基于穿透電極的Electro-peroxone技術(shù)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(shù)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(xué)環(huán)境學(xué)院,北京 100084；2.贛南師范大學(xué)地理與環(huán)境工程學(xué)院,江西 贛州 341000)

利用網(wǎng)狀玻碳電極(RVC)作為陰極,構(gòu)建了一種基于穿透電極的electro-peroxone(E-peroxone)反應(yīng)器,并系統(tǒng)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(jié)果表明,E-peroxone可以在30min內(nèi)完全去除初始濃度為2.5mg/L的布洛芬,而電化學(xué)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(yīng)溶液流速為300mL/min時, E-peroxone技術(shù)去除布洛芬的效率最高,且能耗(EEO)僅為傳統(tǒng)臭氧氧化技術(shù)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(zhì),從而強化布洛芬的去除,并降低EEO.

Elecrtro-peroxone；穿透電極；網(wǎng)狀玻碳電極；布洛芬

藥物和個人護理品(PPCPs)對飲用水供應(yīng)、人體健康和生態(tài)系統(tǒng)構(gòu)成潛在的威脅[1,2].污水處理廠傳統(tǒng)的處理方法難以有效降解PPCPs,導(dǎo)致很多PPCPs及其代謝物質(zhì)在二沉池出水中仍能被檢出[2-6].高級氧化技術(shù)具有良好的礦化效果[7-22],被廣泛應(yīng)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(xué)技術(shù)受電流和傳質(zhì)限制[16],臭氧氧化具有明顯選擇氧化性且中間產(chǎn)物多、能耗高[18-20], O3/H2O2(peroxone)技術(shù)由于需外部投加H2O2導(dǎo)致安全性較低[17].將臭氧與電化學(xué)技術(shù)耦合的electro- peroxone(E-peroxone)技術(shù),可將O2電化學(xué)原位轉(zhuǎn)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(chǎn)物的深度處理工藝[23-33].

電化學(xué)氧化的反應(yīng)機理決定了其受到污染物與活性物質(zhì)在電極表面?zhèn)髻|(zhì)擴散的限制[16].目前E-peroxone技術(shù)中多采用平板電極,比表面積較小,污染物的傳質(zhì)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(dāng)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(zhì)的傳質(zhì)擴散,從而提高污染物氧化速率[16,34-39].網(wǎng)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(dǎo)電性良好,有利于電化學(xué)反應(yīng)過程中污染物的傳質(zhì)和轉(zhuǎn)化[40].使用RVC電極作為E-peroxone系統(tǒng)中的穿透陰極,利用穿透電極流速越大,傳質(zhì)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(zhì),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(gòu)建了一種基于RVC穿透電極的E- peroxone系統(tǒng),并對其去除水中布洛芬的性能進行了系統(tǒng)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(xué)和運行參數(shù)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(tǒng)產(chǎn)生的高純水(阻抗18.2MΩ)配制.

1.2 實驗裝置

如圖1所示,系統(tǒng)主要包括:內(nèi)置陰陽電極的聚四氟柱形反應(yīng)器、直流電源(LONG WEI PS-305DM)、臭氧發(fā)生器(Yanco INDUSTRIES LTD. OzoneLabTM Instrument OL80F/ DST)、臭氧檢測儀、蠕動泵(LongerPump YZ1515x)等.反應(yīng)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(yīng)溶液以恒定流速流入反應(yīng)器,并以恒定流速向反應(yīng)器中曝氣,進口處采用三通接頭使氣體和反應(yīng)溶液同時進入反應(yīng)器,反應(yīng)器出水流回廢水池.通過控制直流電源、臭氧發(fā)生器的啟停可以分別對污染物進行單獨臭氧氧化、單獨電化學(xué)氧化以及E-peroxone技術(shù)處理.

圖1 穿透電極反應(yīng)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(diào)節(jié)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(shù)

實驗中運行參數(shù)如表1所示.

表1 實驗運行參數(shù)

2 結(jié)果與討論

2.1 RVC產(chǎn)過氧化氫性能研究

2.1.1 電流對RVC電產(chǎn)H2O2的影響 在E- peroxone過程中,H2O2的產(chǎn)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(yīng)器和水槽中循環(huán)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(yīng)體系中RVC電產(chǎn)H2O2的濃度與反應(yīng)時間基本呈線性關(guān)系.當(dāng)反應(yīng)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(nèi)電化學(xué)產(chǎn)生H2O2的過程是受電流限制的.但是,當(dāng)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(chǎn)H2O2的過程受到了O2向電極的傳質(zhì)限制.

RVC電產(chǎn)生H2O2的電流效率(CE(%))可由式(3)計算:

式中:為電化學(xué)反應(yīng)轉(zhuǎn)移的電子數(shù)目(本反應(yīng)中=2);為法拉第常數(shù)(96486C/mol);H2O2為電化學(xué)反應(yīng)過程中產(chǎn)生的H2O2濃度,mol/L;為反應(yīng)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(yīng)時間, s.

計算發(fā)現(xiàn),在反應(yīng)過程中電流效率先下降然后逐漸穩(wěn)定.這是由于反應(yīng)初期RVC內(nèi)有一定的氧氣,電流效率相對較高,隨著反應(yīng)進行和氧氣的消耗,其他副反應(yīng)增多,導(dǎo)致產(chǎn)H2O2的電流效率逐漸下降并趨于穩(wěn)定.此外,圖2顯示,當(dāng)電流由2.83mA/cm2增長至7.07mA/cm2時,產(chǎn)H2O2的電流效率略有降低,但進一步提高電流至14.15mA/cm2會導(dǎo)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(xué)還原O2產(chǎn)生H2O2的反應(yīng)變?yōu)槭躉2的傳質(zhì)限制,增大電流不能促進陰極產(chǎn)H2O2的反應(yīng),反而會增強H2O2在陽極和陰極的分解反應(yīng)[41],導(dǎo)致觀察到的產(chǎn)H2O2電流效率下降.

圖2 電流對網(wǎng)狀玻碳電極產(chǎn)H2O2的影響

內(nèi)插圖為產(chǎn)H2O2電流效率

2.1.2 進水流速對RVC電產(chǎn)H2O2的影響 由圖3可知,產(chǎn)H2O2濃度隨時間基本呈現(xiàn)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(yīng)溶液流速分別為150和300mL/min時,反應(yīng)20min后產(chǎn)H2O2濃度分別為9.0和11.8mg/L.這是由于反應(yīng)溶液流速越大,對流增強,傳質(zhì)效果越好[43],有利于O2傳質(zhì)到電極并轉(zhuǎn)化為H2O2.

RVC產(chǎn)H2O2電流效率隨時間逐漸下降并趨于穩(wěn)定.5.66mA/cm2條件下,反應(yīng)溶液流速分別為150和300mL/min時,經(jīng)過20min后,產(chǎn)H2O2電流效率分別為43%和56%.此結(jié)果表明,在穿透電極反應(yīng)體系中,增大流速可改善電化學(xué)反應(yīng)過程中氧氣等活性物質(zhì)的傳質(zhì)效果,從而提高電流效率.

圖3 流速對網(wǎng)狀玻碳電極產(chǎn)H2O2性能的影響

內(nèi)插圖為產(chǎn)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(nèi)曝入系統(tǒng)的O3劑量為0.083mmol/L,電流密度2.83~14.15mA/ cm2時產(chǎn)生的H2O2為0.072~0.143mmol/L, O3與H2O2物質(zhì)的量比為5.84~11.57,如表2所示.與傳統(tǒng)peroxone反應(yīng)中報道的最佳O3與H2O2物質(zhì)的量比(2:1)相比,E-peroxone系統(tǒng)的O3與H2O2物質(zhì)的量比要高很多.這是由于在E-peroxone過程中,O3除了與H2O2反應(yīng)生成×OH之外,還會在陰極發(fā)生還原反應(yīng)產(chǎn)生O2或×OH等.本試驗結(jié)果表明,電流密度為5.66~ 14.15mA/cm2, O3與H2O2物質(zhì)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(shù)處理布洛芬廢水的研究

2.2.1 E-peroxone技術(shù)與電化學(xué)氧化、臭氧氧化技術(shù)處理布洛芬廢水效果的比較 如圖4所示,實驗發(fā)現(xiàn),電化學(xué)氧化技術(shù)和臭氧氧化技術(shù)在經(jīng)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(shù)在5min時即可實現(xiàn)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(xué)氧化、臭氧氧化和E-peroxone技術(shù)中布洛芬降解的反應(yīng)速率常數(shù)及能耗(EEO)比較

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

電化學(xué)氧化過程初期布洛芬降解速率較快,但反應(yīng)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(xué)氧化的中間產(chǎn)物,在陽極與布洛芬發(fā)生競爭反應(yīng),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(huán)且沒有與O3反應(yīng)的活性基團(O3= 9.6L/(mol×s))[12].與之相比,E-peroxone過程中產(chǎn)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(xué)氧化、單獨臭氧氧化和E-peroxone技術(shù)對布洛芬的降解情況

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

對電化學(xué)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(xué)擬合,其反應(yīng)速率常數(shù)見表3.臭氧氧化與E-peroxone過程均符合一級反應(yīng)動力學(xué),電化學(xué)氧化過程分為0~10和10~30min兩段分別進行一級動力學(xué)擬合.根據(jù)各處理過程的反應(yīng)速率常數(shù)擬合電化學(xué)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(yōu)于電化學(xué)氧化加臭氧氧化,表明E-peroxone技術(shù)中電化學(xué)和臭氧氧化技術(shù)具有明顯的協(xié)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(xié)同效應(yīng)(式(4)).計算發(fā)現(xiàn),E-peroxone過程對于電化學(xué)氧化和臭氧氧化具有明顯協(xié)同作用,且處理10min后,由于單獨電化學(xué)氧化受到抑制,協(xié)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(jù)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(wěn)定,其中,E-peroxne過程中×OH穩(wěn)態(tài)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(shù)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(yīng)溶液體積400mL;氣相臭氧濃度CO3= 8mg/L;氣體流速250mL/min;反應(yīng)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(shù)對布洛芬的去除速率相應(yīng)增加.電流為2.83mA/cm2時經(jīng)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(xiàn)布洛芬的完全去除.這是因為增大電流可以提高電極反應(yīng)的速率,增加反應(yīng)過程中原位產(chǎn)生的H2O2,并進而強化臭氧轉(zhuǎn)化產(chǎn)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(yīng)溶液體積400mL;臭氧濃度CO3= 8mg/L;氣體流速為250mL/min;反應(yīng)溶液流速為300mL/min

圖7 不同反應(yīng)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(yīng)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(yīng)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(yīng)溶液流速為300mL/min時,反應(yīng)10min基本達到88%的去除效率,20min時基本實現(xiàn)布洛芬的完全去除.這表明,在穿透電極E-peroxone系統(tǒng)中,提高流速可以增強反應(yīng)體系中的對流傳質(zhì),可以強化污染物和活性物質(zhì)在電極和溶液間的傳質(zhì),促進電化學(xué)過程的進行,從而提高污染物的去除效率.

2.2.4 動力學(xué)擬合與反應(yīng)速率常數(shù)計算 根據(jù)動力學(xué)擬合與計算,在E-peroxone過程中,布洛芬的降解為偽一級反應(yīng),其不同條件下的反應(yīng)速率常數(shù)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(yīng)速率常數(shù)相應(yīng)增大.此外,隨著反應(yīng)溶液流速增大,布洛芬降解的反應(yīng)速率常數(shù)也相應(yīng)增大.由此可以看出,穿透電極E-peroxone體系具有流速越大、傳質(zhì)越好的特點,在提高單位時間內(nèi)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(zhì).

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(shù)的能耗和經(jīng)濟性[45].表3顯示了臭氧氧化和E-peroxone技術(shù)中去除布洛芬的EEO(式(6)和(7))[33].

式中:是產(chǎn)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(yīng)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(shù)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(shù)的EEO為5.30kWh/m3-log,約為E-peroxone技術(shù)能耗的7倍.

以上結(jié)果表明,E-peroxone技術(shù)能比傳統(tǒng)臭氧技術(shù)更加高效低耗地降解布洛芬.此外,與其他技術(shù)相比,E-peroxone技術(shù)處理也更加高效.楊麗娟等[46]利用Fenton法在40min實現(xiàn)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(fù)合材料光催化降解布洛芬在120min實現(xiàn)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(shù)在20min即可基本實現(xiàn)布洛芬的完全降解,是一種高效的處理技術(shù).

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(chǎn)物進行進一步分析.

3 結(jié)論

3.1 RVC產(chǎn)H2O2性能受電流和溶液流速影響.提高電流可以加快H2O2的產(chǎn)生速率,但超過一定電流范圍后,會受到氧氣的傳質(zhì)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(zhì)傳質(zhì)增強,有利于H2O2的產(chǎn)生.電流5.66mA/cm2,溶液流速300mL/min條件下,反應(yīng)20minRVC產(chǎn)H2O2電流效率為56%.

3.2 E-peroxone技術(shù)基本可實現(xiàn)布洛芬的完全降解,且反應(yīng)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(yīng)速率常數(shù)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(shù)最大,為0.173min-1.

3.3 E-peroxone技術(shù)進行水處理的EEO明顯低于臭氧氧化技術(shù),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(shù)的能耗為0.76kWh/m3-log,僅為臭氧技術(shù)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(zé)任作者, 副教授, wangyujue@tsinghua.edu.cn

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