雙波長紫外線(VUV/UV)對有機污染物強化去除特性與原理

邵婉婷， 王文龍， 杜 燁， 吳乾元， 何志明， 付志敏， 胡洪營1,*

1.清華大學(xué)環(huán)境學(xué)院， 環(huán)境模擬與污染控制國家重點聯(lián)合實驗室， 北京 100084 2.清華大學(xué)深圳國際研究生院， 國家環(huán)境保護環(huán)境微生物利用與安全控制重點實驗室， 廣東 深圳 518055 3.清華-伯克利深圳學(xué)院深圳環(huán)境科學(xué)與新能源技術(shù)工程實驗室， 廣東 深圳 518055 4.廣東省佛山市柯維光電股份有限公司， 廣東 佛山 528518

紫外線廣泛用于水處理消毒，可有效滅活病原(指示)微生物，抑制藻類生長，對隱孢子蟲和賈第鞭毛蟲等氯消毒抗性微生物有很好的滅活效果[1-3]. 紫外線也可活化氧化劑(H2O2、O3、自由氯等)、催化劑(TiO2、ZnO等)生成強氧化性自由基(·OH、ClO·、SO4-·等)[4-7]，形成紫外線高級氧化技術(shù)，用于去除水中內(nèi)分泌干擾物、藥品和個人護理品等難降解有機污染物[8-10]. 紫外線/氯、紫外線/H2O2等高級氧化技術(shù)已應(yīng)用于美國地下水回灌、直接/間接補充飲用水等污水再生深度處理工程[11].

低壓汞蒸氣紫外燈(LPUV，254 nm)和中壓汞蒸氣紫外燈(MPUV，200～400 nm)是應(yīng)用中最常用的消毒和高級氧化紫外線光源[12]. 但實際應(yīng)用中面臨基質(zhì)競爭吸收紫外線及消耗自由基、紫外線照射下氧化劑利用效率和自由基產(chǎn)率不佳等難題.

真空紫外線(Vacuum UV，VUV)波長在100～200 nm，以185 nm最為常見，傳統(tǒng)低壓汞蒸汽發(fā)射法可同時發(fā)射254和185 nm紫外線，但常規(guī)玻璃材料會阻隔185 nm部分. 近年來，隨著高透石英管壁、汞齊合金、供電電流技術(shù)的發(fā)展，可同時發(fā)射185 nm (VUV)和254 nm (UV)的紫外線新型光源在水處理領(lǐng)域受到關(guān)注. 與LPUV相比，VUV/UV光源的制造成本、運行電耗相近，但VUV光子具有能量高、水分子吸收強、氧化劑活化和自由基生成效率高等優(yōu)點，有望克服傳統(tǒng)紫外線光源的缺點[13]. VUV/UV無需額外添加氧化劑，即可生成豐富的強氧化自由基，是一種綠色的高級氧化技術(shù)，在飲用水處理、污水再生深度處理和超純水制備等領(lǐng)域備受關(guān)注.

針對飲用水、污水再生深度處理中難降解、高風險有機污染物的去除需求，該文總結(jié)分析了無化學(xué)試劑添加下，VUV/UV高級氧化生成強氧化性自由基的主要機制，深入討論了VUV/UV高級氧化相比UV光解在去除難降解污染物方面的提升效果，闡明了常見水質(zhì)條件對VUV/UV高級氧化的影響，為VUV/UV的未來研究方向提出了結(jié)論與建議.

1 VUV/UV高級氧化原理

1.1 自由基生成過程

VUV/UV光照下，水中生成·OH、O2·-、HO2·等強氧化性自由基和氫原子(H·)、水合電子(eaq-)等強還原性自由基，生成路徑及反應(yīng)方程如圖1、表1所示. 其中，·OH是主要強氧化性自由基，由VUV光照下水分子均質(zhì)裂解〔見式(1)〕和光化學(xué)離子化〔見式(2)〕生成，量子產(chǎn)率(Φ)分別為0.33和0.045 mol/mol(產(chǎn)物/光子)[16]. 研究[17]發(fā)現(xiàn)，VUV/UV光照下水中·OH濃度為10-10～10-9mol/L. 因此，VUV/UV也被稱作VUV/UV高級氧化.

表1 VUV/UV高級氧化過程的主要反應(yīng)[14-16]

圖1 VUV/UV強氧化性自由基生成過程Fig.1 Formation of strong oxidizing radicals in VUV/UV system

VUV/UV可通過光解次生氧化劑H2O2，間接生成強氧化性自由基. VUV可被水分子強烈吸收(吸收系數(shù)為1.8 cm-1)，5.6 mm水層內(nèi)衰減率達90%[18]. 因此，VUV/UV燈管附近水層的·OH濃度較高，并與

溶解氧、OH-及其他自由基發(fā)生復(fù)雜鏈式反應(yīng)，生成O2·-、O3·-、H2O2等強氧化性活性物質(zhì)，共同去除難降解污染物[14]. 此外，H2O2會擴散至距燈管較遠水層，形成UV/H2O2高級氧化. 總而言之，作為降解污染物的主要自由基，·OH可由多個氧化途徑生成和消耗，包括VUV/H2O、VUV/H2O2、UV/H2O2. 因此，H2O2的生成和光解是影響VUV/UV高級氧化效率的重要因素之一.

1.2 雙氧水生成特性

VUV光照生成的·OH集中于紫外線燈管附近，但·OH半衰期約4×10-9s，傳質(zhì)距離約60 nm[19]. 大部分·OH會發(fā)生自淬滅，生成其他氧化活性物質(zhì)，其中以生成H2O2為主[20]. 在序批式VUV/UV反應(yīng)器中，生成的H2O2濃度隨光照劑量升高而升高，最終濃度穩(wěn)定在240 μg/L左右[21]；在連續(xù)流式反應(yīng)器中，出水H2O2濃度也高達(90±50)μg/L[17].

·OH復(fù)合反應(yīng)〔見式(6)〕、H·還原溶解氧生成HO2·并發(fā)生復(fù)合反應(yīng)〔見式(3)(7)〕是生成H2O2的兩條主要途徑[22]. 基于上述原理，pH、溶解氧被認為是影響水中H2O2穩(wěn)態(tài)濃度的重要因素. 當pH由弱酸性(pH=6.3)升至堿性(pH=10.0)時，H2O2生成濃度由240 μg/L降至50 μg/L；當溶解氧濃度降低時，H2O2生成和分解速率均加快[21]. 生成的H2O2在UV和VUV光照下光解生成·OH〔見式(9)(10)〕，特別是擴散至距燈管較遠的H2O2對UV光化學(xué)氧化效率具有強化作用，但其對污染物降解的強化效率尚鮮見報道.

2 VUV/UV的強化氧化效果與影響因素

2.1 VUV/UV的強化氧化效果

與傳統(tǒng)低壓紫外線(UV)相比，VUV/UV可通過直接光解和自由基間接氧化去除污染物，在紫外線吸光率、紫外線利用效率、處理效果及成本費用等方面都具有優(yōu)勢，如表2所示.

表2 VUV/UV與UV的光解特性比較

VUV/UV包括自由基氧化作用和UV紫外線直

接光解作用，對大部分難降解有機污染物去除效果顯著優(yōu)于UV光解，去除速率是UV直接光解的2.0～19.3倍(見圖2). 根據(jù)污染物結(jié)構(gòu)特征，可被分為鹵代烷烴(三鹵甲烷、一氯/二氯/三氯乙腈)、全氟化合物(全氟辛酸)、烷基醚類(丁基黃原酸鈉、甲基叔丁基醚)、苯環(huán)取代物(苯酚、苯胺、對氯苯甲酸、4-叔辛基苯酚)和含苯環(huán)多官能團化合物(布洛芬、酮洛芬、萘普生、四環(huán)素、磺胺甲惡唑)等.

圖2 VUV/UV高級氧化與UV光解對典型污染物降解速率比較Fig.2 Comparison of the elimination of representative pollutants between VUV/UV and UV

VUV/UV對鹵代烷烴的強化效率為1.8～15.8倍，其中對氯代乙腈的強化效率為2.8～15.8倍，對碘代甲烷的強化效率為1.8倍[30-32]. 一方面，鹵代烷烴類污染物對UV254吸收較低、光敏化降解過程較弱，直接光解速率較低；另一方面，其與VUV/UV光照系統(tǒng)中的·OH反應(yīng)速率較快，其中氯代乙腈與·OH二級反應(yīng)速率為0.16×109～1.35×109L/(mol·s)[31]，三碘代甲烷(CHI3)與·OH反應(yīng)速率為833 m2/Ein[32]. 因此，VUV/UV通過生成強氧化性自由基，顯著提升了UV直接光解速率較低的鹵代烷烴類污染物的降解速率.

類似地，VUV/UV對全氟化合物、烷基醚類等紫外線吸收較低、直接光解/光敏化降解較弱的污染物強化效果顯著，強化效率為14.0～18.3倍[33-36]. 但VUV/UV對丁基黃原酸鈉強化效率較低，僅為1.58倍[35].

VUV/UV對含苯環(huán)多官能團化合物的強化效率存在較大差異，如對四環(huán)素和布洛芬的強化效率分別為UV的6.2和7.7倍，但對酮洛芬的強化效率基本維持不變，這主要與苯環(huán)外其他特征官能團的結(jié)構(gòu)與性質(zhì)相關(guān)[37-38]. 四環(huán)素和布洛芬自身結(jié)構(gòu)穩(wěn)定，吸收UV后直接光解速率較慢，但在VUV產(chǎn)生的·OH作用下會發(fā)生開環(huán)斷鍵反應(yīng). 酮洛芬結(jié)構(gòu)中的羰基在吸收UV后易發(fā)生斷裂，VUV產(chǎn)生的自由基對其降解促進效果不明顯.

VUV/UV對多種難降解污染物都具有較好的去除效果. VUV/UV體系中，大部分含苯環(huán)多功能團化合物如萘普生、布洛芬、酮洛芬、磺胺甲惡唑等，15 min內(nèi)可被100%去除[38-40]. VUV/UV對烷基醚類如甲基叔丁基醚、丁基黃原酸鈉可分別實現(xiàn)30 min 97.4%和40 min 95%的去除率[34-35]. 但VUV/UV對鹵代烷烴去除效果不佳，三鹵甲烷、一氯乙腈、二氯乙腈、三氯乙腈等污染物15 min僅能被去除約20%[30-31]. 具體VUV/UV降解部分有機物的指標如表3所示.

表3 VUV/UV降解部分有機物相關(guān)指標

總的來說，VUV/UV對難降解污染物去除的強化效果與污染物直接光解速率、·OH二級反應(yīng)速率相關(guān)[43]. 如圖2所示，VUV/UV的強化效率與UV光解速率存在一定關(guān)聯(lián)，UV光解速率小于10 m2/Ein時，強化效果為2～18倍，UV光解速率大于10 m2/Ein時，強化效果僅為0.3～2.3倍. VUV/UV的強化效率與·OH二級反應(yīng)速率呈正相關(guān). 此外，VUV光照僅能穿透5.6 mm厚水層，當反應(yīng)器水層過厚時，VUV光化學(xué)活性體積占比較小，對難降解污染物強化去除效果較弱.

2.2 pH的影響

溶液pH是影響VUV/UV氧化去除難降解污染物的重要水質(zhì)因素. 一方面，溶液pH會影響VUV光照下·OH生成和利用效率；另一方面，也會改變污染物化學(xué)形態(tài)和降解速率，并對水質(zhì)基質(zhì)產(chǎn)生影響. 因此溶液pH對VUV/UV氧化效率的影響是多種因素共同作用的結(jié)果，且影響效果隨水中污染物種類而變化(見圖3和表4).

表4 pH對VUV/UV降解污染物的影響

圖3 VUV/UV降解污染物速率隨pH變化情況[38,44-46]Fig.3 Schematic diagram of pollutants degradation rate changing with pH[38,44-46]

2.2.1pH對·OH生成效率和利用效率的影響

pH會直接影響·OH的生成和利用效率. 一方面，隨pH升高，·OH氧化電位下降(由pH=0時的2.59 V降至pH=7時的2.18 V)，解離為氧化性較低的O-·(·OHH++O-·，pKa=11.9)，氧化能力減弱；另一方面，堿性條件下OH-濃度的升高會消耗更多·OH[47]，使作用于微量有機污染物的·OH減少[32]. pH減少一級·OH生成的同時，會減少H2O2及二級自由基的生成.

2.2.2pH對污染物形態(tài)和氧化效率的影響

溶液pH會改變污染物的聚集狀態(tài)和解離形態(tài)，

繼而影響其氧化降解特性[48]. 酸性條件下，污染物的氨基等結(jié)構(gòu)易質(zhì)子化形成正電形態(tài)；堿性條件下，污染物的羥基、羧基等易解離質(zhì)子，形成負電形態(tài).

因此諾氟沙星、環(huán)丙沙星等氟喹諾酮類抗生素的VUV/UV光解特性受pH顯著影響，當pH由3升至9時，諾氟沙星和環(huán)丙沙星由正電與質(zhì)子化形態(tài)，轉(zhuǎn)變?yōu)橐资堋H進攻分解的負電形態(tài)，光降解速率常數(shù)先顯著升高后降低[44].

pH對常見抗生素四環(huán)素也有類似作用機制[37]，而左氧氟沙星雖然也存在解離形態(tài)的變化，但pH對其光降解動力學(xué)常數(shù)影響并不明顯[44]. 此外，殺蟲劑涕滅威和滅梭威的氨基甲酸酯基團在堿性條件下發(fā)生顯著水解，加快了它們在VUV/UV體系中的分解速率[46].

2.2.3pH對水質(zhì)基質(zhì)的影響

含碳體系中，pH影響無機碳形態(tài). 當pH呈堿性時，水中HCO3-濃度下降，CO32-濃度升高(HCO3-+OH-H2O+CO32-)，而CO32-與·OH的反應(yīng)速率是HCO3-的45.9倍，即pH通過影響無機碳形態(tài)加強其對·OH的淬滅效果[49].

2.3 無機陰離子對VUV/UV氧化的影響

2.3.1硝酸根

硝酸根是水中常見的光化學(xué)活性陰離子，且光化學(xué)活性會隨紫外線光源變化. 中壓紫外線光源(300～360 nm)照射下，硝酸根產(chǎn)生·OH，促進卡馬西平的降解[50]；但在低壓紫外線直接光解和高級氧化中，硝酸根會抑制污染物的降解[51].

VUV/UV光照下，硝酸根發(fā)生更加復(fù)雜的光化學(xué)轉(zhuǎn)化(見表5)，并抑制VUV/UV對污染物的降解效率. 例如，當硝酸根濃度從0增至500 μmol/L時，VUV/UV降解1,4-二惡烷的一級反應(yīng)速率降低90%[54].

表5 VUV/UV光照下硝酸根/亞硝酸根相關(guān)反應(yīng)[52-53]

硝酸根的主要抑制機理為競爭吸收紫外線和消耗自由基. 首先，硝酸鹽對VUV的摩爾吸光系數(shù)為 4 779 L/(mol·cm)，遠高于對UV的摩爾吸光系數(shù)3.51 L/(mol·cm)[55]. VUV/UV體系中，硝酸根和水分子競爭吸收VUV，并生成亞硝酸根和·OH、氧原子，但自由基量子產(chǎn)率低于水分子裂解[23]. 其次，硝酸根及其光解產(chǎn)物亞硝酸根會和污染物競爭消耗·OH、H·、eaq-等[56-57].

以城市污水處理廠二級處理出水為例，硝酸根濃度約為0.5 mmol/L，水分子濃度約為55.5 mol/L. 計算得硝酸根的VUV吸收約是水分子的22%，該結(jié)果表明，硝酸根競爭吸收紫外線和消耗自由基均是抑制VUV/UV氧化效果的重要原因[18].

2.3.2碳酸根/碳酸氫根

碳酸根/碳酸氫根被認為是地表水和城市污水廠二級出水中淬滅·OH的主要無機離子〔見圖4及表6中式(29)(30)〕，與·OH的二級反應(yīng)速率分別為3.9×108和8.5×106L/(mol·s)，抑制了紫外線高級氧化對難降解有機污染物的去除[49,58]. 在VUV/UV高級氧化中，碳酸根/碳酸氫根還會強烈吸收VUV，摩爾吸光系數(shù)分別為630和269 L/(mol·cm)[55]，抑制了VUV生成強氧化性自由基及降解污染物的效率[32].

圖4 VUV/UV光照下碳酸根/碳酸氫根轉(zhuǎn)化示意Fig.4 Schematic diagram of carbonate / bicarbonate conversion under VUV/UV irradiation

表6 VUV光照下碳酸根/碳酸氫根相關(guān)反應(yīng)[53]

當碳酸氫根/碳酸根濃度由0.5 mmol/L升至5 mmol/L時，VUV/UV對亞甲基藍的降解速率常數(shù)降低15.6%[59]. 另有研究[60]顯示，當碳酸氫根/碳酸根濃度由6.39×10-3mmol/L升至4.9 mmol/L時，雙氯西林降解速率常數(shù)約下降90%. 污染物濃度和碳酸根/碳酸氫根濃度比值變化試驗表明，自由基淬滅過程是其主要抑制原理. 例如,當羅丹明b與碳酸根/碳酸氫根的濃度比由0.05升至0.5時，VUV/UV對羅丹明b的降解速率常數(shù)升高了3.3倍[49].

2.3.3鹵素陰離子

鹵素離子是常見的光化學(xué)活性陰離子，會競爭吸收VUV/UV光子，抑制其對污染物的降解效率. 如溴離子在VUV/UV體系中會生成溴酸鹽，不僅競爭吸收VUV，也會消耗VUV間接光解產(chǎn)生的H2O2(HO2-+HOBr→Br-+O2+H2O)，削弱VUV/UV的氧化降解能力(見圖5)[61-63].

圖5 VUV/UV光照中溴離子轉(zhuǎn)化示意[61-63]Fig.5 Diagram of bromine conversion under VUV/UV irradiation[61-63]

此外，部分鹵素離子在VUV/UV體系中會生成有毒有害副產(chǎn)物. 60 min VUV照射下，1 mg/L的碘離子約被轉(zhuǎn)化83%，且大部分生成物為高毒性碘酸根離子[64]. 但一些鹵素離子如氯離子在VUV照射下轉(zhuǎn)化率不超過0.5%，對VUV/UV去除難降解污染物影響不明顯[65-66].

2.3.4DOM的影響

DOM成分復(fù)雜，對VUV/UV體系的影響遠大于傳統(tǒng)UV體系，主要通過降低污染物吸收VUV的效率，消耗包括·OH、H·、eaq-在內(nèi)的強氧化性自由基，從而削弱VUV/UV去除目標污染物的優(yōu)勢[52,67].

部分DOM、中間體及降解副產(chǎn)物會淬滅強氧化性自由基(DOM+·OH→CO2+H2O+無機酸)，與·OH反應(yīng)速率高達3×108L/(mol·s)[68-69]. 因此DOM會顯著抑制VUV/UV體系對難降解有機污染物的去除效率. 如VUV/UV對二級出水中丙咪嗪的降解效率僅為超純水體系的50%[70]；當DOM濃度從1 mg/L升至2 mg/L，從2 mg/L升至4 mg/L時，VUV/UV對1,4-二甲烷的去除率分別降低13%和22%[15].

3 結(jié)論與建議

a) VUV/UV光源可在不額外添加氧化劑條件下，生成·OH、O2·-等強氧化性自由基，實現(xiàn)難降解污染物快速去除，且具有自由基產(chǎn)率高、污染物降解速率快、抗水質(zhì)干擾能力強等優(yōu)點，具有較好的水處理應(yīng)用前景，值得開展后續(xù)研究.

b) VUV/UV生成強氧化性自由基的途徑主要包括VUV直接裂解水分子和VUV/UV光解次生氧化劑H2O2，但不同來源自由基對污染物的降解貢獻率還不清楚. 此外，VUV/UV的直接光解和自由基氧化降解會受到pH、無機陰離子及DOM等水質(zhì)條件影響，但各水質(zhì)因素對水分子裂解和次生氧化劑H2O2光解等不同來源自由基氧化的影響研究還未開展.

c) VUV/UV受水層厚度影響顯著，而現(xiàn)有研究多以平行光照系統(tǒng)和紫外線劑量當量的實驗室研究為主，實際連續(xù)流式運行和水力參數(shù)對水層擾動及氧化效果的影響還有待進一步研究，未來從實驗室規(guī)模向?qū)嶋H規(guī)模的轉(zhuǎn)變必不可少.

參考文獻(References)：

[1] HIJNEN W A M,BEERENDONK E F,MEDEMA G J.Inactivation credit of UV radiation for viruses,bacteria and protozoan (oo)cysts in water:a review[J].Water Research,2006,40(1):3-22.

[2] 郭美婷,胡洪營,陳健,等,紫外線對銅綠微囊藻的抑制效果及特性研究[J].環(huán)境科學(xué),2011,32(6):1608-1613.

GUO Meiting,HU Hongying,CHEN Jian,etal.Inhibitory effects of ultraviolet irradiation on the growth of microcystis aeruginosa[J].Environmental Science,2011,32(6):1608-1613.

[3] ANTONOPOULOU M,EVGENIDOU E,LAMBROPOULOU D,etal.A review on advanced oxidation processes for the removal of taste and odor compounds from aqueous media[J].Water Research,2014,53:215-234.

[4] LIU Kai,RODDICK-FELICITY A,FAN Linhua.Impact of salinity and pH on the UVC/H2O2treatment of reverse osmosis concentrate produced from municipal wastewater reclamation[J].Water Research,2012,46(10):3229-3239.

[5] ALEXANDER J C,RAMIREZ-CORTINA C R.A comparative study:degradation of 2,5-dichlorophenol in wastewater and distilled water by ozone and ozone-UV[J].Ozone-Science & Engineering,2016,38(3):181-193.

[6] YANG Haiyan,LI Yi,CHEN Yiihua,etal.Comparison of ciprofloxacin degradation in reclaimed water by UV/chlorine and UV/persulfate advanced oxidation processes[J].Water Environment Research,2019,91(12):1576-1588.

[7] KANDAVELU V,KASTIEN H,THAMPI K R.Photocatalytic degradation of isothiazolin-3-ones in water and emulsion paints containing nanocrystalline TiO2and ZnO catalysts[J].Applied Catalysis B:Environmental,2004,48(2):101-111.

[8] THOMSON J,RODDICK F,DRIKAS M,etal.Natural organic matter removal by enhanced photooxidation using low pressure mercury vapour lamps[J].Water Science & Technology Water Supply,2002,2(5/6):435-443.

[9] IMOBERDORF G,MOHSENI M.Degradation of natural organic matter in surface water using vacuum-UV irradiation[J].Journal of Hazardous Materials,2011,186(1):240-246.

[10] DUBOWSKI Y,ALFIYA Y,GILBOA Y,etal.Removal of organic micropollutants from biologically treated greywater using continuous-flow vacuum-UV/UVC photo-reactor[J].Environmental Science and Pollution Research,2020,27(7):7578-7587.

[11] MARISA T,RYAN A,ROBERT B.2017 Potable reuse compendium[M].Washington DC:US EPA,2017.

[12] AFIFI M Z,BLATCHLEY E R.Effects of of UV-based treatment on volatile disinfection byproducts in a chlorinated,indoor swimming pool[J].Water Research,2016,105:167-177.

[13] LI Mengkai,QIANG Zhimin,HOU Pin,etal.VUV/UV/Chlorine as an enhanced advanced oxidation process for organic pollutant removal from water:assessment with a novel mini-fluidic VUV/UV photoreaction system (MVPS)[J].Environmental Science & Technology,2016,50(11):5849-5856.

[14] BAGHERI M,MOHSENI M.A study of enhanced performance of VUV/UV process for the degradation of micropollutants from contaminated water[J].Journal of Hazardous Materials,2015,294:1-8.

[15] BAGHERI M,MOHSENI M.Pilot-scale treatment of 1,4-dioxane contaminated waters using 185 nm radiation:experimental and CFD modeling[J].Journal of Water Process Engineering,2017,19:185-192.

[16] GONZALEZ M G,OLIVEROS E,WORNER M,etal.Vacuum-ultraviolet photolysis of aqueous reaction systems[J].Journal of Photochemistry and Photobiology C-Photochemistry Reviews,2004,5(3):225-246.

[17] BAGHERI M,MOHSENI M.Computational fluid dynamics (CFD) modeling of VUV/UV photoreactors for water treatment[J].Chemical Engineering Journal,2014,256:51-60.

[18] MORA A S,MOHSENI M.Temperature dependence of the absorbance of 185 nm photons by water and commonly occurring solutes and its influence on the VUV advanced oxidation process[J].Environmental Science-Water Research & Technology,2018,4(9):1303-1309.

[19] RUTH R,SHIGEFUMI OKADA.Estimation of life times and diffusion distances of radicals involved in X-ray-induced DNA strand breaks or killing of mammalian cells[J].Radiation Research Society,1975,64(2):306-320.

[20] YANG Laxiang,LI Mengkai,LI Wentao,etal.A green method to determine VUV (185 nm) fluence rate based on hydrogen peroxide production in aqueous solution[J].Photochemistry and Photobiology,2018,94(4):821-824.

[21] ZHANG Qi,WANG Lei,CHEN Baiyang,etal.Understanding and modeling the formation and transformation of hydrogen peroxide in water irradiated by 254 nm ultraviolet (UV) and 185 nm vacuum UV (VUV):effects of pH and oxygen[J].Chemosphere,2020.doi:https://doi.org/10.1016/j.chemosphere.2019.125483.

[22] IMOBERDORF G,MOHSENI M.Modeling and experimental evaluation of vacuum-UV photoreactors for water treatment[J].Chemical Engineering Science,2011,66(6):1159-1167.

[23] ZOSCHKE K,BOERNICK H,WORCH E.Vacuum-UV radiation at 185 nm in water treatment:a review[J].Water Research,2014,52:131-145.

[24] MASON J D,CONE M T,FRY E S.Ultraviolet (250-550 nm) absorption spectrum of pure water[J].Applied Optics,2016,55(25):7163-7172.

[25] FU Pingfeng,MA Yanhong,LEI Bolan,etal.Decomposition of refractory aniline aerofloat collector in aqueous solution by an ozone/vacuum-UV (O3/VUV) process[J].Environmental Technology,2019.doi:10.1080/09593330.2019.1642389.

[26] HUANG Haibao,LEUNG D Y C,KWONG P C W,etal.Enhanced photocatalytic degradation of methylene blue under vacuum ultraviolet irradiation[J].Catalysis Today,2013,201:189-194.

[27] PUSPITA P,RODDICK F A,PORTER N A.Decolourisation of secondary effluent by UV-mediated processes[J].Chemical Engineering Journal,2011,171(2):464-473.

[28] LI Mengkai,LI Wentao,BOLTON-JAMES R,etal.Organic pollutant degradation in water by the vacuum-ultraviolet/ultraviolet/H2O2process:inhibition and enhancement roles of H2O2[J].Environmental Science & Technology,2019,53(2):912-918.

[29] BOLTON-JAMES R,BIRCHER-KEITH G,TUMAS-WILLIA M,etal.Figures-of-merit for the technical development and application of advanced oxidation technologies for both electric- and solar-driven systems (IUPAC Technical Report) [J].Journal of Advanced Oxidation Technologies,2001,1(4):627-637.

[30] HIRUN-UTOK C,PHATTARAPATTAMAWONG S.Degradation and transformation of natural organic matter accountable for disinfection byproduct formations by UV photolysis and UV/chlor(am)ine[J].Water Science and Technology,2019,79(5):929-937.

[31] KIATTISAKSIRI P,KHAN E,PUNYAPALAKUL P,etal.Photodegradation of haloacetonitriles in water by vacuum ultraviolet irradiation:mechanisms and intermediate formation[J].Water Research,2016,98:160-167.

[32] HU Jun,WANG Chen,YE Zhen,etal.Degradation of iodinated disinfection byproducts by VUV/UV process based on a mini-fluidic VUV/UV photoreaction system[J].Water Research,2019,158:417-423.

[33] CAO Menghua,WANG Beibei,YU Hongsheng,etal.Photochemical decomposition of perfluorooctanoic acid in aqueous periodate with VUV and UV light irradiation[J].Journal of Hazardous Materials,2010,179(1/2/3):1143-1146.

[34] AMANOLLAHI H,MOUSSAVI G,GIANNAKIS S.VUV/Fe(Ⅱ)/H2O2as a novel integrated process for advanced oxidation of methyl tert-butyl ether (MTBE) in water at neutral pH:process intensification and mechanistic aspects[J].Water Research,2019,166.

[35] FU Pingfeng,FENG Jie,YANG Huifen,etal.Degradation of sodium n-butyl xanthate by vacuum UV-ozone (VUV/O3) in comparison with ozone and VUV photolysis[J].Process Safety and Environmental Protection,2016,102:64-70.

[36] GIRI R R,OZAKI H,GUO X,etal.Oxidative-reductive photodecomposition of perfluorooctanoic acid in water[J].International Journal of Environmental Science and Technology,2014,11(5):1277-1284.

[37] YAO Hong,PEI Jin,WANG Hui,etal.Effect of Fe(Ⅱ/Ⅲ) on tetracycline degradation under UV/VUV irradiation[J].Chemical Engineering Journal,2017,308:193-201.

[38] SZABO R K,MEGYERI C,ILLES E,etal.Phototransformation of ibuprofen and ketoprofen in aqueous solutions[J].Chemosphere,2011,84(11):1658-1663.

[39] ARANY E,SZABO R K,APATI L,etal.Degradation of naproxen by UV,VUV photolysis and their combination[J].Journal of Hazardous Materials,2013,262:151-157.

[40] MOUAMFON M V N,WENZHEN L I,SHUGUANG L U,etal.Photodegradation of sulfamethoxazole applying UV- and VUV-based processes[J].Water Air and Soil Pollution,2011,218(1/2/3/4):265-274.

[41] ALAPI T,GAJDA-SCHRANTZ K,ILISZ I,etal.Comparison of UV- and UV/VUV-induced photolytic and heterogeneous photocatalytic degradation of phenol,with particular emphasis on the intermediates[J].Journal of Advanced Oxidation Technologies,2008,11(3):519-528.

[42] HUANG Li,JING Hengye,CHENG Zhonghong,etal.Different photodegradation behavior of 4-tert-octylphenol under UV and VUV irradiation in aqueous solution[J].Journal of Photochemistry and Photobiology A:Chemistry,2013,251:69-77.

[43] 吳彥霖,余焱,袁海霞,等,水溶液中對叔辛基酚的紫外光降解研究[J].中國環(huán)境科學(xué),2010,30(10):1333-1337.

WU Yanlin,YU Yan,YUAN Haixia,etal.UV photodegradation of p-tert-octyl phenol(4-OP) in water[J].China Environmental Science,2010,30(10):1333-1337.

[44] GENG Cong,LIANG Zhijie,CUI Fuyi,etal.Energy-saving photo-degradation of three fluoroquinolone antibiotics under VUV/UV irradiation:kinetics,mechanism,and antibacterial activity reduction[J].Chemical Engineering Journal,2020,383:123145.

[45] KUTSCHERA K,BOERNICK H,WORCH E.Photoinitiated oxidation of geosmin and 2-methylisoborneol by irradiation with 254 nm and 185 nm UV light[J].Water Research,2009,43(8):2224-2232.

[46] YANG Laxiang,LI Mengkai,LI Wentao,etal.Bench- and pilot-scale studies on the removal of pesticides from water by VUV/UV process[J].Chemical Engineering Journal,2018,342:155-162.

[47] RATPUKDI T,SIRIPATTANAKUL S,KHAN E.Mineralization and biodegradability enhancement of natural organic matter by ozone-VUV in comparison with ozone,VUV,ozone-UV,and UV:effects of pH and ozone dose[J].Water Research,2010,44(11):3531-3543.

[48] 楊毅,楊霞霞,馬新培,等,pH對城市污水二級出水中溶解性有機物的荷電、聚集與光譜特性的影響[J].環(huán)境化學(xué),2015,34(10):1804-1808.

YANG Yi,YANG Xiaxia,MA Xinpei,etal.Effect of pH on the charge aggregation and spectral characteristics of DOM in secondary effluent of municipal wastewater[J].Environmental Chemistry,2015,34(10):1804-1808.

[49] MEROUANI S,HAMDAOUI O,SAOUDI F,etal.Influence of bicarbonate and carbonate ions on sonochemical degradation of Rhodamine B in aqueous phase[J].Journal of Hazardous Materials,2010,175(1/2/3):593-599.

[50] LI Boqiang,MA Xiaoyan,LI Qingsong,etal.Factor affecting the role of radicals contribution at different wavelengths,degradation pathways and toxicity during UV-LED/chlorine process[J].Chemical Engineering Journal,2020.doi:10.1016/j.cej.2020.124552.

[51] WANG Wenlong,WU Qianyuan,HUANG Nan,etal.Synergistic effect between UV and chlorine (UV/chlorine) on the degradation of carbamazepine:influence factors and radical species[J].Water Research,2016,98:190-198.

[52] BUCHANAN W,RODDICK F,PORTER N.Formation of hazardous by-products resulting from the irradiation of natural organic matter:comparison between UV and VUV irradiation[J].Chemosphere,2006,63(7):1130-1141.

[53] GONZALEZ M C,BRAUN A M.VUV photolysis of aqueous-solutions of nitrate and nitrite[J].Research on Chemical Intermediates,1995,21(8/9):837-859.

[54] MATSUSHITA T,SUGITA W,ISHIKAWA T,etal.Prediction of 1,4-dioxane decomposition during VUV treatment by model simulation taking into account effects of coexisting inorganic ions[J].Water Research,2019.doi:10.1016/j.watres.2019.114918.

[55] WANG Lei,ZHANG Qi,CHEN Baiyang,etal.Some issues limiting photo(cata)lysis application in water pollutant control:a critical review from chemistry perspectives[J].Water Research,2020.doi:10.1016/j.watres.2020.115605.

[56] ZOSCHKE K,DIETRICH N,BOERNICK H,etal.UV-based advanced oxidation processes for the treatment of odour compounds:efficiency and by-product formation[J].Water Research,2012,46(16):5365-5373.

[57] MACK J,BOLTON J R.Photochemistry of nitrite and nitrate in aqueous solution:a review[J].Journal of Photochemistry and Photobiology A:Chemistry,1999,128(1/2/3):1-13.

[58] BUXTON G V,GREENSTOCK C L,HELMAN W P,etal.Critical review of rate constants for reactions of hydrated electrons,hydrogen atoms and hydroxyl radicals (·OH/·O-) in aqueous solution[J].Journal of Physical and Chemical Reference Data,1988,17(2):513-886.

[59] WEN Dong,LI Wentao,LV Jinrong,etal.Methylene blue degradation by the VUV/UV/persulfate process:effect of pH on the roles of photolysis and oxidation[J].Journal of Hazardous Materials,2020.doi:10.1016/j.jhazmat.2019.121855.

[60] VILLEGAS-GUZMAN P,SILVA-AGREDO J,FLOREZ O,etal.Selecting the best AOP for isoxazolyl penicillins degradation as a function of water characteristics:effects of pH,chemical nature of additives and pollutant concentration[J].Journal of Environmental Management,2017,190:72-79.

[61] RATPUKDI T,CASEY F,DESUTTER T,etal.Bromate formation by ozone-VUV in comparison with ozone and ozone-UV:effects of pH,ozone dose,and VUV power[J].Journal of Environmental Engineering,2011,137(3):187-195.

[62] LIANG S,PALENCIA L S,YATES R S,etal.Oxidation of MTBE by ozone and peroxone processes[J].Journal American Water Works Association,1999,91(6):104-114.

[63] VON GUNTEN U.Ozonation of drinking water.Part Ⅱ:disinfection and by-product formation in presence of bromide,iodide or chlorine[J].Water Research,2003,37(7):1469-1487.

[64] BU Yinan,SONG Mingrui,HAN Jiarui,etal.A facile and green pretreatment method for nonionic total organic halogen (NTOX) analysis in water-Step Ⅱ.using photolysis to convert NTOX completely into halides[J].Water Research,2018,145:579-587.

[65] ALEGRE M L,GERONES M,ROSSO J A,etal.Kinetic study of the reactions of chlorine atoms and Cl-2(center dot-) radical anions in aqueous solutions.1. reaction with benzene[J].Journal of Physical Chemistry A,2000,104(14):3117-3125.

[66] COSTA C R,OLIVI P.Effect of chloride concentration on the electrochemical treatment of a synthetic tannery wastewater[J].Electrochimica Acta,2009,54(7):2046-2052.

[67] IMOBERDORF G,MOHSENI M.Kinetic study and modeling of the vacuum-UV photoinduced degradation of 2,4-D[J].Chemical Engineering Journal,2012,187:114-122.

[68] MCKAY G,DONG M M,KLEINMAN J L,etal.Temperature dependence of the reaction between the hydroxyl radical and organic matter[J].Environmental Science & Technology,2011,45(16):6932-6937.

[69] XIE Pengchao,YUE Siyang,DING Jiaqi,etal.Degradation of organic pollutants by Vacuum-Ultraviolet (VUV):kinetic model and efficiency[J].Water Research,2018,133:69-78.

[70] XIE Pengchao,ZOU Yujia,JIANG Shan,etal.Degradation of imipramine by vacuum ultraviolet (VUV) system:influencing parameters,mechanisms,and variation of acute toxicity[J].Chemosphere,2019,233:282-291.