UV/Oxone降解水中扑热息痛的效能及影响模型

张梦文,陈菊香,,杨 静,高乃云

UV/Oxone降解水中扑热息痛的效能及影响模型

张梦文1,陈菊香1,2*,杨 静1,高乃云2*

(1.新疆大学建筑工程学院,新疆 乌鲁木齐 830047；2.同济大学,污染控制与资源化研究国家重点实验室,上海 200092)

采用UV、oxone和UV/Oxone3种工艺降解ACE,同时对体系中氧化活性物质种类和贡献率进行鉴别和计算.采用响应面曲线法研究HCO3−、Cl−、NO3−、pH值和温度5因素、3水平条件下UV/Oxone对ACE的去除效果的综合影响,并选用3种实际水体作为原水水质背景来评价UV/Oxone降解ACE的实际降解值和模型预测值的差距,最后比较了3种工艺的效能.结果表明UV、oxone、UV/Oxone3种工艺对ACE的去除率分别为2.1 %、53.7 %和98.3 %.活性物质的鉴别实验发现UV激活oxone会产生•OH、SO4•–和活性氯3种活性物质,且对ACE降解的贡献率分别为37.05 %、19.22 %和43.73 %.通过响应面曲线法得到影响降解ACE效果的回归方程式,该回归方程对应的p值小于0.0001,拟合缺失项不显著,校正决定系数R2＞0.8,说明该模型可信度高.选用实际水体进行实际降解和模型预测比较时发现实际降解值基本符合模型预测值.最后对两种不同工艺进行效能比较发现在同等时间和降解率的情况,UV/Oxone耗能最低,是一种高效、快速、可行的降解工艺.

扑热息痛；UV/Oxone；动力学；响应面曲线法；效能评价

扑热息痛(ACE)是一种非抗炎解热镇痛药,由于其适用性广、价格低廉等优点,得到广泛使用.据调查,国内外多种水体中已检测到ACE的存在[1-3].其中我国天然水体中检测到ACE的浓度可达6~ 10μg/L[4],欧洲某污水处理厂检测到ACE的浓度达6~11.3μg/L[5],ACE浓度较高时具有肝毒性和其他副作用,可能通过富集作用进入生物链,长此以往会对人类的健康以及生态系统造成潜在的不利影响[6-7].因此水体中ACE的检测和去除得到国内外环境学界的广泛关注[8-9].传统水处理工艺对ACE降解效果不理想,现亟需研究开发一种高效、经济的处理技术来去除水体中的ACE.

UV/PMS(过硫酸氢盐)和UV/PS(过硫酸盐)是近年来水处理领域高级氧化工艺的研究热点之一,其可以产生羟基自由基×OH和硫酸根自由基SO4•−[10-13],其中SO4•–的氧化还原电位为2.5~3.1V,可降解水中大多数的污染物[14],所以基于SO4•–的高级氧化技术成为研究重点之一.本文采用的氧化剂水王子(oxone)为一种复合型氧化剂,主要成分为PMS,还包含辅助剂、络合剂和稳定剂等[15].本实验中考察了UV、oxone和UV/Oxone 3种氧化体系降解水中ACE的动力学以及UV/Oxone体系中活性物质的鉴别及其贡献率的计算,采用响应面曲线法研究了不同水体中ACE的去除效果和降解ACE的效能.

1 材料与方法

1.1 实验材料

ACE(³99.9%)和oxone(³99.7%)购买于阿拉丁贸易有限公司.甲醇(MeOH³99.9%),叔丁醇(TBA³99.9%),硫代硫酸钠(Na2S2O3³99.0%)购买于国药集团化学试验有限公司.碳酸氢钠(NaHCO3³99.5%),硝酸钠(NaNO3³99.0%)和氯化钠(NaCl³99.9%)均购买于海信玻璃有限公司.高效液相色谱仪(HPLC)检测所需流动相乙腈为色谱纯,购自美国Sigma-Aldrich有限公司,试验中所用样本溶液均采用Milli-Q超纯水(18MΩ·cm) 配制.

分别从横山水库、锡东水厂和西氿水库进水口取样作为不同水质背景,于2018年7,8,9,10,11月各调查采样一次,取其5次采样的平均值,具体水质参数见表1.

表1 实际水体的水质参数表

1.2 分析方法

采用高效液相色谱仪(HPLC2010)对ACE浓度进行定量,装配有C18色谱柱(250nm´4.6nm´5μm, Waters)和UV可见光检测器.流动相采用乙腈(15%)和水(85%),流速为1.0mL/min,紫外装置采用准平行光束仪,检测波长为242nm,柱温维持在35℃,检测时间为10min.

1.3 实验方法

在实验条件下,用超纯水配制100mL的目标污染物加入到200mL的结晶皿中,再加入所需的氧化剂溶液oxone,然后将结晶皿放置在紫外装置台上(紫外装置已提前预热30min),反应开始并计时,在指定的反应时间采用移液枪取样0.8mL加至预先放置了足量的淬灭剂硫代硫酸钠的液相棕色小瓶中,保证残余氧化剂反应完毕.平行实验进行3次,取其平均值,见式(1).采用方差分析实验数据的误差棒,见式(2).

式中:1,2,3—3次实验后ACE的浓度;C—3次平行实验的平均值;2—实验方差.

2 结果与分析

2.1 不同氧化工艺降解ACE

图1 3种工艺降解ACE的效果及动力学拟合

如图1所示,采用UV单独降解ACE15min后降解效果不明显,仅为2.1%,这一结果与唐敏康[16]的研究结果较为一致,证实了ACE的光稳定性.而oxone和UV/Oxone对ACE的去除率分别为53.7%和98.3%,产生这种现象是因为oxone单独降解ACE时,Cl-可以与PMS发生反应生成活性氯从而达到降解ACE的目的,具体反应如下式(3~4)所示.此结论与徐蕾等[17]降解2,4,6-三氯苯酚的结论相似. UV/Oxone协同工艺降解ACE时,降解率高达98.3%,充分说明oxone在紫外光照激活下产生了其他活性物质,从而使ACE的降解效率大大提高.分别对oxone和UV/oxone 2种工艺降解ACE的数据进行动力学拟合,均遵循拟一级反应动力学,具体动力学参数见表2.

表2 oxone和UV/Oxone工艺降解ACE的拟一级动力学速率常数

2.2 活性物质的鉴别

之前报道表明PMS在紫外激活下可产生×OH和SO4•–[10-13],且oxone的主要成分为PMS.为了鉴别UV/Oxone工艺中起氧化作用的活性物质,分别向系统溶液中加入MeOH和TBA. MeOH可有效淬灭•OH和SO4•–,而TBA只能作为×OH的有效淬灭剂[18-19],如式(5~8)所示.从图2可以看出:加入MeOH/TBA之后反应速率常数显著降低,且加入MeOH的系统比加入TBA下降得更快.同时随着MeOH/TBA浓度的增加,反应速率常数不断降低,但降低幅度逐渐减小.这是因为:×OH和MeOH/TBA的反应速率快,加入低浓度的MeOH或TBA时,主要淬灭系统中的×OH,导致ACE的降解速率下降.随着MeOH或TBA的浓度逐渐增大,相继开始淬灭系统中的SO4•–,导致体系中ACE降解速率减小,进而说明oxone在UV激活下可以产生活性自由基(×OH和SO4•–).从图2看出随着MeOH浓度增加,ACE仍有一定程度的降解,说明体系中除了生成×OH和SO4•–,还有其他活性物质. 古振川等人[20]在研究Cl-/PMS降解甲氧苄啶时发现其反应系统中的活性物质主要是活性氯.为了进一步的验证活性氯的存在,设计验证实验:在反应体系中同时加入足量的MeOH和NH4+,ACE无降解.在反应体系中加入MeOH,再加入氯离子时,反应速率变慢.以上结果表明,在UV/Oxone工艺降解ACE过程中起氧化作用的活性物质有3种:×OH、SO4•–和活性氯.

为了计算出各活性物质的贡献率,分别向系统中加入足量的淬灭剂MeOH、TBA和NH4+,得到如图3所示的ACE降解图.由图3可知分别加入不同淬灭剂后ACE的降解率分别为52.39%、75.41%和67.41%,得到不同活性物质降解ACE的降解率方程.通过联立方程可求解×OH、SO4•–.和活性氯单独对ACE的降解率,进而计算出各活性物质对ACE降解的贡献率分别为37.05%、19.22%和43.73%.

图3 MeOH、TBA和NH4+对ACE降解率的影响

2.3 响应面曲线法实验模型

在实际背景水体中存在多种因素,可能对ACE降解产生影响,例如实际水体中包含各种类型的无机阴离子(如HCO3-、Cl−、NO3-), pH值和温度()等.采用响应面曲线法[21](5因素3水平)探究3种阴离子、pH值和温度等因素在不同水平条件下的ACE降解效果及模型方程,详见表3.对应的响应值为ACE的去除率(),水平响应面实验设计及响应值见表4,基于响应面曲线法得到如图4所示的三维模型图.通过方差分析法(ANOVA)验证模型的准确和适用性,结果见表5,的值为11.96,对应的值小于0.0001,模型显著.拟合缺失项不显著,校正决定系数2>0.8,说明该模型可信度高,能够很好的预测实际水体中ACE的降解效果.

表3 因素水平

表4 5因素、3水平响应面实验设计及响应值

续表4

表5 方差分析结果

图4 响应面曲线图

基于上述响应面曲线法可以得到如式(9)所示的5因素、3水平的影响模型方程式:

2.4 模型预测值与实验降解值的比较

为了验证响应面曲线法(RSM)设计影响模型的准确性和适用性,特选取不同原水水质进行研究.图5将ACE实验降解值和模型预测值进行比较,如图5所示,模型预测值与实际降解值接近,略小于实际降解值,这可能是因为在实际水体中还存在其他因素(例如其他微生物,溴离子等)会影响ACE的降解效果.但模型预测值和实验值误差不大,说明该模型可以较好的预测不同水质背景下ACE的降解率.

图5 ACE实测去除率和RSM模型预测值的比较

2.5 不同工艺效能比较

采用单位电能效率(EE/O)比较oxone和UV/Oxone2种工艺降解水中ACE时所消耗的能量.单位电能效率(EE/O kW×h/m3/order)可以采用式(10)进行计算[22]:

式中:代表总输入电量,kW;为反应时间,0.25h;溶液的体积,1´10-4m3.在实际工艺中还包含药剂的投加费用,而上式10仅能用来表示直接消耗的电能,所以在具体计算时将药剂投加费用换算为间接消耗的电能来综合考察.表6为在同等时间和降解率的条件下2种工艺降解ACE的能耗(控制反应时间均为15min,降解率均为98.3%,此时单独oxone的投加量为UV/oxone的3.2倍). EE/O1和EE/O2分别表示为:直接和间接消耗的电能.从表6中可以看出在同等时间和相同降解率条件下UV/Oxone工艺降解ACE的能耗最小,最为经济.所以UV/Oxone效率最高,是一种高效可行的降解方法.

表6 2种工艺电能消耗

注:Cost1为系统化学试剂的投加费用,Cost2为系统化学试剂投加费用根据电费折算成的用电量.电价取0.1元/(kW⋅h),化学试剂oxone的价格取0.054元/g.

3 结论

3.1 Oxone 在UV激活下生成了其他高效的氧化活性物质,大大提高oxone降解ACE的去除率;通过活性物质鉴别实验可知UV/Oxone降解ACE时起氧化作用的活性物质有3种:×OH、SO4•–和活性氯,对ACE降解的贡献率分别为37.05%、19.22%和43.73%.

3.2 通过响应面曲线法得到ACE降解回归方程式,通过方差分析可知该模型可信度高.选用实际水体背景降解发现实际降解值略接近于模型预测值,基本符合模型预测值误差范围,进一步证明该模型方程的可信度高.

3.3 对两种工艺进行效能比较分析,发现在同等反应时间和降解率的情况下,UV/Oxone更为高效、经济可行.

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Efficiency and effect model of acetaminophen degradation by UV/Oxone.

ZHANG Meng-wen1, CHEN Ju-xiang1,2*, YANG Jing1, GAO Nai-yun2*

(1.College of Architecture and Civil Engineering, Xinjiang University, Xinjiang Urumqi 830047, China；2.State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai 200092, China)., 2019,39(8)：3293~3299

This work reported the efficiency of degradation ACE used three degradation processes (i.e. UV、oxone and UV/Oxone). Meanwhile, the kinds of oxidative active substances and contribution in the system were identified and calculated. Response surface curve method (RSM) was used to study the comprehensive effect of UV/Oxone on ACE removal under five factors including HCO3-, Cl-, NO3-, pH and T and three levels. Furthermore, three kinds of actual water were chosen as the quality indicator of raw water to evaluate the difference between actual degradation values and model predictive values of degradation ACE by UV/Oxone. Finally, the degradation efficiencies of three processes were evaluated. The results showed that the degradation rates of UV、oxone and UV/Oxone were 2.1%, 53.7% and 98.3%, respectively. Identification experiments of active substances found that three active substances were produced by UV activation of oxone, such as•OH、SO4•–and reactive chlorine, and the contribution of three active substances to ACE degradation were 37.05%、19.22% and 43.73%, respectively. The regression equation of ACE degradation was obtained by RSM. The p value was less than 0.0001, the missing fitting term was not obvious and2>0.8, which indicated that the model was highly reliable. Actual waters, as degradation substance, were selected to compare the actual and model predicted and found that two values were matched basically. Compared with the efficiency of two different processes, the result showed that UV/Oxone was an effective, rapid and feasible degradation process with the lowest energy consumption at the same time and degradation rate.

acetaminophen；UV/Oxone；dynamics；RSM；effectiveness evaluation

X703

A

1000-6923(2019)08-3293-07

张梦文(1994-),女,陕西咸阳人,硕士研究生,主要从事水处理研究.发表论文3篇.

2019-02-12

国家自然科学基金资助项目(51768067)

* 责任作者, 陈菊香, 副教授, chenyu1816@126.com; 高乃云, 教授, gaonaiyun@126.com