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由于抗菌谱广、可以口服、吸收较迅速等优点,磺胺类抗生素(sulfonamides, SAs)被大量应用于治疗和预防疾病[1 − 3]. 但是由于早期的认知缺失,我国存在严重的SAs滥用情况,其对环境存在潜在的严重危害[4]. 以磺胺对甲氧嘧啶(sulfamethoxydiazine,SMD)为例,目前已监测到其在地表水和地下水中广泛存在[5 − 7]. 虽然SMD在环境中呈现出低浓度水平,但通过食物链的传播和积累,其潜在毒性不可忽视[8],极易产生致癌、致畸和致突变等系列危害. 目前,电化学高级氧化法(electrochemical advanced oxidation process, EAOPs)因其降解污染物彻底、处理无害、见效快以及温和的工艺条件等独特优势[9],成为降解磺胺类抗生素最有前景的技术,Tröster等[10]构建了以掺硼金刚石膜[11](boron doped diamond, BDD)电极为阳极的电化学氧化系统,研究结果表明BDD电极的化学惰性和独特的电化学性质对电化学水处理具有巨大潜力,EAOP适用于废水处理,且已经在实验室内获得成功. 从实验室研究到工业应用过程中,反应器放大所引起的尺度效应对于降解效率具有重要影响,因此反应器的尺度效应和尺寸的优化研究具有重要意义.
目前,已经有研究人员通过构建不同尺寸的反应器对污染物降解尺度效应做出探讨. 其中,Zhu等[12 − 13]构建了一个大型BDD阳极系统(阳极面积为2904 cm2)按比例放大后在批量处理模式下未发现效率明显降低,认为BDD阳极系统的电化学氧化反应器尺度放大具有可行性. 针对垃圾填埋场渗滤液电化学氧化实验,Urtiaga等[14 − 15]构建了BDD阳极面积为1.05 m2中试规模反应器,并对放大效果进行评估,结果表明,中试系统对铵离子去除率明显降低,反应器尺寸效应影响显著. 为了降低化学实验成本,计算流体力学软件(computational fluid dynamics,CFD)被引入到污染物降解模拟中,CFD模型在实验初和验证阶段可提供设计、优化和综合分析[16],并预测电化学反应器的性能[17]. van Walsem[18]等利用CFD模型计算新型多管反应器中吸附和解吸速率常数并利用实验确定的出口浓度分布,验证了该模型的模拟结果与实验数据具有良好的一致性,证实了CFD在化学实验研究中的可行性. Bagheri等[19]利用CFD模型对用于水处理的双波长紫外线(VUV/UV)光反应器进行了模拟,预测了VUV/UV反应器中污染物的降解速率. 由于CFD模型和化学实验分属不同的学科领域,利用CFD软件模拟反应器内的污染物降解机制,评估反应器放大效应对于降解效率的影响,目前尚缺乏深入的研究.
本研究以SMD为目标污染物,采用以BDD电极为阳极的电化学氧化系统处理模拟废水,建立循环系统中污染物降解的CFD模型,利用实验测试确定电极表面反应速率,结合反应器几何尺寸进行流场模拟研究,探究反应器放大倍数与降解效率的关系,为电化学降解有机污染物的工业化应用提供依据.
电化学氧化反应器尺度效应对于抗生素模拟废水降解的影响
Scale effect of electrochemical oxidation reactor on the degradation of antibiotic simulated wastewater
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摘要: 反应器的尺寸对于污水处理效率具有显著的影响,是污水处理从实验室小型反应器到实际中大型反应器应用的关键. 本研究建立了尺寸为33.6 cm3 (3 cm×8 cm×1.4 cm)的电化学反应器,以掺硼金刚石膜(boron doped diamond,BDD)电极为阳极,对磺胺对甲氧嘧啶(sulfametoxydiazine,SMD)的氧化降解进行实验测试. 在实测数据的基础上,利用计算流体力学(Computational fluid dynamics,CFD)软件fluent建立电化学氧化反应器降解SMD的数学模型,率定不同电流密度下的电化学表面反应速率,分析反应器尺寸对污染物流动特征分布和浓度特征分布影响,利用CFD模拟,分别将BDD阳极面积放大100倍、225倍和400倍,探究3种工况下的尺度效应模拟. 结果表明,BDD体系降解反应器的尺度效应显著,在20 mA·cm−2的电流密度下持续60 min后,3种BDD阳极体系中SMD的降解率分别达到72.7%、68.0%和40.4%,相比实验室反应器降解能力分别下降5.7%、11.8% 和47.6%,建议反应器放大尺度小于200倍以免显著影响降解能力.Abstract: The size of reactor has a significant impact on the efficiency of wastewater treatment, which is the key to the application of wastewater treatment from laboratory small reactors to actual medium and large reactors. This study established a size of 33.6 cm3 (3 cm×8 cm×1.4 cm) electrochemical reactor, with BDD (Boron Doped Diamond) electrode as anode, to conduct experimental test on the oxidative degradation of sulfamethazine (SMD). On the basis of measured data, the mathematical model of electrochemical oxidation reactor degrading SMD was established by using Computational fluid dynamics (CFD) software fluent, the electrochemical surface reaction rate under different current densities was calibrated, and the influence of reactor size on the distribution of pollutant flow characteristics and concentration characteristics was analyzed. The BDD anode area was magnified by 100 times, 225 times and 400 times respectively by using CFD simulation, Explore the scale effect simulation under 3 working conditions. The results showed that the scale effect of the BDD system degradation reactor was significant. After 60 min at a current density of 20 mA·cm−2, the degradation rates of SMD in the three BDD anode systems were 72.7%, 68.0% and 40.4%, respectively, which decreased by 5.7%, 11.8% and 47.6% compared with the degradation capacity of the laboratory reactor. It was suggested that the reactor magnification should be less than 200 times to avoid significant impact on the degradation capacity.
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Key words:
- mathematical model /
- scale effect /
- sulfamethoxine /
- electrochemical oxidation /
- BDD.
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图 5 反应器不同表面SMD质量分数等值线:(a)
$ \mathit{X}= $ 半宽度,(b)$ \mathit{Z}= $ 半厚度Figure 5. Contours of SMD mass fraction in the various middle surfaces of the reactor:(a)
$ X=\mathrm{h}\mathrm{a}\mathrm{l}\mathrm{f}\mathrm{w}\mathrm{i}\mathrm{d}\mathrm{t}\mathrm{h} $ and (b)$ Z=\mathrm{h}\mathrm{a}\mathrm{l}\mathrm{f}\;\mathrm{t}\mathrm{h}\mathrm{i}\mathrm{c}\mathrm{k}\mathrm{n}\mathrm{e}\mathrm{s}\mathrm{s} $ 表 1 出口反应速率常数的实验值与模拟值的比较
Table 1. Comparison between experimental and simulated values of kinetic constants of first order reaction
电流密度/(mA·cm−2)
Current density数据来源
Data sources出口反应速率常数
Outlet reaction rate constant相对误差/%
Relative error20 实验值 0.0256 0.40 模拟值 0.0257 表 2 实验室反应器和中试反应器装置参数
Table 2. Parameter of the experimental set-ups at laboratory scale and pilot plant scale
运行参数
Operating parameters实验室反应器
Laboratory reactor扩大反应器
Expanded reactor扩大100倍
100 times扩大225倍
225 times扩大400倍
400 times流量/(L·min−1) 0.1 10 22.5 40 阳极面积/cm2 24 2400 5400 9600 电极间距/cm 1.4 1.4 1.4 1.4 处理的污水体积/L 0.5 50 112.5 200 -
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