劉 春,王聰聰,劉 穎,張瑞娜,陳曉軒,張 靜,張 磊

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生物膜反應器-單寧酸鐵處理低C/N廢水的脫氮性能

劉 春*,王聰聰,劉 穎,張瑞娜,陳曉軒,張 靜,張 磊

(河北科技大學環(huán)境科學與工程學院,河北省污染防治生物技術重點實驗室,河北 石家莊 050018)

采用生物膜反應器耦合包埋型單寧酸鐵處理低C/N比廢水,考察其脫氮性能,分析了生物脫氮過程功能菌群的變化,以及單寧酸鐵強化脫氮的作用機制.結果表明,生物膜反應器耦合包埋型單寧酸鐵,具有低C/N比廢水高效脫氮性能.進水C/N比為1:2.7時,TN平均去除率可達80.0%,TN平均去除負荷為1.38kg/(m3·d).生物膜反應器內隨著進水C/N比降低,優(yōu)勢脫氮過程從同步硝化-反硝化過程向同步短程硝化-厭氧氨氧化-反硝化(SNAD)過程轉變,厭氧氨氧化過程對TN去除的貢獻率逐漸升高至76.2%,亞硝化菌群和厭氧氨氧化菌群成為優(yōu)勢生物脫氮功能菌群.包埋型單寧酸鐵在生化處理后,通過吸附-催化氨氧化作用同步去除氨氮和亞硝酸鹽氮,進一步提高TN去除性能.因此,耦合單寧酸鐵強化生物膜反應器SNAD脫氮過程,是實現低C/N比廢水高效脫氮新的有效途徑.

生物膜反應器；包埋型單寧酸鐵；脫氮；SNAD過程；催化氨氧化

生物脫氮是廢水處理研究領域的熱點[1].傳統(tǒng)硝化-反硝化生物脫氮過程能耗高、碳源需求量大,不適于低氮碳比(C/N)廢水脫氮處理[2-3].同步短程硝化-厭氧氨氧化-反硝化(SNAD)過程是一種新型生物脫氮工藝[4-6],可在單個反應器內利用短程硝化、厭氧氨氧化和反硝化過程同時去除總氮(TN)和有機物[7-8],為低C/N比廢水生物脫氮提供了高效低耗的新途徑[9-10].

厭氧氨氧化是SNAD過程的關鍵環(huán)節(jié)[11],但厭氧氨氧化菌群的形成和工藝穩(wěn)定運行較為困難[13],成為SNAD脫氮過程應用的主要限制因素.研究表明,由單寧酸與鐵離子絡合形成的金屬-有機骨架材料單寧酸鐵,能夠同步吸附氨氮和亞硝酸鹽氮[14],并將氨氮和亞硝酸鹽氮通過催化氨氧化轉化為氮氣,從而實現氨氮和亞硝酸鹽氮吸附-催化氨氧化脫氮過程[15].因此,在實現SNAD過程的生物反應器中耦合單寧酸鐵,形成厭氧氨氧化和催化氨氧化的協(xié)同作用,有助于獲得更為穩(wěn)定高效的脫氮效率.

生物膜反應器可在生物膜內形成氧濃度梯度,為亞硝化細菌、厭氧氨氧化細菌和反硝化細菌的生長提供適宜的生長環(huán)境,能夠實現SNAD脫氮過程[13,16].本研究運行生物膜反應器處理低C/N比廢水,使其逐漸實現SNAD脫氮過程;在此基礎上耦合包埋型單寧酸鐵,進一步強化SAND脫氮過程以獲得更高的脫氮能力.同時,通過高通量測序分析生物膜內脫氮功能菌群變化,并對包埋型單寧酸鐵脫氮過程和機制加以探究,從而為低C/N比廢水脫氮處理提供新的解決途徑.

1 材料與方法

1.1 實驗裝置

實驗裝置如圖1所示,包括生物膜反應器(R1)和生物膜/單寧酸鐵復合反應器(R2). R1有效容積為16.6L,底部設有微孔曝氣盤,反應器內填充10L環(huán)狀碳纖維填料(直徑10mm,高8mm,流化態(tài)),作為生物膜生長載體.R2有效容積2.5L,底部填充1.5L環(huán)狀碳纖維填料(運行至一定階段后由R1移入,固定床),上部填充0.4L包埋型單寧酸鐵(固定床).廢水經過進水計量泵1進入R1底部,處理后由上部溢流出水至中間水箱,而后經過進水計量泵2由底部進入R2,處理后由上部溢流出水.

圖1 耦合工藝系統(tǒng)實驗裝置示意

1.2 包埋型單寧酸鐵的制備

在常溫下,將單寧酸(0.01mol/L)溶液和FeCl3(0.2mol/L)溶液按體積比1:1混合,而后滴加NaHCO3(0.65mol/L)溶液調節(jié)pH值至7左右,靜置至出現黑色沉淀即為單寧酸鐵.用去離子水將單寧酸鐵洗滌后,離心(8000r/min,2min)并冷凍干燥(-70℃)40h左右,得到單寧酸鐵粉末(圖2A).

將制得的單寧酸鐵粉末按照1g單寧酸鐵與50mL海藻酸鈉溶液(2%,/)比例混合,然后將混合液滴加到氯化鈣溶液(2%,/)中,迅速形成凝膠球,靜置12h使其充分包埋,從而得到海藻酸鈉包埋型單寧酸鐵(圖2B).

圖2 單寧酸鐵粉末(A)和海藻酸鈉包埋單寧酸鐵(B)

1.3 實驗方法

向生物膜反應器內接種某城鎮(zhèn)污水處理廠二沉池回流污泥,初始接種污泥濃度(MLSS)約為0.8g/L,悶曝48h后將懸浮污泥排出,投加人工模擬生活污水,以葡萄糖為碳源,以NH4Cl為氮源,調節(jié)葡萄糖和NH4Cl投加量以控制C/N,同時添加P、Ca、Mg、Fe、Mn等微量元素,添加NaHCO3調節(jié)pH值并提供無機碳源[17].按照設定條件連續(xù)運行.運行溫度為(30±2)℃,進出水pH值范圍保持在7.4~8.2.

表1 運行條件

系統(tǒng)連續(xù)運行過程可分為4個階段,啟動階段~Phase2階段僅運行R1,運行過程中,調節(jié)空氣流量控制生物膜反應器內溶解氧(DO)濃度逐漸低于1.0mg/L,并提高氨氮負荷及C/N比.Phase3階段串聯運行R1和R2,生物填料總量不變(R1向R2移入1.5L生物填料,R1出水經過R2內生物填料層消耗DO,為包埋型單寧酸鐵催化氨氧化創(chuàng)造低DO條件).各階段運行條件見表1.

運行過程中,測定進出水COD、氨氮、TN、亞硝酸鹽氮、硝酸鹽氮、DO濃度和生物膜生物量變化,并在Phase2階段結束時檢測分析生物膜細脫氮功能菌群及豐度.

1.4 分析方法

水質指標COD、氨氮、硝酸鹽氮、亞硝酸鹽氮、TN等,均采用國標方法測定.DO濃度采用溶解氧測定儀(cell Oxi330,德國WTW)測定.

運行過程中,每周從反應器中取一定量填料進行超聲清洗,使生物膜脫落并懸浮于液相中,并測定其SS和VSS,根據所取填料占反應器內總填料的比例核算反應器內生物膜生物量(以SS和VSS濃度計)[19-20].在Phase2階段結束時,按同樣方法收集生物膜樣品,進行高通量測序(上海派森諾生物科技股份有限公司),獲得生物膜樣品屬水平細菌種群構成和相對豐度數據,分析其中的脫氮功能菌群,包括亞硝化菌群(AOB)、硝化菌群(NOB)、厭氧氨氧化菌群(AnAOB)和反硝化菌群(DNB),并計算其豐度[21].

2 結果與討論

2.1 處理系統(tǒng)運行性能

2.1.1 生物膜生物量變化 運行各階段處理系統(tǒng)中生物量變化如圖3所示.可以看到,R1單獨運行時,啟動階段生物膜生物量逐漸升高,至啟動階段運行結束時SS達到1.50g/L,VSS達到1.15g/L,VSS/SS為0.77,完成掛膜.Phase1~Phase2階段生物膜生物量波動上升并趨于穩(wěn)定,兩個階段平均SS分別為1.40, 1.66g/L,平均VSS分別為1.03,1.29g/L,平均VSS/SS分別為0.74,0.78.Phase3階段R1、R2耦合運行后,系統(tǒng)中平均SS為1.67g/L,平均VSS為1.35g/L, VSS/SS為0.81,與Phase2階段基本相當.

2.1.2 COD去除性能 運行各階段COD進出水濃度及去除率變化如圖4所示.可以看到,R1單獨運行時,啟動階段~Phase2階段進水COD平均濃度分別為54.4,58.5,56.1mg/L,出水COD平均濃度分別為30.8,27.1,16.5mg/L,COD平均去除率分別為43.0%、53.4%、70.3%.COD平均去除負荷分別為0.28,0.38, 0.48kg/(m3·d).COD去除率不斷提高,COD去除負荷也隨之升高.

圖3 處理系統(tǒng)中生物膜生物量變化

圖4 處理系統(tǒng)COD去除性能

Phase3階段R1、R2耦合運行后,平均COD進出水濃度、去除率和去除負荷分別為56.3mg/L、11.5mg/L、79.4%和0.54kg/(m3·d),COD去除性能進一步提高.

2.1.3 氨氮去除性能 運行各階段氨氮進出水濃度及去除率變化如圖5所示.可以看到, R1單獨運行時,啟動階段~Phase2階段進水氨氮平均濃度分別為54.4,105.2,152.1mg/L,出水氨氮平均濃度分別為24.3,33.8,47.0mg/L,氨氮平均去除率分別為55.2%、67.6%、68.9%,氨氮平均去除負荷分別為0.36,0.86, 1.26kg/(m3·d).可見,啟動階段~Phase2階段氨氮去除率持續(xù)升高并趨于穩(wěn)定,氨氮去除負荷亦隨之升高.Phase3階段R1、R2耦合運行后,平均氨氮出水濃度、去除率和去除負荷分別為27.3mg/L、80.9%和1.39kg/(m3·d),去除性能高于Phase2階段,表明耦合包埋型單寧酸鐵能夠促進氨氮去除.

2.1.4 TN去除性能 運行各階段TN進出水濃度及去除率變化如圖6所示.可以看到,R1單獨運行時,啟動階段~Phase2階段進水TN平均濃度分別為54.4,105.2,152.1mg/L,出水TN平均濃度分別為28.6, 37.7,51.7mg/L,TN平均去除率分別為47.5%、63.7%、66.0%,TN平均去除負荷分別為0.31,0.81,1.20kg/ (m3·d).TN去除過程與氨氮去除過程類似,啟動階段TN去除率逐漸升高,Phase1~Phase2階段TN去除率繼續(xù)升高并趨于穩(wěn)定.同時,隨著進水TN負荷升高, TN去除負荷隨之升高.

圖5 處理系統(tǒng)氨氮去除性能

圖6 處理系統(tǒng)總氮(TN)去除性能

Phase3階段R1、R2耦合運行后,平均TN進出水濃度、去除率和去除負荷分別為150.8mg/L、27.6mg/L、80.0%和1.38kg/(m3·d),TN去除性能比Phase2階段有明顯提高,表明耦合包埋型單寧酸鐵能夠促進TN去除.

2.1.5 亞硝酸鹽氮和硝酸鹽氮累積 進水中氮的存在形式僅有氨氮,各運行階段亞硝酸鹽氮和硝酸鹽氮出水濃度即為累積程度,其變化如圖7所示. R1單獨運行時,啟動階段出水中硝酸鹽氮平均濃度為3.54mg/L,亞硝酸鹽氮平均濃度為0.73mg/L.Phase1~ Phase 2階段亞硝酸鹽氮累積顯著增加,平均濃度分別為3.31,4.44mg/L,而硝酸鹽氮累積降低,平均濃度分別為0.65,0.28mg/L. 啟動階段~Phase2階段亞硝酸鹽氮、硝酸鹽氮累積量的變化,表明隨著提高TN負荷逐漸形成低C/N比進水條件,并控制DO濃度低于1.0mg/L,可能使得R1中TN去除由硝化-反硝化過程向SNAD過程轉變.

圖7 處理系統(tǒng)出水亞硝酸鹽和硝酸鹽濃度變化

Phase3階段R1、R2耦合運行后,亞硝酸鹽氮累積明顯減少,平均濃度降至1.16mg/L,同時氨氮和TN去除亦明顯增加,表明包埋型單寧酸鐵可以加速亞硝酸鹽氮和氨氮去除,從而提高TN去除效率.

已有研究表明,SNAD過程獲得較高的氨氮和TN去除效率通常所需HRT較長(>24h)[13,22].本研究中生物膜反應器Phase 2階段HRT僅為2h時,即可獲得基本相當的氨氮和TN去除效率,氨氮和TN去除負荷可達1.26,1.20kg/(m3·d),顯著高于已有研究中普遍達到的TN去除負荷(0.2~1.0)kg/(m3·d)[9]. Phase3階段生物膜反應器耦合單寧酸鐵后,整體氨氮和TN去除負荷進一步提高至1.39,1.38kg/(m3·d).

2.2 生物脫氮機制分析

2.2.1 生物脫氮過程 R1單獨運行時,TN去除依賴于硝化-反硝化過程和SNAD過程及同化作用.在同化作用中,假設典型的微生物細胞分子式為C5H7O2N,則N在微生物細胞(以VSS計)中所占質量比約為12.4%(干重);由此,根據VSS增長量(圖3)可粗略估算啟動階段~ Phase2階段同化作用去除TN貢獻率分別為: 0.63%、0.12%、0%.可見,啟動階段和Phase1階段,生物膜VSS增長明顯,同化作用對去除TN略有貢獻;Phase2階段生物膜VSS總體穩(wěn)定,因而同化作用對TN去除貢獻率幾乎為0.因此,微生物增殖的同化作用對TN去除量相對于反應器內TN的去除總量而言可以忽略.

不考慮同化作用,硝化-反硝化過程和SNAD過程主要脫氮反應方程式如式(1)~(5)所示.其中,硝化-反硝化過程包括反應方程式(1)、(2)、(4)和(5),SNAD過程包括反應方程式(1)、(3)、(4)和(5).

圖8 脫氮過程氮平衡估算模型(Phase 2)

依據脫氮反應方程式(1)~(5)所反映的化學計量關系,同時根據生物膜反應器運行各階段進出水COD、氨氮、TN、亞硝酸鹽氮和硝酸鹽氮濃度變化,進行氮平衡模型計算[22],以反映各生物脫氮過程,特別是厭氨氧化過程和反硝化過程對TN去除的貢獻率,結果如圖8所示(以Phase 2階段為例).可以看到,Phase 2階段厭氧氨氧化過程對TN去除的貢獻率為76.2%,反硝化過程對TN去除的貢獻率為23.8%,可見Phase 2階段SNAD過程為TN去除的主要途徑.

啟動階段~Phase 2階段厭氧氨氧化過程和反硝化過程對TN去除的貢獻率如表2所示.可以看到,厭氧氨氧化過程對TN去除的貢獻率由啟動階段的30.7%提高至Phase 2階段的76.2%;反硝化過程對TN去除的貢獻率由啟動階段的69.3%下降至Phase 2階段的23.8%.可見,啟動階段~Phase 2階段R1內,厭氧氨氧化過程在TN去除作用逐漸提高并占據優(yōu)勢,是實現生物脫氮過程由硝化-反硝化過程向SNAD過程轉變的關鍵.

表2 厭氧氨氧化和反硝化過程對TN去除的貢獻率

2.2.2 生物脫氮功能菌群分析 R1運行至Phase2階段實現了SNAD脫氮過程,對Phase2階段SNAD生物脫氮過程相關功能菌群進行分析,結果如表3所示.可以看到,生物膜樣品中AOB菌群為(亞硝化單胞菌屬)和(亞硝化葉菌屬);NOB菌群為(硝化桿菌屬)和(硝化螺旋菌屬); AnAOB菌群為和; DNB菌群為、(假單胞菌屬)、(脫氯單胞菌屬)、(索氏菌屬)以及(黃桿菌屬)[21-24].

表3 生物膜內生物脫氮功能菌群(Phase 2)

計算Phase2階段生物脫氮功能菌群的平均相對豐度,結果如表3所示.可以看到,Phase2階段AOB、NOB、AnAOB和DNB平均相對豐度分別為23.7%、11.6%、39.9%和14.4%.可見, Phase2階段AOB和AnAOB成為優(yōu)勢生物脫氮功能菌群,因而實現了SNAD脫氮過程.

2.3 包埋型單寧酸鐵脫氮機制分析

如前所述,Phase3階段R1、R2耦合運行時,氨氮和TN去除性能均有明顯提高,表明包埋型單寧酸鐵對脫氮性能具有強化作用.Phase3階段對R2反應器生化處理后(R2取樣口)和包埋型單寧酸鐵處理后(R2出水口2)出水氨氮和亞硝酸鹽氮濃度進行測定.結果表明,生化處理后再經過包埋型單寧酸鐵處理,氨氮平均濃度由40.5mg/L降至27.3mg/L,亞硝酸鹽氮平均濃度由15.6mg/L降至1.2mg/L,而TN平均去除率分由60.8%升至80.0%.可見,包埋型單寧酸鐵可以同步去除氨氮和亞硝酸鹽氮,從而提高TN去除性能.

圖9 單寧酸鐵處理中亞硝酸鹽氮與氨氮去除量比值(Phase 3)

進一步計算Phase3階段包埋型單寧酸鐵處理中亞硝酸鹽氮去除量與氨氮去除量的比值(),結果如圖9所示.可以看到,開始運行階段值較低,而后逐漸升高,接近并穩(wěn)定在1.32左右.造成這一變化趨勢的原因是:開始運行階段,單寧酸鐵吸附對亞硝酸鹽氮和氨氮去除具有重要作用,而單寧酸鐵對氨氮的吸附能力更強[14],因此氨氮去除量相對較高,值較低;隨著運行時間延長,單寧酸鐵逐漸吸附飽和,亞硝酸鹽氮和氨氮主要通過催化氨氧化作用去除,因此值逐漸接近并穩(wěn)定在催化氨氧化的理論值1.32.可見,單寧酸鐵通過吸附-催化氨氧化作用同步去除亞硝酸鹽氮和氨氮.因此,在生物膜反應器中實現SNAD脫氮過程,并耦合單寧酸鐵吸附-催化氨氧化作用加以強化,是實現低C/N比廢水高效脫氮的新的有效途徑.

3 結論

3.1 生物膜反應器耦合包埋型單寧酸鐵,可獲得低C/N比廢水高效脫氮性能.進水C/N比為1:2.7時,TN平均去除率可達到80.0%,TN平均去除負荷為1.38kg/(m3·d).

3.2 生物膜反應器內控制DO濃度并降低進水C/N比,脫氮過程從硝化-反硝化向SNAD過程轉變,厭氧氨氧化過程對TN去除的貢獻率逐漸升高至76.2%,亞硝化菌群和厭氧氨氧化菌群成為優(yōu)勢生物脫氮功能菌群,SNAD過程成為生物脫氮的主要途徑.

3.3 包埋型單寧酸鐵在生化處理后,通過吸附-催化氨氧化作用同步去除氨氮和亞硝酸鹽氮, 進一步提高TN去除性能.

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Nitrogen removal process in low C/N ratio wastewater treatment using a biofilm reactor coupled with embedded ferric tannate.

LIU Chun*, WANG Cong-cong, LIU Ying, ZHANG Rui-na, CHEN Xiao-xuan, ZHANG Jing, ZHANG Lei

(Pollution Prevention Biotechnology Laboratory of Hebei Province, School of Environmental Science and Engineering, Hebei University of Science and Technology, Shijiazhuang 050018, China)., 2019,39(5)：1993~1999

A biofilm reactor coupled with embedded ferric tannate was used to treat low C/N ratio wastewater and its nitrogen removal performance was investigated. The biological nitrogen removal process and the corresponding functional bacterial populations in the biofilm were also analyzed. The enhanced nitrogen removal by ferric tannate and its mechanism were also discussed. The results showed that the efficient nitrogen removal for low C/N ratio wastewater could be achieved in the biofilm reactor coupled with embedded ferric tannate. When the influent C/N ratio was 1:2.7, the average total nitrogen (TN) removal efficiency was 80.0%, and the average TN loading rate removed was 1.38kg/(m3·d). The dominant biological nitrogen removal process was converted from simultaneous nitrification-denitrification to simultaneous partial nitrification, ANAMMOX and denitrification (SNAD) process in the biofilm reactor when the influent C/N ratio decreased. As a result, the contribution of ANAMMOX process to TN removal increased up to 76.2% in the biofilm reactor. The populations of nitrosate bacteria and anammox bacteria became dominant for biological nitrogen removal. The ammonia nitrogen and nitrite nitrogen could be removed simultaneously by embedded ferric tannate due to the adsorption-catalytic ammonia oxidation process after biological treatment, resulting in further improvement of TN removal. Therefore, the enhancement of SNAD process by ferric tannate in a biofilm reactor is a new and effective solution for efficient nitrogen removal of low C/N ratio wastewater.

biofilm reactor；embedded ferric tannate；nitrogen removal；SNAD process；catalytic ammonia oxidation

X703

A

1000-6923(2019)05-1993-07

劉 春(1976-),男,河南安陽人,教授,博士,主要從事廢水處理理論與技術研究工作.發(fā)表論文80余篇.

2018-10-27

國家自然科學基金資助項目(51808186)

*責任作者, 教授, liuchun@hebust.edu.cn