低溫投加短程硝化污泥下城市污水SPN/A工藝運行特性

王思萌,苗圓圓,彭永臻

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低溫投加短程硝化污泥下城市污水SPN/A工藝運行特性

王思萌,苗圓圓,彭永臻*

(北京工業大學,城鎮污水深度處理與資源化利用技術國家工程實驗室,北京市水質科學與水環境恢復工程重點實驗室,北京 100124)

以城市污水為研究對象,考察低溫條件下通過生物添加強化氨氧化菌(AOB)活性,并進一步提高短程硝化-厭氧氨氧化一體化(SPN/A)工藝脫氮效果的可行性.平行運行2個序批式反應器(SBR)SBR1與SBR2,在間歇曝氣條件下運行,控制溫度由30℃梯度下降至15℃(30,27,24,21,18,15℃),隨后逐步回升至30℃.在降溫與升溫過程中,向SBR2中定期投加短程硝化污泥強化AOB活性,SBR1作為空白試驗不進行投加.結果表明,30℃時SBR1與SBR2在不外加短程硝化污泥的條件下均可成功啟動并穩定運行,脫氮效果均良好;溫度降至15℃時,SBR1與SBR2出水NH4+-N分別為36.38,33.10mg/L,總氮去除率分別為30.72%與35.76%,2個反應器脫氮效果均變差,SBR2較SBR1抗低溫能力較強;梯度升溫至30℃時,SBR1與SBR2總氮去除率分別升至52.43%與63.60%.通過考察SBR1與SBR2菌群活性可知,2個反應器的菌群活性均隨著溫度降低而降低,但SBR2的AOB豐度活性均高于SBR1;溫度回升階段,2個反應器的菌群活性有所升高,其中SBR2亞硝酸鹽氧化細菌(NOB)活性受到抑制持續降低,推測這是因為SBR2中的AOB活性得到強化后,產生更多的亞硝酸鹽,厭氧氨氧化菌(Anammox)可獲得基質增多,造成Anammox活性豐度較高,所以SBR2脫氮效果相對較好.因此,在低溫條件下通過生物添加強化SPN/A系統中AOB活性,可提高系統抗溫度沖擊能力,利于系統脫氮效果的恢復.

短程硝化厭氧氨氧化一體化；城市污水；生物添加；溫度；AOB活性

在短程硝化-厭氧氨氧化一體化(SPN/A)工藝中,AOB在好氧條件下,將生活污水中的部分氨氮(NH4+-N)轉化為亞硝酸鹽氮(NO2--N),Anammox在缺氧條件下,將生成的NO2--N與剩余NH4+-N轉化為氮氣[1-3].

SPNA工藝的反應方程式:

NH4++0.85O2?0.44N2+0.11NO3-+0.14H++1.43H2O (1)

SPN/A工藝中AOB、Anammox為自養菌,與傳統硝化反硝化脫氮工藝相比,剩余污泥產量減少約90%,且無需外加碳源.反應過程中僅部分NH4+-N轉化為NO2--N,可減少60%的曝氣量[2],且具有節能降耗等優點.

目前,SPN/A工藝主要用于處理高溫高NH4+-N和低C/N(低于0.5)廢水[3-6],在反應器的啟動與運行[7-8]、系統破壞和恢復[9]、污泥富集培養[10]等方面做了大量研究,在低NH4+-N廢水的處理方面尚處于試驗研究階段.在低NH4+-N廢水SPN/A工藝中,由于缺乏游離氨(FA)和游離亞硝酸(FNA)等抑制條件,NOB易富集,導致出水硝酸鹽增加、脫氮效果變差[11-14],因此,NOB的抑制是低NH4+-N廢水SPN/A系統穩定的一大難點.Miao等[15]發現采用間歇曝氣(好氧7min/缺氧21min)的運行方式可有效抑制NOB活性,提高城市污水SPN/A脫氮效果.但是,由于間歇曝氣中好氧時間較少,AOB活性會出現下降的現象[12,16-17],不利于SPN/A工藝長期穩定運行及脫氮效果的提高,因此強化AOB活性對于城市污水SPN/A工藝十分重要.Wett等[18]報道稱通過向SPN/A工藝投加含有AOB和Anammox的污泥,實現了NOB活性的抑制和AOB活性的提高,且在該條件下,系統出水NO3--N濃度逐漸降低,脫氮效果有所改善.但城市污水季節性的水溫變化較大[11-12,16],冬季溫度較低[11,19-21].在低溫條件下, SPN/A工藝內主要功能菌群受溫度的影響程度不同,相比AOB和Anammox,NOB對溫度變化更加敏感,因此低溫下抑制NOB活性將更為困難[22].投加短程硝化污泥雖然強化AOB活性,但一定程度上也增加了系統內NOB的量,因此在低溫條件下投加短程硝化污泥提高SPN/A工藝脫氮性能的可能性需要進一步驗證.本文研究目的是考察在溫度波動條件下,投加短程硝化污泥對SPN/A工藝的影響.本試驗采用間歇曝氣的運行方式,平行運行2個SBR反應器處理城市污水,向其中一個反應器定期投加短程硝化污泥,另一個不投加污泥作為空白試驗.模擬城市污水水溫波動的特點,考察溫度波動條件下SPN/A工藝出水氮濃度變化規律,探究低溫下強化AOB活性對系統中菌群活性的影響.

1 材料與方法

1.1 試驗裝置

短程硝化-厭氧氨氧化一體化工藝裝置如圖1所示.試驗采用SBR反應器,直徑13cm,高70cm,有效體積10L.通過加熱及溫控裝置控制反應器溫度;設置攪拌裝置,通過微型曝氣泵進行曝氣,并通過轉子流量計調節曝氣量.

1.2 接種污泥和試驗用水

試驗接種的短程硝化污泥取自中試規模的短程硝化反硝化SBR[23],厭氧氨氧化污泥取自小試規模厭氧氨氧化UASB[23],SBR1與SBR2反應器分別接種4L短程硝化污泥和0.5L厭氧氨氧化污泥,接種后MLSS分別為4676與4594mg/L,MLVSS分別為3904與3896mg/L,試驗用水取自9~12月某高校家屬區化糞池的實際生活污水,經曝氣預處理環節去除水中大部分可降解有機物,SPN/A工藝進水水質指標見表1.

圖1 SBR反應器示意

1.加熱棒;2.流量計;3.時間繼電器;4.曝氣泵;5.中間水箱;6.進水泵;7.溫控儀;8.pH,DO,溫度在線監測;9.攪拌槳;10.取樣口; 11.曝氣頭

表1 SPN/A工藝進水水質

1.3 試驗檢測項目與方法

溫度、pH值、DO采用德國WTW便攜多功能檢測儀(Multi340i)進行實時監測.水樣經0.45μm濾膜過濾后檢測各參數.NH4+-N采用納氏試劑分光光度法檢測;NO2--N采用N-(1-萘基)-乙二胺分光光度法檢測;NO3--N采用麝香草酚分光光度法檢測;COD采用5B-3型COD快速檢測儀檢測;MLSS采用濾紙稱重法檢測;MLVSS采用馬弗爐灼燒重量法檢測.在反應周期末期(第44,69,95與126d)從SBR1與SBR2取泥樣,采用冷凍干燥機(LABCONCO Co., Free Zone,USA)凍干污泥;采用qPCR技術(SYBR Green法)對活性污泥系統中AOB、NOB(和)和Anammox進行檢測.首先根據試劑盒(MP Biomedicals, OH, USA)說明對污泥樣品進行DNA的提取,之后將DNA樣品稀釋100~1000倍待測(DNA濃度約1~ 10ng);采用MX3000P實時定量PCR儀(Stratagene, La Jolla,CA)檢測,擴增PCR反應體系(20μL)包括: SYBR Green exTaq (Takara,大連,中國)10μL,去離子水7μL,ROX Reference Dye500.4μL,前引物(10mmol/L)后引物(10mmol/L)各0.3μL,DNA樣品2μL.擴增程序為:95℃預變性3min,隨后開始40個擴增循環(95℃變性30s,退火30s,72℃延伸45s).AOB所用引物amoA-1F(5’-GGGGTTTCTACTGGTGGT -3’)[24]、所用引物NSR 1113F(5’- CCTGCTTTCAGTTGCTACCG-3’)[25]、所用引物FGPS872f(5’-CTAAAACTCAAAGGA- ATTGA-3’)[26]、Anammox所用引物Amx368f(5’- TTCGCAATGCCCGAAAGG-3’)[27].當標線涵蓋5~7個標準樣,且標線相關系數(2)高于0.99,擴增效率在90%~110%范圍內時,認為標線合格.

1.4 試驗方法

本試驗分為3個階段(表2):第I階段(1~48d)在30℃下平行啟動SBR1與SBR2反應器,第II階段(49~102d)溫度梯度降低至15℃,第III階段(103~ 126d)溫度逐漸從15℃梯度回升至30℃;其中,第I階段不進行污泥投加,第II、III階段(49,71,92,114d)向SBR2投加短程硝化污泥,投加量為SBR2VSS的10%,分別約為380,340,400及340mg/L.SBR1作為空白試驗不進行投加,分別在第8,44,69,95,126d測量污泥濃度.

SPN/A工藝運行方式如下:進水4min,缺氧/好氧交替共330min,其中缺氧21min,DO小于0.1mg/L,好氧7min,DO如表2所示.沉淀21min,排水4min.每天運行4個周期,運行周期為6h;通過控制溫控儀及加熱棒模擬城市污水在反應器中的溫度變化,調節轉子流量計對溶解氧進行控制,實時監測DO與pH值.進水通過投加KHCO3使反應器pH值維持在7.0~7.8之間.

表2 不同運行階段溫度的變化

2 結果與分析

2.1 強化AOB活性對SPN/A工藝脫氮特性的影響

2.1.1 系統啟動與穩定運行 SBR1與SBR2啟動與穩定運行階段(1~48d)脫氮效果如圖2第I階段所示.反應器均在30℃下啟動運行,通過對SBR1與SBR2的DO、pH值等運行條件的監控,保證2個反應器運行條件一致,且均不進行污泥投加.SBR1平均出水NH4+-N濃度為9.95mg/L,出水NO2--N及NO3--N濃度分別為0.13與6.02mg/L,平均總氮去除率為76.41%,DO約為0.81mg/L;SBR2平均出水NH4+-N濃度為14.70mg/L,出水NO2--N及出水NO3--N濃度分別為0.19與4.16mg/L,平均總氮去除率為71.83%,DO約為0.79mg/L.SBR1與SBR2總氮去除負荷(圖3)分別為101.80和95.30gN/(m3·d).試驗結果表明,成功啟動SBR1與SBR2,脫氮效果較為穩定.

2.1.2 梯度降溫條件下系統的脫氮效果 階段II(49~102d),SBR1與SBR2溫度由30℃梯度下降至15℃,試驗過程中定期向SBR2投加短程硝化污泥,SBR1不進行投加.結果表明隨著溫度降低,2個反應器脫氮效果均下降(表3).當溫度降至15℃時,2個反應器的DO分別調高約至1.20mg/L.SBR1與SBR2出水NH4+-N由9.95與14.70mg/L上升至36.38與33.10mg/L,說明溫度降低,2個反應器中的AOB及Anammox活性受到影響,而SBR2的受影響程度小于SBR1.

圖2 SBR1與SBR2氮濃度變化

圖3 SBR1與SBR2氮負荷變化

SBR1與SBR2的出水NO3--N濃度隨溫度降低呈現先升高后降低的趨勢,不同的是,SBR1出水NO3--N濃度迅速升高,在24℃時升至9.55mg/L,而SBR2出水NO3--N濃度緩慢升高,在24℃時升至6.32mg/L.溫度由21℃繼續降低的過程中,2個反應器出水NO3--N均下降,15℃時分別降至2.41與2.63mg/L.在整個梯度降溫過程中,通過投加短程硝化污泥的SBR2出水NO3--N變化幅度小于SBR1.

由表3可知,當溫度降低至15℃時,SBR1與SBR2總氮去除率分別由76.41%與71.83%降至30.72%與35.76%,總氮去除負荷分別由101.80, 95.30gN/(m3·d)降至36.00,40.89gN/(m3·d),說明SPN/A工藝的脫氮效果受溫度影響較大.由表4可知,溫度由21℃降至15℃過程中,SBR2出水總氮濃度變化幅度小于SBR1,且脫氮效果優于SBR1,證明向SPN/A工藝投加短程硝化污泥,可在一定程度上降低低溫環境對SPN/A工藝脫氮性能的影響.

2.1.3 梯度升溫條件下系統的恢復效果 階段III(103~126d),SBR1與SBR2溫度從15℃梯度回升至30℃,2個反應器DO均約為0.8mg/L,脫氮效果明顯提高,SBR1與SBR2出水NH4+-N分別降至21.45與15.57mg/L,出水NO2--N分別為0.22與0.33mg/L,氮去除負荷分別約為56.22與67.35gN/(m3·d),出水NO3--N分別約為3.49與3.38mg/L,平均總氮去除率分別升高至52.43%與63.60%.結果表明在梯度升溫的過程中,SBR1和SBR2脫氮效果逐漸提高,其中SBR2好于SBR1.但是在短時間內SBR1和SBR2脫氮效果沒有提高至第I階段的水平,推測經過低溫環境之后,系統中主要功能菌群AOB和Anammox活性降低,在短期內還沒有完全恢復.

表3 梯度變溫階段出水水質指標

表4 梯度降溫階段出水指標變化幅度(%)

圖4 SBR1與SBR2 NO3--N生成量與NH4+-N轉化比值變化

2.1.4 強化AOB活性對NO3--N生成比的影響 由SPN/A工藝的反應方程式(1)可知,單個反應周期內NO3--N生成量占NH4+-N降解量的比值(ΔNO3--N/ΔNH4+-N)理論值為0.11.如圖4所示,當溫度為30℃,SBR1與SBR2的ΔNO3--N/ΔNH4+-N值分別為0.01與0.08,低于理論比值.盡管城市污水中大部分的可降解有機物在預處理反應器中被去除,SPN/A工藝進水中仍存在部分可降解有機物,因此反應器中可能存在反硝化現象,造成比值低于理論值. 溫度由30℃降至24℃的過程中,SBR1與SBR2的ΔNO3--N/ΔNH4+-N均值分別升高至0.20與0.13;隨著溫度進一步降低至15℃,ΔNO3--N/ ΔNH4+-N比值開始降低.當溫度回升至30℃,SBR1與SBR2比值近似理論值0.11,整個過程變化趨勢與2個反應器脫氮效果一致,投加短程硝化污泥的SBR2在溫度波動時ΔNO3--N/ΔNH4+-N低于SBR1.

2.2 強化AOB活性對菌群活性的影響

當溫度從30℃梯度降至15℃時,SBR1與SBR2的AOB活性(圖5)均隨著溫度的降低而降低,分別由4.10,4.01mgN/(h·gVSS)降至1.89,1.93mgN/(h·gVSS);對應PCR結果,SBR1與SBR2中的AOB豐度由1.33×109與1.89×109copies/g干污泥下降至2.87×108與9.31×108copies/g干污泥,相比而言,SBR2在溫度降低時AOB活性下降較慢;此外,與脫氮效果對應,說明AOB受低溫影響活性降低,導致SPN/A工藝脫氮效果變差.當溫度回升至30℃,SBR1與SBR2的AOB活性分別升高至2.36與2.61mgN/(h·gVSS), AOB豐度分別回升至6.42×108與1.28×109copies/g干污泥,說明當溫度升高,AOB活性提高,系統脫氮效果隨之變好,其中SBR2的AOB活性升高較SBR1更快.但是,SBR1與SBR2在階段III的AOB活性均沒有升高至階段I的水平,推測這是導致階段III系統脫氮性能較差于階段I的主要原因.由圖5可知,SBR1在降溫階段的MLSS約為4500mg/L,升溫階段約為4200mg/L,污泥濃度整體變化不大;而SBR2在降溫與升溫階段的MLSS一直約為4600mg/L,說明投加短程硝化污泥并沒有使SBR2的MLSS明顯增長,推測投加的污泥中存在異養菌,由于反應器中的有機物濃度較低,且缺氧時間較長,導致大量異養菌裂解衰亡,因而SBR2的MLSS較為穩定.此外,當溫度從30℃梯度降至15℃時, SBR1與SBR2中的Anammox活性分別由2.14與2.01mgN/ (h·gVSS)降至0.69與0.77mgN/(h·gVSS), SBR1與SBR2中的Anammox豐度分別由2.5×109, 2.06× 109copies/g干污泥分別下降至4.33×108, 6.25× 108copies/g干污泥,SBR2中的Anammox活性與豐度在低溫過程中下降幅度均小于SBR1,與AOB在低溫過程中變化相似;當溫度回升至30℃, SBR1與SBR2中的Anammox活性分別升至0.92, 1.04mgN/ (h·gVSS),Anammox豐度分別升至4.64×108,1.06× 109copies/g 干污泥.在升溫過程中SBR2的Anammox活性與豐度恢復較快,這與升溫階段脫氮效果相符,說明投加短程硝化污泥也有利于Anammox活性的穩定與恢復.在降溫與升溫過程中, SBR2中AOB與Anammox活性之間的關系如圖6所示,AOB與Anammox活性具有良好的相關性,2值為0.961,由此投加短程硝化污泥提高SPN/A工藝中AOB活性的過程中,AOB為Anammox提供了更多的NO2--N基質,從而Anammox活性得到提高.

隨著溫度的降低,2個反應器中NOB活性均出現下降現象.盡管向SBR2投加短程硝化污泥在一定程度上增加了系統NOB的量,但由于采用間歇曝氣的運行方式,NOB活性并沒有明顯增高,且NOB活性的降低與2個反應器脫氮效果變化趨勢一致.由表5可知,SBR1與SBR2中優勢NOB菌種豐度均呈下降趨勢,分別由2.12×1010,8.78× 109copies/g干污泥下降至5.49×109,6.33× 108copies/ g干污泥,這可能與反應器在間歇曝氣條件下運行,利于抑制NOB活性有關.當溫度回升, SBR1中的NOB活性回升,而SBR2中的NOB活性繼續降低,推測經過投加短程硝化污泥的SBR2中的AOB得到強化成為優勢菌群,在對DO的競爭中較NOB更占優勢.此外,間歇曝氣運行方式進一步利于NOB的抑制和Anammox的富集,與Miao等[16]的結論一致.Anammox對NO2--N的競爭也逐漸優于NOB,造成NOB活性逐漸降低.由此可通過強化AOB活性提高系統脫氮效果及穩定性,并且可有效抑制NOB活性,穩定Anammox活性,從而更有效的提高SPN/A工藝自養脫氮效果.

表5 不同溫度下AOB、NOB和Anammox豐度變化情況(×108copies/g干污泥)

2.3 討論

城市污水SPN/A工藝采用間歇曝氣的運行方式,在30℃且不外加短程硝化污泥的條件下成功穩定運行,具有良好的脫氮效果.在溫度波動階段, SBR2的脫氮效果優于SBR1.其中,在梯度降溫階段,SBR1與SBR2脫氮效果均下降,SBR2中的AOB及Anammox活性相對較高于SBR1;溫度升溫階段,SBR1與SBR2脫氮效果均提高,SBR2中的AOB及Anammox活性回升的更快,且NOB的抑制效果更好.因此通過本試驗結論可知,低溫使得SPN/A工藝脫氮效果下降;強化AOB活性利于SPN/A工藝Anammox活性的提高和NOB的抑制,并進一步降低低溫對脫氮效果的影響.因此,可在低溫下或溫度降低前強化AOB活性,以提高SPN/A工藝在溫度波動時的脫氮效果和穩定性.本試驗選擇的生物投加為短程硝化污泥強化AOB活性,選擇不同種類的生物投加對城市污水SPN/A工藝菌群活性影響不同,可選擇不同種類的污泥[28]、添加Fe(Ⅲ)[29]、NaCl鹽度等[30]或者控制DO濃度[31-32]提高AOB活性,探究強化菌群過程對城市污水SPN/A工藝自養脫氮效果的影響.除此之外,在北方冬季城市污水廠處理污水的過程中,最低溫度可能低于本試驗采用的15℃[33],對自養脫氮效果是否有其他影響,值得繼續探究.

圖6 SBR2中AOB與Anammox活性的相關性

3 結論

3.1 在30℃條件下啟動SPN/A工藝,2個反應器總氮去除率分別約為76%與72%,不外加短程硝化污泥可成功啟動城市污水短程硝化-厭氧氨氧化一體化系統并具有良好的脫氮效果.

3.2 在低溫條件下,SPN/A工藝受溫度影響,2個反應器脫氮效果下降,NH4+-N去除率分別降至35%與40%,向SBR2定期投加短程硝化污泥可在一定程度上增強系統的抗低溫能力;在溫度梯度回升過程中,SBR1與SBR2的NH4+-N去除率分別約為59%與71%,投加短程硝化污泥利于SPN/A系統脫氮效果較快較好的回升.

3.3 向SPN/A工藝定期投加短程硝化污泥,可增強AOB豐度與活性,AOB活性得到強化后,更利于抑制NOB活性.此外,AOB活性與Anammox活性之間具有良好的相關性,利于Anammox活性的穩定與提高.

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Operation characteristics of the SPN/A process for municipal wastewater under low temperature shortcut nitrification sludge.

WANG Si-meng, MIAO Yuan-yuan, PENG Yong-zhen*

(1.Key Laboratory of Beijing for Water Quality Science and Water Environment Recovery Engineering, National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology, Beijing University of Technology, Beijing 100124, China)., 2019,39(4)：1456~1463

In this study, feasibility of enhancing ammonia-oxidizing bacteria (AOB) activity by biological addition under the condition of temperature fluctuation and further improving the denitrification effect of Single-stage Partial Nitrification and Anammox (SPN/A) process in municipal wastewater treatment was investigated. Two sequencing batch reactors (SBR) SBR1 and SBR2 were operated in intermittent aeration. The controlled temperature was reduced from 30℃ gradient to 15℃ (30, 27, 24, 21, 18, 15℃), and then gradually increased to 30℃.Shortcut nitri?cation sludge was regularly added to SBR2 to enhance AOB activity during the cooling and heatingprocess, and SBR1was used as the control process. The results showed that SBR1 and SBR2 started successfully and run stably without shortcut nitri?cation sludge, and the nitrogen removal efficiency of SBR1 and SBR2 was good at 30℃. When the temperature was dropped to 15℃, the concentration of the ammonia nitrogen in effluents of of SBR1 and SBR2 were 36.38mg/L and 33.10mg/L, and the total nitrogen removal efficiency was 30.72% and 35.76%, respectively. Both rectors’ efficiency become worse in low temperature settings, SBR2 shown a better cold resistance performance. When temperature were increased gradient back to 30℃,the total nitrogen removal rates of SBR1 and SBR2 increased back to 52.43% and 63.60% respectively. The activity of bacteria in SBR1 and SBR2 decreased with the decrease of temperature, but the AOB activity of SBR2 was higher than that of SBR1. During the temperature rising stage, the activity of bacteria in SBR1 and SBR2 both increased, and the inhibition of nitrite-oxidizing bacteria (NOB) activity in SBR2 was continuously decreasing. The better denitrification performance of SBR2 was suspected because when the AOB activity of SBR2 was enhanced, more nitrite was produced, and the substrate of Anammox was increased, which resulted in the higher activity abundance of Anammox. Therefore, it was conclude that the AOB activity in SPN/A system can be enhanced by biological addition at low temperature, which can improve the resistance performance of the system to the temperature shocks and facilitate the recovery of denitrification capacity.

single-stage partial nitrification and anammox；municipal wastewater；biological addition；temperature；AOB activity

X703

A

1000-6923(2019)04-1456-08

2018-09-28

北京市科技計劃(D171100001017001);水體污染控制與治理科技重大專項(2017ZX07102-003)

*責任作者, 教授, pyz@bjut.edu.cn

王思萌(1993-),女,北京人,北京工業大學碩士研究生,主要從事城市污水短程硝化-厭氧氨氧化一體化自養脫氮的應用研究.發表論文2篇