劉春爽 張璐遙 尹海 李世文 王明艷 劉力嘉 王勝淵 孫志超
摘要:采用序批式生物膜反應(yīng)器(SBR),在溫度為30 ℃條件下,在短程硝化/厭氧氨氧化生物膜的基礎(chǔ)上耦合小球藻構(gòu)建藻菌耦合生物膜體系,通過改變光照時長和曝氣量組合條件的運行方式共運行85 d,分析組合條件下體系的脫氮性能、藻菌耦合體系特性和氮轉(zhuǎn)化路徑,以得到最佳脫氮條件及藻菌耦合脫氮機制。結(jié)果表明:當(dāng)進水氨氮質(zhì)量濃度為(400±50) mg/L時,光暗比(單位為h/h)設(shè)置為6/4,曝氣強度為200 mL/min時,脫氮效果最好,NH4+-N及總氮平均去除率最高可達92.31%和87.56%;藻菌耦合體系運行過程中污泥質(zhì)量濃度與小球藻干重calgae比始終約為5.5,表明生物膜中藻類和細菌的比例達到相對穩(wěn)定狀態(tài),并形成良好的互利共生關(guān)系,集中在生物膜外部的小球藻通過光合作用產(chǎn)生的氧氣被硝化細菌消耗,因此產(chǎn)生的厭氧環(huán)境和亞硝酸鹽底物來維持厭氧氨氧化菌的活性;在氮的去除機制中,生物吸收量約占45.71%,PN/A(短程硝化-厭氧氨氧化)過程N2的生成量及氮損失約占54.29%。
關(guān)鍵詞:小球藻; 藻菌耦合體系; 短程硝化/厭氧氨氧化; 生物膜; 自養(yǎng)脫氮
中圖分類號:X 522 文獻標志碼:A
引用格式:劉春爽,張璐遙,尹海,等.微藻曝氣強化短程硝化/厭氧氨氧化自養(yǎng)脫氮工藝性能[J].中國石油大學(xué)學(xué)報(自然科學(xué)版),2023,47(6):185-191.
LIU Chunshuang, ZHANG Luyao, YIN Hai, et al. Performance of autotrophic denitrification enhanced by microalgae aeration and anaerobic ammox[J].Journal of China University of Petroleum(Edition of Natural Science),2023,47(6):185-191.
Performance of autotrophic denitrification enhanced
by microalgae aeration and anaerobic ammox
LIU Chunshuang1, ZHANG Luyao1,2, YIN Hai3, LI Shiwen4, WANG Mingyan1, LIU Lijia1, WANG Shengyuan4, SUN Zhichao1
(1.College of Chemistry and Chemical Engineering in China University of Petroleum(East China), Qingdao 266580,China;
2.Judicial Bureau of Pingyi County, Linyi 273399,China;
3. Fengcheng Oilfield Operation Area of Xinjiang Oilfield Company, PetroChina, Karamay 834000, China;
4.Qingdao West Coast Utility Group Water Company, Qingdao 266000, China)
Abstract: A sequencing batch biofilm (SBR) reactor was used to cultivate an algae-coupled biofilm system based on short-range nitrification/anaerobic ammonia oxidation biofilm with Chlorella vulgaris at a temperature of 30 ℃. The system was operated for 85 d by changing the combination of light duration and aeration. The nitrogen removal performance, algae-coupled system characteristics and nitrogen conversion pathways were analyzed to obtain the optimal nitrogen removal conditions and algal-bacterial coupling nitrogen removal mechanism. The results show that when the influent ammonia nitrogen concentration is 400±50 mg/L, the light/dark ratio is 6 h/4 h, and the aeration intensity is 200 mL/min, the best denitrification effect was achieved, in which the average removal rates of NH4+-N and total nitrogen were up to 92.31% and 87.56%, respectively. The ratio of cMLVSS(wastewater mass concentration) to calgae(dry weight of chlorella vulgaris) is always around 5.5 during the operation of the algae coupled system, which indicates that the ratio of algae and bacteria in the biofilm reaches a relatively stable state and forms a good mutually beneficial symbiotic relationship. The oxygen produced by the photosynthesis of Chlorella vulgaris concentrated outside the biofilm is consumed by nitrifying bacteria, and nitrifying bacteria provided anaerobic environment and nitrite substrate to maintain the activity of anaerobic ammonia oxidizing bacteria. In the nitrogen removal mechanism, the biological uptake accounts for about 45.71%, and the amount of N2 production and nitrogen loss in the PN/A(partial nitrification-anaerobic ammonium oxidation) process accounts for about 54.29%.
Keywords: chlorella; algal and bacterial coupling system; short-cut nitrification and anammox; biological membrane; autotrophic nitrogen removal
污水中氮的過量排放大大加劇了水體的富營養(yǎng)化,對水質(zhì)構(gòu)成威脅[1-2]。氮污染控制已經(jīng)成為全球關(guān)注的問題[3-4]。短程硝化與厭氧氨氧化(PN/A)工藝相結(jié)合,首先好氧氨氧化菌(AOB)在特定溶解氧等條件下將部分NH4+-N轉(zhuǎn)化為NO2--N,再通過Anammox菌代謝作用將NH4+-N和NO2--N轉(zhuǎn)化為N2,該工藝可以在不添加有機物的情況下實現(xiàn)廢水高效自養(yǎng)脫氮[5-6],同時還具有工藝流程簡單、占地面積小的優(yōu)點[7-8]。然而在PN/A工藝中,溶解氧(DO)是影響系統(tǒng)穩(wěn)定性的重要因素,因為AOB和Anammox菌對溶解氧的需求不同??刂艱O濃度是實現(xiàn)穩(wěn)定運行PN/A工藝的必要條件。藻菌共生系統(tǒng)被應(yīng)用于處理營養(yǎng)物質(zhì)豐富的廢水[9]。在光照下,微藻利用溶解在水中或通過細菌呼吸釋放的二氧化碳,通過光合作用為細菌產(chǎn)生氧氣,而細菌反過來為微藻的生長提供代謝物和無機碳源[10-11],藻菌共生系統(tǒng)可以節(jié)省大部分或全部曝氣能耗[12-13]。用于廢水處理的微藻和細菌組合可以比單一微藻或細菌系統(tǒng)更好地去除營養(yǎng)物質(zhì)[14-15]。將微藻與好氧細菌結(jié)合以實現(xiàn)有效去除NH4+-N和有機物,需要額外有機物來實現(xiàn)總氮的去除[16-17]。將微藻與PN/A工藝相結(jié)合,微藻光合作用所產(chǎn)生的氧氣被AOB利用將部分NH4+-N轉(zhuǎn)化為NO2--N,在硝化細菌消耗氧氣產(chǎn)生的厭氧環(huán)境中,厭氧氨氧化菌利用剩余NH4+-N和亞硝酸鹽底物進行反應(yīng),此過程可大大減少外源有機物的添加,并實現(xiàn)高效的自養(yǎng)脫氮。Tang等[18]通過單因素試驗研究表明,0.2 L/min(空氣)是藻菌體系所需的最佳曝氣量;Zhang等[19]在無曝氣輔助條件下探究藻類-細菌共生最佳光照時長表明當(dāng)間歇光時間(L)/暗時間(D)(L/D,單位為h/h)設(shè)置為8/2,NH4+-N的平均去除速率為8.9 mg/(L·h),TN的平均去除率最高為63%。相同的DO質(zhì)量濃度可以在生物膜系統(tǒng)的不同部位形成好氧區(qū)和缺氧區(qū)[20],為不同類型的細菌提供適宜的生長環(huán)境。此外生物膜具有抗沖擊性及高生物多樣性的特點[21]。目前關(guān)于生物膜形式的藻菌共生系統(tǒng)的研究較少,筆者利用序批式反應(yīng)器(SBR)將小球藻與PN/A工藝結(jié)合,構(gòu)建藻菌耦合體系,解析該系統(tǒng)在不同光照及曝氣組合條件下的脫氮性能、藻菌耦合體系特性及氮轉(zhuǎn)化路徑。
1 試驗材料與方法
1.1 進水和污泥
試驗用水采用人工配水,其組成為 NH4Cl(提供NH4+-N),MgSO4·7H2O、CaCl2、NaHCO3和KH2PO4質(zhì)量濃度分別為0.03、0.2、3和0.16 g/L,微量元素濃縮液 Ⅰ、Ⅱ,各加入2和1mL/L,具體成分與Xie等[20]報道相同。進水pH控制在8.0±0.2。
一體式短程硝化厭氧氨氧化污泥來自課題組前期培養(yǎng)的母反應(yīng)器生物膜,生物膜上的生物量(揮發(fā)性懸浮物質(zhì)量/載體質(zhì)量)為2393 mg/g,接種藻種選用BG11培養(yǎng)基培養(yǎng)的小球藻,按藻菌質(zhì)量比1∶3進行接種。
1.2 試驗裝置和操作程序
試驗采用改進的SBR反應(yīng)器(圖 1(a)),其有效容積為6.0 L,外柱為水浴加熱層,將恒溫加熱棒固定于外層壁,加熱水溫保持在(30±1) ℃,并在水浴加熱層中預(yù)留的4個和反應(yīng)器高度相同的有機玻璃空管放置LED燈管。選擇聚氨酯海綿作為反應(yīng)器中藻菌共生生物膜的載體。SBR反應(yīng)器配有攪拌器和曝氣盤,攪拌器控制在20 r/min的速度,曝氣強度根據(jù)試驗所需調(diào)節(jié)。每周期水交換體積比為50%。
在接種小球藻后,小球藻隨出水會有流失,持續(xù)間歇光照以促進小球藻在生物膜上的生長(持續(xù)9 d),待出水穩(wěn)定后進行光照及曝氣組合條件對系統(tǒng)脫氮變化的探究。SBR反應(yīng)器每天運行2個周期,每周期運行12 h,其中反應(yīng)時間固定為10 h。L/D設(shè)置為4/6、6/8、8/2、10/0,每個光暗比階段曝氣量分別采用100和200 mL/min。反應(yīng)器運行程序如圖1(b)所示,其中x為反應(yīng)期間光照及曝氣組合時間,x1、x2、x3、x4分別為4、6、8、10 h。不同反應(yīng)條件下反應(yīng)器的操作條件如表1所示。
1.3 化學(xué)分析方法
NH4+-N 分析采用納氏試劑比色法[21],NO2- -N 采用乙二胺分光光度法[22],NO3--N采用酚二磺酸法[22]。pH值、污泥固體懸浮物(VSS)和VSS質(zhì)量濃度采用常規(guī)測定方法[22]。EPS(胞外聚合物)根據(jù)根據(jù)Hao等[23]方法測定。葉綠素質(zhì)量濃度的提取和測定參考文獻 [24],小球藻葉綠素質(zhì)量濃度與小球藻干重之間的關(guān)系為
calgae=0.62835cchl(a+b)+0.05557,R2=0.9923.
式中,calgae為小球藻干重,g/L;cchl(a+b)為葉綠素質(zhì)量濃度,mg/L。
藻菌耦合SBR中氮平衡式為
Nin=Nout= Nuptake +Nv+Nd+Neff.
式中,Nin為反應(yīng)器氮輸入量即進水總氮量,mg/L,等于進水氨氮質(zhì)量濃度;Nout為反應(yīng)器氮輸出量,mg/L;Nd為PN/A的N2生成量及氮損失,mg/L;Nuptake為生物吸收量,mg/L;Neff為出水總氮量,mg/L;Nv為NH3揮發(fā)量,mg/L。
通過假設(shè)藻類的化學(xué)計量法[25]確定Nuptake。Neff為出水NH4+-N、NO2--N、NO3-N的質(zhì)量濃度,氨的揮發(fā)現(xiàn)象為NH4+-N在高pH條件下(pH>10)生成氨氣溢出系統(tǒng)相較于其他轉(zhuǎn)化路徑,Nv可以近似為0。故PN/A的N2生成量及氮損失為Nd=Nin-Nuptake+Nv-Neff。
2 結(jié)果分析
2.1 反應(yīng)器運行效能
在接種小球藻后,階段Ⅰa 在不曝氣的條件下提供間歇光照,以促進小球藻的生長,待出水穩(wěn)定后開始試驗。之后調(diào)節(jié)不同光暗比為4/6、6/4、8/2、10/0以及曝氣量設(shè)置為100和200 mL/min以探究藻菌耦合脫氮最佳操作條件,共運行85 d,結(jié)果如圖2所示。在L/D=4/6時,提供 100 mL/min的曝氣量時系統(tǒng)表現(xiàn)出對NH4+-N的去除能力,出水NH4+-N濃度大幅度降低,當(dāng)曝氣量增大到200 mL/min時,出水NH4+-N質(zhì)量濃度進一步降低,NH4+-N及總氮平均去除率為72.00%和68.63%,說明此前系統(tǒng)受溶解氧限制導(dǎo)致氨氮去除能力較低,在提供曝氣后系統(tǒng)脫氮能力逐漸恢復(fù)。同時由于厭氧氨氧化反應(yīng)產(chǎn)生的部分NO3--N及少量未被利用的NO2--N在系統(tǒng)中,所以總氮去除率低于NH4+-N去除率。在L/D=6/4時得到同樣的規(guī)律,但在100 mL/min的曝氣強度下,較上一階段曝氣量減少了25%,NH4+-N平均去除率由72.0%提升到至78.09%,總氮平均去除率由68.63%提升至74.49%,這是因為隨著光照時間的增加,藻類產(chǎn)生更多的DO,有利于提高硝化細菌的活性,從而提高NH4+-N的去除率。但在L/D=8/2以及L/D=10/0時,雖延長了光照及曝氣時間,在與之前同樣的曝氣強度下,出水NH4+-N質(zhì)量濃度卻升高,這是因為當(dāng)外界所提供的溶解氧質(zhì)量濃度增大時,雖然可以增強硝化細菌的供氧來源促進其活性,但對厭氧氨氧化菌可能產(chǎn)生一定程度的抑制,使其不能充分利用NH4+-N。同時如果一味增大曝氣強度,藻類的光合作用被限制,藻類活性受抑制,即打破了藻菌之間一致的生長速率,破壞了共生系統(tǒng)的平衡。因此當(dāng)光暗比設(shè)置為6/4、曝氣強度為200 mL/min時,出水NH4+-N平均質(zhì)量濃度為34.38 mg/L,NH4+-N及總氮平均去除率最高可達92.31%和87.56%。
2.2 藻菌耦合體系特性
圖3為藻菌共生生物膜表觀形態(tài),圖4為第50 d生物膜掃描電鏡結(jié)果。可以看出,反應(yīng)器內(nèi)的生物膜在接種小球藻后,不同時期生物膜外觀差別較大。隨著培養(yǎng)過程的進行,生物膜外小球藻分布逐漸均勻,由最初的黃褐色加深為深綠色。從第50 d不同放大倍數(shù)的掃描電鏡觀察結(jié)果可知,與內(nèi)部相比,外部生物膜較厚且小球藻主要分布在外部,這為小球藻利用光照產(chǎn)氧提供了有利條件并形成生物膜從外到內(nèi)溶解氧逐漸減少的氧氣梯度,細菌形態(tài)主要為桿狀、球狀并有少量長桿狀或絲狀形態(tài)。
在培養(yǎng)過程中,生物膜上所負載的生物參數(shù)也有不同程度的變化:載體負載生物量由2056 mg/g載體升至3784 mg/g;污泥質(zhì)量濃度(cMLVSS)及calgae從第1 d的3.02和0.56 g/L升至第85 d的0.56和2.45 g/L,兩者比值始終約為5.5(表2),表明生物膜中藻類和細菌的比例達到相對穩(wěn)定狀態(tài),并形成了良好的互利共生關(guān)系。此外S-EPS、TB-EPS和LB-EPS的含量逐漸上升(圖5),蛋白質(zhì)(PN)分別從最初的11.36、11.07和6.23 mg/g上升至30.86、35.10和35.40 mg/g。在生物膜生長繁殖階段,EPS具有聚集、連接菌藻細胞以及作為暫存和傳遞營養(yǎng)物質(zhì)媒介的作用,構(gòu)成了菌藻耦合生物膜的骨架[26]。
2.3 氮轉(zhuǎn)化路徑分析
藻菌共生系統(tǒng)主要是通過藻菌協(xié)同作用實現(xiàn)高效脫氮,一部分是活性污泥菌群的短程硝化/厭氧氨氧化作用脫氮,另一部分是微藻生物同化吸收氮。整個系統(tǒng)中氮形態(tài)的變化是聯(lián)動的,利用氮元素質(zhì)量守恒原則分析藻菌共生SBR穩(wěn)定運行階段每周期氮的遷移轉(zhuǎn)化路徑,結(jié)果見圖6。
藻菌耦合SBR系統(tǒng)在穩(wěn)定運行階段的氮平衡分析數(shù)據(jù)見表3。
SBR穩(wěn)定階段,進水NH4+-N質(zhì)量濃度為449.73 mg/L時,NH4+-N去除率約為92.03%,TN去除率約為87.43%,其中生物吸收量約占45.71%,PN/A過程N2的生成量及氮損失約占54.29%。系統(tǒng)中氮損失可能有兩方面原因:一是異養(yǎng)硝化反應(yīng)過程會產(chǎn)生中間產(chǎn)物從而造成氮損失,硝化過程中產(chǎn)生N2、N2O和NO,其比例可達氮除去率的 10%以上[26-28];二是可能存在同時硝化反硝化現(xiàn)象 (SND),即硝化反應(yīng)和反硝化反應(yīng)在同一反應(yīng)器中、相同操作條件下同時發(fā)生[26-28]。
3 結(jié) 論
(1)采用SBR反應(yīng)器,以聚氨酯海綿負載的一體式短程硝化厭氧氨氧化污泥為接種污泥,在溫度為(30±1) ℃,通過改變光照時長及曝氣量方式,連續(xù)運行85 d。當(dāng)進水氨氮質(zhì)量濃度為(400±50) mg/L、光暗比設(shè)置為6/4、曝氣強度為200 mL/min時,NH4+-N及總氮平均去除率最高可達92.31%和87.56%。
(2)藻菌耦合體系生物膜外觀為深綠色,小球藻主要集中在生物膜外部。藻菌耦合體系運行過程中cMLVSS與calgae比值始終約為5.5,表明生物膜中藻類和細菌的比例達到相對穩(wěn)定狀態(tài),并形成了良好的互利共生關(guān)系。系統(tǒng)運行過程中EPS含量逐漸上升,構(gòu)成了菌藻共生生物膜的骨架。
(3)在穩(wěn)定運行的第45~55 d,NH4+-N去除率約為92.03%,TN去除率約為87.43%;在氮的去除機制中,生物吸收量約占45.71%,PN/A過程N2的生成量及氮損失約占54.29%。
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