王 琪,李 冬*,李鵬垚,陳曉義,張 杰,2

厭/缺氧時(shí)間對(duì)好氧顆粒污泥同步硝化內(nèi)源反硝化和除磷的影響

王 琪1,李 冬1*,李鵬垚1,陳曉義1,張 杰1,2

(1.北京工業(yè)大學(xué)水質(zhì)科學(xué)與水環(huán)境恢復(fù)工程北京市重點(diǎn)實(shí)驗(yàn)室,北京 100124；2.哈爾濱工業(yè)大學(xué)城市水資源與水環(huán)境國家重點(diǎn)實(shí)驗(yàn)室,黑龍江 哈爾濱 150090)

選用4組同規(guī)格SBR反應(yīng)器,在A/O/A模式下以水解酸化液為進(jìn)水,調(diào)整厭/缺氧時(shí)間分別為50min/170min、90min/130min、130min/90min、180min/40min,探討顆粒污泥在不同厭/缺氧時(shí)間下脫氮除磷特性.結(jié)果表明,厭氧時(shí)間從50min延長至90min時(shí),污泥內(nèi)碳源儲(chǔ)存量和釋磷量增加,同步硝化反硝化(SND)效率提高至62.65%,TN、TP去除率分別從81.1%、 82.2%上升92.9%、98.5%.當(dāng)厭氧時(shí)間從90min升至180min時(shí),釋磷量反而下降,厭氧內(nèi)源性條件刺激胞外聚合物(EPS)增加造成聚羥基烷酸(PHA)合成下降,TP去除率降至88.1%;同時(shí)缺氧時(shí)間從130min降至40min,系統(tǒng)殘留的NO-較多,造成TN去除率降低至84%.機(jī)理分析表明系統(tǒng)中TN在好氧段由反硝化聚磷菌(DPAOs)和反硝化聚糖菌(DGAOs)利用PHA以SND方式消耗,并在缺氧段由DGAOs內(nèi)源反硝化進(jìn)一步去除,TP由PAOs和DPAOs去除,由批次實(shí)驗(yàn)估算得DPAOs占比在R2中最高,達(dá)41%,4組反應(yīng)器運(yùn)行期間顆粒均未發(fā)生解體,以水解酸化液為基質(zhì)培養(yǎng)的顆粒結(jié)構(gòu)完整、穩(wěn)定性強(qiáng).結(jié)果表明,厭/缺氧時(shí)間的適當(dāng)延長有利于加強(qiáng)內(nèi)碳源的貯存與轉(zhuǎn)化,強(qiáng)化厭氧釋磷、SND和后置內(nèi)源反硝化效果,實(shí)現(xiàn)同步硝化內(nèi)源反硝化和除磷高效穩(wěn)定運(yùn)行.

SBR；好氧顆粒污泥；內(nèi)碳源；后置反硝化；反硝化聚磷菌；厭/缺氧時(shí)間

好氧顆粒污泥(AGS)內(nèi)部的層狀空間結(jié)構(gòu)可為微生物提供所需的好氧/缺氧/厭氧環(huán)境[1],同時(shí)厭氧/好氧/缺氧(A/O/A)模式運(yùn)行的序批式反應(yīng)器(SBR)在時(shí)間上為微生物提供不同環(huán)境[2-3],從而為同步脫氮除磷提供理想環(huán)境.He等[4]報(bào)道了在A/O/A模式下應(yīng)用SBR進(jìn)行同步硝化、內(nèi)源反硝化和除磷的可行性.

在SBR中內(nèi)碳源的儲(chǔ)存與利用效果對(duì)系統(tǒng)高效穩(wěn)定運(yùn)行有重要影響.有研究表明[5]厭氧條件下一些微生物通過吸收揮發(fā)性脂肪酸(VFA)轉(zhuǎn)化為細(xì)胞內(nèi)聚羥基烷酸(PHA)作為內(nèi)部電子供體和儲(chǔ)能化合物,若外部碳源不足,可分解胞內(nèi)聚合物進(jìn)行內(nèi)源性反硝化和吸磷,經(jīng)研究證實(shí)利用細(xì)胞內(nèi)碳源去除污染物過程可以降低能耗[6].PHA作為細(xì)胞的能量轉(zhuǎn)化中心,在不同微生物代謝中具有重要作用.如反硝化聚磷菌(DPAOs)能在厭氧條件下將體內(nèi)的聚磷(poly-P)水解為正磷酸鹽釋放到胞外,利用水解產(chǎn)生的ATP吸收VFA,合成PHA貯存于細(xì)胞內(nèi),在缺氧段以PHA為電子供體,NO-為電子受體反硝化吸磷,達(dá)到“一碳兩用”,進(jìn)一步節(jié)約碳源[7].而有研究發(fā)現(xiàn)由反硝化聚糖菌(DGAOs)利用PHA和糖原(Gly)驅(qū)動(dòng)內(nèi)源反硝化實(shí)現(xiàn)低C/N比廢水中氮的深度去除[8-9].為了提高脫氮除磷效果,呂冬梅等[10]通過延長厭氧時(shí)間發(fā)現(xiàn)細(xì)胞內(nèi)碳源的儲(chǔ)存增加,系統(tǒng)處理效果提高;Lemaire等[11]發(fā)現(xiàn)在厭氧/缺氧(A/A)運(yùn)行的系統(tǒng)中缺氧時(shí)間過短會(huì)使反硝化不徹底,相反,缺氧時(shí)間過長,微生物在缺氧后期缺乏電子供體造成活性下降,脫氮除磷效果不佳.而水解酸化液內(nèi)VFA含量豐富[12],作為進(jìn)水碳源時(shí)可供微生物合成PHA.并由以上可知,SBR中厭氧和缺氧時(shí)間會(huì)對(duì)脫氮除磷效果產(chǎn)生影響.

基于以上分析,本研究以水解酸化液為進(jìn)水基質(zhì),設(shè)置了4組同規(guī)格SBR反應(yīng)器,通過調(diào)整不同厭/缺氧時(shí)間,探討系統(tǒng)中污染物去除性能、去除路徑、污泥物理特性及胞外聚合物(EPS)分泌情況,以期為好氧顆粒污泥脫氮除磷性能的提升提供參考.

1 材料和方法

1.1 實(shí)驗(yàn)裝置與運(yùn)行方法

采用4套相同的有機(jī)玻璃制成的SBR反應(yīng)器R1、R2、R3和R4,每套SBR高50cm,內(nèi)徑14cm,高徑比3.5:1,工作體積為6L,換水比為60%,SBR采用A/O/A運(yùn)行模式,每天運(yùn)行4個(gè)周期,每周期運(yùn)行360min,包括進(jìn)水5min,厭氧/好氧/缺氧共340min,沉淀3min,排水5min,其余時(shí)間閑置,其中厭氧/好氧/缺氧具體時(shí)間如表1所示,好氧段時(shí)長設(shè)置為120min,曝氣強(qiáng)度維持在1.0L/min,并在SBR周期末沉降階段結(jié)束后手動(dòng)排泥,控制污泥齡為30d,實(shí)驗(yàn)共運(yùn)行45d.

表1 反應(yīng)器運(yùn)行參數(shù)

1.2 接種污泥及原水水質(zhì)

反應(yīng)器接種污泥是實(shí)驗(yàn)室前期培養(yǎng)穩(wěn)定運(yùn)行的成熟顆粒污泥,污泥濃度為3500mg/L,實(shí)驗(yàn)用水取自具有穩(wěn)定水解酸化性能的水解產(chǎn)酸前處理反應(yīng)器出水,水解酸化液具體水質(zhì)指標(biāo)如表2,用NaHCO3和NaOH調(diào)節(jié)pH值穩(wěn)定.

表2 水解酸化液水質(zhì)情況

注:COD主要VFA類物質(zhì)組成,VFA組成與含量(以COD濃度計(jì))如下:乙酸85～115(mg/L),丙酸25～35(mg/L),丁酸10 ～20(mg/L),異戊酸5～10(mg/L).

1.3 分析項(xiàng)目與檢測(cè)方法

采用標(biāo)準(zhǔn)方法對(duì)NH4+-N、NO2--N、NO3--N、MLSS和SVI等指標(biāo)進(jìn)行測(cè)定[13],DO和pH值使用WTW多參數(shù)測(cè)定儀測(cè)定,顆粒粒徑采用激光粒度儀(Mastersize 2000)測(cè)定.聚羥基烷酸(PHA)、糖原(Gly)分別采用有機(jī)溶劑萃取紫外分光光度法和蒽酮比色法測(cè)定[14].EPS中蛋白質(zhì)(PN)測(cè)定采用Lowry法測(cè)定,多糖(PS)采用蒽酮硫酸法測(cè)定[15].

1.4 計(jì)算方法和批次實(shí)驗(yàn)

1.4.1 CODin效率 系統(tǒng)厭氧階段細(xì)胞內(nèi)碳源儲(chǔ)存效率(CODin)定義為通過PAOs和GAOs儲(chǔ)存為內(nèi)碳源的COD占總消耗COD比例.計(jì)算方法如下:

式中:CODintra為內(nèi)碳源儲(chǔ)存量,ΔCODan、ΔNO2-an、ΔNO3-an為厭氧段COD、NO2-和NO3-濃度變化量, mg/L,1.71和2.86分別為異養(yǎng)菌反硝化單位質(zhì)量濃度NO2-和NO3-所消耗的COD量(以N/COD計(jì)), mg/mg

1.4.2 同步硝化反硝化(SND)效率 計(jì)算公式如下:

式中:ΔNO2-、ΔNO3-、ΔNH4+分別為好氧段NO2-、NO3-和NH4+濃度變化量,mg/L

1.4.3 聚磷菌內(nèi)碳源貢獻(xiàn)比 計(jì)算公式如下:

式中:PAO指PAOs在內(nèi)碳源儲(chǔ)存過程中的貢獻(xiàn)比例;PRA為厭氧段釋磷量,mg/L;0.5為PAOs厭氧條件下每吸收單位質(zhì)量的有機(jī)碳源所釋放的磷量, mol/mol[16].

1.4.4 批次實(shí)驗(yàn) 基于最大缺氧和好氧磷酸鹽吸收率估算DPAOs相對(duì)活性[17].具體步驟為:取每個(gè)SBR內(nèi)穩(wěn)定時(shí)期的污泥2L于燒杯中,將污泥用去離子水清洗3遍,去除上清液后恢復(fù)體積至2L,在反應(yīng)器中加入乙酸鈉,將COD濃度控制為300mg/L,厭氧攪拌反應(yīng)180min,再用去離子水清洗混合液并定容至2L,將污泥均分成2份,分別加入相同量磷酸鹽進(jìn)行缺氧和好氧吸磷實(shí)驗(yàn).其中一份使用微孔曝氣,DO濃度保持在3mg/L以上,進(jìn)行好氧吸磷;另一份加入硝酸鉀,控制初始硝氮濃度為30mg/L,并通入氮?dú)獗ＷC缺氧環(huán)境,進(jìn)行缺氧吸磷.實(shí)驗(yàn)過程中定期取樣測(cè)缺氧和好氧階段的TP濃度.

2 結(jié)果和討論

2.1 不同厭/缺氧時(shí)間下運(yùn)行期間系統(tǒng)C、N、P去除效果

如圖1所示,盡管進(jìn)水COD濃度有所波動(dòng),但運(yùn)行過程中R1、R2、R3和R4出水COD均可保持在50mg/L以下,達(dá)到《城鎮(zhèn)污水處理廠污染物排放標(biāo)準(zhǔn)》(GB 18918-2002)[13]的一級(jí)A標(biāo)準(zhǔn),表明4種運(yùn)行方式下系統(tǒng)均具有較高的有機(jī)物去除能力,厭/缺氧時(shí)間的改變對(duì)系統(tǒng)COD的去除影響不大.R1、R2、R3和R4對(duì)TN和TP去除有明顯差異,運(yùn)行初期由于顆粒污泥需適應(yīng)新的運(yùn)行環(huán)境,致使出水TN、TP有所波動(dòng),隨著運(yùn)行時(shí)間延長,4組SBR出水TN、TP濃度不斷降低,并在35d左右基本維持穩(wěn)定,穩(wěn)定時(shí)期R1、R2、R3和R4出水TN分別為9.8, 3.8, 5.0, 8.1mg/L左右,TN去除率為81.1%、92.9%、90.4%、84.0%,出水TP分別為1.35, 0.12, 0.42, 0.89mg/L左右,TP去除率分別為82.2%、98.5%、94.5%、88.1%,其中R2和R3 具有更高的N、P去除效果,出水TN、TP達(dá)到《城鎮(zhèn)污水處理廠污染物排放標(biāo)準(zhǔn)》(GB 18918-2002)的一級(jí)A標(biāo)準(zhǔn),表明適當(dāng)延長厭/缺氧時(shí)間提高了系統(tǒng)脫氮除磷效果.

2.2 不同厭/缺氧時(shí)間下典型周期內(nèi)系統(tǒng)C、N、P去除效果

選取每個(gè)反應(yīng)器穩(wěn)定時(shí)期(40d)的一個(gè)典型周期,考察不同厭/缺氧時(shí)間下系統(tǒng)中C、N、P去除效果.如圖2所示,R1厭氧時(shí)間較短,厭氧末COD濃度為67.2mg/L,R2、R3、R4在厭氧階段COD迅速降解,前60min內(nèi)絕大部分COD得到去除,厭氧階段結(jié)束時(shí)COD濃度與出水COD濃度幾乎相同,其中R2的COD降至最低,釋磷變化趨勢(shì)與之一致,釋磷量在前60min達(dá)90%以上,而后緩慢釋磷,TP濃度在厭氧末達(dá)到最大值.當(dāng)厭氧時(shí)間從50min(R1)增加到90min(R2)時(shí),釋磷量得到極大增加;厭氧時(shí)間從90min(R2)增加到180min(R4)時(shí),釋磷量和釋磷速率均下降,這和Wang等[6]研究結(jié)果不同,可能是由于本研究采用水解酸化液主要為VFA物質(zhì),易被微生物利用,所需厭氧時(shí)間縮短.伴隨COD降解厭氧段還發(fā)生了外源反硝化,R1和R4上一階段殘留的NO-更多,NO-均在前20min降解至最低,說明反硝化菌優(yōu)先利用碳源進(jìn)行反硝化,從而降低了DGAOs和DPAOs的內(nèi)碳源儲(chǔ)存作用.

在好氧段,TP濃度呈現(xiàn)快速下降,本研究中大部分磷酸鹽在好氧段得以去除;同時(shí)NH4+被氧化為NO-(主要以NO3-為主);除R1外,其余3組SBR的COD濃度幾乎不變,表明微生物利用細(xì)胞內(nèi)儲(chǔ)存的PHA進(jìn)行內(nèi)源反硝化和吸磷,而R1COD濃度繼續(xù)下降用于脫氮和除磷.由圖可知,4組反應(yīng)器的NH4+濃度減少量均大于NO-濃度增加量,系統(tǒng)出現(xiàn)氮損失,說明同步硝化反硝化的發(fā)生.

在隨后的缺氧階段COD、NH4+幾乎沒有變化,TP有少量殘留,而NO-剩余較多,并在缺氧段進(jìn)一步下降,優(yōu)化脫氮效果.但R1和R4出水殘留的NO-仍較高,分析其原因是R4缺氧時(shí)間過短,好氧末殘留的DO未消耗完,缺乏嚴(yán)格的缺氧環(huán)境,不利于反硝化的進(jìn)行;同時(shí)有研究表明厭氧時(shí)間過長導(dǎo)致VFA耗盡后,微生物會(huì)在饑餓條件下內(nèi)源性消耗糖原影響PHA合成[18],造成反硝化不徹底.R1是由于厭氧時(shí)間過短,內(nèi)碳源儲(chǔ)存不足,造成內(nèi)源反硝化缺乏電子供體,使微生物活性下降,同時(shí)R1缺氧時(shí)間過長,缺氧末出現(xiàn)了二次釋磷,導(dǎo)致除磷效果差.而R2和R3在適當(dāng)延長厭/缺氧時(shí)間下,出水P濃度均在0.5mg/L以下,系統(tǒng)能保持良好的除磷性能.

pH值與細(xì)胞膜電位有關(guān),是本研究的重要指示參數(shù).如圖2e所示,4個(gè)反應(yīng)器周期內(nèi)pH值都在7.5～8.5之間,pH值呈弱堿性,對(duì)硝化菌、反硝化菌和聚磷菌的生存有利.在厭氧初期,4組反應(yīng)器均有pH值上升趨勢(shì),其中R1和R4上升明顯,主要是反硝化菌利用外碳源去除上一周期殘留較多的NO-產(chǎn)生堿度.隨后聚磷菌儲(chǔ)存內(nèi)碳源進(jìn)行釋磷作用, pH值下降,隨著釋磷變緩,pH值下降也變緩,直至最低.R4厭氧階段后期,由于PAOs活性逐漸降低,釋磷量少造成pH值幾乎未變.在好氧段,R2和R3的pH值變化較小,由于反硝化反應(yīng)產(chǎn)生的堿度可用于硝化反應(yīng)消耗,pH值變化小說明反應(yīng)器內(nèi)同步硝化反硝化效率高.在缺氧段,R1pH值在前期無明顯變化,但在缺氧末時(shí)pH值下降明顯,分析是由于R1缺氧時(shí)間過長,二次釋磷造成pH值下降.R2和R3在缺氧段先上升后下降與DPAOs缺氧吸磷有關(guān).

2.3 不同厭/缺氧時(shí)間下系統(tǒng)C、N、P去除途徑

如表3所示,在厭氧段,根據(jù)公式1、2計(jì)算R1、R2、R3、R4分別有87.19%、97.26%、95.29%、90.79%的COD被PAOs和GAOs儲(chǔ)存為內(nèi)碳源(CODin),厭氧時(shí)間從50min延長至90min時(shí),CODin增加,但繼續(xù)延長厭氧時(shí)間時(shí),CODin反而降低,分析其原因是厭氧時(shí)間過長,微生物饑餓發(fā)生內(nèi)源代謝,消耗PHA供自身生長,造成PHA的浪費(fèi),這與實(shí)驗(yàn)所測(cè)結(jié)果一致;SBR的厭氧CODin越高,其釋磷量(PRA)越高,在厭氧時(shí)間為90min(R2)三者均達(dá)最大值,進(jìn)一步說明了內(nèi)碳源的儲(chǔ)存有利于磷的釋放,并根據(jù)公式3計(jì)算PAOs對(duì)內(nèi)碳源儲(chǔ)存貢獻(xiàn)比例,分別為27.9%、51.7%、49.5%和43.2%,其中R2占比最高,表明厭氧90min更多的內(nèi)碳源被PAOs以PHA存儲(chǔ).

在好氧段,除R1外其余3組SBR的COD濃度幾乎不變,沒有VFA用于外源反硝化,因此在好氧段N、P的去除反應(yīng)是由PHA驅(qū)動(dòng)的內(nèi)源反硝化和吸磷,吸磷量(PUA)為 39.02, 34.09和27.75mg/L,而R1的PUA為15.63mg/L.計(jì)算4個(gè)反應(yīng)器PUA/ΔPHA (0.34, 0.30, 0.31, 0.33)低于PAOs代謝的模型值0.41[19],高于DPAOs代謝模型值0.15～0.20[16,20],表明好氧段磷的去除是由PAOs和DPAOs共同參與,其中R2值更接近于DPAOs模型值,推測(cè)其DPAOs占比較高.由于PAOs、DPAOs、DGAOs會(huì)在好氧/缺氧條件下利用PHA合成Gly,通過計(jì)算ΔGly/ΔPHA比值發(fā)現(xiàn),4組反應(yīng)器ΔGly/ΔPHA(0.64, 0.70, 0.71和0.68)均高于PAOs模型值(約0.42)和DPAOs模型值(約0.2),低于DGAOs模型值(0.95)[21],表明好氧段有DGAOs參與代謝,若TN均由DGAOs反硝化去除,根據(jù)DGAOs的ΔTN/ΔPHA模型(0.24～0.28),需消耗PHA為3.43～3.99mmolC/L,對(duì)應(yīng)PUA低于實(shí)際值,說明DPAOs也參與了好氧階段氮的去除.4組反應(yīng)器的SND效率分別為50.34%、62.65%、57.85%和57.34%,其中R2的SND效率更高,主要是由于R2反應(yīng)器PHA儲(chǔ)量更高,有利于同步硝化內(nèi)源反硝化進(jìn)行,結(jié)果表明適當(dāng)延長厭氧時(shí)間有利于SND發(fā)生.

在缺氧段,4組反應(yīng)器的的PUA幾乎為0,但TN(NO-)、PHA進(jìn)一步降低,推測(cè)DGAOs內(nèi)源反硝化脫氮是PHA降低的主要原因,而ΔGly/ΔPHA比值分別為0.72, 0.77, 0.80和0.76,接近DGAOs模型值,證實(shí)了后置缺氧段TN減少是由DGAOs消耗PHA內(nèi)源反硝化造成.

根據(jù)厭氧/好氧/缺氧段TN損失占比,計(jì)算出4組反應(yīng)器在好氧段分別除去51.6%、60.7%、54.9%和56.8%,其中R1和R4約有25.1%和22.7%的TN通過厭氧段去除,更多的COD用于外源反硝化,側(cè)面反應(yīng)其內(nèi)碳源儲(chǔ)存效果差,而R2和R3中約有 28.8%和30.9%的TN通過后置缺氧段去除,表明適當(dāng)延長厭/缺時(shí)間有利于DGAOs后置內(nèi)源反硝化.

通過化學(xué)計(jì)量模型確定SBR內(nèi)TN是主要由DPAOs和DGAOs利用PHA內(nèi)源反硝化去除,TP主要在好氧段由PAOs和DPAOs共同去除,其中R2厭氧內(nèi)碳源儲(chǔ)存和釋磷量,及好氧段同步硝化內(nèi)源反硝化效率均最高,并通過后置缺氧段DGAOs進(jìn)一步去除TN,優(yōu)化處理效果.因此,適當(dāng)延長厭/缺時(shí)間可以提高污染物去除效率.

表3 不同厭/缺氧時(shí)間下典型周期(第40d)系統(tǒng)動(dòng)力學(xué)參數(shù)比較

2.4 不同厭氧/缺氧時(shí)間下除磷動(dòng)力學(xué)研究

為進(jìn)一步探究系統(tǒng)中不同微生物對(duì)除磷所占貢獻(xiàn)比,根據(jù)批次實(shí)驗(yàn)結(jié)果,計(jì)算最大缺氧和好氧磷酸鹽吸收率,以估算DPAOs相對(duì)活性,結(jié)果如表4所示.4個(gè)反應(yīng)器中均有缺氧吸磷作用,這主要與進(jìn)水水質(zhì)和好氧段DO濃度有關(guān),低DO濃度有利于維持良好的缺氧區(qū)環(huán)境,實(shí)現(xiàn)硝化、內(nèi)源反硝化吸磷的同時(shí)進(jìn)行[6],且有研究表明DPAOs可以吸收的碳源只有VFA[22],本研究采用VFA為進(jìn)水碳源,實(shí)現(xiàn)了DPAOs的富集.當(dāng)厭氧時(shí)間為90min(R2)時(shí),缺氧吸磷速率最高,表明R2中DPAOs活性較強(qiáng),DPAOs占PAOs比例為41.0%,系統(tǒng)中磷酸鹽的去除由PAOs占主導(dǎo)作用,而適當(dāng)延長厭氧時(shí)間有利于DPAOs的富集,與上述推測(cè)一致.

表4 不同厭/缺氧時(shí)間下DPAOs占比

對(duì)運(yùn)行期間4組SBR的好氧和缺氧總P吸收率和P釋放率之間關(guān)系分別進(jìn)行建模.由圖3可知,4組反應(yīng)器在不同厭/缺氧條件運(yùn)行過程中P釋放率均與總P吸收率呈線性關(guān)系,2接近于1,擬合度較好[23],表明污泥釋放的磷越多,吸收的P越多,因此通過適當(dāng)延長厭氧時(shí)間提高釋磷率有助于高效除磷.

圖3 4組SBR中P吸收率與P釋放率之間的關(guān)系

2.5 運(yùn)行期間不同厭/缺氧時(shí)間對(duì)污泥物化特性影響

2.5.1 EPS的變化 如圖4所示,不同運(yùn)行條件下污泥EPS的總量和組成發(fā)生變化.其中R2、R3PN、PS在運(yùn)行過程中無顯著變化,R1的EPS含量緩慢增加至57mg/g左右,但R4中的PS和EPS總量明顯增加并高于其他幾組, PN/PS值下降,這是由于厭氧時(shí)間過長,饑餓造成微生物內(nèi)源性呼吸,Wang等[24]認(rèn)為微生物頻繁暴露在內(nèi)源性條件下會(huì)產(chǎn)生更多的EPS以應(yīng)對(duì)惡劣環(huán)境.而EPS會(huì)增加微生物與介質(zhì)之間的傳質(zhì)阻力,微生物分泌較多的PS使顆粒表面孔隙堵塞,影響底物的擴(kuò)散速率[25];對(duì)于R4,其高EPS及PS含量阻礙了VFA的擴(kuò)散,導(dǎo)致厭氧PHA合成不足釋磷量低,PHA含量的下降與上述分析一致;也有研究認(rèn)為[26]EPS會(huì)吸附磷酸鹽,可能是R4厭氧釋磷量不高的另一原因.

圖4 運(yùn)行期間不同厭/缺氧時(shí)間下EPS含量變化

2.5.2 SVI值變化 如圖5所示,反應(yīng)器接種的好氧顆粒污泥沉降性能較好,SVI值為45.8mL/g,隨著反應(yīng)運(yùn)行, R2和R3的SVI值維持在較低值,沉降性能好;而R1的SVI值在第15d呈現(xiàn)上升趨勢(shì),可能是由于R1厭氧時(shí)間過短,有機(jī)物泄露至好氧段,使快速生長的異養(yǎng)菌增殖,污泥結(jié)構(gòu)松散,導(dǎo)致SVI值升高;而R4的SVI值在中后期(第25d)上升,反應(yīng)器沉降性能變差可能與R4中污泥EPS的分泌有關(guān).有研究表明[27]EPS對(duì)微生物聚集體的沉降性有不利影響,由于EPS帶負(fù)電荷,高濃度的EPS會(huì)增加微生物的表面電荷,從而導(dǎo)致細(xì)胞間排斥力增加,沉降性降低.

圖5 運(yùn)行期間不同厭/缺氧時(shí)間下SVI值變化

2.5.3 污泥粒徑及外觀形態(tài) 如圖6所示,由于接種污泥為成熟的好氧顆粒污泥,其平均粒徑約為700μm,隨著反應(yīng)運(yùn)行,4組SBR顆粒粒徑呈緩慢增長趨勢(shì)并在35d左右基本維持穩(wěn)定,分析其原因是由于水解酸化液主要為VFA物質(zhì),DPAOs、DGAOs等微生物會(huì)吸收VFA轉(zhuǎn)化為內(nèi)聚物以較低速度生長[28-29],從而使顆粒粒徑保持在650～850μm范圍內(nèi).由圖7可知, 4組SBR均未發(fā)生絲狀菌過度生長、顆粒解體現(xiàn)象,顆粒大多呈球形和橢球形,形態(tài)完整.這主要是由于以VFA為底物培養(yǎng)的AGS形成了以慢速生長微生物構(gòu)成的缺氧核心,穩(wěn)定性強(qiáng),可以通過分泌EPS抵御外界環(huán)境的影響.

圖6 運(yùn)行期間不同厭/缺氧時(shí)間下顆粒平均粒徑變化

圖7 穩(wěn)定期(40d)不同SBR污泥顯微鏡圖

Fig.7 Microscopy images of different SBR sludge in stable period (40d)

3 結(jié)論

3.1 從處理性能看,隨著厭/缺氧時(shí)間從50min/ 170min調(diào)整至90min/130min時(shí),內(nèi)碳源儲(chǔ)存量增加, TN、TP去除率提升至92.9%、98.5%,脫氮除磷性能得到明顯改善;當(dāng)厭/缺氧時(shí)間繼續(xù)調(diào)整至180min/ 40min時(shí), PHA貯存量反而下降、反硝化不徹底,TN、TP去除率降至84.0%和88.1%.適當(dāng)延長厭/缺氧時(shí)間通過加強(qiáng)內(nèi)碳源貯存與轉(zhuǎn)化提高了脫氮除磷性能.

3.2 從去除路徑看,通過好氧段SND和后置缺氧內(nèi)源反硝化提高了脫氮效果,其中DPAOs和DGAOs均參與反硝化,TP是由PAOs和DPAOs協(xié)同去除,R2中DPAOs占比高,達(dá)41%.通過適當(dāng)延長厭/缺氧時(shí)間實(shí)現(xiàn)了同步硝化反硝化、后內(nèi)源反硝化和除磷高效協(xié)同.

3.3 擬合表明厭氧磷釋放速率越高,總磷吸收率越高,提高厭氧磷釋放效果可實(shí)現(xiàn)高效除磷.污泥特性分析表明,厭氧時(shí)間為180min時(shí)污泥EPS分泌增多導(dǎo)致PHA合成不足、顆粒沉降性能變差.4組SBR運(yùn)行期間均未發(fā)生絲狀膨脹、污泥解體等現(xiàn)象,表明以水解酸化液為基質(zhì)培養(yǎng)的顆粒穩(wěn)定性高.

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Effects of anaerobic/anoxic time on simultaneous nitrification-endogenous denitrification and phosphorous removal from aerobic granular sludge.

WANG Qi1, LI Dong1*, LI Peng-yao1, CHEN Xiao-yi1, ZHANG Jie1,2

(1.Key Laboratory of Beijing Water Quality Science and Water Environment Recovery Engineering, Beijing University of Technology, Beijing 100124, China；2.State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China)., 2022,42(9)：4199～4206

In this study, four groups of SBR reactors with the same specification was selected to explore effects of total nitrogen (TN) and total phosphorus (TP) removal from aerobic granular sludge under different anaerobic/anoxic time as 50/170, 90/130, 130/90, 180/40min and the hydrolytic acidification liquid as the influent matrix in A/O/A mode. The results show that the carbon (C) source reserves and P release from granular sludge increased with an increment in the anaerobic time from 50 to 90min. The efficiency of simultaneous nitrification and denitrification (SND) increased to 62.65%, and the removal rates of TN and TP increased from 81.1% to 92.9% and 82.2% to 98.5%, respectively. When the anaerobic time increased from 90 to 180min, the P release decreased and the anaerobic endogenous conditions stimulated the increase in EPS and the decrease in PHA synthesis, which led to a decrease in the TP removal rate to 88.1%. At the same time, when the anoxic time was shortened from 130 to 40min, more NOx-remained in the system, resulting in a reduction in TN removal rate to 84%. Mechanism analysis suggests that TN was consumed by denitrifying polyphosphate accumulating organisms and denitrifying glycogen accumulating organisms in the aerobic section by means of PHA in the form of SND; then further removed by endogenous denitrification of DGAOs in the anoxic section; and finally, TP was removed by PAOs and DPAOs. Our batch experiments demonstrated the highest proportion of DPAOs in R2, up to 41%. During the operation of the four groups of reactors, the particles did not disintegrate, implying that the particles cultured with hydrolytic acidification solution had complete structure and strong stability. We conclude that appropriate extension of anerobic/anoxic is conducive to strengthening the storage and transformation of internal C source, enhancing the effects of anaerobic P release, SND, and post endogenous denitrification, and realizing the efficient and stable operation of simultaneous nitrification-endogenous denitrification and P removal.

SBR；aerobic granular sludge；internal carbon source；post-denitrification；denitrifying phosphorus removal bacteria；anaerobic/anoxic reaction time

X703.1

A

1000-6923(2022)09-4199-08

2022-02-08

北京高校卓越青年科學(xué)家計(jì)劃項(xiàng)目(BJJWZYJH01201910 005019)

*責(zé)任作者, 教授, lidong2006@bjut.edu.cn

王 琪(1996-),女,安徽宣城人,北京工業(yè)大學(xué)碩士研究生,主要研究方向?yàn)樗|(zhì)科學(xué)與水環(huán)境恢復(fù)技術(shù).