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近年来,药品和个人护理产品(PPCPs)的消费量逐年增加[1],引起的环境污染越来越受到关注[2-3]。大多数PPCPs在污水处理厂无法完全去除,其会随着污水厂出水进入受纳水体,导致其在自然水环境中的暴露。例如,被广泛用作止疼和抗风湿的双氯芬酸(DCF),在地表水甚至自来水中都被检测出[4],DCF的基本理化性质见表1[5]。此外,低剂量的PPCPs即可对生物产生生理效应[1, 6],这使得处理含有PPCPs的工业废水和生活污水尤为重要。
高级氧化工艺(AOPs)被认为是降解PPCPs的有效方法之一,常用的氧化剂包括过氧化氢(H2O2)、过一硫酸盐(PMS)和过硫酸盐(PS)等[7-9]。过氧乙酸(PAA, CH3C(=O)OOH)是一种类似H2O2的新型氧化剂,近年来在AOPs中得到广泛研究[10-12]。此前,PAA因其良好的消毒性能和副产物的低毒性而被广泛用于废水的消毒[13-15]。PAA的过氧键键能仅为159 kJ·mol−1,低于H2O2的213 kJ·mol−1[16],这意味着PAA更容易被活化[17]。迄今为止,已报道活化PAA的方法有紫外(UV)、过渡金属、热等[15, 18-22]。UV能激活PAA产生活性物质进而降解污染物[18],然而UV在水中的穿透力有限,如果没有足够的UV强度,这一过程很难实现。过渡金属活化PAA的反应条件简单,能够活化PAA的过渡金属离子包括Co2+、Mn2+、Fe2+、Cu2+等[15, 19-21],然而Co2+和Mn2+具有一定毒性,进而可能造成二次污染;Fe2+虽然无毒性,但在非酸性条件下易被氧化而降低活化效率;Cu2+的毒性较低,但低剂量的Cu2+活化PAA效果不佳。热能激活PAA产生活性物质,从而快速降解磺胺甲恶唑(SMX)[22],如公式(1)所示,但断裂过氧键需要消耗大量能量。
根据预实验发现,Cu(Ⅱ)和热联用活化PAA (Cu(Ⅱ)-heat/PAA)只需要较低浓度的Cu(Ⅱ)(低至μmol·L−1级别)和消耗较少的能量(与单独热激活PAA比较);相比于单独Cu(Ⅱ)活化PAA(Cu(Ⅱ)/PAA)和热激活PAA(heat/PAA)体系,Cu(Ⅱ)-heat/PAA体系显著加速了DCF的去除。因此,本文拟对该现象进行深入探讨研究,考察该协同效应的作用机理;调查常见水基质(Cl−、SO42−、NO3−、HCO3−、天然有机质(NOM))对Cu(Ⅱ)-heat/PAA体系降解DCF的影响;评估该技术对实际水体中DCF的去除效果。
Cu(II)协同热活化过氧乙酸降解水中双氯芬酸
Degradation of diclofenac in water by Cu(II)-combined with heat activation of peracetic acid
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摘要: 采用Cu(Ⅱ)协同热活化过氧乙酸(Cu(Ⅱ)-heat/PAA)降解水中双氯芬酸(DCF),识别了Cu(Ⅱ)-heat/PAA体系中的主要活性物质;考察了常见水基质(Cl−、SO42−、NO3−、HCO3−、天然有机质(NOM))对DCF去除的影响;探讨了该体系对天然水体中DCF的去除。结果表明,Cu(Ⅱ)-heat/PAA体系去除DCF的效率明显高于Cu(Ⅱ)/PAA和heat/PAA体系,表明热与Cu(II)两者结合对PAA的活化具有协同作用。在pH 8时,羟基自由基(·OH)和有机自由基R-O·(CH3C(=O)O·和CH3C(=O)OO·)是Cu(Ⅱ)-heat/PAA体系去除DCF的主要活性物质,且R-O·对DCF去除的作用更大。在Cu(Ⅱ)-heat/PAA 体系中,SO42−、NO3−和HCO3−对DCF的去除几乎没有影响;Cl−对DCF去除有微弱的促进效果;而NOM抑制DCF的降解,导致DCF在湖水和河水中的去除受到抑制。Abstract: Removal of diclofenac (DCF) in water by Cu(Ⅱ)-combined with heat activation peracetic acid (Cu(Ⅱ)-heat/PAA) was investigated, and the main active species in Cu(Ⅱ)-heat/PAA system were identified. The effects of common water matrix (Cl−, SO42−, NO3−, HCO3− and natural organic matter (NOM)) on the removal of DCF were explored and the degradation of DCF in natural water was studied. As a result, the removal efficiency of DCF in Cu(Ⅱ)-heat/PAA process presented a relatively faster rate than those in Cu(Ⅱ)/PAA and heat/PAA systems, indicating that the combination of heat and Cu(Ⅱ) had a synergistic effect on the activation of PAA. At pH 8, hydroxyl radical (·OH) and organic radicals (R-O·, CH3C(=O)O· and CH3C(=O)OO·) were the main active substances for DCF removal in Cu(Ⅱ)-heat/PAA system and R-O· played a major role in DCF removal. Presence of SO42−, NO3− and HCO3− had little effect on DCF degradation; Cl− could weakly promote the degradation of DCF; NOM inhibited DCF removal, which resulted in the inhibition on DCF removal in lake water and river water.
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Key words:
- diclofenac /
- peracetic acid /
- Cu(II) /
- heat /
- organic radicals /
- advanced oxidation process
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表 1 DCF的理化性质
Table 1. Physicochemical properties of DCF
分子式
Formula溶解度
Solubility分子量
Molecular weight结构式
StructureC14H11Cl2NO2 2.37 mg·L−1(25 ℃) 296.16 表 2 不同体系的kobs和R2值
Table 2. kobs and R2 in different systems
体系 PAA Cu(Ⅱ)/PAA Cu(Ⅱ)-heat/H2O2 heat/PAA Cu(Ⅱ)-heat/PAA kobs /min−1 0.004 0.008 0.054 0.094 0.394 R2 0.910 0.945 0.990 0.990 0.996 -
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