UV/PS降解水中2,4-二氯苯酚的特性研究

陳菊香,高乃云,楊 靜,王超慧,古振川,江 闖(.新疆大學(xué)建筑工程學(xué)院,新疆 烏魯木齊 80047；.同濟(jì)大學(xué),污染控制與資源化研究國家重點實驗室,上海 0009；.內(nèi)蒙古科技大學(xué)能源與環(huán)境學(xué)院,內(nèi)蒙古 包頭0400)

UV/PS降解水中2,4-二氯苯酚的特性研究

陳菊香1,2,高乃云2*,楊 靜1,王超慧3,古振川2,江 闖2(1.新疆大學(xué)建筑工程學(xué)院,新疆 烏魯木齊 830047；2.同濟(jì)大學(xué),污染控制與資源化研究國家重點實驗室,上海 200092；3.內(nèi)蒙古科技大學(xué)能源與環(huán)境學(xué)院,內(nèi)蒙古 包頭014010)

比較采用PS,UV和UV/PS工藝降解2,4-DCP的去除效果及一級動力學(xué)常數(shù),研究光解反應(yīng)中OH? 和SO4?的貢獻(xiàn)率,計算SO4?與2,4-DCP反應(yīng)的二級動力學(xué)反應(yīng)常數(shù),考察實際水體中UV/PS光解2,4-DCP的效果,以及兩種有效工藝UV和UV/PS經(jīng)濟(jì)性計算和比較.結(jié)果表明,分別單獨(dú)采用PS,UV降解,降解率是4%和46.2%,而采用UV/PS去除率高達(dá)96.4%,大大提高單獨(dú)PS系統(tǒng)降解2,4-DCP的效率,表明 UV/PS系統(tǒng)可高效去除 2,4-DCP.采用 PS,UV和 UV/PS降解 2,4-DCP基本遵循擬一級反應(yīng)動力學(xué),一級反應(yīng)動力學(xué)常數(shù)分別為0.4×10-3,6.2×10-3和 35.1×10-3min-1.光解反應(yīng)中起主作用的是自由基 SO4?.SO4?與 2,4-DCP二級動力學(xué)反應(yīng)常數(shù)是 7.07×109(mol/L)-1s-12,4-DCP在3種實際水體(錫東水廠,西氿水庫,橫山水庫)中降解率比在超純水中的高.經(jīng)濟(jì)計算中UV/PS協(xié)同系統(tǒng)的能量利用率最高.

2, 4-DCP；UV/PS；反應(yīng)動力學(xué)；實際水體；經(jīng)濟(jì)預(yù)算

氯酚是一類弱酸性的弱電解質(zhì),其中大部分有強(qiáng)毒性,強(qiáng)化學(xué)穩(wěn)定性和熱穩(wěn)定性,難生物降解并容易通過食物鏈在生物體內(nèi)富集,難以在環(huán)境中去除,對環(huán)境和人類造成很大危害,因而被美國環(huán)保局(USEPA)和歐盟環(huán)保署(EEA)列為優(yōu)先污染物(環(huán)境水法[1]和歐洲決議2455/2001E[2]).吸入一定量氯酚可能引起支氣管的炎癥、水腫、痙攣等病癥,甚至對人的中樞神經(jīng)系統(tǒng)、肝臟、腎臟造成很大的傷害,對氯酚污染的控制己成全世界科研工作者的研究熱點.開發(fā)氯酚廢水的高效處理技術(shù)已成為環(huán)境保護(hù)領(lǐng)域的當(dāng)務(wù)之急.

過硫酸鹽可被紫外激活活化分解為 SO4?或OH?,SO4?的氧化還原電位為 2.5～3.1V,可降解水中大部分污染物質(zhì)[3-6],但其對污染物的降解具有選擇性.故UV/PS系統(tǒng)降解2,4-DCP效果以待考察,溶液中SO4?和OH?兩種自由基在氧化實驗過程中貢獻(xiàn)率情況,SO4?與2,4-DCP二級反應(yīng)動力學(xué)常數(shù),實際水體里UV/PS工藝降解效果,UV和UV/PS工藝降解過程經(jīng)濟(jì)性計算等問題之前鮮見報道,以待研究.

1 材料與方法

1.1 試劑與裝置

2,4 -二氯苯酚(色譜純)購自阿拉丁(上海)貿(mào)易有限公司(物理性質(zhì)見表 1),過硫酸鈉、甲醇( MEOH≥99.7%)、乙醇(ETOH≥99.7%)、叔丁醇(TBA≥99.5%)、磷酸氫二鈉、磷酸二氫鈉、苯甲酸(BA))等試劑均購自國藥集團(tuán)化學(xué)試驗有限公司.甲醇、乙腈(色譜純)購自西格瑪奧德里奇(上海)貿(mào)易有限公司.

表1 2,4-DCP物理化學(xué)性質(zhì)Table 1 Physical and chemical properties of 2, 4-DCP

紫外光照實驗裝置采用準(zhǔn)平行光束儀,該裝置根據(jù)國際紫外協(xié)會標(biāo)準(zhǔn)進(jìn)行設(shè)計自制, 低壓汞燈(75W,天津新景有限公司).2,4-DCP濃度檢測采用高效液相色譜儀(HPLC2010)(日本島津),配有C18色譜(250mm×4.62mm×5 μm, Waters).實際水體是分別從錫東水廠、西氿水庫、橫山水庫進(jìn)水口取的水樣添加 2,4-DCP后配制2,4-DCP溶液.與超純水同等反應(yīng)條件下進(jìn)行光解反應(yīng),實驗所需源水水質(zhì)指標(biāo)(表2)

表2 實際水體的水質(zhì)表Table 2 Water qualityTable of actual water body

1.2 實驗方法

實驗室條件下,用去離子水配制溶液,在200mL結(jié)晶皿中加入含目標(biāo)污染物(2,4-DCP)的溶液 100mL(已采用磷酸鹽緩沖溶液將溶液 pH值調(diào)至 7.0),加入按規(guī)定的摩爾比配好的過硫酸鈉溶液作氧化劑,隨后將結(jié)晶皿放置在紫外光照儀器試驗臺上,同時開始計時,且控制好室內(nèi)反應(yīng)溫度,采用移液槍每次取0.8mL樣品于預(yù)先放置了足量淬滅劑甲醇的棕色液相小瓶中,實驗進(jìn)行3次取平均值.

2 結(jié)果與分析

2.1 不同氧化工藝(PS,UV,UV/PS)降解2,4-DCP

圖1可知采用UV單獨(dú)降解2,4-DCP45min降解率達(dá) 46%,這是因為紫外線主要輻射波長254nm,正好在2,4-DCP物質(zhì)吸光度吸收波段[7-8].采用PS單獨(dú)降解2,4-DCP時降解率僅有4%,而同樣反應(yīng)時間,同樣反應(yīng)條件下,UV/PS工藝光解降解速率迅速增大,降解率可達(dá)96%.說明PS在紫外光照激發(fā)后加快了2,4-DCP的降解速率,進(jìn)而也證明了先前文獻(xiàn)報道的紫外激發(fā)PS溶液生成大量的OH?或SO4?-[9-10].分別將PS,UV,UV/PS的光解數(shù)據(jù)進(jìn)行擬一級反應(yīng)動力學(xué)擬合,擬合線性相關(guān)系數(shù)均大于 R2=0.99,符合擬一級反應(yīng)動力學(xué)模型,PS,UV,UV/PS降解的一級反應(yīng)速率常數(shù)分別是0.4×10-3,6.2×10-3和35.1×10-3min-1.

圖1 PS,UV,UV/PS工藝降解2,4-DCP的效果及一級動力學(xué)擬合Fig.1 Degradation of 2, 4-DCP in PS, UV, UV/PS processes

2.2 SO4?和OH?光解2,4-DCP中的作用

通過反應(yīng)方程(1)-(4)的反應(yīng)速率常數(shù)可知,SO4?和 OH?與甲醇發(fā)生反應(yīng)的速率常數(shù)差別不大,而 SO4?和 OH?與叔丁醇發(fā)生反應(yīng)的速率常數(shù)差別 3個數(shù)量級.甲醇是有效清除 SO4?和OH?的淬滅劑,而叔丁醇只是OH?高效猝滅劑.在同等反應(yīng)條件下通過添加同等容積的甲醇或叔丁醇,2,4-DCP的不同去除率可以研究 SO4?或OH?的貢獻(xiàn)率.由圖2可知在剛投加少量甲醇和叔丁醇時,反應(yīng)速率常數(shù)瞬間降低,隨著后續(xù)投加量增多而繼續(xù)降低,但降低速率變慢. 2,4-DCP的降解率隨甲醇投加量從0到6μmol/L時2,4-DCP的反應(yīng)速率常數(shù)已下降了89.9%,當(dāng)劑量達(dá)到60μmol/L時降解率的下降可達(dá)97.9%.在投加0到6μmol/L的叔丁醇時2,4-DCP的降解率已下降了 60.1%,當(dāng)劑量達(dá)到 60μmol/L時降解率已下降可達(dá)62.9%.該實驗證明,UV活化過硫酸鈉溶液中確實同時存在SO4?和OH?兩種自由基,尤其是 SO4?在降解2,4-DCP過程中起了主要作用.

2.3 SO4?與2,4-DCP反應(yīng)的反應(yīng)速率

圖2 SO4?和OH?降解2,4-DCP中的作用Fig.2 The role of SO4?and OH? during degradation of 2,4-DCP

圖3 2,4-DCP與SO4?反應(yīng)速率常數(shù)計算Fig.3 Determination of the reaction rate constants of SO4?with 2, 4-DCP

由 2.2部分證實 UV/PS的 SO4?和 OH?對2,4-DCP光解過程起主要的作用.自由基氧化有機(jī)物的動力學(xué)速率常數(shù)必須采用相對速率法來計算[13-14].實驗選用苯甲酸(BA)作為 2,4-DCP的參照對象,在相同的反應(yīng)條件下,將不同時間下被測定 2,4-DCP濃度和參照物 BA濃度按Ln(C0/Ct)2,4-DCP～Ln(C0/Ct)BA做圖,進(jìn)行線性回歸分析,由圖 3所示,所得的兩條線性相關(guān)系數(shù) R2均大于0.99.2,4-DCP和苯甲酸在pH=7.0條件下分別與 SO4?反應(yīng)的反應(yīng)速率常數(shù)比 k2,4-DCP/ kBA=a=5.89±0.05,因已知BA與SO4?反應(yīng)速率常數(shù) kBA=1.2×109(mol/L)-1s-1[15],采用相對速率法及公式(7)對數(shù)據(jù)進(jìn)行處理,可計算出 2,4-DCP與SO4?反應(yīng)的反應(yīng)速率常數(shù) k2,4-DCP=(7.07±0.6)× 109(mol/L)-1s-1.

2.4 實際水體UV/PS工藝光解效果

如表2列出了12月份錫東水廠、西氿水庫、橫山水庫的部分陰離子濃度檢測數(shù)值,水廠和兩水庫陰離子濃度中,NO3離子濃度和 pH值差距不大,只有CO32和Cl濃度數(shù)值差別很大.由圖4可知,光氧化時間 45min,錫東水廠,西氿水庫,橫山水庫,超純水的光解效率分別可達(dá) 96.7%、94.5%、89%、86.4%.有相關(guān)研究表明[16-19],小濃度的CO32/HCO3和Cl對UV/PS工藝光解有機(jī)物是有促進(jìn)作用的.這也較好的解釋了原水水質(zhì)條件下(含小濃度的陰離子溶液)2,4-DCP光解效率高于超純水水質(zhì)條件.

圖4 UV/PS光解不同水質(zhì)背景2,4-DCP的效果Fig.4 Effect of UV/PS on different water quality backgrounds2, 4-DCP

2.5 經(jīng)濟(jì)性預(yù)算

為了比較PS,UV,UV/PS成本費(fèi)用,本文獻(xiàn)采用單位電能效率(EE/O)對比了兩種方法降解有機(jī)污染物所需要的電能.單位電能消耗率 EE/O為將單位體積廢水(1m3)特征污染指標(biāo)降低一個數(shù)量級的污染物所需要的電能(kW?h/m3/order),采用如下公式計算：

式中：P為總用電量,kW;t為紫外線總的輻射時間, h;v為被處理水的總體積,m3.

表3 兩種工藝直接電能消耗EE/O-eTable 3 Direct electric energy consumption of the two processes EE/O-e

表4 兩種工藝的間接電能消耗EE/O-c和總電能效率EE/OTable 4 Indirect electric energy consumption (EE/O-c) and total electric energy efficiency (EE/O) of the two processes

其他條件為：過硫酸鈉鹽摩爾投加量為 0.1mmol/L,初始 pH值為 7.0,紫外線的光強(qiáng)為410mJ/cm2.EE/O-e和EE/O-c分別表示為：直接消耗的電能和藥劑投機(jī)對應(yīng)的費(fèi)用折算成間接消耗的電能.

通過表3可知UV,UV/PS的電能效率分別為5.00和 3.00kW?h/(m3?order).相比于 UV單一系統(tǒng),UV/PS協(xié)同系統(tǒng)的能量利用率更高.UV/PS協(xié)同系統(tǒng)的能量利用率是單一系統(tǒng)的1.67倍.

3 結(jié)論

3.1 PS,UV,UV/PS 3種工藝可去除2,4-DCP基本遵循擬一級反應(yīng)動力學(xué),反應(yīng)動力學(xué)常數(shù)分別是0.4×10-3,6.1×10-3和35.1×10-3min-1.

3.2 采用相對速率法計算出 SO4?與 2,4-DCP的二級反應(yīng)速率常數(shù)7.07×109(mol/L)-1s-1.

3.3 對 UV/PS工藝進(jìn)行經(jīng)濟(jì)性預(yù)算,結(jié)果表明UV/PS協(xié)同系統(tǒng)的能量利用率高,可達(dá)到單一系統(tǒng)的1.67倍.

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Study on the characteristics of 2, 4-dichlorophenol in water degraded by UV/PS.

CHEN Ju-xiang1,2, GAO Nai-yun2*,YANG Jing1, WANG Chao-hui3, GU Zhen-chuan2, Jiang Chuang2(1.College of Architecture and Civil Engineering, Xinjiang University, Urumqi 30047, China；2.State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai 200092, China；3.School of Energy and Environment, Inner Mongolia University of Science and Technology, Baotou 014010, China). China Environmental Science, 2017,37(6)：2145～2149

The study compared the removal effects and the first order reaction kinetics constants of 2, 4-DCP with PS、UV and UV/PS processes, respectively. Investigated the contribution rate of OH? and SO4?in the photolysis reaction, calculated the two order kinetics constants for SO4?with 2, 4-DCP reactions. Meanwhile, the degradation rates in actual water conditions were tested and the economic budge of UV and UV/PS processes were calculated and compared. The results showed that the removal rate of 2, 4-DCP was only 4% in the PS process alone, 46.2% in UV process. The degradation percentage can reach as high as 96.4% with UV/PS process, which effectively improved the degradation effect of 2, 4-DCP, meanwhile 2, 4-DCP degradation by PS, UV and UV/PS fitted the pseudo-first-order reaction equation and the kobs(reaction rate constant) was 0.4×10-3, 6.2×10-3and 35.1×10-3min-1, respectly. The main contribution function of the photolysis reaction was SO4?, the second-order-reaction constants for SO4?with 2, 4-DCP was 7.07×109(mol/L)-1s-1. The photo-degradation rates of 2, 4-DCP in three actual water conditions (Xidong water works, Xijiu reservoir, Hengshan reservoir) were higher than in the ultrapure water. The energy utilization rate of UV/PS cooperative system is the highest during economic calculation.

2, 4-DCP；UV/PS；reaction kinetics；actual water body；economic budge

X703

A

1000-6923(2017)06-2145-05

陳菊香(1979-),女,重慶大足人,副教授,博士研究生,主要從事水處理理論與技術(shù)研究.發(fā)表論文20余篇

2016-10-17

國家科技重大專項(2012ZX07403-001,2014ZX07406002);國家自然科學(xué)基金資助項目(51178321)

* 責(zé)任作者, 教授, Gaonaiyun@sina.com