賀昭銘,劉佳妮,田亞茹,于德爽,苗圓圓*,張文克,馬國成,趙鑫超,袁 悅
外源全程硝化污泥對城市污水SPNA系統(tǒng)的影響
賀昭銘1,劉佳妮1,田亞茹1,于德爽1,苗圓圓1*,張文克1,馬國成1,趙鑫超1,袁 悅2
(1.青島大學環(huán)境科學與工程學院,山東 青島 266071;2.上海市政工程設計研究總院(集團)有限公司,上海 200092)
為強化城市污水短程硝化-厭氧氨氧化(SPNA)系統(tǒng)脫氮性能與穩(wěn)定性,在間歇曝氣條件下研究投加外源全程硝化污泥對城市污水SPNA系統(tǒng)的影響及機理.結果顯示,空白組(SBR3)總氮去除率由35.5%升高至66.3%,短周期分批次投加外源全程硝化污泥(SBR2,投加周期為5d,投加比為2.5%)與長周期分批次投加(SBR1,投加周期為20d,投加比為10%)的SPNA系統(tǒng)總氮去除率分別由31.7%和36.5%升高至76.3%和67.2%,這表明,投加全程硝化污泥有利于提高SPNA系統(tǒng)的脫氮性能,且當投加總量相同時,短周期分批次投加的效果優(yōu)于長周期分批次投加.功能菌活性結果與脫氮效果一致,SBR1~SBR3的厭氧氨氧化菌(AnAOB)最大活性分別由3.43mg-N/(L·h)升高至7.66,8.19和7.31mg-N/(L·h),氨氧化細菌(AOB)與亞硝酸鹽氧化菌(NOB)活性比分別為8.79,9.83和8.78.在間歇曝氣條件下投加全程硝化污泥,可選擇性抑制NOB、富集AOB,提高AOB與NOB的活性比,利于穩(wěn)定短程硝化效果,為AnAOB提供穩(wěn)定的基質,且短周期分批次投加可降低外源硝化污泥中的NOB對系統(tǒng)的沖擊,更有利于實現高AOB與NOB活性比,提高系統(tǒng)穩(wěn)定性.此外,內源短程反硝化菌相對豐度明顯升高,可為AnAOB提供更多的亞硝酸鹽氮,進一步利于AnAOB富集.
短程硝化-厭氧氨氧化一體化;生物添加;全程硝化污泥;間歇曝氣;高通量測序;影響因素
由于城市污水的碳氮比過低,在傳統(tǒng)的全程硝化-反硝化污水處理工藝中,往往需要添加外碳源強化反硝化效果,使出水的氮濃度達到排放標準.但外加碳源不僅會給后續(xù)運行帶來一定的壓力,還會提高運行成本[1-2].短程硝化-厭氧氨氧化一體化(SPNA)工藝即在一個反應器中同時實現短程硝化和厭氧氨氧化,氨氧化細菌(AOB)將部分氨氮氧化成亞硝酸鹽氮,隨后厭氧氨氧化菌(AnAOB)將這部分亞硝酸鹽氮與剩余的氨氮轉化成氮氣和少量的硝酸鹽氮,完成污水脫氮[3-4].該工藝主要脫氮功能菌為自養(yǎng)菌,不需要外加有機碳源,且只需將約一半的氨氮氧化為亞硝酸鹽氮,因此具有節(jié)省曝氣能耗和有機碳源、剩余污泥產量少等優(yōu)點[5],有望實現低能耗城市污水深度脫氮,具有重要意義.
城市污水SPNA工藝的可行性,已初步得到驗證,但仍存在諸多難點有待解決.城市污水SPNA工藝的瓶頸是難以有效抑制亞硝酸鹽氧化菌(NOB).由于缺少高游離氨和高游離亞硝酸濃度等抑制NOB的條件,NOB極易大量生長,與AnAOB競爭亞硝酸鹽氮[6],一方面,造成城市污水SPNA系統(tǒng)出水硝酸鹽氮濃度升高,脫氮性能惡化;另一方面,可導致AnAOB活性和豐度逐漸下降,加劇系統(tǒng)失穩(wěn).有研究發(fā)現,可以通過控制低溶解氧(DO)濃度和間歇曝氣等條件抑制NOB活性[7-8],但這些條件并不充分,由于NOB大量生長造成的SPNA系統(tǒng)脫氮性能惡化的現象屢見報道[9]. Wang等[10]報道,控制DO在0.10~0.13mg/L并不能有效抑制NOB活性,城市污水SPNA系統(tǒng)出水硝酸鹽氮濃度逐漸升高至18.1mg-N/L;Karol等[11]發(fā)現,單純控制間歇曝氣并不能充分抑制NOB活性.利用高游離氨和游離亞硝酸濃度對SPNA系統(tǒng)中污泥進行預處理,可短期內抑制NOB活性,但增大了工藝運行復雜度和運行能耗,且長期運行過程中,NOB可能會逐漸適應高游離氨和游離亞硝酸濃度,導致系統(tǒng)脫氮性能再次下降[12].目前,在城市污水SPNA系統(tǒng)中實現長期穩(wěn)定的短程硝化和NOB抑制和淘洗,仍未取得突破性進展.
近期研究發(fā)現,在城市污水SPNA系統(tǒng)中NOB活性較高的情況下,向其中投加外源全程硝化污泥,未造成系統(tǒng)中NOB活性進一步升高和脫氮性能惡化,反而可選擇性提高AOB活性,促進AnAOB富集,進而提高系統(tǒng)脫氮效果[13].城市污水處理廠普遍采用全程硝化-反硝化工藝處理污水,該工藝會定期排放大量的剩余污泥,因此,本試驗采用的外源全程硝化污泥在污水廠非常常見,具有通用性和普遍性,研究其對SPNA工藝的促進效果和機理具有一定的借鑒意義,該方法有望突破城市污水SPNA工藝的瓶頸,促進該工藝的推廣應用.但外源全程硝化污泥對城市污水SPNA系統(tǒng)脫氮性能的影響機理尚未明了,且外源全程硝化污泥的投加量與投加周期也需要進一步優(yōu)化,值得進一步研究.
利用SBR反應器構建城市污水SPNA系統(tǒng).平行運行3個反應器SBR1,SBR2和SBR3,有效容積為3L,排水比為50%.通過溫控裝置使反應器溫度維持在32℃;通過機械攪拌器進行攪拌;通過微型曝氣泵進行曝氣;通過轉子流量計調節(jié)曝氣量(圖1).反應器采用前置缺氧攪拌的間歇曝氣方式運行,間歇曝氣的周期通過繼電器調控,其中前置缺氧攪拌時間為40min,隨后按照好氧9min/缺氧21min方式運行,曝氣階段DO濃度控制在0.5~0.8mg/L.
圖1 反應器裝置示意
表1 各試驗階段運行條件
試驗共分為3個階段(表1):階段Ⅰ(1~58d),不投加外源全程硝化污泥;階段Ⅱ(59~124d),因假期與疫情原因反應器未運行,為反應器閑置階段;階段III(125~317d),定期向SBR1和SBR2反應器中投加外源全程硝化污泥,其中,SBR1投加量為反應器中污泥總量(以重量計)的10%,投加周期為20d,分別在反應運行的第140, 160, 180, 200, 220, 240, 260, 280和300天投加;SBR2投加量為反應器中污泥總量的2.5%,投加周期為5d,在第140~300天之間每隔5d投加1次;SBR3為空白組,不進行投加.
試驗用水為模擬廢水,配水成分為:NH4+-N 60mg-N/L、COD(乙酸鈉) 200mg/L、MgSO4·7H2O、CaCl2·2H2O、KH2PO4及微量元素溶液Ⅰ和Ⅱ根據報道配制[14].SBR1-SBR3的接種污泥均為全程硝化和厭氧氨氧化污泥,其中全程硝化污泥取自小試規(guī)模全程硝化-反硝化SBR反應器,厭氧氨氧化污泥取自小試規(guī)模的升流式厭氧污泥床反應器,全程硝化污泥與厭氧氨氧化污泥的接種比例為25:1.后續(xù)生物添加污泥均取自全程硝化-反硝化SBR反應器.
1.3.1 常規(guī)檢測項目 所取水樣經0.45μm定性濾紙過濾后,按照《水和廢水監(jiān)測方法》[15]測定以下參數:采用納氏試劑分光光度法測定氨氮濃度,采用麝香草酚法測定亞硝酸鹽氮濃度,采用N-(1-萘基)-乙二胺光度法測定硝酸鹽氮濃度,SV、SVI、MLSS均采用重量法測定.pH值、DO值均采用便攜式pH和DO在線監(jiān)測記錄儀(WTW,德國)測定. 取約25mL混合污泥樣品進行污泥粒徑的檢測,采用激光粒度儀(Winner2308A)測定.
1.3.2 微生物最大活性檢測 在第304d(階段III)測定SBR1-SBR3中AOB、NOB和AnAOB的最大活性[16].測定AOB和NOB最大活性時,取300mL泥水混合液放入500mL的錐形瓶中,先采用去離子水潤洗3遍,再進行測定,初始氨氮和亞硝酸鹽氮濃度分別為30和15mg-N/L,DO維持在3~4mg/L.在反應周期的末期采用原位測定AnAOB最大活性,以避免DO和COD對AnAOB的影響,初始氨氮和亞硝酸鹽氮濃度分別為30和15mg-N/L.
1.3.3 菌群多樣性檢測 在運行第1和317d時取反應器中混合污泥樣品50mL,4000r/min離心后倒掉上清液,泥樣通過冷凍干燥處理后,送至美吉生物醫(yī)藥科技有限公司,采用Illumina MiSeq PE300平臺進行和高通量測序.
如圖2和表2所示, 在階段I(1~58d),SBR1~ SBR3均未投加全程硝化污泥.SBR1~SBR3的平均氨氮降解率分別為54.3%,48.8%和53.8%,平均出水硝酸鹽氮濃度分別為6.7,7.1和7.5mg-N/L,同時, SBR1~SBR3的平均總氮去除率較低(36.5%,31.7%和35.5%).這表明,在階段I,3個反應器的整體脫氮效果均較差,且脫氮效果波動較大.
圖2 SBR1~SBR3脫氮性能變化規(guī)律
階段III前期(125~139d)為污泥恢復期.從第140天開始,分別定期向SBR1和SBR2中投加全程硝化污泥,SBR3為空白組.在140~317d,SBR1~SBR3的出水氨氮濃度均逐漸下降,平均出水氨氮濃度分別由5.3,7.5和10.2mg-N/L下降至4.6,2.7和5.1mg-N/L,平均氨氮去除率分別由78.9%,75.5%和65.1%上升至84.3%,90.4%和83.6%.結果表明,SBR2的氨氮去除效果明顯優(yōu)于SBR1和SBR3.在第140~219d, SBR1~SBR3的出水硝酸鹽氮濃度分別為8.1,9.4和7.5mg-N/L,仍然處于較高的水平.階段III后期(260~ 317d),出水硝酸鹽氮濃度均逐漸下降,SBR1~SBR3的平均出水硝酸鹽氮濃度分別下降至4.6,4.1和4.2mg-N/L.與之相對應地,SBR1~SBR3的總氮去除率逐漸增加,分別升高至67.2%,76.3%和66.3%.隨著試驗的進行,SBR1~SBR3的脫氮性能逐漸變好, SBR2的脫氮性能明顯優(yōu)于SBR1和SBR3,SBR1的脫氮性能略好于SBR3,此外,由圖2可看出,SBR1與SBR2的脫氮性能較為穩(wěn)定.這表明,外源全程硝化污泥對短程硝化厭氧氨氧化系統(tǒng)穩(wěn)定脫氮有一定程度的促進作用,與前期報道結果一致,且短周期分批次投加的促進效果更為明顯[13]
表2 SBR1-SBR3各階段脫氮性能
為了進一步探究外源全程硝化污泥對系統(tǒng)脫氮性能的影響機理,在階段III后期(第304 天)考察了3個反應器中AnAOB最大活性以及AOB與NOB的最大活性比(圖3).有研究表明,AOB與NOB的活性比是啟動和穩(wěn)定短程硝化的重要因素,可以作為短程硝化快速啟動的一個控制條件[17].在SPNA系統(tǒng)中,AOB與NOB的活性比值越高,意味著AOB比NOB更具有生長優(yōu)勢,越有利于維持短程硝化效果,也更利于AnAOB競爭亞硝酸鹽氮基質,最終提高系統(tǒng)脫氮性能和穩(wěn)定性[18-19].
由圖3可得,在第304d,SBR1~SBR3的AOB與NOB活性比分別為8.79,9.83和8.78.可以看出投加外源全程硝化污泥可能可提高SBR1與SBR2系統(tǒng)中AOB與NOB的活性差值,且短周期分批次投加的效果要明顯高于長周期分批次投加.定期向SPNA系統(tǒng)中投加全程硝化污泥,可提高系統(tǒng)中AOB與NOB活性,但在間歇曝氣條件下,NOB活性受到明顯抑制[12],而AOB活性受到的影響較小,因此,間歇曝氣條件下投加外源全程硝化污泥,可能選擇性地強化了AOB活性,提高AOB與NOB的活性比,促進短程硝化效果,進而為AnAOB提供更多亞硝酸鹽氮,促進厭氧氨氧化反應和AnAOB富集,這與前期研究結果一致.同時,對比SBR1和SBR2,短周期分批次投加對于系統(tǒng)而言是一種更為穩(wěn)定的投加方式,即每次只加少量的NOB對系統(tǒng)中總AOB/ NOB活性比的沖擊和影響較小,系統(tǒng)的穩(wěn)定性更強. SBR1~SBR3中AnAOB最大活性分別由3.43mg-N/ (L·h)升高至7.66,8.19和7.31mg-N/(L·h).與不作任何投加的空白組相比,投加外源全程硝化污泥的SBR1和SBR2有更高的AnAOB活性,驗證了上述推測,且與脫氮性能變化一致.這說明,投加外源全程硝化污泥有利于SPNA系統(tǒng)的厭氧氨氧化脫氮,且在總投加量一樣的條件下,短周期分批次投加的效果好于長周期分批次投加.
圖3 AnAOB最大活性與AOB、NOB最大活性比
在第1和317d對SBR1~SBR3中微生物群落結構進行分析(圖4,表3).SBR1~SBR3的兩大優(yōu)勢菌門均為變形菌門(Proteobacteria)和綠彎菌門(Chloroflexi).其中,混合接種污泥中變形菌門和綠彎菌門的比例分別為34.06%和20.57%,試驗第317天,SBR1~SBR3的變形菌門比例分別為51.09%, 54.05%和53.58%,綠彎菌門分別為13.41%,13.14%和13.70%,整體比例有所升高.有相關研究報道稱Proteobacteria和Chloroflexi與反硝化作用有關[20-22].此外,AnAOB所屬的浮霉菌門(Planctomycetota)相對豐度也在不斷增加,SBR1~SBR3的Planctomycetota豐度分別由1.43%升高至3.47%, 3.93%和3.61%.這些結果可能是試驗后期SBR1~SBR3脫氮性能均有所提高的原因之一.
圖4 SBR1~SBR 3門水平上微生物組成
在屬水平上,SBR1~SBR3中的相對豐度分別由1.75%(1d)上升到2.58%、1.94%和2.18%(317d).表明SBR1~SBR3中NOB均有不同程度的提高,且SBR1中的NOB豐度明顯高于另外兩組,分析是因為試驗投加的外源全程硝化污泥有較高的NOB豐度,投加后會使系統(tǒng)的相對豐度升高.但值得注意的是,SBR2中NOB相對豐度增加幅度最小,低于空白組,表明短周期分批次投加外源全程硝化污泥不會造成SPNA系統(tǒng)中NOB豐度的額外增加,反而有一定抑制NOB生長的作用.為NOB的典型菌屬,其含量越低越利于實現短程硝化,同時SBR1~SBR3中AOB的優(yōu)勢菌種的相對豐度分別由0.19%上升至1.6%、1.66%和1.66%.該結果與AOB和NOB活性比的變化規(guī)律一致,表明短周期分批次投加外源全程硝化污泥更有利于穩(wěn)定短程硝化效果.
在試驗后期,為SBR1~SBR3中優(yōu)勢菌屬,SBR1~SBR3中的相對豐度由8.8%分別上升至32.75%、37.96%和36.96%,有研究指出作為一種內源短程反硝化菌,可以將COD轉換為內碳源,有利于亞硝酸鹽氮積累,進而有利于促進系統(tǒng)的厭氧氨氧化反應的進行[23-24].SBR2中豐度最高,短周期分批次投加全程硝化污泥可能利于促進富集,這可能也是SBR2脫氮性能較好的原因之一.為優(yōu)勢AnAOB,其相對豐度由0.03%分別上升至0.28%、0.26%、0.32%,與AnAOB活性的變化規(guī)律有所不同,分析可能是因為高通量測序數據使用的是相對豐度,定期向SBR1和SBR2添加全程污泥,全程硝化污泥中AnAOB豐度較低,而空白組未做任何生物添加,所以導致SBR1與SBR2的AnAOB相對豐度略低于空白組.
表3 SBR1~SBR3屬水平上微生物群落相對豐度
注:不同灰度底色代表屬水平上微生物群落相對豐度大小,底色越深,豐度越大.
分別于第185和315天,對SPNA系統(tǒng)中污泥粒徑進行檢測(圖5).結果表明SBR1的小絮體污泥(0~100μm)由55.71%增加至70.59%,SBR2由 41.26%增加至75.54%,SBR3由67.17%降低至48.71%,而SBR1中粒徑較大的活性污泥(>200μm)由13.58%降低至1.95%,SBR2由31.6%降低至2.7%,SBR3由2.59%增加至19.42%.可以得出,投加外源全程硝化污泥使得反應器內小絮體所占比例增高,推測原因為投加的外源全程污泥粒徑較小,使系統(tǒng)中的污泥粒徑整體有所下降.
有相關研究證明污泥顆粒越大,越有利于SPNA系統(tǒng)脫氮效果[25].因為隨著粒徑的增大,相同體積的顆粒污泥的比表面積變小,污泥顆粒單位面積的氨氮負荷增加,氧的傳質效率變低,進而使得顆粒內的好氧面積變小,缺氧面積變大.一方面,AOB的氧親合力大于NOB,在此條件下利于短程硝化效果的穩(wěn)定;另一方面,有利于厭氧氨氧化菌生長和持留,所以大顆粒污泥在理論上更有利于AOB、AnAOB的富集和NOB的不斷淘洗,進而有利于提高系統(tǒng)的脫氮性能[26].因此,若投加的外源全程硝化污泥的粒徑較大,可能會提高SPNA系統(tǒng)中的污泥粒徑范圍,進一步促進AnAOB富集,提高系統(tǒng)穩(wěn)定性.
本試驗所用的全程硝化污泥粒徑較小,導致投加外源全程硝化污泥的SBR1和SBR2中粒徑范圍均顯著低于SBR3,但即便如此,SBR1和SBR2的整體脫氮效果仍明顯優(yōu)于SBR3,SBR1與SBR2中AnAOB的活性以及AOB/NOB活性比值均高于SBR3.上述結果表明,即使在粒徑較小的情況下,試驗組的脫氮效果仍好于空白組,投加外源全程硝化污泥對系統(tǒng)運行性能的提高效果可以彌補由于粒徑小對系統(tǒng)性能的影響.
圖5 SBR1-SBR3在D185和D315的粒徑分布
3.1 向城市污水短程硝化-厭氧氨氧化系統(tǒng)中投加外源全程硝化污泥利于提高系統(tǒng)脫氮性能和穩(wěn)定性,其中,在投加總比例相同的條件下,短周期分批次投加(投加周期為5d,投加量為2.5%)全程硝化污泥效果更好.
3.2 全程硝化污泥中含有較高的AOB和NOB豐度,在間歇曝氣條件下向SPNA系統(tǒng)中投加全程硝化污泥,可選擇提高SPNA系統(tǒng)中AOB與NOB的活性比,進而可為AnAOB提供更穩(wěn)定的亞硝酸鹽氮,促進AnAOB富集.
3.3 短周期分批次投加外源全程硝化污泥可實現更高的AOB與NOB活性比值,有利于抑制NOB活性和維持穩(wěn)定的短程硝化效果,促進厭氧氨氧化脫氮;此外,短周期分批次投加更利于富集內源短程反硝化菌,進一步促進厭氧氨氧化反應和維持系統(tǒng)穩(wěn)定.因此,不同的污泥投加方式對系統(tǒng)脫氮效果的促進程度不同,將本研究成果應用于其他系統(tǒng)中時,可能需要對投加量與周期進行進一步優(yōu)化.
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Effects of exogenous nitrification sludge on the single-stage partial nitrification-anammox system of municipal sewage.
HE Zhao-ming1, LIU Jia-ni1,TIAN Ya-ru1, YU De-shuang1, MIAO Yuan-yuan1*, ZHANG Wen-ke1, MA Guo-cheng1, ZHAO Xin-chao1, YUAN Yue2
(1.Department of Environment Science and Engineering, Qingdao University, Qingdao 266071, China;2.Shanghai Municipal Engineering Design and Research Institute Co. Ltd, Shanghai 200092, China)., 2022,42(9):4122~4128
In order to improve the nitrogen removal performance and stability of the single-stage partial nitrification-anammox (SPNA) system treating municipal sewage, the effects and mechanisms of adding exogenous nitrification sludge to mainstream SPNA system were evaluated under intermittent aeration condition. The results showed that the total nitrogen removal efficiency of the control SPNA system (SBR3) increased from 35.5% to 66.3%. The total nitrogen removal efficiencies of SPNA systems with nitrification sludge added in batches in a short cycle (SBR2, the dosing period was 5d, the dosing ratio was 2.5%) and in batches in a long cycle (SBR1, the dosing period was 5d, the dosing ratio was 2.5%) increased from 31.7% and 36.5% to 76.3% and 67.2%, respectively. And the addition of nitrification sludge was beneficial to the nitrogen removal performance of mainstream SPNA system and adding nitrification sludge in batches in a short cycle showed better performance. The maximum activities of anaerobic ammonium oxidation bacteria (AnAOB) in SBR1-SBR3 increased from 3.43mg-N/(L·h) to 7.66, 8.19% and 7.31mg-N/(L·h), respectively, and the activity ratios of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were 8.79, 9.83 and 8.78, respectively. Adding nitrification sludge under intermittent aeration condition could selectively inhibit NOB and enrich AOB, leading to a higher activity ratio of AOB and NOB and more stable partial nitrification, which provided stable substrates for AnAOB. In addition, adding the nitrification sludge in batches in a short cycle could reduce the impact of NOB of exogenous nitrification sludge on the system, which was more conducive to achieve high AOB/NOB activity ratio and improved the stability of system. Moreover, the relative abundance of, thought to be the endogenous partial denitrification bacteria, increased obviously, providing AnAOB with more nitrite and was further beneficial to AnAOB enrichment. Therefore, this study provided new ideas for promoting the application of mainstream anammox process.
single-stage of partial nitrification-anammox;bioaugmentation;nitrification sludge;intermittent aeration;high- throughput sequencing;influencing factors
X703
A
1000-6923(2022)09-4122-07
2022-02-28
國家自然科學基金資助項目(51978348),青島市科技計劃項目科技惠民示范引導專項(2022-3-7-cspz-11-nsh),山東省大學生創(chuàng)新創(chuàng)業(yè)計劃(S202011065123),上海市青年科技英才揚帆計劃資助(20YF1445600)
*責任作者, 講師, Miaoyy@qdu.edu
賀昭銘(2000-),女,山東棗莊人,青島大學本科生,環(huán)境工程專業(yè).