宗宇凱,金 鑫,2,李 堯,金鵬康,2*,王曉昌

初始pH值對(duì)連續(xù)投加鋁鹽混凝去除小分子有機(jī)物的影響機(jī)制

宗宇凱1,金 鑫1,2,李 堯1,金鵬康1,2*,王曉昌1

(1.西安建筑科技大學(xué)環(huán)境與市政工程學(xué)院,陜西 西安 710055；2.西安交通大學(xué)人居環(huán)境與建筑工程學(xué)院,陜西 西安 710049)

以污水廠二級(jí)出水中小分子有機(jī)物強(qiáng)化混凝去除為目的,提出了連續(xù)投加混凝工藝(CDC),并以水楊酸為模型小分子有機(jī)物,研究了初始pH值對(duì)CDC工藝去除效果的影響以及鋁離子與水楊酸的絡(luò)合特性.結(jié)果表明,初始pH值6時(shí)CDC工藝的去除率最高,比常規(guī)混凝工藝提升了13.8%.但是初始pH值5和7時(shí)CDC工藝的提升效果較小.三維熒光結(jié)果表明,不同pH值下水楊酸和鋁離子的絡(luò)合特性不同.X射線光電子能譜和電噴霧質(zhì)譜結(jié)果表明,pH值5時(shí)CDC工藝前期主要生成1:1絡(luò)合物Al(OH)(C7H4O3)(H2O)2.其絡(luò)合作用強(qiáng)烈,穩(wěn)定性較高,難以從水中去除.pH值6時(shí)前期主要生成中等聚合鋁(如原位Al13),其與水楊酸形成的絡(luò)合物可以參與到鋁離子的生長(zhǎng)過(guò)程,最終生成表面崎嶇形態(tài)松散的珊瑚礁狀絮體,強(qiáng)化了水楊酸的去除.pH值7時(shí),主要生成不定形氫氧化鋁,通過(guò)絮體表面吸附小分子有機(jī)物.

連續(xù)投加混凝(CDC)；初始pH值；絡(luò)合作用；珊瑚礁狀絮體；小分子有機(jī)物

為了緩解水資源短缺對(duì)生產(chǎn)生活的影響,城市污水資源化回用是一個(gè)重要途徑[1].而污水處理廠二級(jí)出水含有的難降解有機(jī)物是限制污水再生回用的主要因素[2].混凝工藝常被應(yīng)用于污水深度處理[3],但是其對(duì)溶解性有機(jī)物去除效率較低[4],特別是小分子有機(jī)物[5-6].金屬離子(例如鋁和鐵)在水中會(huì)隨著自身濃度和pH值升高,逐漸從溶解態(tài)聚合生長(zhǎng)到膠體態(tài),最后到懸浮態(tài)[7-8].常規(guī)混凝工藝(CC)一次性投加全部劑量的混凝劑,導(dǎo)致水解產(chǎn)物迅速形成[9],其對(duì)小分子有機(jī)物的去除機(jī)理主要是化學(xué)吸附[10].為了提高小分子有機(jī)物的去除率,或許可以調(diào)整混凝劑投加方式來(lái)優(yōu)化金屬離子聚合過(guò)程并改善絮體表面特性[11],以充分利用金屬鹽混凝劑的捕獲能力.

對(duì)此,本課題組前期提出了連續(xù)投加混凝工藝(CDC),在預(yù)酸化的水中連續(xù)投加混凝劑與堿,誘導(dǎo)形成珊瑚礁狀絮體,強(qiáng)化污水深度處理過(guò)程中小分子有機(jī)物的去除率[12].體系初始pH值是該工藝操作運(yùn)行過(guò)程中的一項(xiàng)重要參數(shù),不僅會(huì)影響處理效果,更與工藝的運(yùn)行成本息息相關(guān).此外,在該工藝的初始階段,存在“低金屬離子濃度、低pH值”的環(huán)境,其中會(huì)發(fā)生小分子有機(jī)物與金屬離子的絡(luò)合作用,類(lèi)似于自然環(huán)境中天然有機(jī)物與金屬離子的絡(luò)合[13].然而,初始pH值和金屬-有機(jī)物的絡(luò)合作用對(duì)于CDC工藝的影響機(jī)理尚不明確.水楊酸(SA)的摩爾質(zhì)量為138.12g/mol,其結(jié)構(gòu)中含有一個(gè)苯環(huán),一個(gè)羥基和一個(gè)羧基,其結(jié)構(gòu)特征類(lèi)似于腐殖酸,容易與金屬離子發(fā)生絡(luò)合.并且水楊酸是天然水體中常見(jiàn)的芳香酸和污水廠二級(jí)出水中常見(jiàn)的藥物與個(gè)人護(hù)理品[14].因此,本研究以水楊酸為模型小分子有機(jī)污染物,研究初始pH值對(duì)CDC工藝去除小分子有機(jī)物效果的影響,并采用多種表征手段,探究不同pH值下,金屬離子與有機(jī)物的絡(luò)合特性,揭示反應(yīng)早期的絡(luò)合作用對(duì)污染物去除的影響機(jī)理,為深刻認(rèn)識(shí)CDC工藝作用機(jī)理,并為工藝的優(yōu)化運(yùn)行提供參考.

1 材料與方法

1.1 實(shí)驗(yàn)試劑

水楊酸(salicylic acid),結(jié)晶氯化鋁(AlCl3·6H2O),碳酸氫鈉(NaHCO3),氫氧化鈉(NaOH),硝酸(HNO3)均購(gòu)于阿拉丁試劑(上海)有限公司,純度均為分析純.實(shí)驗(yàn)用水為超純水(18.2MΩ·cm).參考西安某污水廠二級(jí)出水水質(zhì),其溶解性有機(jī)碳(DOC)濃度為(6.31± 1.06)mg/L,因此模擬水樣中水楊酸濃度為10mg/L (理論DOC濃度為6.09mg/L).另外加入1mmol/L碳酸氫鈉來(lái)調(diào)節(jié)水樣的堿度.混凝劑儲(chǔ)備液濃度為4g/L(以鋁計(jì)).

1.2 實(shí)驗(yàn)方法

常規(guī)混凝過(guò)程:混凝劑與堿同時(shí)加入含有500mL水樣的燒杯中,采用磁力攪拌器(color squid,德國(guó)IKA)對(duì)水樣以200r/min的轉(zhuǎn)速攪拌2min,隨后降為20r/min的轉(zhuǎn)速攪拌15min,最后靜置沉淀30min.堿的投加量使得出水pH值為7.反應(yīng)結(jié)束后通過(guò)注射器取樣,用0.45μm的濾膜過(guò)濾后進(jìn)行后續(xù)測(cè)定.

連續(xù)投加混凝過(guò)程:首先將水樣酸化至特定pH值,采用2臺(tái)蠕動(dòng)泵分別同時(shí)緩慢投加混凝劑溶液與堿溶液.混凝劑投加速率為2mg/(L·min),堿的投加速率控制原則為:使得水樣pH值從初始值緩慢上升,在混凝劑投加完畢時(shí)水樣pH值上升至7.在混凝劑投加階段保持200r/min的轉(zhuǎn)速,投加完畢后降為20r/min的轉(zhuǎn)速攪拌15min,最后靜置沉淀30min.反應(yīng)全程用pH計(jì)(STARTER 3100,奧豪斯)監(jiān)測(cè)水樣pH值變化.

1.3 分析方法

1.3.1 有機(jī)物去除率測(cè)定 有機(jī)物去除率利用TOC分析儀(TOC-VCPH,日本島津),采用NPOC法測(cè)定反應(yīng)前后溶液的DOC得到.

1.3.2 三維熒光分析 反應(yīng)初期的水樣用于三維熒光分析.采用熒光分光光度計(jì)(日立)測(cè)定.測(cè)定參數(shù):m為330～500nm、x為250～340nm、發(fā)射波長(zhǎng)間隔為5nm,激發(fā)波長(zhǎng)間隔2nm,電壓為300V,掃描速率為12000nm/min.

1.3.3 鋁形態(tài)分析 反應(yīng)初期的水樣用Al-Ferron法分析鋁形態(tài).根據(jù)鋁離子和Ferron試劑的反應(yīng)動(dòng)力學(xué)差異將鋁形態(tài)分為Ala,Alb和Alc[15].

1.3.4 電噴霧質(zhì)譜(ESI-MS)分析 反應(yīng)初期的水樣用于電噴霧質(zhì)譜(ESI-MS)分析.采用質(zhì)譜儀(Waters Xevo TQD)測(cè)定.電噴霧(ESI)電離,負(fù)離子狀態(tài)下測(cè)定,噴霧電壓3000V.

1.3.5 X射線光電子能譜(XPS)分析 反應(yīng)結(jié)束后的絮體經(jīng)凍干處理后進(jìn)行X射線光電子能譜(XPS)分析.采用X射線光電子能譜儀(Thermo Fisher Scientific, UK),結(jié)合能范圍為100～1000eV,并測(cè)量C 1s的特征峰.

1.3.6 絮體形貌觀測(cè) 在反應(yīng)過(guò)程中用冷凍透射電鏡(Talos F200C, FEI)原位觀測(cè)絮體形貌.用掃描電子顯微鏡(Gemini SEM 300, ZEISS)觀測(cè)反應(yīng)結(jié)束后凍干絮體表面形貌.

2 結(jié)果與討論

2.1 CDC工藝的去除特性

如圖1a所示,在整個(gè)混凝劑投加量范圍內(nèi),相比于CC工藝,CDC工藝對(duì)水楊酸的去除都有提升.在投加量為32mg/L時(shí)去除率提升最大(16.46%).在相同投加量下,CDC工藝對(duì)水楊酸的去除率平均提升了15%左右.這表明混凝劑連續(xù)投加的混凝過(guò)程對(duì)小分子有機(jī)物的去除具有促進(jìn)作用.如圖1b所示,CC工藝對(duì)水楊酸的去除率僅為25.25%.CDC工藝的水楊酸去除能力受初始pH值影響較大.在初始pH值6時(shí),去除率最高為39.05%,比CC工藝提升了13.8%.但是在初始pH值5和7時(shí),去除率比常規(guī)混凝工藝提升很小(分別為2.33%和3.09%).通常認(rèn)為,酸性條件(pH值5～6)有利于有機(jī)物的去除[16-17].雖然同屬于酸性條件,但是酸性更強(qiáng)的pH值=5條件下對(duì)小分子有機(jī)物的混凝去除卻沒(méi)有提升效果.這表明在CDC工藝反應(yīng)前期,不同pH值下前期投加的低濃度鋁離子與水中水楊酸的結(jié)合特性存在差異,對(duì)最終的去除率產(chǎn)生了影響.

2.2 鋁形態(tài)分布特性

pH值對(duì)有機(jī)物的形態(tài)影響較小.在pH值5～8時(shí),水楊酸的羧基為去質(zhì)子化狀態(tài),而酚羥基為質(zhì)子化狀態(tài)(pa1=2.88,pa2=13.56)[18].但是pH值對(duì)鋁形態(tài)的影響較大[19].如圖2所示,初始pH值5時(shí),Ala形態(tài)占主要成分(58.21%),主要是單體鋁;初始pH值6時(shí),Alb形態(tài)占主要成分(85.75%),主要是中等聚合鋁,如原位Al13;初始pH值7時(shí),Alc形態(tài)占主要成分(95.94%),如不定形氫氧化鋁[20].在CDC工藝反應(yīng)前期,鋁離子濃度較低,此時(shí)溶液呈現(xiàn)無(wú)色透明狀態(tài),并未有絮體生成,但是此時(shí)不同鋁形態(tài)與水中的有機(jī)物已經(jīng)發(fā)生了結(jié)合,這可能對(duì)后續(xù)投加的鋁離子的進(jìn)一步聚合產(chǎn)生影響.

圖1 CDC工藝去除水楊酸的特性

(a)CDC工藝初始pH值為6;(b)混凝劑投加量為16mg/L

圖2 不同初始pH值下,CDC工藝前期鋁形態(tài)的分布特性

2.3 水楊酸和鋁離子的絡(luò)合特性

2.3.1 三維熒光分析 在不同pH值下,土壤富里酸會(huì)和鋁離子絡(luò)合引起熒光增強(qiáng)或減小[21].如圖3所示,熒光強(qiáng)度的變化受pH值影響較大.雖然同屬于酸性條件,在pH值5時(shí)熒光強(qiáng)度增強(qiáng),而pH值6時(shí)熒光強(qiáng)度減小.在pH值7時(shí)熒光強(qiáng)度也減小,但是其變化比pH值6時(shí)小.此外,熒光強(qiáng)度在投量大于8mg/L后達(dá)到穩(wěn)定,表明絡(luò)合反應(yīng)達(dá)到飽和狀態(tài)[22].因此,后續(xù)研究水楊酸在不同pH值下的三維熒光圖譜變化時(shí)(圖4),混凝劑投加量選擇為8mg/L.

Elkins等[23]觀測(cè)Al-SFA絡(luò)合物時(shí)發(fā)現(xiàn)熒光圖譜的最大值會(huì)明顯地移動(dòng)到更長(zhǎng)的激發(fā)波長(zhǎng)和更短的發(fā)射波長(zhǎng)處.在沒(méi)有鋁離子時(shí),水楊酸三維熒光圖譜中在激發(fā)/發(fā)射波長(zhǎng)為294/405nm處有一個(gè)顯著的熒光中心,即熒光強(qiáng)度最大處.在pH值5時(shí),熒光強(qiáng)度最大處從激發(fā)波長(zhǎng)294nm移動(dòng)到312nm,發(fā)射波長(zhǎng)從405nm移動(dòng)到375nm.但是在pH值6和7時(shí),熒光強(qiáng)度最大處的位置幾乎沒(méi)有移動(dòng).綜上所述,在pH值5時(shí),熒光強(qiáng)度最大處發(fā)生移動(dòng)且熒光強(qiáng)度增強(qiáng),表明水楊酸的官能團(tuán)參與到與鋁離子的絡(luò)合反應(yīng)中,且水楊酸電子結(jié)構(gòu)發(fā)生了顯著變化[24].在pH值6和7時(shí),熒光強(qiáng)度減小但是熒光強(qiáng)度最大處保持不動(dòng),表明在pH值5和pH值6,7時(shí),水楊酸和鋁的水解產(chǎn)物均發(fā)生了絡(luò)合反應(yīng),但是絡(luò)合反應(yīng)特性完全不同

圖3 不同pH值下,EEM光譜中顯著峰的熒光強(qiáng)度隨投加量的變化

圖4 不同pH值下水楊酸與鋁離子的三維熒光圖譜

圖5 初始pH值5時(shí),CDC工藝中水楊酸-鋁絮體的背景去除高分辨C 1s譜圖

2.3.2 XPS分析和質(zhì)譜分析 對(duì)于水楊酸鈉,其在286.54和288.93eV的信號(hào)峰被歸于單個(gè)氧(即酚羥基)和羧基碳[25].對(duì)于初始pH值5時(shí)的CDC工藝中水楊酸-鋁絮體,結(jié)合能從286.54eV移動(dòng)到286.14eV,表明酚羥基參與了絡(luò)合反應(yīng).羧基碳的結(jié)合能從288.93eV移動(dòng)到290.37eV,表明羧基也參與了絡(luò)合反應(yīng)(圖5).

如圖6所示,在pH值5時(shí),荷質(zhì)比為214.90的信號(hào)占主要成分(67.97%).結(jié)合XPS分析結(jié)果,該信號(hào)為1:1絡(luò)合物Al(OH)(C7H4O3)(H2O)2,其特征為鋁離子通過(guò)水楊酸的羧基與酚羥基與其形成具有六元環(huán)結(jié)構(gòu)的1:1絡(luò)合物[26].但是在pH值6和7時(shí),由于鋁離子的聚合,離子峰數(shù)量減少,相對(duì)強(qiáng)度也降低.因此無(wú)法檢測(cè)到水楊酸-鋁絡(luò)合物.荷質(zhì)比為136.97的信號(hào)在所有pH值下均能檢測(cè)到,這屬于水楊酸分子.

圖6 不同pH值下水楊酸-鋁絡(luò)合物的ESI-MS譜圖

2.4 初始pH值對(duì)CDC工藝混凝去除小分子有機(jī)物的影響機(jī)制

首先,初始pH值會(huì)影響鋁形態(tài)的分布.pH值5時(shí),主要的鋁形態(tài)為單體鋁,根據(jù)XPS與質(zhì)譜分析結(jié)果,此時(shí)鋁離子與水楊酸絡(luò)合生成1:1絡(luò)合物Al(OH) (C7H4O3)(H2O)2.其具有很高的穩(wěn)定性[27],后續(xù)投加的鋁離子無(wú)法與其發(fā)生聚合生長(zhǎng).該1:1絡(luò)合物最終只能以溶解態(tài)殘留在水中,不但降低了有機(jī)物的去除率,而且增加了殘留鋁的風(fēng)險(xiǎn)[28].因此,必須避免在CDC工藝反應(yīng)初期出現(xiàn)Ala形態(tài),即初始pH值不應(yīng)過(guò)低.

pH值6時(shí),主要的鋁形態(tài)為中等聚合鋁,如原位Al13.根據(jù)三維熒光的結(jié)果,推斷其與水楊酸形成了絡(luò)合物.但是此時(shí)水樣呈透明狀態(tài),無(wú)絮體形成,說(shuō)明所形成的絡(luò)合物尺度較小.隨著混凝劑濃度和pH值的不斷升高,水樣開(kāi)始出現(xiàn)膠體狀態(tài),最后變?yōu)闇啙釥顟B(tài),可以觀測(cè)到明顯的絮體形成.依據(jù)此絮體形成過(guò)程,可以推斷CDC工藝前期生成的中等聚合鋁-水楊酸絡(luò)合物作為初級(jí)核心,使得后續(xù)投加的鋁離子黏附其上,不斷聚合生長(zhǎng)至較大尺度形成絮體.原位Al13形成的絮體具有較大的孔容、孔徑和比表面積[11].根據(jù)掃描電鏡觀測(cè)結(jié)果(圖7a),CDC工藝產(chǎn)生的絮體表面極度不規(guī)則,凹凸深淺不一,類(lèi)似于為無(wú)數(shù)海洋動(dòng)植物提供棲息地的復(fù)雜的珊瑚礁生態(tài)系統(tǒng).根據(jù)冷凍透射電鏡對(duì)反應(yīng)過(guò)程中不斷生長(zhǎng)的絮體的原位觀測(cè)結(jié)果(圖7b),絮體形態(tài)極度松散,其內(nèi)部存在空隙且外部具有明顯的分形特征,可以為小分子有機(jī)物提供更多的結(jié)合點(diǎn)位,從而強(qiáng)化其去除.因此,為了保證CDC工藝的有效性,必須營(yíng)造有利于中等聚合形態(tài)的鋁產(chǎn)生的條件.

圖7 初始pH值為6時(shí)CDC工藝產(chǎn)生絮體的形貌

(a)掃描電鏡圖;(b)冷凍透射電鏡圖

圖8 不同初始pH值下,CDC工藝對(duì)水楊酸的去除機(jī)理

pH值7時(shí),主要的鋁形態(tài)為無(wú)定形氫氧化鋁,其主要通過(guò)網(wǎng)掃吸附作用來(lái)去除污染物.但是由于其已經(jīng)屬于大聚合形態(tài),絮體內(nèi)部的鋁并沒(méi)有發(fā)揮其捕獲作用,導(dǎo)致此時(shí)的CDC工藝相比于CC工藝并沒(méi)有明顯的提升效果.因此,降低水樣的pH值是必要的,僅改變混凝劑投加方式而不調(diào)節(jié)pH值并不能充分發(fā)揮混凝劑的捕獲能力(圖8).

3 結(jié)論

3.1 在初始pH值為6時(shí),CDC工藝對(duì)以水楊酸為代表的小分子有機(jī)物混凝去除效果最好.混凝劑投加量為16mg/L時(shí),相較于常規(guī)混凝工藝去除率提升了13.8%.但是初始pH值為5和7時(shí),CDC工藝的提升效果不大.

3.2 在初始pH值為6時(shí),CDC工藝前期混凝劑主要水解生成中等聚合鋁形態(tài),如原位Al13,其與水楊酸形成的絡(luò)合物可以作為初級(jí)核心參與到鋁離子的聚合生長(zhǎng)過(guò)程,最終生成表面極度不規(guī)則、形態(tài)極度松散的珊瑚礁狀絮體,其更多的結(jié)合點(diǎn)位強(qiáng)化了小分子有機(jī)物的去除,此時(shí)混凝劑的捕獲能力得到了充分發(fā)揮.

3.3 在初始pH值為5時(shí),CDC工藝前期單體鋁離子通過(guò)水楊酸的羧基與酚羥基與其形成具有六元環(huán)結(jié)構(gòu)的1:1絡(luò)合物Al(OH)(C7H4O3)(H2O)2,其絡(luò)合作用強(qiáng)烈,穩(wěn)定性較高,不利于其參與后續(xù)投加鋁離子的聚合生長(zhǎng)過(guò)程,最終只能殘留在水中,因此過(guò)低的pH值不利于小分子有機(jī)物的去除.在初始pH值為7時(shí),主要生成不定形氫氧化鋁,其混凝機(jī)理與常規(guī)混凝相似,只能通過(guò)絮體表面的吸附作用去除小分子有機(jī)物,絮體內(nèi)部的鋁并沒(méi)有發(fā)揮其捕獲作用,整體混凝劑利用率不高.此時(shí)CDC工藝的去除率相比常規(guī)混凝提升較小.

[1] 張國(guó)珍,孫加輝,武福平.再生水回用的研究現(xiàn)狀綜述 [J]. 凈水技術(shù), 2018,37(12):40-45.

Zhang G Z, Sun J H, Wu F P. General review of current situation in research of reclaimed water reuse technology [J]. Water Purification Technology, 2018,37(12):40-45.

[2] 郭 瑾,盛 豐,馬民濤,等.污水二級(jí)生化出水有機(jī)物(EfOM)性質(zhì)表征及去除研究現(xiàn)狀 [J]. 北京工業(yè)大學(xué)學(xué)報(bào), 2011,37(1):131-138.

Guo J, Sheng F, Ma M T, et al. Effluent organic matter ( EfOM) in biological treatment sewage effluent: The status of characterization and removal [J]. Journal of Beijing University of Technology, 2011, 37(1):131-138.

[3] 金 鑫.臭氧混凝互促增效機(jī)制及其在污水深度處理中的應(yīng)用 [D]. 西安:西安建筑科技大學(xué), 2016.

Jin X. Mechanism of synergism analysis in hybrid ozonation- coagulation system and its application in advanced wastewater treatment [D]. Xi'an: Xi'an University of Architecture and Technology, 2016.

[4] 侯 瑞,金 鑫,金鵬康,等.污水廠二級(jí)出水中難凝聚有機(jī)物的臭氧化特性 [J]. 環(huán)境科學(xué), 2018,39(2):844-851.

Hou R, Jin X, Jin P K, et al. Ozonation characteristics of low coagulability organic matter from the secondary effluent of WWTPs [J]. Environmental Science, 2018,39(2):844-851.

[5] Zhao H, Wang L, Hanigan D, et al. Novel ion-exchange coagulants remove more low molecular weight organics than traditional coagulants [J]. Environmental Science & Technology, 2016,50(7): 3897-3904.

[6] 程 拓,徐 斌,朱賀振,等.南水北調(diào)丹江口水庫(kù)原水有機(jī)物分子組成規(guī)律及其強(qiáng)化混凝處理的效能對(duì)比 [J]. 環(huán)境科學(xué), 2015,36(3): 898-904.

Cheng T, Xu B, Zhu H Z, et al. Composition of NOM in raw water of Danjiangkou reservoir of south-to-north water diversion project and comparison of efficacy of enhanced coagulation [J]. Environmental Science, 2015,36(3):898-904.

[7] Zhao H, Liu H, Qu J. Effect of pH on the aluminum salts hydrolysis during coagulation process: Formation and decomposition of polymeric aluminum species [J]. Journal of Colloid and Interface Science, 2009,330(1):105-112.

[8] Bi S, Wang C, Cao Q, et al. Studies on the mechanism of hydrolysis and polymerization of aluminum salts in aqueous solution: correlations between the “Core-links” model and “Cage-like” Keggin-Al13model [J]. Coordination Chemistry Reviews, 2004,248(5):441-455.

[9] 葉 健.絮凝動(dòng)力學(xué)及其絮體的特性的初步研究 [D]. 廣州:華南理工大學(xué), 2011.

Ye J. Study on formation kinetics of flocs and properties of coagulation process [D]. Guangzhou: South China University of Technology, 2011

[10] Guan X, Chen G, Shang C. Combining kinetic investigation with surface spectroscopic examination to study the role of aromatic carboxyl groups in NOM adsorption by aluminum hydroxide [J]. Journal of Colloid and Interface Science, 2006,301(2):419-427.

[11] 陳桂霞,胡承志,朱靈峰,等.鋁鹽混凝除砷影響因素及機(jī)制研究 [J]. 環(huán)境科學(xué), 2013,34(4):1386-1391.

Chen G X, Hu C Z, Zhu L F, et al. Influencing factors and mechanism of arsenic removal during the aluminum coagulation process [J]. Environmental Science, 2013,34(4):1386-1391.

[12] Zong Y, Jin X, Li Y, et al. Assessing the performance of coral reef-like floc towards the removal of low molecular weight organic contaminant [J]. Science of the Total Environment, 2022,811:152413.

[13] 謝亞萍.利用紫外可見(jiàn)差分光譜法研究金屬離子之間對(duì)溶解性有機(jī)物的競(jìng)爭(zhēng)絡(luò)合 [D]. 西安:長(zhǎng)安大學(xué), 2019.

Xie Y P. Study on competitive complexation of dissolved organic matter between metal ions by differential spectroscopy [D]. Xi'an: Chang'an University, 2019.

[14] Chen L, Fu W, Tan Y, et al. Emerging organic contaminants and odorous compounds in secondary effluent wastewater: Identification and advanced treatment [J]. Journal of Hazardous Materials, 2020,408: 124817.

[15] 彭建雄,薛 安,趙華章,等.以Al-Ferron逐時(shí)絡(luò)合比色法研究有機(jī)硅鋁復(fù)合絮凝劑中鋁的形態(tài)分布 [J]. 環(huán)境科學(xué), 2008,29(9):2513-2517.

Peng J X, Xue A, Zhao H Z, et al. Al species distribution of organic silicate aluminum hybrid flocculants by Al-Ferron complexation timed spectrophotometric method [J]. Environmental Science, 2008,29(9): 2513-2517.

[16] 董秉直,曹達(dá)文,范瑾初.最佳混凝投加量和pH去除水中有機(jī)物的研究 [J]. 工業(yè)水處理, 2002,22(6):29-31.

Dong B Z, Cao D W, Fan J C. Optimum dosage and pH for the removal of organic substance by enhanced coagulation [J]. Industrial Water Treatment, 2002,22(6):29-31.

[17] Wang P, Ding S, Xiao R, et al. Enhanced coagulation for mitigation of disinfection by-product precursors: A review [J]. Advances in Colloid and Interface Science, 2021,296:102518.

[18] 宋吉娜.腐殖酸質(zhì)子化基團(tuán)與鋁離子在水中的遷變及凝聚行為表征 [D]. 西安:西安建筑科技大學(xué), 2018.

Song J N. The proton migration and coagulation characteristics between the protonated groups of humic acid and aluminum ions [D]. Xi'an: Xi'an University of Architecture and Technology, 2018.

[19] Zhao H, Liu H, Qu J. Aluminum speciation of coagulants with low concentration: Analysis by electrospray ionization mass spectrometry [J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011,379(1):43-50.

[20] 王趁義,張彩華,畢樹(shù)平,等.Al-Ferron逐時(shí)絡(luò)合比色光度法測(cè)定聚合鋁溶液中Ala, Alb和Alc三種鋁形態(tài)的時(shí)間界限研究 [J]. 光譜學(xué)與光譜分析, 2005,25(2):252-256.

Wang C Y, Zhang C H, Bi S P, et al. Assay of three kinds of aluminum fractions (Ala, Alband Alc) in polynuclear aluminum solutions by Al ferron timed spectrophotometry and demarcation of their time limits [J]. Spectroscopy and Spectral Analysis, 2005,25(2):252-256.

[21] Ryan D K, Shia C-P, O'connor D V. Fluorescence spectroscopic studies of Al—fulvic acid complexation in acidic solutions [M]. Humic and Fulvic Acids. American Chemical Society. 1996:125-139.

[22] Plaza C, Brunetti G, Senesi N, et al. Molecular and quantitative analysis of metal ion binding to humic acids from sewage sludge and sludge-amended soils by fluorescence spectroscopy [J]. Environmental Science & Technology, 2006,40(3):917-923.

[23] Elkins K M, Nelson D J. Fluorescence and FT-IR spectroscopic studies of Suwannee river fulvic acid complexation with aluminum, terbium and calcium [J]. Journal of Inorganic Biochemistry, 2001,87 (1):81-96.

[24] Song J, Jin X, Wang X C, et al. Preferential binding properties of carboxyl and hydroxyl groups with aluminium salts for humic acid removal [J]. Chemosphere, 2019,234:478-487.

[25] Guan X , Chen G, Shang C. ATR-FTIR and XPS study on the structure of complexes formed upon the adsorption of simple organic acids on aluminum hydroxide [J]. Journal of Environmental Sciences, 2007, 19(4):438-443.

[26] Yokoyama T, Abe H, Kurisaki T, et al. 13C and 27Al NMR study on the interaction in acidic aqueous solution between aluminium ion and tiron, salicylic acid and phthalic acid: as model compounds with functional groups of fulvic acid [J]. Analytical Sciences, 1997,13: 425-428.

[27] 施雯晶.密度泛函理論研究鋁—水楊酸配合物的形態(tài)結(jié)構(gòu)和水交換反應(yīng) [D]. 南京:南京大學(xué), 2013.

Shi W J. Density functional theory studies on the static structures and water-exchange reactions of aluminum-salicylate complexes [D]. Nanjing: Nanjing University, 2013.

[28] Yang Z, Gao B, Yue Q, et al. Effect of pH on the coagulation performance of Al-based coagulants and residual aluminum speciation during the treatment of humic acid–kaolin synthetic water [J]. Journal of Hazardous Materials, 2010,178(1):596-603.

Mechanisms of initial pH value affecting the removal of small molecular organics by coagulation with continuously added aluminum salts.

ZONG Yu-kai1, JIN Xin1,2, LI Yao1, JIN Peng-kang1,2*, WANG Xiao-chang1

(1.School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, Xi’an 710055, China；2.School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, Xi'an 710049, China)., 2022,42(9)：4183～4189

To improve the removal efficiency of small molecular organics in the secondary effluent from the wastewater treatment plants, continuous dosing coagulation (CDC) was proposed. Salicylic acid (SA) was chosen as model small molecular organics to evaluate effects of initial pH value on the removal performance in the CDC process and the complexation characteristics of SA and aluminum. The CDC process with initial pH 6had the best removal efficiency that was 13.8% higher than that of conventional coagulation (CC). But the CDC process with initial pH 5 and 7 had limited promotion effect. According to the EEM results, the complexation characteristics of SA and aluminum varied with pH value. According to the XPS and ESI-MS results, 1:1 complexes Al(OH)(C7H4O3)(H2O)2formed in the early stage of CDC process with initial pH 5. The complexation reaction was strong so the stable complexes were difficult to remove. In the early stage of CDC process with initial pH 6, the medium polymer Al (such as in situ Al13) formed and complexed with SA, which could polymerize with added aluminum and form coral reef-like flocs with rough surface and loose structure. As a result, the removal of SA was enhanced. The small molecular organics were removed by the adsorption of floc surface at initial pH 7 due to the formation of amorphous aluminum hydroxide.

continuous dosing coagulation (CDC)；initial pH value；complexation reaction；coral reef-like floc；small molecular organics

X701

A

1000-6923(2022)09-4183-07

2022-02-21

國(guó)家自然科學(xué)基金資助項(xiàng)目(52070151,51908177);陜西省重點(diǎn)研發(fā)計(jì)劃項(xiàng)目(2021ZDLSF05-06)

*責(zé)任作者, 教授, pkjin@xjtu.edu.cn

宗宇凱(1996-),男,江蘇宜興人,西安建筑科技大學(xué)博士研究生,主要研究方向?yàn)槲蹚U水深度處理與資源化利用.發(fā)表論文3篇.