鐵強化厭氧氨氧化脫氮機理研究進展

王 倩,胡嘉源,李天皓,王彩霞,陳 潔,沈耀良,2,劉文如,2*

鐵強化厭氧氨氧化脫氮機理研究進展

王 倩1,胡嘉源1,李天皓1,王彩霞1,陳 潔1,沈耀良1,2,劉文如1,2*

(1.蘇州科技大學環(huán)境科學與工程學院,江蘇 蘇州 215000；2.蘇州科技大學,城市生活污水資源化利用技術(shù)國家地方聯(lián)合工程實驗室,江蘇 蘇州 215000)

如何強化厭氧氨氧化細菌生長代謝,提高厭氧氨氧化工藝脫氮效能以及保障工藝長期穩(wěn)定運行是有關(guān)厭氧氨氧化研究的熱點之一.鐵強化厭氧氨氧化是當前研究最為廣泛且最具經(jīng)濟性和實用性的一種措施.本文簡述了鐵強化厭氧氨氧化技術(shù)及其強化脫氮效能;重點從優(yōu)化厭氧氨氧菌的生長環(huán)境、促進胞外聚合物分泌、加速脫氮功能菌群富集、誘導細胞結(jié)構(gòu)演變、調(diào)控關(guān)鍵酶和功能基因表達、促進信號分子合成以及強化非生物脫氮反應等方面總結(jié)了鐵強化厭氧氨氧化菌生長代謝和厭氧氨氧化系統(tǒng)脫氮效能的機理.最后對鐵強化厭氧氨氧化技術(shù)進行總結(jié)展望,并提出廢鐵屑強化厭氧氨氧化技術(shù)的構(gòu)想.

厭氧氨氧化；鐵；脫氮強化；機理

厭氧氨氧化(ANAMMOX)在厭氧環(huán)境下以亞硝酸鹽(NO2-)為電子受體,將氨(NH3)轉(zhuǎn)化為氮氣[1].厭氧氨氧化技術(shù)相較于傳統(tǒng)硝化反硝化脫氮技術(shù),具有節(jié)省曝氣、無需有機碳源、溫室氣體排放少等優(yōu)點[2-3].然而,當前厭氧氨氧化技術(shù)的推廣應用仍然面臨如厭氧氨氧化菌倍增時間長且對環(huán)境因子(如溫度)變化敏感性高、亞硝酸鹽氧化菌(NOB)長期有效抑制(即NO2-穩(wěn)定高效供給)難等諸多挑戰(zhàn)[4-6].對于如何強化厭氧氨氧化細菌生長代謝、提高厭氧氨氧化工藝脫氮效能以及保障工藝長期穩(wěn)定運行,研究者們進行了大量嘗試.研究表明,投加Fe/Mn、氧化石墨烯等化學物質(zhì)以及施加電場、磁場、超聲波等均是實現(xiàn)厭氧氨氧化系統(tǒng)強化脫氮行之有效的方法[7-11],其中投加Fe方法(即鐵強化厭氧氨氧化)是研究最為廣泛的,也是最具經(jīng)濟性和實用性的措施.目前,有關(guān)鐵強化厭氧氨氧化的研究中所投加的鐵主要包括零價鐵(包括nZVI、mZVI、海綿鐵及鐵碳材料等)、亞鐵離子、鐵離子以及其他鐵化合物(如鐵礦物、Fe3O4NPs)等.研究證實,盡管投加的鐵種類不同,但它們均能不同程度地促進厭氧氨氧化菌生長代謝、強化厭氧氨氧化系統(tǒng)脫氮效能,從而形成了一系列基于不同鐵材料的鐵強化厭氧氨氧化技術(shù).一般認為厭氧氨氧化菌只能攝取Fe2+/ Fe3+ [12],基于不同鐵材料的鐵強化厭氧氨氧化技術(shù)所涉及的作用機制可能有所不同.鐵強化厭氧氨氧化脫氮的影響因素眾多、作用機理十分復雜,這就使得鐵強化厭氧氨氧化技術(shù)在鐵投加量控制、運行條件優(yōu)化、內(nèi)在機制解釋等方面難以形成共識.本文在總結(jié)當前眾多文獻報道的基礎(chǔ)上,嘗試對鐵強化厭氧氨氧化脫氮機理進行梳理、評述,以期為鐵強化厭氧氨氧化技術(shù)的發(fā)展與應用提供理論借鑒.

1 鐵強化厭氧氨氧化脫氮技術(shù)

1.1 厭氧氨氧化菌對鐵過量需求

鐵的天然豐度及其氧化還原特性,使其成為微生物異養(yǎng)呼吸和自養(yǎng)生長的普遍底物[12].研究表明,厭氧氨氧化菌內(nèi)鐵含量遠高于一般的微生物,鐵不僅是厭氧氨氧化菌體內(nèi)血紅素合成的重要組分,還可以提高細胞膜傳質(zhì)能力[13].厭氧氨氧化菌的生理活動高度依賴鐵結(jié)合蛋白,鐵結(jié)合蛋白中鐵價態(tài)的變化在厭氧氨氧化反應電子轉(zhuǎn)移過程中發(fā)揮關(guān)鍵作用[12].此外,鐵還是亞硝酸鹽還原和氨氧化過程關(guān)鍵酶(例如硝酸鹽還原酶、肼合成酶(HZS)和肼脫氫酶(HDH))的重要組成部分[14-16].總之,鐵在厭氧氨氧化過程中扮演重要角色,因此鐵的穩(wěn)定供應十分重要[17].

1.2 鐵強化厭氧氨氧工藝脫氮效能

投加鐵對厭氧氨氧工藝的強化作用主要體現(xiàn)在縮短厭氧氨氧化工藝啟動時間、提高厭氧氨氧化系統(tǒng)脫氮負荷和效率等方面.表1總結(jié)了部分文獻報道的鐵強化厭氧氨氧工藝的脫氮效能.不同鐵材料對厭氧氨氧工藝脫氮效能的強化能力不同,例如相同條件下施加Fe2O3納米顆粒(Fe2O3NPs)、Fe3+、Fe納米顆粒(Fe NPs)、Fe3O4納米顆粒(Fe3O4NPs)和Fe3+,厭氧氨氧化反應器脫氮效率分別為34.8%、49.4%、74.8%、84.9%和91.3%[28].與微米零價鐵(mZVI)相比,納米零價鐵(nZVI)可以進一步縮短反應器啟動時間約16.7%[27].

續(xù)表1

注:“*”表示反應器中鐵均在試驗初期一次性投加.UASB:上流式厭氧污泥床;SBR:序批式反應器;SBBR:序批式生物膜反應器;UABR:上流式厭氧耦合生物膜反應器;UFBR:上流式固定床反應器;ASBR:厭氧序批式反應器;IFFASR:綜合浮膜活性污泥反應器;EPS:胞外分泌物;PN:蛋白質(zhì).

鐵強化厭氧氨氧化系統(tǒng)的效果也與鐵投加量密切相關(guān).研究發(fā)現(xiàn),在添加3.36,5.04mg/L Fe2+的條件下,厭氧氨氧化工藝的啟動時間由未添加Fe2+時的70d分別縮短到58,50d[17].馬嬌等[26]實驗結(jié)果指出,當nZVI濃度由0mg/L增加到100mg/L時,反應器總氮去除率從70.3%提高到90.1%,但當nZVI的濃度繼續(xù)增加時,其總氮去除率降低.鐵添加過量會降低系統(tǒng)內(nèi)厭氧氨氧化菌豐度,減少血紅素c濃度,抑制肼脫氫酶活性[18].一般而言,鐵投加量對厭氧氨氧化工藝啟動和脫氮效能的影響主要表現(xiàn)為低濃度促進,高濃度抑制.

2 鐵輔助厭氧氨氧化工藝強化脫氮機理

如圖1所示,鐵強化厭氧氨氧化的作用機理主要表現(xiàn)在優(yōu)化厭氧氨氧化菌的生長環(huán)境、促進厭氧氨氧化菌分泌胞外分泌物(EPS)、加速功能菌富集、改變細胞結(jié)構(gòu)、調(diào)控功能基因表達、強化關(guān)鍵酶和輔因子活性、促進信號分子合成和強化非生物因素脫氮效能等方面.

圖1 鐵輔助厭氧氨氧化工藝強化脫氮機制

2.1 優(yōu)化厭氧氨氧化菌的生長環(huán)境

2.1.1 氧化還原電位(ORP) 厭氧氨氧化系統(tǒng)適宜的ORP范圍較廣,為-107～375mV[31-33].厭氧氨氧化是一種復雜的生物反應,ORP影響厭氧氨氧化菌比活性(SAA)的機理較為復雜.SAA在一定ORP范圍內(nèi)(-100～110mV),隨著ORP的增加而降低.向反應器中投加適量零價鐵(ZVI)可以降低ORP,從而促進厭氧氨氧化菌代謝[31].Guo等[34]報道,添加1000mg/L ZVI的厭氧氨氧化系統(tǒng)ORP的波動范圍和均值均小于對照組.相反地,Gao等[35]發(fā)現(xiàn)加入ZVI后的厭氧氨氧化系統(tǒng)中SAA與ORP的數(shù)值呈正相關(guān),加入750mg/L的ZVI后,反應器的ORP上升到209.4mV,相較于對照組提高了82.1mV,而SAA則提高0.04kgN/kgVSS/d,即此研究表明較高的ORP值似乎有利于厭氧氨氧化菌的生長.ZVI通過改變ORP影響SAA和系統(tǒng)脫氮效能的結(jié)果不一,尚需要深入研究.

2.1.2 pH值堿度 適于厭氧氨氧化菌生存的pH值范圍一般為6.4～8.3,最適pH值為7.5～8.0[36].不同形態(tài)鐵的投加會改變厭氧氨氧化系統(tǒng)中pH值,從而影響厭氧氨氧化菌活性. Li等[37]研究發(fā)現(xiàn),當厭氧氨氧化反應器中Fe3+投加量由2mg/L上升到6mg/L時,反應器中pH值由7.7上升到8.1,當 Fe3+濃度為10～ 120mg/L時,反應器中pH值在7.65～7.89范圍內(nèi)波動,但當Fe3+濃度進一步升高至120mg/L時pH值出現(xiàn)下降,這是由于反應器中生成Fe(OH)3沉淀,大量消耗OH-.Feng等[38]關(guān)于Fe2+對厭氧氨氧化系統(tǒng)pH值影響的研究與Li等[37]的研究結(jié)果基本類似,當Fe2+的濃度為1mg/L時,厭氧氨氧化系統(tǒng)內(nèi)pH值為7.8～8.0,而當Fe2+的濃度上升到4～6mg/L時, pH值上升到8.1;但當Fe2+的濃度達到120mg/L時,pH值則下降至7.65～7.8.因此可以推測,低濃度Fe2+和Fe3+可以提高系統(tǒng)脫氮效能,促進厭氧氨氧化反應并產(chǎn)生大量OH-,致使反應器pH值上升.高濃度Fe2+和Fe3+不僅會抑制厭氧氨氧化菌活性,還會直接消耗大量OH-,生成Fe(OH)2和Fe(OH)3沉淀,導致反應器內(nèi)pH值下降. Feng等[38]還提出了用pH值增量預測厭氧氨氧化系統(tǒng)氨氮去除率(NRE)的線性方程式:

NRE = 0.51ΔpH + 45.55 (1)

基于國內(nèi)外關(guān)于厭氧氨氧化反應器運行的相關(guān)文獻,對投加鐵和不投加鐵的反應器運行時的pH值數(shù)據(jù)進行分析[24,38-47].投加鐵對厭氧氨氧化系統(tǒng)最適pH值無顯著影響,最適pH值仍在7.5～8之間,但可以顯著提高系統(tǒng)抵抗pH值沖擊的能力,投加鐵后厭氧氨氧化正常運行的pH值范圍由原來的7.3～ 8.0拓寬到6.5～8.2.這一發(fā)現(xiàn)為鐵強化厭氧氨氧化工藝處理酸性含氮廢水提供了新的思路.

ZVI粉末的投加可以緩沖厭氧氨氧化系統(tǒng)內(nèi)pH值的波動,使系統(tǒng)內(nèi)pH值維持在相對穩(wěn)定的范圍,從而提高系統(tǒng)脫氮效能.Guo等[32]報道,在ZVI投入?yún)捬醢毖趸w系的前期,系統(tǒng)pH值波動較大,而運行一段時間后,系統(tǒng)pH值逐漸升高(從6.5上升到7.8),即系統(tǒng)中H+被ZVI消耗致使pH值上升,相應地,系統(tǒng)氮去除率也隨之提高.當然,厭氧氨氧化系統(tǒng)pH值不宜過高,過高的pH值會導致厭氧氨氧化菌失活.

2.2 促進厭氧氨氧化菌EPS分泌

鐵可以刺激厭氧氨氧化系統(tǒng)中微生物分泌EPS,Ren等[27]報道,分別向厭氧氨氧化反應器中加入25g的mZVI和nZVI,運行一段時間后EPS含量相較于對照組分別提高了21.2,27.7mg/gVSS.EPS對微生物細胞的聚集具有重要作用.Tang等[23]指出,Fe2+可以刺激厭氧氨氧化污泥EPS的分泌,促進顆粒污泥的形成,投加Fe2+后系統(tǒng)中粒徑大于2mm的污泥顆粒所占比例可達58.3%.同時,隨著污泥直徑的增大,EPS對Fe的吸附能力下降,更多的Fe轉(zhuǎn)運到厭氧氨氧化菌細胞內(nèi),提高了系統(tǒng)的脫氮能力.反應器中PN/PS(蛋白質(zhì)含量/多糖含量)也由8.51± 0.71逐漸下降至4.91±0.37,PN/PS比率反映了厭氧氨氧化顆粒污泥的結(jié)構(gòu)穩(wěn)定性[48],比率越高,穩(wěn)定性越差[49].這表明,長期添加Fe2+可以增強厭氧氨氧化顆粒污泥的結(jié)構(gòu)穩(wěn)定性.

2.3 加速功能菌富集

2.3.1 促進厭氧氨氧化菌富集 厭氧氨氧化系統(tǒng)中ZVI的投加,為厭氧氨氧菌創(chuàng)造了更好的生存環(huán)境,有利于其生長繁殖.Yang等[50]發(fā)現(xiàn),ZVI的投加能夠加速優(yōu)勢菌群從異養(yǎng)反硝化細菌向自養(yǎng)厭氧氨氧化菌和Feammox(鐵氨氧化)細菌的轉(zhuǎn)變.需要注意的是,鐵過量投加會對厭氧氨氧化菌生長繁殖產(chǎn)生抑制作用.隨著Fe3+濃度從2.24mg/L增至5.60mg/ L,在厭氧氨氧化體系中比例從30.7%增加到35.3%,當Fe3+濃度繼續(xù)增加到6.72mg/ L,比例下降到31.9%.高Fe3+濃度下會在厭氧氨氧化菌細胞內(nèi)誘發(fā)類芬頓反應 ,導致厭氧氨氧化菌死亡[33].Wang等[51]發(fā)現(xiàn),在投加50, 1000mg/LnZVI的厭氧氨氧化反應器中,相對豐度分別為52.5%和45.3%,優(yōu)勢厭氧氨氧化菌屬的含量分別提高了46.5%和37.9%.因此,針對不同形態(tài)的鐵,其最佳的投加量是鐵強化厭氧氨氧化技術(shù)未來研究的重要內(nèi)容之一.

2.3.2 促進其他功能菌富集 Yang等[50]指出,添加ZVI反應一段時間后,與接種污泥相比AOB(氨氧化細菌)的相對豐度(10.3%)顯著高于對照組(3.0%).王海月等[52]報道,分別添加2.24,4.48,7.84mg/L Fe3+的厭氧氨氧化反應器中反硝化菌屬的相對豐度均有所增加,且Fe3+投加量越多其相對豐度增加越高.此外, Zhang等[53]發(fā)現(xiàn),當nZVI的添加量為5mg/L時,的相對豐度由6.6%增加到10.6%,和的相對豐度分別由31.6%下降到27.1%和10.4%下降到7.5%.而當nZVI的進水濃度增加到20mg/L時,的相對豐度下降至7.5%,和的相對豐度分別增加到31.1%和5.7%.、和等異養(yǎng)微生物常與厭氧氨氧化菌共存,它們可以分解厭氧氨氧化菌產(chǎn)生的胞外蛋白、多肽及細胞碎片等,并通過NO3-還原和交互共生作用促進厭氧氨氧化細菌生長代謝[54].例如厭氧氨氧化菌不具有合成葉酸的能力,而參與了葉酸合成.具有參與大部分磷酸碳水化合物合成的能力,但缺少糖核苷酸生物合成的能力,而厭氧氨氧化菌具有大量糖核苷酸生物合成途徑相關(guān)功能基因.這些微生物在次級代謝物生物合成、碳水化合物代謝、細胞外蛋白質(zhì)和肽降解以及部分反硝化方面的潛力與厭氧氨氧化菌的代謝潛力相輔相成[55].

此外,還可促進微生物細胞聚集與顆粒污泥完整.因此,鐵的投加可以通過調(diào)節(jié)系統(tǒng)中、等共生細菌的豐度,促進厭氧氨氧化菌的生長代謝、厭氧氨氧化顆粒污泥的形成以及提高厭氧氨氧化系統(tǒng)的脫氮效能.外源添加鐵還可以提高部分Feammox菌豐度,例如和.Zhu等[56]研究表明,在厭氧氨氧化系統(tǒng)中添加Fe3+化合物,可以促進顯著富集.此外,Yang等[57]也有類似的發(fā)現(xiàn),添加了高鐵水合礦石的厭氧氨氧化系統(tǒng)中相對豐度由0.004%增長到0.05%,使系統(tǒng)脫氮效能得到提升.Yang等[50]研究報道添加ZVI一段時間后,異養(yǎng)微生物顯著富集,其相對豐度與對照組相比增加12.4%.因此,鐵對厭氧氨氧化反應體系的影響不應僅聚焦于鐵對厭氧氨氧化菌的豐度的改變,還應重視鐵對厭氧氨氧化反應器中其他功能微生物豐度的影響.

2.4 改變厭氧氨氧化菌細胞的結(jié)構(gòu)

圖2 厭氧氨氧化過程中Fe促進血紅素c合成模型[12]

張蕾等[58]發(fā)現(xiàn),添加鐵離子可以改變厭氧氨氧化細菌的細胞結(jié)構(gòu),促使細胞內(nèi)出現(xiàn)灰色區(qū)域.這一區(qū)域可能是儲存有大量納米鐵顆粒的厭氧氨氧化體,在這里鐵以球形中空蛋白質(zhì)復合物的形式儲存[59].如圖2所示,厭氧氨氧化菌胞內(nèi)鐵濃度過低會抑制血紅素b和Fe-S蛋白的合成,影響微生物正常生理活動,但鐵濃度過高亦會導致微生物氧化損傷,因此厭氧氨氧化體內(nèi)的納米鐵顆?？赡軈⑴c了厭氧氨氧化菌胞內(nèi)鐵濃度穩(wěn)態(tài)的維持[16].Niftrik等[60]報道厭氧氨氧化細菌體內(nèi)具有和這2個與鐵貯存相關(guān)的基因,鐵可以以無機礦物的形式儲存于胞內(nèi).由于厭氧氨氧化菌缺乏將鐵蛋白轉(zhuǎn)運厭氧氨氧化體的通道,因此有學者提出厭氧氨氧化體可能與在細菌和古生菌體內(nèi)發(fā)現(xiàn)的膠囊蛋白功能類似,即可利用蛋白質(zhì)室對其生理代謝營養(yǎng)物質(zhì)儲存進行空間調(diào)控,并為特定的生理過程創(chuàng)造獨特的微環(huán)境[61-62].目前,雖觀察到了鐵進入?yún)捬醢毖趸w的途徑,但是對于血紅素降解和鐵從厭氧氨氧化體中輸出的機制尚不明確[12].

2.5 調(diào)控關(guān)鍵酶、功能基因等表達

2.5.1 調(diào)控系統(tǒng)脫氮基因表達 外源鐵的添加對厭氧氨氧化系統(tǒng)中硝化反應(AOA-AOB-)、反硝化反應()、異化硝酸鹽還原()等相關(guān)基因的表達有顯著影響[53].Shu等[63]實驗結(jié)果表明,低濃度Fe2+(1.12～3.36mg/L)可以提高厭氧氨氧化體系中AOA-AOB-基因的豐度和反硝化微生物活性.Fe對厭氧氨氧化系統(tǒng)中反硝化過程相關(guān)基因表達的影響較為復雜. Bi等[39]證實添加了Fe0的厭氧氨氧化系統(tǒng)中拷貝數(shù)明顯增多,酶活性隨Fe/NO3-比例升高而增強.同時,Nap的功能基因表達明顯增強,而且在反應過程中始終可以檢測到酶功能基因的表達,這表明Fe0的投加可以促進反硝化菌生長.但Bi等[19]的實驗結(jié)果指出,施加鐵后基因豐度下降,基因豐度顯著上升,反硝化微生物活性減弱,反硝化作用可能不是引起系統(tǒng)中硝酸鹽減少的主要原因.這與Chen等[64]觀點一致,Chen等指出反應器中反硝化細菌的豐度未顯著增加,因此可能是異化硝酸鹽還原為氨(DNRA)反應利用Fe2+作為電子供體將硝酸鹽轉(zhuǎn)化為亞硝酸鹽和氨.

2.5.2 強化厭氧氨氧化菌關(guān)鍵酶和輔因子活性 外源Fe的添加還可以提高厭氧氨氧化相關(guān)功能基因的豐度.肼合成酶是厭氧氨氧化菌必需的功能酶,其合成需要這3個功能基因參與,添加Fe可以顯著提高的豐度,促進HZS的合成[65].厭氧氨氧化能量代謝極度依賴血紅素c和Fe-S簇這兩類輔因子[66].如圖3所示,低濃度的Fe3+可以使三價鐵還原酶(fhuF)和鐵攝取(FeoA、FeoB和fur)相關(guān)的基因表達顯著上調(diào),從而導致更多的血紅素c合成、HDH酶活性和SAA的提高[33].

Zhang等[53]研究表明加入低濃度的Fe3+(10mg/L)的反應器中血紅素c含量與酶HDH活性顯著增加,而加入高濃度的Fe3+(100mg/L)的反應器中血紅素c含量與HDH活性顯著降低.有研究表明,HDH氧化肼會生成氮氣,為亞硝酸鹽還原和肼合成提供電子,HDH還可能是負責將N2H4轉(zhuǎn)化為最終N2的關(guān)鍵酶[67](圖3).因此在實際運行過程中需要靈活變換添加Fe的形態(tài),通過短期添加Fe2+與鐵氧化物反應以恢復傳質(zhì)效果、強化電子傳遞過程、加速硝酸鹽還原[68-70].最近,Shaw等[71]證實厭氧氨氧化菌具有電活性,可以將氨氮氧化過程中釋放的電子傳遞至胞外不溶性電子受體,而鐵基材料和鐵氧化物可能可以成為充當電子受體的角色.該過程無需NO2-,對氨氮廢水的節(jié)能(甚至產(chǎn)能)處理具有重要意義.

圖3 厭氧氨氧化過程中Fe調(diào)控酶活性提高系統(tǒng)脫氮效率機理

2.6 強化厭氧氨氧化菌信號分子傳遞和群體感應

混合菌群中微生物之間依靠群體感應傳遞信號,以此調(diào)節(jié)微生物間的生理活動,抵抗外界不良因素的影響[72].環(huán)二鳥苷酸(c-di-GMP)是一種群體感應信號分子,如圖4所示,厭氧氨氧化菌吸收的鐵離子不僅使基因的豐度顯著增加還使基因的豐度降低,因此添加nZVI可以提高c-di-GMP合成酶的豐度,降低c-di-GMP降解蛋白豐度從而促進c-di-GMP的合成.

c-di-GMP參與細菌分裂抑制蛋白的水解,加速厭氧氨氧化菌的分裂,從而增加厭氧氨氧化菌的豐度. Wang等[51]研究證實,添加50mg/L的nZVI后厭氧氨氧化菌()的相對豐度從42.1%增長到52.5%. c-di-GMP的富集還可以降低反應器內(nèi)微生物的運動性,促進細菌分泌EPS,有利于厭氧氨氧化反應器內(nèi)污泥顆粒的形成[73-74].

此外添加鐵還可以使反應器上清液中含有群體感應信號C12-HSL,可以縮短厭氧氨氧化反應器啟動時間17.5%,提高氮負荷率60%[75].

圖4 鐵通過促進c-di-GMP合成調(diào)控厭氧氨氧化菌生理活動示意[51]

2.7 強化反應器中非生物途徑

Chen等[64]研究指出,在添加Fe2+的反應器中ΔNO3--N/ΔNH4+-N比低于理論值,且隨Fe2+濃度的增加而降低.這一現(xiàn)象在其他報道中也有出現(xiàn).然而,這些反應器中的反硝化細菌數(shù)量與Fe3+反應器相比沒有明顯變化.雖然Fe2+與硝酸鹽的反應在熱力學上是可行的,但不會自發(fā)進行.該反應受到pH值和Fe2+/NO2-物質(zhì)的量比的影響,其反應機理和最終產(chǎn)物仍需研究[76].生物脫氮過程中N2O主要由硝化反硝化反應產(chǎn)生,N2O不參與厭氧氨氧化細菌的代謝,因此,在氧氣和有機物缺乏的厭氧氨氧化系統(tǒng)中N2O的產(chǎn)率受到抑制[77-78].但是,從不同F(xiàn)e2+濃度的反應器中檢測到N2O釋放,其產(chǎn)量與反應時間和Fe投加量呈正相關(guān),這意味著Fe2+可以通過該化學反應(4Fe2++ 2NO2–+ 5H2O → 4FeOOH + N2O + 6H+)促進N2O的產(chǎn)生,提高反應器的脫氮效率[79].

鐵的物理特性可以促進厭氧氨氧化菌生長和厭氧氨氧化污泥顆粒形成.李天皓等[80]在實驗中觀察到大量球狀菌附著在廢鐵屑溝壑處,這表明廢鐵屑表面粗糙且存在大量溝壑,可為厭氧氨氧化菌提供棲息空間.可溶性Fe2+和Fe3+會通過鹽橋效應使更多厭氧氨氧化菌聚集,從而促進厭氧氨氧化污泥顆?；痆35].

3 結(jié)論與展望

3.1 適量的鐵的投加對厭氧氨氧化菌有明顯的促進作用,投加鐵可以優(yōu)化厭氧氨氧化菌的生長環(huán)境,提高厭氧氨氧化體系中浮霉門菌的相對豐度和厭氧氨氧化菌的活性,促進厭氧氨氧化菌分泌EPS.但是鐵輔助厭氧氨氧化工藝內(nèi)氮轉(zhuǎn)化途徑極其復雜,優(yōu)勢厭氧氨氧化菌各有不同,再加上影響因素眾多,目前尚無統(tǒng)一、明確的機理解釋,有待深入研究.

3.2 厭氧氨氧化系統(tǒng)中鐵的氧化還原也常有報道,鐵氧化物是否可以替代氧化石墨烯或碳基電極作為胞外電子受體,輔助厭氧氨氧化細菌完成胞外呼吸并氧化NH3有待研究.

3.3 在實際運用過程中鐵輔助厭氧氨氧化工藝中抑制現(xiàn)象經(jīng)常發(fā)生,這與鐵投加量、鐵的種類、工藝運行條件等密切相關(guān),投加不同的類型的鐵,最適量也不同,過量添加鐵會對厭氧氨氧化菌產(chǎn)生毒性,抑制厭氧氨氧化菌活性,甚至使厭氧氨氧化菌失活. 對此文獻報道結(jié)論不一,有待進一步研究.

3.4 工程推廣時鐵離子、納米零價鐵及特殊的鐵材料長期持續(xù)投加成本高,鐵來源需要優(yōu)化,廢鐵屑作為一種經(jīng)濟易得的工業(yè)副產(chǎn)物,相較于以往研究中直接添加零價鐵及其衍生物,具有持續(xù)的、緩慢的釋放鐵離子的優(yōu)點,實現(xiàn)廢物資源化利用.

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Research progress on the mechanisms of iron-assisted anaerobic ammonia oxidation process.

WANG Qian1, HU Jia-yuan1, LI Tian-hao1, WANG Cai-xia1, CHEN Jie1, SHEN Yao-liang1,2, LIU Wen-ru1,2*

(1.School of Environmental Science and Engineering, Suzhou University of Science and Technology, Suzhou 215000, China；2.National and Local Joint Engineering Laboratory for Municipal Sewage Resource Utilization Technology, Suzhou University of Science and Technology, Suzhou 215000, China)., 2022,42(11)：5153～5162

How to promote the proliferation and metabolism of anammox bacteria, improve the nitrogen removal efficiency of anammox process, and ensure the long-term stable operation of the process are the hotspots of anammox research. Iron-assisted anammox is the most widely studied measure with high economical and practical potential. This paper briefly describes the iron-assisted anammox technology and its nitrogen removal performance. The mechanisms of iron-assisted anammox process in promoting anammox cells growth and enhancing systems nitrogen removal performance are summarized from the aspects of optimizing the habitats of anammox bacteria, stimulating the secretion of extracellular polymer, accelerating the accumulation of denitrification functional bacteria, inducing the evolution of cell microstructure, regulating the expression of key enzymes and functional genes, promoting signal molecular synthesis, and enhancing abiotic nitrogen removal. Finally, the iron-assisted anammox technology is summarized and prospected, and the concept of waste iron scrap-anammox process is proposed.

anaerobic ammonia oxidation；iron；enhanced nitrogen removal；mechanism

X703

A

1000-6923(2022)11-5153-10

王 倩(1998-),女,安徽蕪湖人,蘇州科技大學碩士研究生,研究方向為廢水處理及其資源化.發(fā)表論文3篇.

2022-04-10

國家自然科學基金項目(51808367);城市生活污水資源化利用技術(shù)國家地方聯(lián)合工程實驗室開放課題項目(2018KF05);江蘇省研究生科研創(chuàng)新計劃(KYCX20_2778)

* 責任作者, 副教授, liuwenru1987@126.com