纳米银和银离子对活性污泥系统污染物去除效率的影响

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。

Effects of silver nanoparticle and silver ions on pollutants removal efficiency of activated sludge system

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.