氧化鋅納米顆粒對(duì)污泥厭氧消化過(guò)程的影響研究

王樹(shù)濤,陳玲波,張真瑞,巫 川,姜 瑞,尤 宏(.哈爾濱工業(yè)大學(xué)城市水資源與水環(huán)境國(guó)家重點(diǎn)實(shí)驗(yàn)室,黑龍江 哈爾濱 50090；.黑龍江省環(huán)境保護(hù)科學(xué)研究院,黑龍江 哈爾濱 50056)

氧化鋅納米顆粒對(duì)污泥厭氧消化過(guò)程的影響研究

王樹(shù)濤1*,陳玲波1,張真瑞1,巫 川1,姜 瑞2,尤 宏1(1.哈爾濱工業(yè)大學(xué)城市水資源與水環(huán)境國(guó)家重點(diǎn)實(shí)驗(yàn)室,黑龍江 哈爾濱 150090；2.黑龍江省環(huán)境保護(hù)科學(xué)研究院,黑龍江 哈爾濱 150056)

建立了污泥厭氧消化反應(yīng)器,以氧化鋅納米顆粒(ZnO-NPs)為研究對(duì)象,研究了不同濃度ZnO-NPs(0,2,30,60,90,120,150mg/g-VSS)對(duì)污泥厭氧消化過(guò)程的影響,分析了可能存在的劑量-效應(yīng)關(guān)系.低濃度(2mg/g-VSS)ZnO-NPs對(duì)污泥厭氧消化過(guò)程影響較小;較高濃度下,ZnO-NPs對(duì)污泥厭氧消化產(chǎn)氣效率、有機(jī)物降解效率和污泥減量效果等具有顯著影響,而對(duì)揮發(fā)酸產(chǎn)量及其組成無(wú)顯著影響.ZnO-NPs暴露濃度為30,60,90,120mg/g-VSS時(shí),平均日產(chǎn)氣量直線下降,在120mg/g-VSS濃度后平均日產(chǎn)氣量為對(duì)照組的10%左右.ZnO-NPs對(duì)有機(jī)物降解效和污泥減量存在明顯抑制作用,且隨著ZnO-NPs濃度的升高,SCOD去除率、TCOD去除率和R(VSS/TSS)值降低.ZnO-NPs濃度升高到120mg/g-VSS時(shí),SCOD去除率、TCOD去除率和R(VSS/TSS)值分別減少到對(duì)照組的3%、36.5%和74%.此外,當(dāng) ZnO-NPs暴露濃度從2mg/g-VSS升高到150mg/g-VSS 時(shí),污泥減量率從23%左右下降至4.8%左右.

氧化鋅納米顆粒(ZnO-NPs)；生物毒性；污泥厭氧消化；污泥減量

隨著納米科技的發(fā)展,納米材料已廣泛應(yīng)用于生活和工業(yè)多個(gè)領(lǐng)域[1],而這些含有納米材料的物質(zhì)在使用和作為廢棄物處理時(shí)不可避免地會(huì)進(jìn)入環(huán)境[2].由于納米顆粒(NPs)尺寸微小,比表面積巨大,具有更大的反應(yīng)活性,其環(huán)境行為及其毒性效應(yīng)備受關(guān)注[3].Brayner等[4]研究發(fā)現(xiàn)ZnO-NPs能誘導(dǎo)活性氧(ROS)的產(chǎn)生,而ROS的氧化作用可導(dǎo)致細(xì)菌細(xì)胞膜損壞和細(xì)胞質(zhì)泄漏;Thill等[5]觀察到CeO2-NPs可在大腸桿菌表面吸附,認(rèn)為CeO2-NPs能夠改變細(xì)胞膜的粘滯性,破壞特定離子泵,從而影響細(xì)胞與外界的物質(zhì)交換,抑制細(xì)菌生長(zhǎng).

城市污水處理廠是環(huán)境中 NPs遷移的重要途徑.NPs進(jìn)入污水生物處理系統(tǒng)后,很可能對(duì)各種微生物活性產(chǎn)生負(fù)面影響,進(jìn)而影響污染物降解效率和生物系統(tǒng)穩(wěn)定性.已有研究表明, 50mg/L Al2O3-NPs能明顯降低活性污泥中反硝化細(xì)菌的豐度[6],ZnO-NPs濃度達(dá)到20mg/L時(shí),微生物脫氮作用受到嚴(yán)重抑制[7].Zheng等[8]研究發(fā)現(xiàn)ZnO-NPs釋放出的Zn2+能夠?qū)е挛⑸矬w內(nèi)ROS增加,Zn2+和ROS共同作用抑制了聚磷菌的活性,降低了聚磷酸鹽激酶及外切聚磷酸酶的數(shù)量,從而影響了系統(tǒng)的生物除磷效率.進(jìn)入污水處理系統(tǒng)中的 NPs絕大多數(shù)最終將匯集到剩余污泥中[9].有調(diào)查顯示,ZnO-NPs、Ag-NPs和碳納米管(CNTs)在污泥中的濃度分別可以達(dá)到 57、5.86和0.147mg/kg[10-11].2011年(139所)與2009年(107所)中國(guó)的一些污水廠污泥中各種納米材料的總濃度為 1.03g/kg SS,最大達(dá)到 9.14g/kg

SS[12-13].

目前采用厭氧消化技術(shù)對(duì)剩余污泥進(jìn)行處理是主要的手段.因此,研究剩余污泥中存在的NPs對(duì)污泥厭氧消化過(guò)程的影響對(duì)于保證污泥處理系統(tǒng)的穩(wěn)定運(yùn)行以及加強(qiáng)NPs污染物的排放控制具有重要意義.Mu等[14]研究發(fā)現(xiàn)在厭氧生物處理過(guò)程中 ZnO-NPs的濃度為 10和50mg/g-TSS時(shí),對(duì)厭氧顆粒污泥的EPS和甲烷產(chǎn)量影響較小,但是當(dāng)暴露濃度為大于 100mg/ g-TSS時(shí),ZnO-NPs使EPS和甲烷產(chǎn)量減少,對(duì)甲烷化過(guò)程有嚴(yán)重的抑制作用.Jorge等[15]研究了幾種NPs對(duì)乙酸分解和產(chǎn)氫產(chǎn)甲烷過(guò)程的毒性效應(yīng),發(fā)現(xiàn)Cu0-NPs和ZnO-NPs對(duì)產(chǎn)甲烷過(guò)程有嚴(yán)重的抑制作用,主要是由于NPs侵蝕和解離釋放出來(lái)的有毒 Cu2+和 Zn2+.Yang等[16]發(fā)現(xiàn),40mg/ LAg-NPs對(duì)甲烷產(chǎn)量無(wú)明顯影響,溶解氧是Ag- NPs氧化溶解的必要條件,厭氧條件下Ag-NPs不會(huì)釋放Ag+,因此不會(huì)抑制厭氧消化過(guò)程產(chǎn)甲烷菌活性,但Ag-NPs對(duì)微生物群落結(jié)構(gòu)影響十分顯著,能夠使與底物降解相關(guān)的菌群減少,而使和生物吸附?生物膨脹等相關(guān)的菌群增加.

納米氧化鋅作為應(yīng)用最廣泛的 3大納米材料(納米二氧化鈦、納米銀和納米氧化鋅)之一,具有良好的抗菌性,對(duì)多種微生物具有一定的毒性作用[17].雖然 ZnO-NPs對(duì)污泥厭氧消化的影響已有報(bào)道,但缺乏系統(tǒng)研究.本文選取 ZnONPs為納米材料的典型代表,建立污泥厭氧消化反應(yīng)系統(tǒng),研究了系統(tǒng)的產(chǎn)氣量、揮發(fā)酸、有機(jī)物降解效率、污泥減量效果等,以揭示ZnO-NPs對(duì)厭氧消化過(guò)程的影響.

1 材料與方法

1.1 實(shí)驗(yàn)材料

實(shí)驗(yàn)用污泥取自哈爾濱信義污水處理廠二沉池污泥.污泥在冰柜中維持 4℃條件保存,靜置沉淀 24h,將靜置的污泥上層清液吸出.吸出清液后的污泥使用40目的篩子對(duì)污泥進(jìn)行過(guò)濾,除去污泥中粒徑較大的雜質(zhì)用于后續(xù)實(shí)驗(yàn).在自行設(shè)計(jì)的有效容積為8L的厭氧消化反應(yīng)器中培養(yǎng)和馴化厭氧消化污泥,培養(yǎng)條件為(55±0.5)℃,pH為7±0.5,避光培養(yǎng).

1.2 儀器和試劑

儀器:掃描電子顯微鏡( SEM,Philips XL30, FEI Company),氣相色譜儀(安捷倫),COD消解儀,馬弗爐.

試劑:ZnO-NPs分散液(CAS no.: 1314-13-2,＜100nm,Sigma公司).其他試劑均為分析純.

1.3 實(shí)驗(yàn)方法

1.3.1 NPs在污泥中的形貌分析 對(duì)污泥進(jìn)行掃描電鏡分析以觀測(cè)污泥加入ZnO-NPs前后的形態(tài)變化,預(yù)處理方法為[18]:(1)取樣:取 50mL污泥混合液,在5000r/min離心3min,用pH為6.8的磷酸鹽緩沖液(PBS)對(duì)下部成分進(jìn)行清洗;(2)固定:用 pH=6.8的 2.5%的戊二醛淹沒(méi)顆粒,于4℃條件下固定2h;(3)沖洗:用0.1mol/L的pH 6.8的磷酸鹽緩沖液沖洗 3次,每次 10min;(4)脫水:污泥樣品分別用30%、50%、70%、80%,90%的乙醇脫水,每次10min;然后用100%的乙醇脫水3次,每次 15min;(5)置換:先用乙醇:乙酸異戊酯=1:1的溶液置換 15min,再用乙酸異戊酯置換15min;(6)干燥:將處理后樣品置于低溫干燥機(jī)中烘干;(7)噴金:在樣品表面噴上一層 1500nm的金膜.(8)觀察:將噴金后的樣品置于SEM下進(jìn)行觀察.由圖1可以看出大部分的ZnO-NPs吸附在污泥顆粒的表面.

圖1 投加120mg/g-VSS ZnO-NPs的掃描電鏡分析(SEM)圖(A)和能譜分析(EDS)圖(B)Fig.1 SEM image (A) and EDS analysis (B) of sludge in the reactors exposed to ZnO-NPs, The dosage of nanoparticles was 120mg/g-VSS

1.3.2 污泥厭氧消化毒性實(shí)驗(yàn) 主要研究了不同濃度ZnO-NPs對(duì)厭氧消化過(guò)程包括水解、酸化、產(chǎn)甲烷的影響,厭氧發(fā)酵時(shí)間為期 20d.厭氧消化實(shí)驗(yàn)在反應(yīng)瓶中進(jìn)行,每個(gè)反應(yīng)瓶的體積為500mL,污泥體積為400mL.實(shí)驗(yàn)開(kāi)始前檢查裝置的密封性能,然后向反應(yīng)瓶中充入氮?dú)?5min,以去除瓶中的氧氣,密封后放入55℃水浴鍋中進(jìn)行厭氧消化反應(yīng).實(shí)驗(yàn)裝置如圖2所示,厭氧消化瓶污泥每天早晚磁力攪拌各1次.啟動(dòng)厭氧消化反應(yīng)器并使其穩(wěn)定運(yùn)行.在加入 ZnO-NPs之前,分別測(cè)定反應(yīng)器的有機(jī)物去除率、TSS和VSS作為對(duì)照.每個(gè)指標(biāo)做3個(gè)平行.

圖2 厭氧消化反應(yīng)實(shí)驗(yàn)裝置Fig.2 Experimental setup and schematic of anaerobic digestion system

1.3.3 污泥指標(biāo)的測(cè)定

表1 實(shí)驗(yàn)污泥的各項(xiàng)指標(biāo)

1.4 數(shù)據(jù)統(tǒng)計(jì)分析

實(shí)驗(yàn)結(jié)果均以“平均值±標(biāo)準(zhǔn)誤差”即(mean±SD)表示.采用SPSS18.0軟件進(jìn)行統(tǒng)計(jì)分析,多組間比較采用方差齊性檢驗(yàn)和單因素方差分析.進(jìn)一步進(jìn)行組間兩兩比較時(shí),采用 LSD檢驗(yàn),以P＜0.05表示差異顯著.

2 結(jié)果與討論

2.1 ZnO-NPs對(duì)污泥厭氧消化產(chǎn)氣量的影響

由圖 3(A)可知,ZnO-NPs暴露濃度為 2mg/ g-VSS時(shí),對(duì)日產(chǎn)氣量變化影響較小,而后隨著ZnO-NPs暴露濃度的升高,厭氧消化系統(tǒng)的日產(chǎn)氣量逐漸減少.由圖3(B)可知,當(dāng)ZnO-NPs暴露濃度為2mg/g-VSS時(shí),總產(chǎn)氣量降低1.9%;而當(dāng)ZnO-NPs暴露濃度從2mg/g-VSS升高到120mg/ g-VSS時(shí),相對(duì)日產(chǎn)氣量直線下降至對(duì)照組的10%左右,而且可以看出在2～120mg/g-VSS濃度范圍內(nèi)存在顯著的劑量-毒性正相關(guān)性.與對(duì)照相比,不同暴露濃度下厭氧消化系統(tǒng)的產(chǎn)氣量差異顯著(P＜0.05).

圖3 不同濃度ZnO-NPs對(duì)污泥厭氧消化日產(chǎn)氣量(A)、總產(chǎn)氣量的和相對(duì)產(chǎn)氣量(B)的影響Fig.3 Changes in daily biogas production ( A) ,Total biogas production and Relative biogas production ( B) of sludge anaerobic digestion under exposure to various concentrations of ZnO-NPs

分析可知,隨著 ZnO-NPs暴露濃度的升高, ZnO-NPs對(duì)產(chǎn)氣量具有明顯影響.ZnO-NPs能夠溶于水,并釋放出游離的 Zn2+和生成鋅的氫氧化物.溶出 Zn2+會(huì)對(duì)一些污水的生物處理過(guò)程產(chǎn)生影響,并對(duì)細(xì)胞的生長(zhǎng)產(chǎn)生毒性作用;鋅的氫氧化物是中性和堿性條件下鋅的主要存在形態(tài),其對(duì)水生生物有高毒性[19].Mu等[20]研究發(fā)現(xiàn),1mg/g-TSS ZnO-NPs不會(huì)對(duì)產(chǎn)甲烷過(guò)程產(chǎn)生影響,而30和150mg/g-TSS下表現(xiàn)出抑制作用,且毒性隨濃度的增大而加,且ZnO-NPs對(duì)產(chǎn)氣量的影響主要是來(lái)自于溶出Zn2+的釋放.

2.2 ZnO-NPs對(duì)揮發(fā)酸生成的影響

揮發(fā)酸主要指乙酸、丙酸、丁酸等短鏈脂肪酸,是厭氧消化過(guò)程的重要中間產(chǎn)物,檢測(cè)揮發(fā)酸的產(chǎn)量可以更好的了解有機(jī)質(zhì)的降解進(jìn)程[21].不同濃度的ZnO-NPs暴露3d后,分別測(cè)定不同種類揮發(fā)酸的濃度,結(jié)果如圖 3所示.由圖 3可知,不同濃度 ZnO-NPs暴露下,總揮發(fā)酸的濃度在1860～1990mg-COD/L之間.不同種類揮發(fā)酸在不同濃度 ZnO-NPs暴露下濃度無(wú)顯著差異(P＞0.05),由此可知,ZnO-NPs對(duì)污泥消化過(guò)程中水解酸化階段的影響較小,這與Mu等[20]的研究結(jié)果一致.同時(shí),有關(guān)研究表明,產(chǎn)酸菌對(duì)金屬毒性的敏感程度低于產(chǎn)甲烷菌.因此,較高濃度(＞2mg/g-VSS)暴露情況下,ZnO-NPs可能主要影響了乙酸到甲烷的生物轉(zhuǎn)化過(guò)程.

圖4 不同濃度ZnO-NPs對(duì)污泥厭氧消化揮發(fā)酸產(chǎn)生量的影響Fig.4 the concentrations of volatile fatty acids(VFAs) products with time of 3d under exposure to various concentrations of ZnO-NPs

2.3 ZnO-NPs對(duì)厭氧消化過(guò)程中有機(jī)物降解的影響

VSS/TSS值反映了污泥中揮發(fā)性有機(jī)物所占的比例,而有機(jī)物的多少直接關(guān)系到消化反應(yīng)的進(jìn)行,有機(jī)物多表示該樣品的可生化性強(qiáng). R(VSS/TSS)表示是 VSS/TSS值的減少量,即消化反應(yīng)中有機(jī)物的減少量,反映了有機(jī)物的去除效果.因此以 R(VSS/TSS)作為評(píng)價(jià)指標(biāo)來(lái)判斷厭氧消化反應(yīng)的程度,R(VSS/TSS)值越大說(shuō)明有機(jī)物被降解的越多,厭氧消化反應(yīng)進(jìn)行的越完全.

R(VSS/TSS)的定義為:

式中:(VSS/TSS)0表示未經(jīng)處理的原污泥樣品的VSS/TSS值.

圖5 ZnO-NPs對(duì)污泥厭氧消化過(guò)程中有機(jī)物降解效率(A)和有機(jī)物減少量(B)的影響Fig.5 Organic matter degradation efficiency(A), R(VSS/TSS)( B) of sludge in anaerobic digestion under exposure to various concentrations of ZnO-NPs

由圖5(A)可以看出,隨著ZnO-NPs濃度的升高,有機(jī)物降解效率逐漸減少.當(dāng) ZnO-NPs濃度較低(2mg/g-VSS)時(shí),對(duì) COD去除率影響較小,SCOD去除率和TCOD去除率均為對(duì)照組的95%左右;而后隨著ZnO-NPs濃度的升高,SCOD去除率和TCOD去除率減小,在ZnO-NPs濃度達(dá)到 120mg/g-VSS后達(dá)到穩(wěn)定,SCOD去除率和TCOD去除率分別減少到對(duì)照組的3%和36.5%.從整體來(lái)看,對(duì)照組與所有 ZnO-NPs 暴露組有顯著差異(P＜0.05).由圖 5(B)可知,對(duì)照組R(VSS/TSS)值最高,達(dá)到23.01%,而后隨著ZnO-NPs暴露濃度的升高,R(VSS/TSS)值減小,在 ZnO-NPs濃度為120mg/g-VSS后,達(dá)到穩(wěn)定,約為17%.對(duì)照組與所有 ZnO-NPs暴露組均有顯著差異(P＜0.05).

由以上結(jié)果推測(cè)高濃度的ZnO-NPs可能導(dǎo)致部分微生物死亡,進(jìn)而影響厭氧消化的效率.類似地,Mei 等[22]研究發(fā)現(xiàn)ZnO-NPs會(huì)抑制MBR對(duì)NaAc的降解,暴露濃度越大抑制作用越強(qiáng),加ZnO-NPs之前基質(zhì) 4h可完全降解,而加入13.6mg/L ZnO-NPs后則需6h.

2.4 ZnO-NPs對(duì)污泥減量效果的影響

圖6 ZnO-NPs對(duì)污泥厭氧消化系統(tǒng)污泥減量率的影響Fig.6 Reduction of sludge during sludge anaerobic digestion under exposure to various concentrations of ZnO-NPs

由于發(fā)酵時(shí)間的限制,厭氧消化過(guò)程只能分解部分有機(jī)組分.有機(jī)物的降解效率和 VSS的減少量通常作為一個(gè)重要參數(shù)來(lái)評(píng)價(jià)污泥厭氧消化的效果[23].從圖 6可以看出,厭氧消化反應(yīng)前VSS的含量為11.52g/L,發(fā)酵20d結(jié)束后,對(duì)于ZnO-NPs投加量為0、2、30、60、90、120和150mg/g-VSS濃度的暴露組VSS含量分別降低到 8.45、8.78、8.77、8.95、9.28、9.95和10.95g/L .隨著ZnO-NPs濃度的升高,污泥減量率逐級(jí)減小,2和30mg/g-VSS的ZnO-NPs濃度污泥減量率在在23%左右,當(dāng)ZnO-NPs濃度在 30～ 150mg/g-VSS時(shí),污泥減量率隨濃度下降較快,而當(dāng)ZnO-NPs的濃度為150mg/g-VSS時(shí),污泥減量下降至 4.8%左右,污泥減量效果下降.對(duì)照組與所有 ZnO-NPs暴露組有顯著差異(P＜0.05).

3 結(jié)論

3.1 ZnO-NPs能使污泥厭氧消化過(guò)程的產(chǎn)氣量減少并且暴露濃度與產(chǎn)氣量變化呈一定的量劑-抑制效應(yīng)關(guān)系;

3.2 不同濃度 ZnO-NPs暴露下,總揮發(fā)酸的濃度在1860～1990mg-COD/L之間,且ZnO-NPs在不同暴露濃度下,不同種類揮發(fā)酸濃度無(wú)顯著差異(P＞0.05);較高暴露濃度情況下,ZnO-NPs可能主要影響乙酸到甲烷的生物轉(zhuǎn)化過(guò)程;

3.3 ZnO-NPs對(duì)有機(jī)物降解效率和污泥減量率存在明顯抑制作用,且隨著 ZnO-NPs濃度的升高,SCOD去除率、TCOD去除率和R(VSS/TSS)值降低,在ZnO-NPs濃度升高到120mg/g-VSS時(shí)達(dá)到最大,SCOD去除率、TCOD去除率和R(VSS/TSS)值分別減少到對(duì)照組的3%、36.5%和74%.污泥減量率隨著 ZnO-NPs濃度的升高逐級(jí)減小,2, 30mg/g-VSS的 ZnO-NPs濃度污泥減量率在23%左右,當(dāng)ZnO-NPs 濃度在30～150mg/g-VSS時(shí),污泥減量率隨濃度下降較快,而當(dāng) ZnO-NPs濃度為 150mg/g-VSS時(shí),污泥減量率下降至4.8%左右.

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Effect of Zinc oxide nanoparticles on anaerobic digestion of excess activated sludge.

WANG Shu-tao1*, CHEN Ling-bo1, ZHANG Zhen-rui1, WU Chuan1, JIANG Rui2, YOU Hong1
(1.State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China；2.Heilongjiang Research Academy of Environmental Sciences, Harbin 150056, China). China Environmental Science, 2017,37(1)：174～180

The impact of Zinc oxide nanoparticles (ZnO-NPs) (0, 2, 30, 60, 90, 120 and 150mg/g-VSS) on the anaerobic digestion of excess activated sludge was investigated and the possible dose-effect relationship was achieved. Results indicated that less adverse effects of ZnO-NPs were found on anaerobic digestion of excess activated sludge at the low exposure concentration (2mg/g-VSS). However, significant effects were observed on the anaerobic digestion including biogas production, degradation efficiency of organics as well as reduction rate of sludge, but no significant effects was found on the volatile fatty acids (VFAs). The average daily gas production plummeted when the exposure concentration of ZnO-NPs was increased from 30mg/g-VSS to 120mg/g-VSS, but no obvious decrease of daily gas production was observed as the concentration was increased from 120mg/g-VSS to 150mg/g-VSS. In additon, ZnO-NPs could significantly inhibit the degradation efficiency of organic matter and the sludge reduction rate, and with the increasing of ZnO-NPs concentration from 30mg/g-VSS to 120mg/g-VSS, soluble chemical oxygen demand (SCOD) removal rate, total chemical oxygen demand (TCOD) removal rate and R(VSS/TSS)value was decreased to 3%, 36.5% and 74% of the control. Sludge reduction rate was reduced from 23% to 4.8% of the control when the ZnO-NPs concentration increased from 2mg/g-VSS to 150mg/g-VSS. The results help evaluating the inhibitory effects of nanoparticles on anaerobic digestion process.

Zinc oxide nanoparticles；biological toxicity；nludge anaerobic digestion；sludge reduction

X703

A

1000-6923(2017)01-0174-07

王樹(shù)濤(1975-),男,黑龍江哈爾濱人,博士,講師,主要研究方向?yàn)榄h(huán)境毒理學(xué)和催化氧化法污水深度處理理論與技術(shù).

2016-05-14

教育部留學(xué)回國(guó)科研啟動(dòng)基金;哈爾濱工業(yè)大學(xué)城市水資源與水環(huán)境國(guó)家重點(diǎn)實(shí)驗(yàn)室開(kāi)放基金(QA201608)

* 責(zé)任作者, 講師, wshutao@hit.edu.cn