基于穿透電極的Electro-peroxone技術降解布洛芬

崔欣欣,林志榮,王會姣,余 剛,王玉玨*

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基于穿透電極的Electro-peroxone技術降解布洛芬

崔欣欣1,林志榮2,王會姣1,余 剛1,王玉玨1*

(1.清華大學環境學院,北京 100084；2.贛南師范大學地理與環境工程學院,江西 贛州 341000)

利用網狀玻碳電極(RVC)作為陰極,構建了一種基于穿透電極的electro-peroxone(E-peroxone)反應器,并系統研究了其對布洛芬的降解性能,考察了電流、流速等因素的影響,進行了能耗計算.結果表明,E-peroxone可以在30min內完全去除初始濃度為2.5mg/L的布洛芬,而電化學氧化和臭氧氧化去除率分別為59%和64%.曝入氣體流速為250mL/min,氣相臭氧濃度為8mg/L的條件下,電流為100mA,反應溶液流速為300mL/min時, E-peroxone技術去除布洛芬的效率最高,且能耗(EEO)僅為傳統臭氧氧化技術的1/7(0.76kWh/m3-log5.30kWh/m3-log).提高流速可以強化穿透電極E-peroxone體系中的傳質,從而強化布洛芬的去除,并降低EEO.

Elecrtro-peroxone；穿透電極；網狀玻碳電極；布洛芬

藥物和個人護理品(PPCPs)對飲用水供應、人體健康和生態系統構成潛在的威脅[1,2].污水處理廠傳統的處理方法難以有效降解PPCPs,導致很多PPCPs及其代謝物質在二沉池出水中仍能被檢出[2-6].高級氧化技術具有良好的礦化效果[7-22],被廣泛應用于水中難降解污染物的去除.但也存在一些缺陷,如電化學技術受電流和傳質限制[16],臭氧氧化具有明顯選擇氧化性且中間產物多、能耗高[18-20], O3/H2O2(peroxone)技術由于需外部投加H2O2導致安全性較低[17].將臭氧與電化學技術耦合的electro- peroxone(E-peroxone)技術,可將O2電化學原位轉化為H2O2(式(1)),進而強化O3生成具有強氧化性的×OH(式(2)),無選擇性地快速氧化各類污染物,能夠顯著提高臭氧難氧化污染物的去除效率,有望成為污水處理廠中高效去除PPCPs及其中間產物的深度處理工藝[23-33].

電化學氧化的反應機理決定了其受到污染物與活性物質在電極表面傳質擴散的限制[16].目前E-peroxone技術中多采用平板電極,比表面積較小,污染物的傳質效率較低.研究表明,使用多孔狀的碳材料(如碳氈、碳布與碳納米管等)充當電極,對有機污染物具有一定的吸附富集作用,且采用穿透電極模式可大大提高污染物及活性物質的傳質擴散,從而提高污染物氧化速率[16,34-39].網狀玻璃碳(RVC)的孔隙容積和比表面積巨大,流體流動阻力小, 導電性良好,有利于電化學反應過程中污染物的傳質和轉化[40].使用RVC電極作為E-peroxone系統中的穿透陰極,利用穿透電極流速越大,傳質越好的特點,可強化O2、H2O2以及污染物在溶液與電極之間的傳質,有望提高污染物去除效率和降低水處理能耗.因此,本研究構建了一種基于RVC穿透電極的E- peroxone系統,并對其去除水中布洛芬的性能進行了系統研究.

1 材料與方法

1.1 試劑與材料

采用典型的抗炎藥物布洛芬作為目標污染物.為了準確檢測污染物濃度變化以分析污染物的降解動力學和運行參數影響,在實驗中采用了較高濃度的布洛芬初始濃度(2.5mg/L).實驗所用布洛芬為分析純級別,購于阿拉丁公司.實驗中使用的其他試劑(如硫酸鈉、磷酸氫二鈉、硫酸等)均為分析純,購于西隴公司.高效液相色譜(HPLC)所用流動相甲醇為色譜純.試驗所需所有溶液均由Thermo Scientific的高純水系統產生的高純水(阻抗18.2MΩ)配制.

1.2 實驗裝置

如圖1所示,系統主要包括:內置陰陽電極的聚四氟柱形反應器、直流電源(LONG WEI PS-305DM)、臭氧發生器(Yanco INDUSTRIES LTD. OzoneLabTM Instrument OL80F/ DST)、臭氧檢測儀、蠕動泵(LongerPump YZ1515x)等.反應器中采用RVC為陰極,鈦鍍釕銥為陽極,兩電極平行放置,陰極在下、陽極在上,利用墊圈固定.采用半批次實驗方式,利用蠕動泵使反應溶液以恒定流速流入反應器,并以恒定流速向反應器中曝氣,進口處采用三通接頭使氣體和反應溶液同時進入反應器,反應器出水流回廢水池.通過控制直流電源、臭氧發生器的啟?？梢苑謩e對污染物進行單獨臭氧氧化、單獨電化學氧化以及E-peroxone技術處理.

圖1 穿透電極反應器示意

1.3 分析方法

溶液中過氧化氫濃度采用鈦鹽光度法測定,臭氧濃度采用indigo試劑法測定,布洛芬濃度通過高效液相色譜儀(Waters 2487 DualAbsorbance Detector; Waters 717 plus Autosampler; Waters 515HPLC Pump)測定[9].測定條件為:色譜柱Agilent TC-C18(2) (5μm,4.6mm×150mm);柱溫30℃;檢測波長220nm;流動相75%甲醇+25%高純水(用2mmol/L醋酸銨和0.01%甲酸調節pH值,使pH = 4);流動相流速1mL/ min;進樣體積50μL;運行時間10min.

1.4 運行參數

實驗中運行參數如表1所示.

表1 實驗運行參數

2 結果與討論

2.1 RVC產過氧化氫性能研究

2.1.1 電流對RVC電產H2O2的影響 在E- peroxone過程中,H2O2的產生是影響處理效果的重要因素[41].在水處理過程中,廢水在穿透電極反應器和水槽中循環流動,所曝入的O2進入水槽后與溶液充分接觸混合.因此,溶解氧在整個處理過程中基本維持在與曝氣中氧氣濃度平衡的濃度(~42mg/L).由圖2可知,在各電流條件下,反應體系中RVC電產H2O2的濃度與反應時間基本呈線性關系.當反應溶液流速為300mL/min時,電流由2.83mA/cm2提高至5.66mA/cm2時,20min后溶液中的H2O2濃度分別為 6.2和11.8mg/L,表明此電流范圍內電化學產生H2O2的過程是受電流限制的.但是,當電流從5.66mA/cm2提高到14.15mA/cm2時,H2O2的濃度增長并不顯著,表明電流超過5.66mA/cm2以后,電產H2O2的過程受到了O2向電極的傳質限制.

RVC電產生H2O2的電流效率(CE(%))可由式(3)計算:

式中:為電化學反應轉移的電子數目(本反應中=2);為法拉第常數(96486C/mol);H2O2為電化學反應過程中產生的H2O2濃度,mol/L;為反應溶液的體積,L;為由直流電源提供的通入電流的大小, A;為反應時間, s.

計算發現,在反應過程中電流效率先下降然后逐漸穩定.這是由于反應初期RVC內有一定的氧氣,電流效率相對較高,隨著反應進行和氧氣的消耗,其他副反應增多,導致產H2O2的電流效率逐漸下降并趨于穩定.此外,圖2顯示,當電流由2.83mA/cm2增長至7.07mA/cm2時,產H2O2的電流效率略有降低,但進一步提高電流至14.15mA/cm2會導致電流效率顯著下降.這是由于電流增大到一定程度之后,RVC電化學還原O2產生H2O2的反應變為受O2的傳質限制,增大電流不能促進陰極產H2O2的反應,反而會增強H2O2在陽極和陰極的分解反應[41],導致觀察到的產H2O2電流效率下降.

圖2 電流對網狀玻碳電極產H2O2的影響

內插圖為產H2O2電流效率

2.1.2 進水流速對RVC電產H2O2的影響 由圖3可知,產H2O2濃度隨時間基本呈現線性增長趨勢.進水流速增大,體系中H2O2濃度增加.外加電流為5.66mA/cm2,反應溶液流速分別為150和300mL/min時,反應20min后產H2O2濃度分別為9.0和11.8mg/L.這是由于反應溶液流速越大,對流增強,傳質效果越好[43],有利于O2傳質到電極并轉化為H2O2.

RVC產H2O2電流效率隨時間逐漸下降并趨于穩定.5.66mA/cm2條件下,反應溶液流速分別為150和300mL/min時,經過20min后,產H2O2電流效率分別為43%和56%.此結果表明,在穿透電極反應體系中,增大流速可改善電化學反應過程中氧氣等活性物質的傳質效果,從而提高電流效率.

圖3 流速對網狀玻碳電極產H2O2性能的影響

內插圖為產H2O2電流效率

H2O2與O3的比例是影響×OH生成和污染物處理效果的重要因素.本研究中20min內曝入系統的O3劑量為0.083mmol/L,電流密度2.83~14.15mA/ cm2時產生的H2O2為0.072~0.143mmol/L, O3與H2O2物質的量比為5.84~11.57,如表2所示.與傳統peroxone反應中報道的最佳O3與H2O2物質的量比(2:1)相比,E-peroxone系統的O3與H2O2物質的量比要高很多.這是由于在E-peroxone過程中,O3除了與H2O2反應生成×OH之外,還會在陰極發生還原反應產生O2或×OH等.本試驗結果表明,電流密度為5.66~ 14.15mA/cm2, O3與H2O2物質的量比為6時,污染物去除效率較好.

表2 E-peroxone過程中O3與H2O2的劑量

Table 2 Dosage of O3and H2O2during the E-peroxone process

2.2 E-peroxone技術處理布洛芬廢水的研究

2.2.1 E-peroxone技術與電化學氧化、臭氧氧化技術處理布洛芬廢水效果的比較 如圖4所示,實驗發現,電化學氧化技術和臭氧氧化技術在經過30min的處理時間后對溶液中布洛芬的去除率分別為59%和64%.而E-peroxone技術在5min時即可實現62%的布洛芬去除率,15min時布洛芬去除率可達93%,25min時布洛芬基本被完全去除.

表3 電化學氧化、臭氧氧化和E-peroxone技術中布洛芬降解的反應速率常數及能耗(EEO)比較

注:電化學氧化過程中,布洛芬的降解在15min后基本停止,降解動力學不符合一級動力學,無法計算EEO[45];“-”表示未添加.

電化學氧化過程初期布洛芬降解速率較快,但反應10min后,去除速率明顯下降.這可能是由于在布洛芬降解過程中生成了更容易電化學氧化的中間產物,在陽極與布洛芬發生競爭反應,抑制了剩余布洛芬的降解[23,44].臭氧氧化對布洛芬的去除能力有限,這是由于布洛芬分子只有一個微活化芳香環且沒有與O3反應的活性基團(O3= 9.6L/(mol×s))[12].與之相比,E-peroxone過程中產生的大量×OH可以快速地氧化布洛芬(·OH= 7.4×109L/(mol×s)).

圖4 單獨電化學氧化、單獨臭氧氧化和E-peroxone技術對布洛芬的降解情況

布洛芬初始濃度2.5mg/L;反應溶液體積400mL;氣相臭氧濃度CO3= 8mg/L;氣體流速250mL/min;反應溶液流速為300mL/min;電流5.66mA/cm2

對電化學氧化、臭氧氧化和E-peroxone過程中布洛芬的降解情況分別進行動力學擬合,其反應速率常數見表3.臭氧氧化與E-peroxone過程均符合一級反應動力學,電化學氧化過程分為0~10和10~30min兩段分別進行一級動力學擬合.根據各處理過程的反應速率常數擬合電化學氧化與臭氧氧化加和的布洛芬降解曲線,如圖4中虛線所示.可以看出,E-peroxone過程對布洛芬的去除效果明顯優于電化學氧化加臭氧氧化,表明E-peroxone技術中電化學和臭氧氧化技術具有明顯的協同作用,能夠強化布洛芬的去除.增強因子(EF)被廣泛用于評價處理過程的協同效應(式(4)).計算發現,E-peroxone過程對于電化學氧化和臭氧氧化具有明顯協同作用,且處理10min后,由于單獨電化學氧化受到抑制,協同作用明顯增強,EF由1.68增長至4.19.

為探究×OH在布洛芬降解中的作用,根據布洛芬濃度變化曲線對×OH暴露量進行反算(式(5)),由圖5可見,臭氧氧化與E-peroxone過程中×OH暴露量隨時間基本呈線性增長趨勢(2= 0.994~0.997),表明在該過程中×OH濃度基本保持穩定,其中,E-peroxne過程中×OH穩態濃度約為0.387×10-9mmol/L,約為臭氧氧化過程(0.077×10-9mmol/L)的5倍.因此,E- peroxone技術可以顯著地強化布洛芬的去除.

布洛芬初始濃度2.5mg/L;反應溶液體積400mL;氣相臭氧濃度CO3= 8mg/L;氣體流速250mL/min;反應溶液流速為300mL/min;電流5.66mA/cm2

2.2.2 電流對E-peroxone過程布洛芬處理效果的影響 如圖6所示,隨著電流的增大,E-peroxone技術對布洛芬的去除速率相應增加.電流為2.83mA/cm2時經過30min的處理時間布洛芬去除率為83%,5.66~14.15mA/cm2時在20min基本可實現布洛芬的完全去除.這是因為增大電流可以提高電極反應的速率,增加反應過程中原位產生的H2O2,并進而強化臭氧轉化產生更多的×OH,高效地降解布洛芬分子.

圖6 不同電流條件對布洛芬廢水處理效果的影響

布洛芬初始濃度2.5mg/L;反應溶液體積400mL;臭氧濃度CO3= 8mg/L;氣體流速為250mL/min;反應溶液流速為300mL/min

圖7 不同反應溶液流速條件對布洛芬廢水處理效果的影響

布洛芬初始濃度2.5mg/L;反應溶液體積400mL;臭氧濃度CO3= 8mg/L;氣體流速為250mL/min;電流為5.66mA/cm2

2.2.3 流速對E-peroxone過程布洛芬處理效果的影響 如圖7所示,反應溶液流速由30mL/min逐步提高到300mL/min的過程中,布洛芬的降解速率逐步加快.反應溶液流速為300mL/min時,反應10min基本達到88%的去除效率,20min時基本實現布洛芬的完全去除.這表明,在穿透電極E-peroxone系統中,提高流速可以增強反應體系中的對流傳質,可以強化污染物和活性物質在電極和溶液間的傳質,促進電化學過程的進行,從而提高污染物的去除效率.

2.2.4 動力學擬合與反應速率常數計算 根據動力學擬合與計算,在E-peroxone過程中,布洛芬的降解為偽一級反應,其不同條件下的反應速率常數如表3所示.在E-peroxone過程中,隨著外加電流增大,布洛芬降解的反應速率常數相應增大.此外,隨著反應溶液流速增大,布洛芬降解的反應速率常數也相應增大.由此可以看出,穿透電極E-peroxone體系具有流速越大、傳質越好的特點,在提高單位時間內處理水量的同時不會降低污染物的去除效率,在水量波動時能夠很好地保證出水水質.

2.2.5 能耗計算 去除1m3水中某種污染物90%的濃度所消耗的能量(EEO, kWh/m3-log)被廣泛用于比較各種技術的能耗和經濟性[45].表3顯示了臭氧氧化和E-peroxone技術中去除布洛芬的EEO(式(6)和(7))[33].

式中:是產生O3的能耗(15kWh/kg);CO3為曝入的混合氣中氣相臭氧的濃度,mg/L;O3為曝入氣體的流速,L/min;為反應時間,h;為溶液體積,L;0與C分別為時間= 0和時刻的污染物濃度,mg/L;為外加電流,A;為平均電極電勢,V.

在E-peroxone技術中,EEO隨電流和流速的增大均呈減小趨勢,電流為14.15mA/cm2,流速為300mL/min條件下EEO最小,為0.76kWh/m3-log.臭氧氧化技術的EEO為5.30kWh/m3-log,約為E-peroxone技術能耗的7倍.

以上結果表明,E-peroxone技術能比傳統臭氧技術更加高效低耗地降解布洛芬.此外,與其他技術相比,E-peroxone技術處理也更加高效.楊麗娟等[46]利用Fenton法在40min實現布洛芬86%的去除,朱宏等[47]利用鐵碳微電解法可在120min達到80%的布洛芬去除率,蘇海英等[48]利用g-C3N4-10/TiO2復合材料光催化降解布洛芬在120min實現81.3%的去除率,活性污泥法處理24h最高只達14.76%的去除率[49]等.而E-peroxone技術在20min即可基本實現布洛芬的完全降解,是一種高效的處理技術.

在今后的研究中,將對低濃度布洛芬的降解進行研究,并對其降解途徑和中間產物進行進一步分析.

3 結論

3.1 RVC產H2O2性能受電流和溶液流速影響.提高電流可以加快H2O2的產生速率,但超過一定電流范圍后,會受到氧氣的傳質限制,并引起H2O2自分解增強,電流效率下降.流速增大,氧氣等活性物質傳質增強,有利于H2O2的產生.電流5.66mA/cm2,溶液流速300mL/min條件下,反應20minRVC產H2O2電流效率為56%.

3.2 E-peroxone技術基本可實現布洛芬的完全降解,且反應體系中布洛芬的降解受電流和溶液流速影響.電流增大,布洛芬降解速率越快,去除速率越高. 流速300mL/min條件下,電流密度14.15mA/cm2時布洛芬降解的反應速率常數最大,為0.284min-1.流速增大,布洛芬的降解更迅速,去除效率更高.電流密度5.66mA/cm2條件下,流速300mL/min時布洛芬降解速率常數最大,為0.173min-1.

3.3 E-peroxone技術進行水處理的EEO明顯低于臭氧氧化技術,且流速越大,能耗越低.在溶液體積為400mL,氣體流速為250mL/min、臭氧濃度8mg/L的情況下,最佳運行條件為,電流14.15mA/ cm2,溶液流速300mL/min,此時E-peroxone技術的能耗為0.76kWh/m3-log,僅為臭氧技術的1/7.

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Effective degradation of ibuprofen by flow-through electro-peroxone process.

CUI Xin-xin1, LIN Zhi-rong2, WANG Hui-jiao1, YU Gang1, WANG Yu-jue1*

(1.School of Environment, Tsinghua University, Beijing 100084, China；2.Collage of Geographical and Environmental Engineering, Gannan Normal University, Ganzhou 341000, China)., 2019,39(4)：1619~1626

By combining conventional ozonation with in situ electro-generation of hydrogen peroxide (H2O2) to enhance ozone (O3) transformation to hydroxyl radicals (×OH), the electro-peroxone (E-peroxone) treatment can significantly enhance the oxidation of ozone-refractory pollutants. A flow-through E-peroxone system was established using a reticulated vitreous carbon (RVC) as the cathode. The effects of main operational parameters (e.g., current and flow rate) on ibuprofen abatement were evaluated systematically. The results showed that the E-peroxone process could completely abate ibuprofen (initial concentration 2.5mg/L) in a synthetic solution in 30min, whereas conventional ozonation and electrolysis could only abated 64% and 59% of ibuprofen, respectively. The electrical energy consumption per log-order removal (EEO, kWh/m3-log) of ibuprofen by ozonation was 5.30kWh/m3-log, but was only 0.76kWh/m3-log by the E-peroxone process under the conditions of 100mA, 250mL/min gas flow rate, 8mg/L ozone and 300mL/min solution flow rate. Increasing the solution flow rate to increase the kinetics of electrode mass transfer, the rate of ibuprofen abatement could be further enhanced in the flow-through E-peroxone process. These results suggest that flow-through E-peroxone process may provide an effective and energy-efficient alternative for the abatement of refractory pollutants in water treatment.

electro-peroxone；flow through；reticulated vitreous carbon；ibuprofen

X522

A

1000-6923(2019)04-1619-08

2018-09-17

國家重大科技專項(2017ZX07202-001)

*責任作者, 副教授, wangyujue@tsinghua.edu.cn

崔欣欣(1993-),女,河北保定人,清華大學碩士研究生,主要研究方向為新興污染物與高級氧化技術.