投加羥胺原位恢復城市污水短程硝化-厭氧氨氧化工藝

李 佳,李夕耀,張 瓊,彭永臻

投加羥胺原位恢復城市污水短程硝化-厭氧氨氧化工藝

李 佳,李夕耀,張 瓊,彭永臻*

(北京工業大學,城鎮污水深度處理與資源化利用國家工程實驗室,北京市污水脫氮除磷處理與過程控制工程技術研究中心,北京 100124)

有效抑制或淘洗亞硝酸鹽氧化菌(NOB)是短程硝化-厭氧氨氧化(PN/A)工藝應用于城市污水處理的關鍵.以因NOB大量增長受到破壞的城市污水PN/A系統為對象(硝酸鹽(NO3--N)生成比例為0.90),考察了羥胺(NH2OH)投加濃度和投加方式對其恢復的效果.結果顯示,當序批式反應器中初始NH2OH投加濃度為10mg/L時,每天投加1次,連續投加20d后,NO3--N生成量占NH4+-N消耗量的比例由0.90逐步降低至0.11.表明NH2OH(10mg/L)可原位恢復PN/A工藝.NH2OH停止投加59d后,出水NO3--N生成比例再次小幅度上升至0.15,此時繼續投加5d NH2OH (10mg/L),PN/A工藝運行良好,因此間歇投加NH2OH可以維持PN/A工藝穩定運行.實時定量PCR結果表明,在投加NH2OH (10mg/L)后,NOB的豐度不斷下降,從(4.52±0.44)×1010copies/g VSS(第6d)下降到(2.30±0.80)×109copies/g VSS(第157d),說明NH2OH的投加有利于抑制和淘洗NOB.

羥胺(NH2OH)；短程硝化-厭氧氨氧化(PN/A)；NOB；城市污水

短程硝化-厭氧氨氧化(PN/A)的脫氮過程為:好氧條件下,原水中部分氨氮(NH4+-N)被氨氧化菌(AOB)氧化為亞硝態氮(NO2--N),生成的NO2--N繼而與NH4+-N在厭氧氨氧化菌(Anammox)的作用下轉化為氮氣(N2)[1-2].與傳統硝化-反硝化脫氮工藝相比,此工藝理論上可節省60%的曝氣量,100%的碳源[3-4].然而,在研究中發現,低氨氮城市污水PN/A工藝很容易出現亞硝酸鹽氧化菌(NOB)的大量增長所導致的系統運行惡化[5-6].

NOB會與Anammox競爭底物NO2--N,從而導致出水硝態氮(NO3--N)的積累,以至PN/A工藝脫氮性能的下降.因此,PN/A工藝成功應用于污水處理的關鍵在于有效的抑制或淘洗NOB[7-8].目前,已經有許多在PN/A系統中解決NOB的增長的策略,如重新接種不含NOB的污泥、加大排泥量、降低系統溶解氧(DO)和采用間歇曝氣方式等,然而這些策略均不能有效的抑制或淘洗NOB,恢復PN/A工藝[9-11].羥胺(NH2OH)是硝化和厭氧氨氧化2個過程的中間產物,可以成功啟動短程硝化[12-15],提高Anammox的活性[16-17].但以NH2OH恢復一體化PN/A工藝鮮有報道.

本研究采用序批式反應器(SBR),以因NOB大量增長受到破壞的城市污水PN/A系統為對象,研究了投加NH2OH恢復PN/A工藝的適宜濃度及投加策略,通過測定SBR系統硝態氮生成比例及功能菌活性和豐度變化,分析了PN/A工藝原位恢復的微生物學機制.

1 材料與方法

1.1 反應裝置及接種污泥

試驗采用敞口圓柱體SBR反應器(圖1),材質為有機玻璃,有效容積10L.反應器用黑色遮光材料包裹,避光運行.為保證反應階段泥水充分混合及傳質均勻,反應器設有攪拌裝置;曝氣采用曝氣泵和曝氣頭實現,由轉子流量計控制DO為0.2~0.5mg/L;反應器中配有便攜式檢測儀(WTW340i, Germany),監測反應過程中的DO、pH值和溫度變化;設置有加熱棒,以保證反應器內溫度在30℃左右.

接種污泥為短程硝化絮體污泥和厭氧氨氧化顆粒污泥,接種前短程硝化絮體污泥的亞硝酸鹽氮積累率平均為96.9%,厭氧氨氧化顆粒污泥總氮去除負荷平均為0.5kgN/(m3×d).短程硝化污泥與厭氧氨氧化顆粒污泥按質量比1:2的比例混合,接種后的混合液懸浮固體濃度為6000mg/L,混合液揮發性懸浮固體濃度為4980mg/L.

圖1 SBR實驗裝置示意

1.進水箱;2.蠕動泵;3.SBR反應器;4.出水箱;5.DO、pH和溫度在線監測儀;6.曝氣泵;7.流量計;8.曝氣頭;9.攪拌器;10.加熱棒;11.電動排水閥;12.取樣口

1.2 進水水質及運行方式

試驗用水為北京市某家屬區化糞池實際生活污水,污水先經過前端預處理后再進入SBR反應器.具體水質:COD為55.7~128.2mg/L,NH4+-N濃度為25.8~83.5mgN/L,NO2--N和NO3--N濃度均小于1.0mgN/L,pH值7.1~7.6.

表1 系統運行階段

反應器每周期進水5L,排水比為50%,污泥齡為10d(只排絮體污泥).每周期運行方式為:進水10min,缺氧攪拌30min,好氧曝氣60~300min,沉淀30min,排水10min, 閑置40~100min.試驗過程分為A~I9個階段(表1),在階段B、D、F和H時向SBR反應器中投加NH2OH,其中階段B投加的NH2OH濃度為4.5mg/L,階段D、F和H為10mg/L.NH2OH濃度均為SBR反應器好氧階段初始時NH2OH濃度. NH2OH通過加藥泵投加,每天投加1次.

1.3 檢測指標及方法

水樣經0.45μm中速濾紙過濾后測定各參數. NH4+-N、NO2--N和NO3--N采用Lachat Quikchem 8500型流動注射儀測定(Lachat Instrument, Milwaukee, Wiscosin),TN為NH4+-N、NO2--N和NO3--N三者濃度之和;NH2OH采用羥基喹啉分光光度法測定[18];MLSS與MLVSS采用標準方法測定[19]; DO、pH值和溫度采用便攜式檢測儀(WTW340i, Germany)檢測.

通過一系列的批次試驗測定功能菌AOB、NOB和Anammox的活性[20],試驗條件如表2所示.采用實時定量PCR(real-time qPCR)對微生物的種群結構進行分析.泥樣DNA采用DNA快速提取試劑盒 (fast DNA spin kit for soil, Q BIOgene Inc., Carlsbad, USA) 提取,通過Nanodrop 分光光度計(NanoDrop Technologies,Wilmington, USA)測定DNA的質量和數量;real-time qPCR采用MX 3500p熒光實時定量PCR擴增儀測定(Agilent Technologies, USA).每個樣品設立平行,取均值,最終以每克干污泥中菌的基因拷貝數表示菌的含量.擴增所用引物及其核苷酸序列見表3.

表2 微生物活性測定的批次實驗條件

表3 real-time qPCR所用的引物及核苷酸序列

2 結果與討論

2.1 NH2OH投加對PN/A工藝的恢復

如圖2中階段A所示,運行初期出水的NO3--N濃度逐漸升高,運行14d后,系統ΔNO3--N/ΔNH4+-N大于理論值0.11[25],說明PN/A工藝被破壞.在SBR反應器運行的第44d,ΔNO3--N/ΔNH4+-N升高至0.86(圖2),PN/A工藝運行失穩.此時,如圖3所示,NOB的活性由0.62mgN/(VSS·h)(第1d)升高為5.9mgN/(VSS·h)(第40d),說明PN/A工藝中短程硝化破壞;Anammox的活性由15.9mgN/(VSS·h)(第1d)下降為3.3mgN/(VSS·h)(第40d),Anammox活性的下降可能是由于NOB活性的提高使其底物NO2--N缺失,這表明Anammox與NOB在底物競爭上處于劣勢地位.在階段B(第46~55d),向反應器中投加NH2OH,使SBR中初始NH2OH濃度為4.5mg/L,每天投加1次,投加10d后系統中ΔNO3--N/ΔNH4+-N僅下降至0.63,PN/A工藝未恢復到較好狀態.

在階段B停止投加NH2OH后,ΔNO3--N/ ΔNH4+-N又上升為0.90(第65d),且NOB的活性在運行第64d升高至8.6mgN/(VSS·h)(圖3),NH2OH的投加有助于PN/A工藝的恢復,但是NH2OH濃度為4.5mg/L對PN/A工藝的恢復效果較差.因此在階段D(第66~85d)提高NH2OH的投加濃度到10mg/L.如圖2所示,在提高NH2OH投加濃度后,SBR反應器出水NO3--N濃度明顯降低,ΔNO3--N/ΔNH4+-N由0.90(第65d)下降到0.11(第85d),并且NOB的活性下降為3.4mgN/(VSS·h)(圖3), NH2OH(10mg/L)的投加有效抑制了NOB的活性,使短程硝化過程在20d內快速恢復.

圖2 SBR中氮素污染物濃度(a)和硝態氮生成比例(b)變化

由于階段E(第86~104)進水NH4+-N的濃度突然大幅度升高(由(30.2±3.4) mgN/L上升為(60.3±7.3) mgN/L),AOB的活性受到進水波動的影響從14.5mgN/(VSS·h)(第74d)下降至6.8mgN/VSS/h(第101d),水質波動會影響硝化菌的活性[26].此時,即使適當延長曝氣時間(從60min延長到150min),出水NH4+-N仍然由(1.1±0.8) mgN/L增長為(26.6±5.6) mgN/L.為了恢復AOB的活性,從第98d繼續延長曝氣時間到300min,運行5d后出水NH4+-N下降到0.6mgN/L.但是隨著硝化效果的轉好,剛剛恢復的短程硝化又因過度曝氣而破環,系統ΔNO3--N/ ΔNH4+-N逐漸升高至0.95(第104d),NOB的活性上升至7.9mgN/(VSS·h)(第101d).可見過曝氣對于短程硝化具有很強的破壞作用[27-28],尤其對于還未運行穩定的短程硝化.

圖3 反應器中功能菌活性變化

在階段F(第105~124d)繼續投加NH2OH (10mg/L)以恢復PN/A工藝, 投加20d后(第124d)出水中的NO3--N濃度大幅度下降至5.75mgN/L,此時ΔNO3--N/ΔNH4+-N為0.11,PN/A工藝恢復.此試驗結果與階段D相似,進一步驗證了NH2OH對PN/A工藝恢復的有效性.在階段G(第125~183d), PN/A工藝運行穩定,出水NH4+-N為(1.7±0.8)mgN/ L,NO3--N為(5.2±1.0) mgN/L,ΔNO3--N/ΔNH4+-N穩定在0.10±0.02.ΔNO3--N/ΔNH4+-N略低于理論值,表明系統中存在微弱的反硝化作用,將小部分NO3--N還原為N2,提高了總氮去除率[29].從圖3中可以看出,Anammox活性隨著NOB活性的降低而逐漸提高,到第131d升高為10.2mgN/(VSS·h).NH2OH的投加可能有利于Anammox在長期缺少底物而失活的情況下較快的恢復活性,有文獻報道向在4℃條件下長期儲存的Anammox系統中投加NH2OH,有利于血紅素含量的提高,進而快速恢復Anammox的活性[17].在階段G末期(第183d) ΔNO3--N/ΔNH4+-N又有小幅的增長(ΔNO3--N/ΔNH4+-N為0.15),故在階段H(第184~189d)投加了5d的NH2OH(10mg/ L),PN/A工藝在階段I(第190~219d)運行良好.因此,短期的NH2OH投加并不能維持PN/A工藝的長久穩定,其它研究也有相同的結論[30],但間歇投加NH2OH的策略可以使NOB持續受到抑制,從而維持PN/A工藝的長久穩定運行.

2.2 PN/A工藝恢復前后的典型周期分析

分析PN/A工藝破壞(第37d)和恢復(第150d)的典型周期內氮素污染物濃度、pH值、DO和溫度變化.如圖4所示,反應過程中pH值在6.6~7.4之間變化,反應初的pH值受進水水質的影響而不同.反應器中溫度均逐漸升高并維持在30℃左右.在好氧階段,2個典型周期的DO均在0.2~0.5mg/L.

圖4(a)為PN/A工藝破壞的典型周期,NH4+-N濃度因上周期剩余泥水混合液的稀釋由34.07mgN/ L變為17.88mgN/L,NO2--N為0.42mgN/L, NO3--N因上周期反應末的剩余由0.51mgN/L變為4.95mgN/L.在缺氧攪拌階段,反硝化菌利用進水中的有機物進行將NO3--N反硝化為N2,30min后NO3--N濃度由4.95mgN/L降低為1.18mgN/L.在好氧階段,曝氣60min后NH4+-N由17.00mgN/L降低為1.17mgN/L(ΔNH4+-N為15.83mgN/L),NO3--N由1.18mgN/L上升為12.56mgN/L(ΔNO3--N為11.83mgN/L).反應過程ΔNO3--N/ΔNH4+-N為0.74,遠大于理論值0.11,TN去除率僅為23.0%,說明Anammox氮去除途徑發揮的作用很小,短程硝化的破壞使PN/A工藝失穩而脫氮性能下降.

圖4(b)為PN/A工藝通過投加NH2OH策略恢復后的典型周期.在好氧階段,曝氣120min后NH4+-N由29.45mgN/L降低為1.53mgN/L(ΔNH4+-N為27.92mgN/L),NO3--N由2.52mgN/L上升為5.49mgN/L(ΔNO3--N為2.97mgN/L),在反應過程中沒有NO2--N的積累.ΔNO3--N/ΔNH4+-N為0.11,即PN/A工藝NO3--N生成比例的理論值,TN去除率為76.8%.此典型周期說明NH4+-N大部分氧化NO2--N而非NO3--N,且生成的NO2--N與進水中的NH4+-N進一步進行厭氧氨氧化反應,PN/A工藝呈現較好的運行狀態.

2.3 NH2OH投加后系統微生物種群結構變化

為了進一步了解系統運行狀態,對反應器中各功能菌AOB、NOB(和之和)及Anammox豐度進行了測定.

從圖5中可以看出,NOB的豐度從第6d的(1.20±0.2)×107copies/g VSS上升到第44d的(2.65± 0.16)×108copies/g VSS,為原來的22倍左右, 此時ΔNO3--N/ΔNH4+-N大幅度上升(圖2).因此NOB豐度的大量增長導致了PN/A工藝破壞.在階段B(第46~50d)投加4.5mg/L的NH2OH后,NOB的豐度沒有下降,反而上升為(4.06±0.80) ×109copies/g VSS(第60d),這與NOB活性升高相對應(圖3).在階段D(第66~86d)和F(第105~124d),提高NH2OH投加濃度到10mg/L后,NOB數量不斷下降,最終降低為(3.03± 0.11)×107copies/g VSS(第157d).系統中NOB活性受到抑制或菌種被淘洗對于PN/A工藝的穩定性非常關鍵[31].本試驗結果表明,NH2OH(10mg/L)的投加不僅抑制了NOB的活性,還抑制了NOB的增長,從而在排泥條件下實現菌種淘洗[13-14],以恢復PN/A工藝.在硝化過程中,AOB在氨單加氧酶(AMO)和羥胺氧化還原酶(HAO)的催化作用下完成NH4+-N的氧化; NOB在亞硝酸鹽氧化還原酶(nitrite oxidoreductase enzyme, NXR)的催化作用下氧化NO2--N.當添加NH2OH后,AOB中HAO的存在可以分解NH2OH以減緩NH2OH的毒性,而在NOB的代謝過程中沒有相應的緩解措施[32].有文獻報道,在反應器中加入NH2OH后的拷貝數下降了一個數量級[33].因此,NH2OH的這種抑制作用可能是因為其對NOB中NXR的活性表達或合成過程的抑制[13].

圖5 反應器中功能菌豐度變化

在運行中AOB的豐度呈現小幅波動,但基本維持在(2.37±0.23)×109copies/g VSS之上,即使在AOB的活性顯著下降時豐度也并沒有明顯降低,這說明在不利條件下微生物的活性和豐度變化并不相一致[34].Anammox豐度在運行過程中逐漸降低,從(4.52±0.44)×1010copies/g VSS(第6d)下降到(2.30± 0.80)×109copies/g VSS(第157d).Anammox豐度的降低可能是由于PN/A工藝運行的不穩定性,即短程硝化的不斷破壞,使得Anammox底物缺失,長期處于饑餓狀態,同時Anammox的有效持留也是PN/A工藝運行的關鍵點之一[35].

3 結論

3.1 向SBR中每天投加1次NH2OH并使其初始NH2OH濃度為10mg/L,20d后系統ΔNO3—N/ ΔNH4+-N逐漸降低至理論值0.11.表明NH2OH可快速原位恢復PN/A工藝.

3.2 NH2OH投加停止59d后,反應器出水NO3--N再次出現積累趨勢,此時繼續投加5dNH2OH,PN/A工藝運行良好,因此間歇投加NH2OH是一種維持PN/A工藝的穩定運行的有效策略.

3.3 實時定量PCR結果表明,在投加NH2OH (10mg/L)后NOB的豐度不斷降低,從(4.52±0.44)× 1010copies/g VSS(第6d)下降到(2.30±0.80)× 109copies/g VSS(第157d),說明NH2OH的投加有利于抑制和淘洗NOB.

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In-situ restoring demostic wastewater partial nitritation/anammox (PN/A) process by addition of hydroxylamine.

LI Jia, LI Xi-yao, ZHANG Qiong, PENG Yong-zhen*

(National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology, Engineering Research Center of Beijing, Beijing University of Technology, Beijing 100124, China)., 2019,39(7)：2789~2795

The effective inhibition or wash-out of nitrite oxidizing bacteria (NOB) is the key challenge for the application of partial nitritation/anammox (PA/N) process in domestic wastewater treatment. The deteriorated domestic wastewater PN/A system was used to investigate the recovery effect of hydroxylamine (NH2OH) concentration and dosing mode on it. The nitrate (NO3--N) production ratio of the PN/A system was 0.90, which was due to the overgrowth of NOB. The results showed that when the initial NH2OH concentration was 10mg/L in the sequencing batch reactor (SBR) and NH2OH was added once a day, the ratio of NO3--Nproducted/NH4+-Nconsumedwas decreased from 0.90 to 0.11 after adding NH2OH for 20d. It indicated that NH2OH (10mg/L) addition could restore PN/A process-. The ratio of NO3--Nproducted/NH4+-Nconsumedincreased to 0.15 again after stopping NH2OH addition for 59d. When continued to add NH2OH into reactor for 5d, the PN/A process operated well. Therefore, the intermittent addition of NH2OH strategy could maintain the stable performance of the PN/A process. The real-time quantitative PCR results showed that the NOB abundance was decreased continuously from (4.52±0.44)×1010copies/g VSS (Day 6) to (2.30±0.80)×109copies/g VSS (Day 157) after NH2OH (10mg/L) addition. It indicated that NH2OH addition was beneficial to inhibit and wash out NOB.

hydroxylamin (NH2OH)；partial nitritation/anammox (PN/A)；NOB；demostic wastewater

X703

A

1000-6923(2019)07-2789-07

李 佳(1994-),女,河北保定人,北京工業大學碩士研究生,主要從事污水生物處理理論與應用研究.

2018-12-03

北京市科技計劃(D171100001017001);北京市教委資助項目

* 責任作者, 教授, pyz@bjut.edu.cn