李 佳,李夕耀,張 瓊,彭永臻

投加羥胺原位恢復(fù)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(yè)大學(xué),城鎮(zhèn)污水深度處理與資源化利用國(guó)家工程實(shí)驗(yàn)室,北京市污水脫氮除磷處理與過程控制工程技術(shù)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(yīng)用于城市污水處理的關(guān)鍵.以因NOB大量增長(zhǎng)受到破壞的城市污水PN/A系統(tǒng)為對(duì)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(duì)其恢復(fù)的效果.結(jié)果顯示,當(dāng)序批式反應(yīng)器中初始NH2OH投加濃度為10mg/L時(shí),每天投加1次,連續(xù)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(fù)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(shí)繼續(xù)投加5d NH2OH (10mg/L),PN/A工藝運(yùn)行良好,因此間歇投加NH2OH可以維持PN/A工藝穩(wěn)定運(yùn)行.實(shí)時(shí)定量PCR結(jié)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(tài)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(zhuǎn)化為氮?dú)?N2)[1-2].與傳統(tǒng)硝化-反硝化脫氮工藝相比,此工藝?yán)碚撋峡晒?jié)省60%的曝氣量,100%的碳源[3-4].然而,在研究中發(fā)現(xiàn),低氨氮城市污水PN/A工藝很容易出現(xiàn)亞硝酸鹽氧化菌(NOB)的大量增長(zhǎng)所導(dǎo)致的系統(tǒng)運(yùn)行惡化[5-6].

NOB會(huì)與Anammox競(jìng)爭(zhēng)底物NO2--N,從而導(dǎo)致出水硝態(tài)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(yīng)用于污水處理的關(guān)鍵在于有效的抑制或淘洗NOB[7-8].目前,已經(jīng)有許多在PN/A系統(tǒng)中解決NOB的增長(zhǎng)的策略,如重新接種不含NOB的污泥、加大排泥量、降低系統(tǒng)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(fù)PN/A工藝[9-11].羥胺(NH2OH)是硝化和厭氧氨氧化2個(gè)過程的中間產(chǎn)物,可以成功啟動(dòng)短程硝化[12-15],提高Anammox的活性[16-17].但以NH2OH恢復(fù)一體化PN/A工藝鮮有報(bào)道.

本研究采用序批式反應(yīng)器(SBR),以因NOB大量增長(zhǎng)受到破壞的城市污水PN/A系統(tǒng)為對(duì)象,研究了投加NH2OH恢復(fù)PN/A工藝的適宜濃度及投加策略,通過測(cè)定SBR系統(tǒng)硝態(tài)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(fù)的微生物學(xué)機(jī)制.

1 材料與方法

1.1 反應(yīng)裝置及接種污泥

試驗(yàn)采用敞口圓柱體SBR反應(yīng)器(圖1),材質(zhì)為有機(jī)玻璃,有效容積10L.反應(yīng)器用黑色遮光材料包裹,避光運(yùn)行.為保證反應(yīng)階段泥水充分混合及傳質(zhì)均勻,反應(yīng)器設(shè)有攪拌裝置;曝氣采用曝氣泵和曝氣頭實(shí)現(xiàn),由轉(zhuǎn)子流量計(jì)控制DO為0.2~0.5mg/L;反應(yīng)器中配有便攜式檢測(cè)儀(WTW340i, Germany),監(jiān)測(cè)反應(yīng)過程中的DO、pH值和溫度變化;設(shè)置有加熱棒,以保證反應(yīng)器內(nèi)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(fù)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(zhì)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(fā)性懸浮固體濃度為4980mg/L.

圖1 SBR實(shí)驗(yàn)裝置示意

1.進(jìn)水箱;2.蠕動(dòng)泵;3.SBR反應(yīng)器;4.出水箱;5.DO、pH和溫度在線監(jiān)測(cè)儀;6.曝氣泵;7.流量計(jì);8.曝氣頭;9.攪拌器;10.加熱棒;11.電動(dòng)排水閥;12.取樣口

1.2 進(jìn)水水質(zhì)及運(yùn)行方式

試驗(yàn)用水為北京市某家屬區(qū)化糞池實(shí)際生活污水,污水先經(jīng)過前端預(yù)處理后再進(jìn)入SBR反應(yīng)器.具體水質(zhì):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(tǒng)運(yùn)行階段

反應(yīng)器每周期進(jìn)水5L,排水比為50%,污泥齡為10d(只排絮體污泥).每周期運(yùn)行方式為:進(jìn)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(yàn)過程分為A~I9個(gè)階段(表1),在階段B、D、F和H時(shí)向SBR反應(yīng)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(yīng)器好氧階段初始時(shí)NH2OH濃度. NH2OH通過加藥泵投加,每天投加1次.

1.3 檢測(cè)指標(biāo)及方法

水樣經(jīng)0.45μm中速濾紙過濾后測(cè)定各參數(shù). NH4+-N、NO2--N和NO3--N采用Lachat Quikchem 8500型流動(dòng)注射儀測(cè)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(cè)定[18];MLSS與MLVSS采用標(biāo)準(zhǔn)方法測(cè)定[19]; DO、pH值和溫度采用便攜式檢測(cè)儀(WTW340i, Germany)檢測(cè).

通過一系列的批次試驗(yàn)測(cè)定功能菌AOB、NOB和Anammox的活性[20],試驗(yàn)條件如表2所示.采用實(shí)時(shí)定量PCR(real-time qPCR)對(duì)微生物的種群結(jié)構(gòu)進(jìn)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(jì)(NanoDrop Technologies,Wilmington, USA)測(cè)定DNA的質(zhì)量和數(shù)量;real-time qPCR采用MX 3500p熒光實(shí)時(shí)定量PCR擴(kuò)增儀測(cè)定(Agilent Technologies, USA).每個(gè)樣品設(shè)立平行,取均值,最終以每克干污泥中菌的基因拷貝數(shù)表示菌的含量.擴(kuò)增所用引物及其核苷酸序列見表3.

表2 微生物活性測(cè)定的批次實(shí)驗(yàn)條件

表3 real-time qPCR所用的引物及核苷酸序列

2 結(jié)果與討論

2.1 NH2OH投加對(duì)PN/A工藝的恢復(fù)

如圖2中階段A所示,運(yùn)行初期出水的NO3--N濃度逐漸升高,運(yùn)行14d后,系統(tǒng)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(yīng)器運(yùn)行的第44d,ΔNO3--N/ΔNH4+-N升高至0.86(圖2),PN/A工藝運(yùn)行失穩(wěn).此時(shí),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(jìng)爭(zhēng)上處于劣勢(shì)地位.在階段B(第46~55d),向反應(yīng)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(tǒng)中ΔNO3--N/ΔNH4+-N僅下降至0.63,PN/A工藝未恢復(fù)到較好狀態(tài).

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(yùn)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(fù),但是NH2OH濃度為4.5mg/L對(duì)PN/A工藝的恢復(fù)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(yīng)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(nèi)快速恢復(fù).

圖2 SBR中氮素污染物濃度(a)和硝態(tài)氮生成比例(b)變化

由于階段E(第86~104)進(jìn)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(jìn)水波動(dòng)的影響從14.5mgN/(VSS·h)(第74d)下降至6.8mgN/VSS/h(第101d),水質(zhì)波動(dòng)會(huì)影響硝化菌的活性[26].此時(shí),即使適當(dāng)延長(zhǎng)曝氣時(shí)間(從60min延長(zhǎng)到150min),出水NH4+-N仍然由(1.1±0.8) mgN/L增長(zhǎng)為(26.6±5.6) mgN/L.為了恢復(fù)AOB的活性,從第98d繼續(xù)延長(zhǎng)曝氣時(shí)間到300min,運(yùn)行5d后出水NH4+-N下降到0.6mgN/L.但是隨著硝化效果的轉(zhuǎn)好,剛剛恢復(fù)的短程硝化又因過度曝氣而破環(huán),系統(tǒng)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(duì)于短程硝化具有很強(qiáng)的破壞作用[27-28],尤其對(duì)于還未運(yùn)行穩(wěn)定的短程硝化.

圖3 反應(yīng)器中功能菌活性變化

在階段F(第105~124d)繼續(xù)投加NH2OH (10mg/L)以恢復(fù)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(shí)ΔNO3--N/ΔNH4+-N為0.11,PN/A工藝恢復(fù).此試驗(yàn)結(jié)果與階段D相似,進(jìn)一步驗(yàn)證了NH2OH對(duì)PN/A工藝恢復(fù)的有效性.在階段G(第125~183d), PN/A工藝運(yùn)行穩(wěn)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(wěn)定在0.10±0.02.ΔNO3--N/ΔNH4+-N略低于理論值,表明系統(tǒng)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(zhǎng)期缺少底物而失活的情況下較快的恢復(fù)活性,有文獻(xiàn)報(bào)道向在4℃條件下長(zhǎng)期儲(chǔ)存的Anammox系統(tǒng)中投加NH2OH,有利于血紅素含量的提高,進(jìn)而快速恢復(fù)Anammox的活性[17].在階段G末期(第183d) ΔNO3--N/ΔNH4+-N又有小幅的增長(zhǎng)(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(yùn)行良好.因此,短期的NH2OH投加并不能維持PN/A工藝的長(zhǎng)久穩(wěn)定,其它研究也有相同的結(jié)論[30],但間歇投加NH2OH的策略可以使NOB持續(xù)受到抑制,從而維持PN/A工藝的長(zhǎng)久穩(wěn)定運(yùn)行.

2.2 PN/A工藝恢復(fù)前后的典型周期分析

分析PN/A工藝破壞(第37d)和恢復(fù)(第150d)的典型周期內(nèi)氮素污染物濃度、pH值、DO和溫度變化.如圖4所示,反應(yīng)過程中pH值在6.6~7.4之間變化,反應(yīng)初的pH值受進(jìn)水水質(zhì)的影響而不同.反應(yīng)器中溫度均逐漸升高并維持在30℃左右.在好氧階段,2個(gè)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?yōu)?7.88mgN/L,NO2--N為0.42mgN/L, NO3--N因上周期反應(yīng)末的剩余由0.51mgN/L變?yōu)?.95mgN/L.在缺氧攪拌階段,反硝化菌利用進(jìn)水中的有機(jī)物進(jìn)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(yīng)過程ΔNO3--N/ΔNH4+-N為0.74,遠(yuǎn)大于理論值0.11,TN去除率僅為23.0%,說明Anammox氮去除途徑發(fā)揮的作用很小,短程硝化的破壞使PN/A工藝失穩(wěn)而脫氮性能下降.

圖4(b)為PN/A工藝通過投加NH2OH策略恢復(fù)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(yīng)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(jìn)水中的NH4+-N進(jìn)一步進(jìn)行厭氧氨氧化反應(yīng),PN/A工藝呈現(xiàn)較好的運(yùn)行狀態(tài).

2.3 NH2OH投加后系統(tǒng)微生物種群結(jié)構(gòu)變化

為了進(jìn)一步了解系統(tǒng)運(yùn)行狀態(tài),對(duì)反應(yīng)器中各功能菌AOB、NOB(和之和)及Anammox豐度進(jìn)行了測(cè)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(shí)ΔNO3--N/ΔNH4+-N大幅度上升(圖2).因此NOB豐度的大量增長(zhǎng)導(dǎo)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(duì)應(yīng)(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(shù)量不斷下降,最終降低為(3.03± 0.11)×107copies/g VSS(第157d).系統(tǒng)中NOB活性受到抑制或菌種被淘洗對(duì)于PN/A工藝的穩(wěn)定性非常關(guān)鍵[31].本試驗(yàn)結(jié)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(zhǎng),從而在排泥條件下實(shí)現(xiàn)菌種淘洗[13-14],以恢復(fù)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(dāng)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(yīng)的緩解措施[32].有文獻(xiàn)報(bào)道,在反應(yīng)器中加入NH2OH后的拷貝數(shù)下降了一個(gè)數(shù)量級(jí)[33].因此,NH2OH的這種抑制作用可能是因?yàn)槠鋵?duì)NOB中NXR的活性表達(dá)或合成過程的抑制[13].

圖5 反應(yīng)器中功能菌豐度變化

在運(yùn)行中AOB的豐度呈現(xiàn)小幅波動(dòng),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(shí)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(yùn)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(yùn)行的不穩(wěn)定性,即短程硝化的不斷破壞,使得Anammox底物缺失,長(zhǎng)期處于饑餓狀態(tài),同時(shí)Anammox的有效持留也是PN/A工藝運(yùn)行的關(guān)鍵點(diǎn)之一[35].

3 結(jié)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(tǒng)ΔNO3—N/ ΔNH4+-N逐漸降低至理論值0.11.表明NH2OH可快速原位恢復(fù)PN/A工藝.

3.2 NH2OH投加停止59d后,反應(yīng)器出水NO3--N再次出現(xiàn)積累趨勢(shì),此時(shí)繼續(xù)投加5dNH2OH,PN/A工藝運(yùn)行良好,因此間歇投加NH2OH是一種維持PN/A工藝的穩(wěn)定運(yùn)行的有效策略.

3.3 實(shí)時(shí)定量PCR結(jié)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(yè)大學(xué)碩士研究生,主要從事污水生物處理理論與應(yīng)用研究.

2018-12-03

北京市科技計(jì)劃(D171100001017001);北京市教委資助項(xiàng)目

* 責(zé)任作者, 教授, pyz@bjut.edu.cn