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地表水中有害藻类爆发(harmful algae bloom, HAB)引发的水体污染已经引起了全球公众的关注[1]。微囊藻是淡水生态系统中分布最普遍的藻类之一,其代谢产物——微囊藻毒素-LR(Microcystin-LR, MC-LR)会随着藻体的死亡和裂解而大量释放到水中[2]。MC-LR是强致癌物质,能够通过影响蛋白磷酸酶活性等途径破坏肝脏细胞,引发癌变。因此,MC-LR的存在会影响饮用水的水质安全,不利于渔业和城市居民的身心健康[3]。
去除饮用水中MC-LR的一种潜在解决方案是高级氧化工艺(AOP)。常规高级氧化技术包括紫外/过氧化氢(UV/H2O2)、紫外/次氯酸(UV/HClO)、H2O2/O3和基于Fenton的铁/H2O2体系可有效去除MC-LR[4]。相比于UV/H2O2体系,UV/HClO体系在pH低于7时的降解效率更高,因此,部分水处理厂已采用UV/HClO替代UV/H2O2[5]。此外,由于UV/HClO体系的余氯可以在饮用水处理中提供多种消毒屏障,从而简化工艺[6]。UV/HClO体系对MC-LR的降解途径包括:与HClO/ClO−的直接反应;通过紫外线辐射的直接光解;活性自由基(氯自由基(Cl·)和羟基自由基(HO·))等介导的间接光解。HO·能够以接近扩散的速率与污染物反应,达到降解的目的。水中的其他化合物(溶解的有机物(DOM)和碳酸氢盐)可以与污染物竞争HO·,但由于其具有快速反应活性,因此,依然可以用于多种类型难降解化合物的降解[7]。
Kintecus模型能够模拟高级氧化工艺反应,当前主要用于化学、生物、核和大气化学动力学及平衡过程的反应进行建模和回归/拟合/优化。一些研究[8-9]用该模型对污染物降解过程进行模拟,模拟得到的数据不仅可以用来支持和验证实验结果,也可以通过模拟实验来预测污染物的降解程度,论述建立的降解模型对实际水处理情况的适用性,并对运行参数的优化提供一定的参考。虽然利用kintecus模型模拟自由基稳态浓度的研究较多,但已有研究仅模拟了特定情境下UV/HClO体系降解污染物时自由基的变化规律,用以验证实验结果。然而,对于UV/HClO体系降解MC-LR过程中主要操作条件的模拟优化却鲜有报导。因此,本研究通过改变pH、次氯酸投加量和紫外光波长来模拟UV/HClO体系降解MC-LR的过程。利用已报导的实验数据来验证本研究建立动力学模型的准确性,并预测不同条件下UV/HClO体系对MC-LR的降解过程,优化UV/HClO体系参数。
基于kintecus模型的紫外/次氯酸降解MC-LR的自由基稳态浓度及反应动力学模拟
Simulation of steady-state radical concentration and reaction kinetics of MC-LR degradation by UV/hypochlorous acid based on kintecus model
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摘要: 蓝藻代谢产生的微囊藻毒素-LR(MC-LR)会污染饮用水源,并对人类健康构成威胁。紫外/次氯酸技术能产生氯自由基(Cl·)和羟基自由基(HO·)等强氧化性物质来降解MC-LR。但该技术的最优参数尚不可知,已报导的实验结果仅能提供部分参数,亟需通过数值模拟来确定更多重要参数。因此,采用kintecus化学动力模型模拟了先前报导过的实验数据并对未报导数据进行了预测。结果表明,模型预测值与实验值的变化趋势一致,误差在1.5倍以内。在pH为6时,紫外/次氯酸技术对MC-LR的降解效果最好,7 min左右降解率可达到90%。HO·和Cl·的稳态浓度分别为6.59×10−14 mol·L−1和1.22×10−14 mol·L−1,与原文献实验结果较为吻合(7.89×10−14 mol·L−1,0.93×10−14 mol·L−1)。在次氯酸添加量超过40 μmol·L−1之后,降解效果提升并不明显。当紫外光波长由257.7 nm增加到301.2 nm时,MC-LR的表观降解速率常数由5.07×10−3 s−1下降到4.69×10−3 s−1,下降了7.5%。而在波长为257.7 nm、pH由6提升至8时,表观降解速率常数由5.07×10−3 s−1下降到3.84×10−3 s−1,下降了24%。因此,改变pH对降解效率的影响大于改变紫外光波长的情况。
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关键词:
- kintecus模型 /
- 紫外/次氯酸 /
- 微囊藻毒素-LR /
- 稳态浓度 /
- 动力学
Abstract: Microcystin-LR (MC-LR) produced by the metabolism of cyanobacteria will contaminate drinking water sources and threaten the human health. UV/Hypochlorous acid technology can generate strong oxidizing substances such as chlorine radicals (Cl·) and hydroxyl radicals (HO·) to degrade MC-LR. However, the optimal parameters of this technology have not yet been known, and the reported experimental results can only provide some parameters. Thus, numerical simulation is urgently needed to determine more important parameters. Therefore, the kintecus chemical kinetic model was used to simulate the previously reported experimental data and predict the unreported data. The results showed that the predicted values of the model were consistent with the experimental values, and the errors were within 1.5 times. When the pH was 6, the UV/hypochlorous acid technology had the best performance on MC-LR degradation, and the degradation rate could reach 90% within 7 minutes. The steady-state concentrations of HO· and Cl· were 6.59×10−14 mol·L−1 and 1.22×10−14 mol·L−1, respectively, which were in accordance with the experimental results of the original literatures (7.89×10−14 mol·L−1, 0.93×10−14 mol·L−1). After the concentration of hypochlorous acid exceeded 40 μmol·L−1, the degradation rate remained constant. When the wavelength of ultraviolet light increased from 257.7 nm to 301.2 nm, the apparent degradation rate constant of MC-LR decreased from 5.07×10−3 s−1 to 4.69×10−3 s−1, a decrease of 7.5%. When the wavelength was 257.7 nm and the pH increased from 6 to 8, the apparent degradation rate dropped from 5.07×10−3 s−1 to 3.84×10−3 s−1 with a decrease rate of 24%. Therefore, the effect of pH on the degradation efficiency was greater than that of ultraviolet light wavelength.-
Key words:
- kintecus model /
- ultraviolet/hypochlorous acid /
- microcystin-LR /
- steady-state concentration /
- kinetics
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表 1 在不同的HClO初始浓度下HClO/ClO−的量子产率
Table 1. Quantum yield of HClO/ClO− based on different initial concentrations of HClO
表 2 不同pH下HClO/ClO−体系中主要水解产物的比例
Table 2. Proportions of major hydrolysis products in the HClO/ClO− process at different pH
pH CHClO投加量/
(mol·L−1)CHClO/
(mol·L−1) /${C _{{\rm{Cl}}{{\rm{O}}^{\rm{ - }}}}} $
(mol·L−1)4 4.2×10−5 4.20×10−5 1.24×10−8 6 4.2×10−5 4.08×10−5 1.20×10−6 7 4.2×10−5 3.24×10−5 9.56×10−6 8 4.2×10−5 1.06×10−5 3.14×10−5 9 4.2×10−5 1.38×10−6 4.06×10−5 11 4.2×10−5 1.42×10−8 4.20×10−5 表 3 HO·与Cl·的稳态浓度预测值与实验值
Table 3. Comparison of the predicted steady-state concentrations of HO· and Cl· with experimental values
pH 本研究预测值/(mol·L−1) 实验值[27]/(mol·L−1) HO· Cl· HO· Cl· 4 6.97×10−14 1.31×10−14 — — 6 6.59×10−14 1.22×10−14 7.89×10−14 9.31×10−15 7 3.08×10−14 6.22×10−15 2.64×10−14 8.29×10−15 8 1.88×10−14 4.42×10−15 1.24×10−14 6.92×10−15 9 1.52×10−14 3.50×10−15 1.17×10−14 2.72×10−15 11 3.02×10−18 2.15×10−15 — — 表 4 不同HClO投加量下HO·和Cl·稳态浓度的变化
Table 4. Changes of HO· and Cl· steady-state concentrations at different chlorine doses
HClO投加量/
(μmol·L−1)自由基稳态浓度/(mol·L−1) HClO投加量/
(μmol·L−1)自由基稳态浓度/(mol·L−1) HO· Cl· HO· Cl· 1 3.41×10−17 2.00×10−17 20 1.06×10−14 2.30×10−15 2 1.32×10−16 6.92×10−17 30 1.62×10−14 3.45×10−15 5 1.12×10−15 3.31×10−16 42 2.24×10−14 4.94×10−15 12 4.26×10−15 1.07×10−15 60 3.05×10−14 7.43×10−15 表 5 不同波长光源下HClO/ClO−的量子产率和摩尔吸收系数[24]
Table 5. Quantum yield and molar absorption coefficient of HClO/ClO− under different wavelength light sources
波长/nm εHClO εClO- ΦHClO ΦClO- Ep 257.7 48.35 83.32 1.18 1.00 1.49×10-6 268 30.82 175.47 1.11 0.97 1.49×10-6 282.3 26.69 305.21 0.98 0.82 1.49×10-6 301.2 25.21 316.15 0.96 0.77 1.49×10-6 注:ε是摩尔吸收系数(L·(mol·cm)−1);Φ是量子产率(mol·E−1);Ep是辐照度(mE·(cm2·s)−1)。 -
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