中的反应活性及生物毒性[10-12]。
活性污泥工艺具有流程简洁、操作简易、运行效果稳定等优点,主要利用活性污泥(微生物聚集体)对水中各种污染物进行吸收、转化和降解[13]。有研究结果表明,AgNPs可导致活性污泥中硝化细菌丰度显著减少,降低活性污泥系统的出水水质,从而影响受纳水体的氮循环[14]。也有研究结果[15]表明,进入活性污泥污水处理系统中的AgNPs溶解释放出的Ag+抑制了系统中微生物活性,从而降低活性污泥系统对污染物的去除效率。关于AgNPs影响活性污泥污水处理系统污染物去除效率的原因是其自身还是其释放Ag+所至,仍有争议。LIANG等[16]分别测定了1 mg·L−1 AgNPs和1 mg·L−1 Ag+对SBR中活性污泥硝化性能的影响,认为AgNPs对活性污泥微生物硝化反应的抑制作用来自其本身。WIRTH等[17]发现,AgNPs对Pseudomomas fluorescens细胞膜的毒性大于AgNPs释放出的Ag+毒性。而RADNIECKI等[18]的研究结果表明,AgNPs释放出的Ag+是对活性污泥中Nitrosomonas europaea产生硝化抑制的主要原因。HOQUE等[19]的研究结果表明,污水中AgNPs质量浓度为0.1~0.2 µg·L−1,随着包含AgNPs的材料广泛应用,AgNPs在污水中的浓度有可能继续升高。
本研究采用序批式反应器(sequencing batch reactor,SBR)模拟活性污泥污水处理系统,在进水中分别添加1 mg·L−1、10 mg·L−1 AgNPs以及相同质量浓度的AgNPs可在水中分别溶解释放出的Ag+,在连续运行50 d后,测定SBR出水的各项水质指标,以期为全面评价AgNPs及其释放的Ag+对污水生物处理系统的生态风险提供参考。
纳米银和银离子对活性污泥系统污染物去除效率的影响
Effects of silver nanoparticle and silver ions on pollutants removal efficiency of activated sludge system
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摘要: 纳米银(silver nanoparticle,AgNPs)及所释放Ag+的毒性会对污水生物处理系统中的微生物造成影响,降低系统对污染物的去除效率。基于此,对表面包被聚乙烯吡咯烷酮的AgNPs在纯水和人工污水中的形貌、粒径分布、表面电位等进行了表征,以序批式反应器(sequencing batch reactor,SBR)模拟活性污泥污水处理系统,在进水中分别添加1 mg·L−1、10 mg·L−1 AgNPs和0.3 mg·L−1、3.0 mg·L−1 Ag+后,SBR连续运行50 d,考察了活性污泥系统污染物去除率的动态变化。结果表明:AgNPs在人工污水中易团聚,AgNPs浓度越高,团聚现象越明显;进水中添加10 mg·L−1 AgNPs可显著降低SBR对COD、
${{\rm{NH}}_4^ + }$ -N及${{\rm{PO}}_4^{3 - }}$ 的去除率,其抑制效应主要来自于AgNPs本身而不是其释放的Ag+;添加1 mg·L−1 AgNPs和0.3 mg·L−1、3.0 mg·L−1 Ag+对活性污泥系统去除COD有抑制效应,但COD去除率仍高于60%,可以满足城镇污水处理厂污染物排放一级A标准(GB 18918-2002);添加1 mg·L−1 AgNPs可显著抑制活性污泥系统对${{\rm{PO}}_4^{3 - }}$ 的去除;进水中分别添加1 mg·L−1、10 mg·L−1 AgNPs和0.3 mg·L−1、3.0 mg·L−1 Ag+对SBR出水中${{\rm{NO}}_2^ -} $ -N和${{\rm{NO}}_3^ -} $ -N去除率没有影响。鉴于目前进入城镇污水处理系统中AgNPs的浓度远低于1 mg·L−1,故AgNPs对活性污泥污水处理系统中污染物的去除没有显著抑制效应。Abstract: The toxicity of silver nanoparticle (AgNPs) and the silver ions released from AgNPs have inhibitory effects on the microorganisms in wastewater treatment plant (WWTP) and reduce the pollutants removal efficiency of activated sludge system. The morphology, particle size distribution and surface charge of polyvinyl pyrrolidone-coated AgNPs dispersed in pure water and artificial wastewater were characterized, respectively. AgNPs significantly agglomerated in artificial wastewater. The result showed that the higher concentration of AgNPs, the easier agglomeration. The sequencing batch reactor (SBR) was used as a simulated activated sludge system and run for 50 days. The effects of 1 mg·L−1 and 10 mg·L−1 AgNPs, 0.3 mg·L−1 and 3.0 mg·L−1 Ag+ added in influent on pollutants removal efficiencies of activated sludge system were investigated, respectively. 10 mg·L−1 AgNPs could significantly reduce the removal efficiencies of COD,${\rm{NH}}_4^ + $ -N and${\rm{PO}}_4^{3 - }$ in SBR. The inhibition effect was mainly induced by AgNPs, while was not induced by the released silver ions from AgNPs. 1 mg·L−1 AgNPs or 0.3 mg·L−1, 3.0 mg·L−1 Ag+ had inhibitory effect on the COD removal of activated sludge system. However, the COD removal rate was above 60% and meet the first level A class criteria specified in the discharge standard of pollutants for municipal wastewater treatment plant (GB 18918-2002). 1 mg·L−1 AgNPs had significant inhibitory effect on the${\rm{PO}}_4^{3 - }$ removal efficiencies of activated sludge system. 1 mg·L−1 AgNPs, 10 mg·L−1 AgNPs, 0.3 mg·L−1 Ag+ or 3.0 mg·L−1 Ag+ fed into SBR had no effects on${\rm{NO}}_2^ - $ -N and${\rm{NO}}_3^ - $ -N removal efficiencies. At present, AgNPs concentration in WWTP is far lower than 1 mg·L−1. This study demonstrated that AgNPs released into sewage had no significant effects on pollutants removal efficiency of activated sludge system.-
Key words:
- silver nanoparticles /
- silver ions /
- activated sludge /
- sequencing batch reactor /
- pollutants removal
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表 1 AgNPs在纯水和人工污水中的平均粒径及Zeta电位
Table 1. Average size and Zeta potential of AgNPs in pure water and artificial wastewater
样品 质量浓度/(mg·L−1) 平均粒径/nm Zeta电位/mV 纯水 1 48.88 ± 13.34 −8.73 ± 0.70 纯水 10 52.25 ± 6.67 −8.24 ± 0.74 人工污水 1 96.26 ± 18.23 −11.16 ± 0.48 人工污水 10 96.52 ± 5.41 −10.26 ± 0.62 -
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