殷霄云,劉芝宏,周愛娟,李亞男,岳秀萍,崔芷瑄

紫外耦合游離亞硝酸強化剩余污泥厭氧發(fā)酵產(chǎn)酸研究

殷霄云,劉芝宏*,周愛娟,李亞男,岳秀萍,崔芷瑄

(太原理工大學(xué)環(huán)境科學(xué)與工程學(xué)院,山西 太原 030024)

為打破傳統(tǒng)厭氧發(fā)酵過程中污泥破壁溶胞困難和產(chǎn)酸效能低的瓶頸,探究了紫外光(UV)耦合游離亞硝酸(FNA)預(yù)處理對污泥發(fā)酵產(chǎn)酸的影響,并與熱(H)和超聲法(US)耦合FNA預(yù)處理進行了對比分析.結(jié)果表明,UV輔助FNA聯(lián)合預(yù)處理(FNA-UV)對細胞破碎和胞外聚合物的剝離具有協(xié)同效應(yīng),?OH和?O2-作為反應(yīng)中間體,其強度遠高于其他預(yù)處理組(FNA-US和FNA-H),與?NO,?NO2及ONOO-等中間產(chǎn)物共同促進了溶解性有機物的釋放,溶解性碳水化合物和蛋白質(zhì)含量相比FNA組分別提升60%和90%,進而為后續(xù)水解產(chǎn)酸過程提供了充足的底物.FNA-UV組短鏈脂肪酸(SCFAs)濃度于第4d達到峰值,為(201.8±4.8)mg COD/g VSS,相比FNA組提升67%,乙酸占比高達56.8%.通過發(fā)酵末期對各體系進行碳平衡分析表明,紫外耦合FNA預(yù)處理在污泥減量、溶解性有機物的釋放與轉(zhuǎn)化、SCFAs的產(chǎn)生方面具有重要作用.微生物群落分析表明,FNA-UV對功能菌群的富集發(fā)揮重要作用,表現(xiàn)為厭氧發(fā)酵菌和反硝化菌的有效增強,相比其他各組提升了23.7%～270.6%.

游離亞硝酸；剩余污泥；短鏈脂肪酸；厭氧發(fā)酵；紫外；高通量測序

近年來,隨著我國城鎮(zhèn)化進程的日益加速,剩余污泥作為市政污水處理廠生物處理段的伴生產(chǎn)物,其產(chǎn)量隨污水處理能力的提升而飛速增長[1].據(jù)報道,剩余污泥可作為能源和資源的載體,回收污泥中的能源和資源成為目前研究的重點和難點[2-3].厭氧發(fā)酵技術(shù)(AF)通過微生物代謝進行水解酸化,進而實現(xiàn)污泥減量和資源回收(如短鏈揮發(fā)性脂肪酸SCFAs、甲烷CH4),成為污泥處理的重要途徑[4]. SCFAs具有高附加值,不僅可以作為各種化工產(chǎn)品生產(chǎn)的原材料,還可以作為污水處理廠的有機碳源[5].然而,由于污泥中有機物受細胞壁和胞外聚合物(EPS)包裹,導(dǎo)致其釋放困難,水解過程成為剩余污泥AF的限速步驟.因此,尋找高效的預(yù)處理技術(shù)成為污泥資源化的先決條件[6].

游離亞硝酸(FNA)作為亞硝酸鹽的質(zhì)子化形式,是一種綠色可再生的抗菌劑[7-8].在百萬分之一水平下,FNA及其衍生物可與細胞/EPS中的脂質(zhì)、蛋白質(zhì)、碳水化合物和脫氧核糖核酸(DNA)反應(yīng),有效破壞微生物細胞膜,分解胞內(nèi)大分子有機物,為產(chǎn)酸菌提供底物[9].單獨采用FNA預(yù)處理可實現(xiàn)污泥有效溶胞(1～2mg N/L預(yù)處理污泥24～48h,可滅活50%～ 80%的細胞[10]).但相關(guān)研究表明,經(jīng)FNA預(yù)處理后仍有大量耐受細胞處于穩(wěn)態(tài),且其對EPS的破壞作用極為有限,進而限制水解產(chǎn)酸效能(3.04mg N/L FNA預(yù)處理污泥,EPS中腐殖質(zhì)等大分子物質(zhì)不能被水解[11])[12-13].因此,越來越多學(xué)者采用物理/機械法(冷凍[14]、熱[15]、超聲[16])和投加化學(xué)試劑(Fenton法[13]、過氧化氫[17]、鼠李糖脂[18])與FNA預(yù)處理耦合,有效強化了水解、產(chǎn)酸和產(chǎn)甲烷過程.然而,化學(xué)法存在反應(yīng)條件苛刻,易造成二次污染等缺陷,限制了其大規(guī)模應(yīng)用[19].相比其他物理預(yù)處理方法,紫外預(yù)處理具有處理效率高、成本低廉和無二次污染等優(yōu)點,通過損傷和破壞生物活性,分解胞內(nèi)物質(zhì),導(dǎo)致細胞破裂,成為重要的污泥預(yù)處理手段[20].研究發(fā)現(xiàn)紫外法(UV)與其它預(yù)處理方式聯(lián)合能有效破壞污泥EPS,使污泥絮體分解(UV輔助零價鐵活化過硫酸鈉(PDS)氧化法、UV耦合CaO2法)[21-22].已有研究表明亞硝酸鹽在UV照射下可能產(chǎn)生活性氮物種(×NO、×NO2、ONOO-、ONOOH)和活性氧物種(×OH、×O2-),通過電子轉(zhuǎn)移、雙鍵加成或氫抽提等方式破壞細胞內(nèi)各種蛋白質(zhì)、脂質(zhì)和DNA結(jié)構(gòu)[11,20],但UV聯(lián)合FNA預(yù)處理對污泥細胞破裂、EPS分解、厭氧發(fā)酵產(chǎn)酸效能及作用機理尚不明晰.

基于此,本研究通過超聲、熱和紫外照射3種方式強化FNA預(yù)處理污泥,考察不同預(yù)處理方式對污泥發(fā)酵產(chǎn)酸性能的影響,以及對污泥微生物多樣性的影響,旨在為剩余污泥資源化利用提供理論參考.

1 材料和方法

1.1 實驗材料

本實驗所用污泥取自山西省太原市楊家堡污水處理廠的污泥濃縮池,所取污泥首先用200目篩子過濾,靜置24h后除去上清液,置于4℃冰箱備用.污泥濃縮后10000r/min離心,經(jīng)0.45μm濾膜過濾后測定其相關(guān)性質(zhì),剩余污泥初始性質(zhì)如表1所示.

表1 剩余污泥初始性質(zhì)

1.2 實驗設(shè)計

為了考察3種物理法輔助FNA預(yù)處理對污泥破壁及厭氧發(fā)酵效果的影響,共設(shè)置5組實驗:未預(yù)處理污泥作為空白對照組,FNA預(yù)處理組,超聲、熱和紫外照射強化FNA預(yù)處理實驗組(FNA-H,FNA-US,FNA-UV).FNA投加量設(shè)置2.13mg N/L[2],FNA預(yù)處理12h后進行1h的物理強化處理,具體參數(shù)如表2所示[23-26].預(yù)處理后,測定EPS中溶解性碳水化合物及蛋白質(zhì)含量.發(fā)酵實驗采用厭氧發(fā)酵瓶,工作容積為400mL,取350mL預(yù)處理污泥和50mL新鮮污泥加入發(fā)酵瓶中,利用1.0mol/L NaOH或10% HCl調(diào)節(jié)pH值至(7.0±0.1),并連續(xù)充氮15min以保證厭氧環(huán)境.每組設(shè)置3個平行,反應(yīng)器置于35 ℃,120r/min的恒溫搖床中進行為期10d的發(fā)酵實驗.每隔24h取定量發(fā)酵污泥混合液,10000r/min離心取上清液,經(jīng)0.45μm濾膜過濾后測定上清液中的NH4+-N,SCFAs,溶解性蛋白質(zhì),溶解性碳水化合物的含量.

表2 實驗組參數(shù)設(shè)置

1.3 分析方法

采用熱提取法對預(yù)處理后EPS進行提取,pH值采用pH計測定,氨氮,SCOD,VSS,TSS采用國標(biāo)法測定,溶解性碳水化合物采用苯酚-硫酸法,溶解性蛋白采用改良型BCA法蛋白質(zhì)濃度測定試劑盒測定,SCFAs采用配有氫火焰離子化檢測器(FID)的安捷倫6890氣相色譜儀測定.

預(yù)處理后用電子順磁共振(EPR)法鑒定自由基種類,以5,5-二甲基-1-吡咯啉-N-氧化物(DMPO)作為自旋捕獲劑對體系內(nèi)自由基進行捕獲,通過JES- FA300光譜儀進行分析.對發(fā)酵末期污泥樣品進行Illumina MiSeq高通量測序.污泥樣品經(jīng)DNA提取后,進行PCR擴增.選取Miseq測序平臺V3-V4區(qū)域的通用引物338F和806R進行Illumina MiSeq測序.

為便于比較分析,上述所測得的物質(zhì)濃度(mg/L)均換算為COD濃度(mg COD/L),其轉(zhuǎn)化因子分別為:1.06g COD/g碳水化合物,1.50g COD/g 蛋白,1.07g COD/g乙酸,1.51g COD/g 丙酸,1.82g COD/g丁酸和2.04g COD/g戊酸[2].

2 結(jié)果與討論

2.1 EPS的剝離與釋放

EPS有機物的剝離和釋放可直觀反映不同預(yù)處理方式的處理效能.一般地,EPS可分為溶解性有機物(DOM)、緊密附著型EPS(TB-EPS)和松散附著型EPS(LB-EPS)3種[27].如圖1所示,相比空白組,FNA組強化了DOM中有機物的釋放,溶解性碳水化合物和蛋白質(zhì)的含量分別提升了54%和36%.3組聯(lián)合預(yù)處理均有效強化了EPS的剝離,DOM在FNA-UV組的含量相比FNA-H和FNA-US分別提升了29.9%和62.0%,溶解性碳水化合物和蛋白質(zhì)含量分別達到最大值(121.1±4.3)和(202.9±6.8) mg COD/L,比FNA單獨預(yù)處理提升了2.2和2.3倍.同時,經(jīng)FNA預(yù)處理,TP-EPS中溶解性碳水化合物和蛋白質(zhì)含量相比空白組分別下降了20.0%和11.9%,而FNA-UV組的溶解性碳水化合物和蛋白質(zhì)相比FNA組下降了29.8%和36.7%.說明UV耦合FNA能明顯促進污泥增溶,利于溶解性有機物從TB-EPS釋放到液相.這是由于FNA-UV預(yù)處理過程生成的活性氮自由基(×NO、×NO2)和過氧亞硝酸鹽(ONOO-、ONOOH)可以破壞污泥絮體結(jié)構(gòu),促進EPS剝離及污泥細胞壁破碎,表現(xiàn)為溶解性有機物的有效釋放.

相比空白組,FNA預(yù)處理及聯(lián)合預(yù)處理后,LB- EPS中有機物含量僅有少量積累,其原因是LB-EPS處于EPS外層,結(jié)構(gòu)松散且流動性強,可以吸附細胞內(nèi)及TP-EPS中有機物,因此不會有明顯積累[11].

2.2 不同預(yù)處理方式對污泥厭氧發(fā)酵的影響

2.2.1 溶解性有機物的變化 溶解性碳水化合物和蛋白質(zhì)是污泥厭氧發(fā)酵過程中主要可利用有機物,因此剩余污泥水解效果可以通過液相中溶解性碳水化合物和蛋白質(zhì)的濃度來衡量.如圖2所示,各組中溶解性碳水化合物和蛋白質(zhì)總體呈現(xiàn)先增加后減小的趨勢,其峰值分別在發(fā)酵第2d和第4d達到.FNA組中溶解性碳水化合物和蛋白質(zhì)含量可以達到(131.1±5.1)和(684.8±7.6) mg COD/L,相比空白組分別提升了2.8和2.1倍.物理法輔助的FNA預(yù)處理進一步提升了溶解性有機物的溶出.其中FNA- UV組效果最為明顯,溶解性碳水化合物和蛋白質(zhì)分別高達(251.1±6.3)和(1117.9±12.7) mg COD/L,分別是FNA組的1.9和1.6倍.這主要是由于UV輔助FNA明顯促進污泥中EPS水解及污泥細胞破裂,釋放大量胞內(nèi)外有機質(zhì)到液相中.各實驗組溶解性碳水化合物和蛋白質(zhì)含量達到最大值后出現(xiàn)下降趨勢,主要是由于溶解性有機物作為發(fā)酵產(chǎn)酸菌的底物,逐步轉(zhuǎn)化為SCFAs[28].

2.2.2 揮發(fā)酸的產(chǎn)量及成分 污泥厭氧發(fā)酵過程中,發(fā)酵菌群利用污泥中多種有機成分代謝產(chǎn)生SCFAs. SCFAs含量隨時間變化情況如圖3a所示,不同發(fā)酵條件下,揮發(fā)酸濃度隨時間呈現(xiàn)先增加后快速下降的趨勢,其峰值均在發(fā)酵第4d達到.FNA預(yù)處理組中的SCFAs產(chǎn)量((115.3±2.9) mg COD/g VSS)比未預(yù)處理污泥((69.1±4.1) mg COD/g VSS)提升了67%.聯(lián)合預(yù)處理進一步強化了SCFAs的產(chǎn)生,其中FNA-UV組SCFAs濃度高達(201.8±4.8)mg COD/g VSS,是FNA組的1.7倍,相比其他聯(lián)合預(yù)處理提升了16%～35%.與類似預(yù)處理方法相比,產(chǎn)酸效果明顯升高(Wu等[29]采用冷凍-FNA預(yù)處理(1.07mg N/L FNA,-5℃ 48h,SCFAs產(chǎn)量124.0mg COD/g VSS)),且明顯高于Gao等[30]中試發(fā)酵產(chǎn)酸效果(pH值10.0,連續(xù)攪拌反應(yīng)器,SCFAs產(chǎn)量1248.6mg COD/L,約113.5mg COD/ g VSS).其原因是紫外照射與FNA協(xié)同作用產(chǎn)生更多自由基,促進污泥解體,破壞污泥細胞結(jié)構(gòu),釋放蛋白質(zhì)、糖、脂類等大分子有機物,為水解菌和產(chǎn)酸菌提供充足基質(zhì).各組中SCFAs第4d的組分分布如圖3b所示,各實驗組中乙酸和丙酸占比達64%～73%,可作為污水廠外加碳源,為反硝化菌和聚磷菌提供最理想的基質(zhì),強化脫氮除磷[31].其中,單獨FNA預(yù)處理組乙酸占比43.8%,比未預(yù)處理實驗組提高20%,而US、H、UV耦合FNA預(yù)處理污泥體系中乙酸占比進一步提高,相比FNA組提高了9%～29%,FNA-UV組乙酸占比達到最高值(56.8± 0.2)%.同時UV耦合FNA預(yù)處理強化了丁酸型發(fā)酵,正丁酸含量較FNA組提高24.3%,該結(jié)果可由溶解性碳水化合物的降解來佐證(圖2a).此外,各聯(lián)合預(yù)處理組中的戊酸含量相比FNA預(yù)處理降低12.6%～29.8%,尤其是紫外照射聯(lián)合組(29.8%)達到最高值,表明該預(yù)處理強化了戊酸向小分子揮發(fā)酸的轉(zhuǎn)化.

2.2.3 發(fā)酵過程中氨氮的釋放效果 污泥發(fā)酵過程中,蛋白質(zhì)分解為氨基酸后,可進一步進行脫氨基作用生成氨氮,因此,氨氮含量的變化可間接反映細胞的死亡情況及有機物的水解效果[32-33].如圖4所示,各實驗組中的NH4+-N濃度都隨著發(fā)酵時間呈現(xiàn)逐漸升高的趨勢,表明在發(fā)酵過程中溶解性蛋白不斷水解轉(zhuǎn)化生成小分子有機物,為產(chǎn)酸菌提供所需基質(zhì)[34].以第4d為例,FNA處理組的NH4+-N濃度是空白組的1.2倍,而聯(lián)合預(yù)處理組的NH4+-N濃度又有了進一步上升,FNA-UV組NH4+-N濃度高達(267±21)mg/L,是FNA組的1.6倍.與溶解性蛋白含量變化一致,各實驗組NH4+-N含量高低順序為: FNA-UV組(267±21) mg/L>FNA-H組(227±11) mg/L>FNA-US組(204±19)mg/L>FNA組(165±14) mg/L>空白組(137±12) mg/L.

圖4 不同預(yù)處理方式下氨氮濃度變化

2.3 微生物群落結(jié)構(gòu)分析

剩余污泥厭氧發(fā)酵過程涉及多種微生物的共同參與,圖5反映了不同反應(yīng)器內(nèi)微生物菌落在屬水平下的相對豐度.對于門水平,主導(dǎo)菌群為變形菌門(Proteobacteria)、擬桿菌門(Bacteroidetes)、厚壁菌門(Firmicutes),均為最常見的發(fā)酵菌門,各處理組常見的發(fā)酵菌門占比高達80%[35-37].從綱水平分析,-變形菌綱(Alphaproteobacteria)、-變形菌綱(Betaproteobacteria)及-變形菌綱(Gammaproteobacteria)都屬于變形菌門,在水解酸化階段發(fā)揮重要作用.其中-變形菌綱主要參與污泥中溶解性碳水化合物的降解和有機酸的積累,FNA預(yù)處理組占比相對空白組提高2.0倍,其在FNA-UV組占比高達36.6%,是FNA組的1.2倍.擬桿菌綱(Bacteroidia)主要參與污泥中大分子有機物的降解和有機酸的積累.

根據(jù)屬水平上的群落分布,可以發(fā)現(xiàn)微生物菌落結(jié)構(gòu)發(fā)生了較大變化.以等為主的碳水化合物降解菌在FNA預(yù)處理條件下得到了明顯富集,相對豐度為13.7%,是空白組的2.3倍,并在物理輔助下進一步積累,相對豐度達15.3%～21.6%,是FNA組的1.1～1.6倍,其中FNA-UV組占比高達21.6%[38-39].可以利用多種碳水化合物產(chǎn)生乙酸,丁酸等,在FNA組含量為11.2%,是空白組的21.0倍,在FNA-UV組含量進一步增至14.1%[40].以、為首的蛋白質(zhì)降解菌,在 FNA預(yù)處理組和空白組的累積豐度分別為1.2%和2.1%,而超聲、熱、紫外輔助FNA組相對豐度達4.8%～9.8%.其中可有效降解蛋白質(zhì)產(chǎn)生乙酸和丙酸,在FNA組占比為1.1%,是空白組的1.1倍,而在FNA-UV組豐度增至6.9%[41].此外,、和等主要的反硝化菌在FNA組累積豐度為6.9%,是空白組的1.9倍,而FNA-UV組豐度高達8.2%,是FNA組的1.2倍[42-44].其中在FNA-UV組含量高達5.9%,是FNA組的18.8倍.說明FNA-UV預(yù)處理可以有效富集反硝化菌,強化了反硝化過程.

圖5 功能微生物在屬水平的相對豐度

2.4 紫外光耦合FNA預(yù)處理強化污泥厭氧發(fā)酵產(chǎn)酸潛在機理分析

如圖6所示,對預(yù)處理后污泥進行EPR分析,各組均檢測出DMPO-OH和DMPO-O2-信號,聯(lián)合預(yù)處理組中DMPO-OH和DMPO-O2-信號強度均強于FNA預(yù)處理組,其中FNA-UV組信號強度明顯強于FNA-US組和FNA-H組,表明3種物理預(yù)處理,尤其是紫外預(yù)處理與FNA之間存在協(xié)同作用,強化了兩種自由基的產(chǎn)生與釋放,與預(yù)處理后EPS中DOM釋放效果相吻合,進一步為上述分析提供了依據(jù)[45].其潛在的強化產(chǎn)酸機理如圖7所示,FNA預(yù)處理過程中產(chǎn)生的活性氮自由基(×NO、×NO2)及活性氮中間體(N2O3和N2O4)通過與胞內(nèi)或EPS發(fā)生反應(yīng),改變蛋白質(zhì)、脂質(zhì)、碳水化合物和DNA的結(jié)構(gòu),從而促進EPS水解及污泥破碎.但FNA對分子結(jié)構(gòu)的破壞作用有限,細胞內(nèi)容物溶出較少[46-48]. FNA在UV照射下強化了×NO和×NO2釋放,同時產(chǎn)生過氧亞硝酸鹽(ONOO-和ONOOH),ONOO-和ONOOH作為內(nèi)源氧化劑和親核試劑,破壞細胞結(jié)構(gòu),導(dǎo)致細胞解體[49]. ONOO-在FNA預(yù)處理的酸性條件下產(chǎn)生×NO和×O2-自由基,ONOOH可分解為×NO2和×OH自由基(式(1 ～ 10)).因此,FNA和UV協(xié)同作用產(chǎn)生的各種活性自由基及中間體(×NO、×NO2、ONOO-、ONOOH、×O2-、×OH),促進細胞裂解,釋放EPS及胞內(nèi)外有機物釋放到液相中為后續(xù)發(fā)酵產(chǎn)酸菌提供更多底物[50-52].

圖7 UV輔助FNA促進污泥厭氧發(fā)酵效能機理

3HNO2?HNO3+ 2×NO+ H2O (1)

2HNO2?×NO +×NO2+ H2O (2)

2NO2→ N2O4(3)

N2O4+ H2O → HNO3+ HNO2(4)

NO3-×NO +×O2-(< 280nm) (5)

NO3-×NO2+×OH (< 280nm) (6)

ONOOH →×NO2+×OH → ONOO-(8)

ONOO-+×OH →H++×NO+×O2-(9)

×O2-+ H2O ?×OH + OH-(10)

表3 發(fā)酵10d不同發(fā)酵體系碳平衡分析

注: COD轉(zhuǎn)換因子分別為:1.42g COD/g VSS,8g COD/g H2,4g COD/g CH4,1.5g COD/g 溶解性蛋白,1.06g COD/g 溶解性碳水化合物,1.07g COD/g 乙酸,1.51g COD/g 丙酸,1.82g COD/g丁酸,2.04g COD/g戊酸[53].

眾所周知,VSS、H2、CH4、溶解性碳水化合物、溶解性蛋白和SCFAs是發(fā)酵系統(tǒng)中典型的中間產(chǎn)物或最終產(chǎn)物.為進一步剖析聯(lián)合預(yù)處理對剩余污泥厭氧發(fā)酵產(chǎn)酸的影響機制,對不同體系進行了碳平衡分析.VSS的變化可直觀反映污泥中有機質(zhì)的降解及其減量化的程度.由表3可知,各預(yù)處理均不同程度實現(xiàn)了污泥的減量,相比空白組(21.94%),FNA組VSS下降至20.92%,進一步在FNA-UV、FNA-H和FNA-US組中降至19.48%,19.25%和20.23%.與VSS變化趨勢相反,溶解性碳水化合物和蛋白質(zhì)含量相比空白組均有不同程度的提升,并在FNA-UV組中占比達到最大,分別為3.07%和24.03%,表明紫外耦合FNA預(yù)處理最大程度地強化了溶解性有機物的釋放.同時,各組中溶解性蛋白質(zhì)占比均高于溶解性碳水化合物,表明蛋白質(zhì)類物質(zhì)相較于碳水化合物更難被微生物所降解,該結(jié)果與Arshad等[54]的研究結(jié)果相一致[54].相應(yīng)地,SCFAs在各預(yù)處理組中的占比均高于空白組,且在整個體系碳分布中占比高達28.52%～38.27%,且在FNA-UV組中達到最高,證實了紫外光的引入強化了溶解性有機物的溶出,并在后續(xù)產(chǎn)酸過程中強化了其向SCFAs的大量轉(zhuǎn)化.

2.5 討論及展望

剩余污泥(WAS)含有豐富的有機化合物,為能源回收和SCFAs生產(chǎn)帶來巨大潛力.紫外光和FNA預(yù)處理均可破壞污泥絮狀物和細胞結(jié)構(gòu),促進胞內(nèi)外有機物釋放[55].研究表明紫外光通過對微生物的輻射損傷和破壞DNA中各種結(jié)構(gòu)鍵致使微生物破裂,同時可改變腐殖酸的結(jié)構(gòu)特性,使得大分子腐殖酸脫穩(wěn)并分解為小分子.相比紫外照射驅(qū)動的光催化氧化技術(shù),FNA預(yù)處理污泥通過FNA及其衍生物(如×NO、×NO2和N2O3)等毒性作用,導(dǎo)致細胞破裂、EPS剝離.FNA與紫外照射聯(lián)合技術(shù)強化并產(chǎn)生活性自由基及中間體(×NO、×NO2、ONOO-、ONOOH),同步強化EPS剝離及污泥細胞破裂.與類似的化學(xué)預(yù)處理、物理預(yù)處理及聯(lián)合預(yù)處理相比,紫外光耦合FNA預(yù)處理法對WAS瓦解和發(fā)酵產(chǎn)酸效果具有優(yōu)越性.如Luo等[57]發(fā)現(xiàn),Ca(OCl)2用量為0.025g/g TSS,SCFAs最大產(chǎn)量為192.8mg COD/g VSS,Zheng等[52]采用紫外照射驅(qū)動的光催化氧化技術(shù)進行厭氧消化(254nm 1h),獲得SCFAs產(chǎn)量約150mgCOD/ gVSS,Wu等[29]采用冷凍-FNA預(yù)處理(1.07mg N/L FNA,-5℃ 48h),SCFAs產(chǎn)量124.0mg COD/g VSS,低于本研究中使用紫外耦合FNA預(yù)處理獲得的SCFAs最大濃度(201.8±4.8) mg COD/g VSS[29,55,57].據(jù)報道,FNA可從污泥厭氧發(fā)酵液中原位合成,且采用FNA預(yù)處理在發(fā)酵過程中FNA會反硝化為氮氣,無二次污染的風(fēng)險,處理成本約3.60元/m[2].本研究證實了紫外光耦合FNA預(yù)處理污泥產(chǎn)酸的可行性,然而目前紫外光耦合FNA預(yù)處理技術(shù)的耦合條件及機理尚不明晰,之后將對耦合方式、照射時間、FNA濃度和紫外線照射強度,以及處理時間等進一步優(yōu)化.

3 結(jié)論

3.1 紫外光耦合FNA預(yù)處理可有效促進污泥溶胞.其DOM中溶解性蛋白及碳水化合物的含量高達(202.9±6.8)和(121.1±4.3) mg COD/L,為其他實驗組的1.3～3.1和1.4～3.4倍.

3.2 紫外光耦合FNA預(yù)處理有效提升了污泥厭氧發(fā)酵過程中SCFAs的產(chǎn)量,在第4d達(201.8±4.8) mg COD/g VSS,相比其他組提升16%～192%.乙酸和丙酸占比高達64%,均高于其他各組.

3.3 紫外光耦合FNA預(yù)處理強化了污泥中發(fā)酵菌和反硝化菌的生長和富集,其豐度分別為31.3%和8.2%,為其他各實驗組的1.2～4.4倍和1.3～2.3倍.

3.4 紫外光耦合FNA預(yù)處理有效強化了×OH和×O2-的產(chǎn)生,與活性自由基及中間體(×NO、×NO2、ONOO-、ONOOH)共同促進了污泥的溶胞和胞外聚合物的破解,發(fā)酵末期有效實現(xiàn)了污泥減量(VSS占比19.48%)和溶解性有機物的釋放與利用.

[1] Bao H X,Yang H,Zhang H,et al. Improving methane productivity of waste activated sludge by ultrasound and alkali pretreatment in microbial electrolysis cell and anaerobic digestion coupled system [J]. Environmental Research,2020,180:108863.

[2] Liu Z H,Zhou A J,Zhang J G,et al. Hydrogen recovery from waste activated sludge: Role of free nitrous acid in a prefermentation– microbial electrolysis cells system [J]. ACS Sustainable Chemistry & Engineering,2018,6(3):3870-3878.

[3] Zhou A J,Liu H Y,Varrone C,et al. New insight into waste activated sludge acetogenesis triggered by coupling sulfite/ferrate oxidation with sulfate reduction-mediated syntrophic consortia [J]. Chemical Engineering Journal,2020,400:125885.

[4] Zurzolo F,Yuan Q,Oleszkiewicz J. Increase of soluble phosphorus and volatile fatty acids during Co-fermentation of wastewater sludge [J]. Waste and Biomass Valorization,2016,7(2):317-324.

[5] Liu X R,Du M T,Yang J N,et al. Sulfite serving as a pretreatment method for alkaline fermentation to enhance short-chain fatty acid production from waste activated sludge [J]. Chemical Engineering Journal,2020,385,123991.

[6] 金寶丹,王淑瑩,邢立群,等.不同發(fā)酵方式對污泥厭氧發(fā)酵性能的影響及其發(fā)酵液利用 [J]. 中國環(huán)境科學(xué),2016,36(7):2079-2089.

Jin B D,Wang S Y,Xing L Q,et al. The effect of different fermentation methods on the sludge anaerobic fermentation performance and the utilization of fermentation liquor [J]. China Environmental Science,2016,(36)7:2079-2089.

[7] Law Y Y,Ye L,Wang Q L,et al. Producing free nitrous acid – A green and renewable biocidal agent – From anaerobic digester liquor [J]. Chemical Engineering Journal,2015,259:62-69.

[8] Liu Z H,Zhou A J,Liu H Y,et al. Extracellular polymeric substance decomposition linked to hydrogen recovery from waste activated sludge: Role of peracetic acid and free nitrous acid co-pretreatment in a prefermentation-bioelectrolysis cascading system [J]. Water Research,2020,176:115724.

[9] Li X M,Zhao J W,Wang D B,et al. An efficient and green pretreatment to stimulate short-chain fatty acids production from waste activated sludge anaerobic fermentation using free nitrous acid [J]. Chemosphere,2016,144:160-167.

[10] Wang Q L,Ye L,Jiang G M,et al. Free nitrous acid (FNA)-based pretreatment enhances methane production from waste activated sludge [J]. Environmental Science and Technology,2013,47(20): 11897-11904.

[11] Chislett M,Guo J H,Bond P L,et al. Structural changes in model compounds of sludge extracellular polymeric substances caused by exposure to free nitrous acid [J]. Water Research,2021,188:116553.

[12] Wang J S,Zhang Z J,Ye X,et al. Enhanced solubilization and biochemical methane potential of waste activated sludge by combined free nitrous acid and potassium ferrate pretreatment [J]. Bioresource Technology,2020,297:122376.

[13] Karimi R,Hallaji S M,Siami S,et al. Synergy of combined free nitrous acid and Fenton technology in enhancing anaerobic digestion of actual sewage waste activated sludge[J]. Scientific Reports,2020,10(1):5027.

[14] Wu Y Q,Song K,Sun X Y,et al. Mechanisms of free nitrous acid and freezing co-pretreatment enhancing short-chain fatty acids production from waste activated sludge anaerobic fermentation [J]. Chemosphere,2019,230:536-543.

[15] Wang Q L,Jiang G M,Ye L,et al. Enhancing methane production from waste activated sludge using combined free nitrous acid and heat pre-treatment [J]. Water Research,2014,63:71-80.

[16] Niu Q Q,Xu Q X,Wang Y L,et al. Enhanced hydrogen accumulation from waste activated sludge by combining ultrasonic and free nitrous acid pretreatment: Performance,mechanism,and implication [J]. Bioresource Technology,2019,285:121363.

[17] Zhang T T,Wang Q L,Ye L,et al. Combined free nitrous acid and hydrogen peroxide pre-treatment of waste activated sludge enhances methane production via organic molecule breakdown [J]. Scientific Reports,2015,5:16631.

[18] Wu Q L,Guo W Q,Bao X,et al. Enhanced volatile fatty acid production from excess sludge by combined free nitrous acid and rhamnolipid treatment [J]. Bioresource Technology,2017,224:727- 732.

[19] 張旭光,陳 宇,張 龍.游離亞硝酸偶聯(lián)生物表面活性劑強化污泥厭氧發(fā)酵產(chǎn)酸[J]. 環(huán)境工程,2019,37(1):56-60,87.

Zhang X G,Chen Y,Zhang L. Enhancement of acid production from sludge anaerobic fermentation by Free nitrous bio-surfactant [J]. Environmental Engineering,2019,37(1):56-60,87.

[20] Erwan C,Jean P ,Vincent J,et al. Impact of suspended particles on UV disinfection of activated-sludge effluent with the aim of reclamation [J]. Journal of Water Process Engineering,2018,22:87-93.

[21] Zheng M,Ping Q,Wang L,et al. Pretreatment using UV combined with CaO2for the anaerobic digestion of waste activated sludge: Mechanistic modeling for attenuation of trace organic contaminants [J]. Journal of Hazardous Materials,2021,402:123484.

[22] Zhang Y P,Li T T,Tian J Y,et al. Enhanced dewaterability of waste activated sludge by UV assisted ZVI-PDS oxidation [J]. Journal of Environmental Sciences,2022,13(3):152-164.

[23] Sun J,Guo L,Li Q Q,et al. Structural and functional properties of organic matters in extracellular polymeric substances (EPS) and dissolved organic matters (DOM) after heat pretreatment with waste sludge [J]. Bioresource Technology,2016,219:614-623.

[24] Yu H W,Anumol T,Park M,et al. On-line sensor monitoring for chemical contaminant attenuation during UV/H2O2advanced oxidation process [J]. Water Research,2015,81:250-260.

[25] Zhang Y P,Li T T,Tian J Y,et al. Enhanced dewaterability of waste activated sludge by UV assisted ZVI-PDS oxidation [J]. Journal of Environmental Sciences,2022,113:152-164.

[26] 楊春雪.嗜熱菌強化剩余污泥水解及短鏈脂肪酸積累規(guī)律研究 [D]. 哈爾濱:哈爾濱工業(yè)大學(xué),2015.

Yang C X. Enhanced effects of thermophiles on waste activated sludge hydrolysis and short-chain fatty acids production [D]. Harbin: Harbin Institute of Technology,2015.

[27] Donlan R M,Costerton J W. Costerton. Biofilms: survival mechanisms of clinically relevant microorganisms [J]. Clinical Microbiology Reviews,2002,15(2):167-193.

[28] Jan T W,Adav S S,Lee D J,et al. Hydrogen fermentation and methane production from sludge with pretreatments [J]. Energy Fuels,2008,22(1):98-102.

[29] Wu Y Q,Song K,Sun X Y,et al. Effects of free nitrous acid and freezing co-pretreatment on sludge short-chain fatty acids production and dewaterability [J]. Science of the Total Environment,2019,669: 600-607.

[30] Gao Y Q,Peng Y Z,Zhang J Y,et al. Biological sludge reduction and enhanced nutrient removal in a pilot-scale system with 2-step sludge alkaline fermentation and A2O process [J]. Bioresource Technology,2011,102(5):4091-4097.

[31] He Z W,Tang C C,Liu W Z,et al. Enhanced short-chain fatty acids production from waste activated sludge with alkaline followed by potassium ferrate treatment [J]. Bioresource Technology,2019,289: 121642.

[32] Pijuan M,Wang Q L,Liu Y,et al. Improving secondary sludge biodegradability using free nitrous acid treatment [J]. Bioresource Technology,2012,116:92-98.

[33] 樊雅欣,劉紅燕,潘凌峰,等.活化方式對過硫酸鹽強化剩余污泥發(fā)酵的影響 [J]. 中國環(huán)境科學(xué),2019,39:2460-2466.

Fan Y X,Liu H Y,Pan L F,et al. Enhancement of waste activated sludge acidification by persulfate: Role of activation methods [J]. China Environmental Science,2019,39:2460-2466.

[34] 馮宇杰,魏瑤麗,李虹瑤,等.醋糟與剩余污泥共發(fā)酵體系中底物配比對揮發(fā)性脂肪酸產(chǎn)量的影響 [J]. 科學(xué)技術(shù)與工程,2020,20(34): 14332-14306.

Feng Y J,Wei Y L,Li H Y,et al. Effect of Substrate Ratio on the Yield of Volatile Fatty Acids in the Cofermentation System of Vinegar Dregs and Residual Sludge [J]. Science Technology and Engineering,2020,20(34):14332-14306.

[35] 劉芝宏,魏瑤麗,樊雅欣,等.游離亞硝酸預(yù)處理對剩余污泥電解及微生物群落結(jié)構(gòu)的影響 [J]. 中國環(huán)境科學(xué),2019,39(7):2953-2959.

Liu Z H,Wei Y L,Fan Y X,et al. Role of free nitrous acid on waste activated sludge bio-electrolysis and key microflora shift [J]. China Environmental Science,2019,39(7):2953-2959.

[36] 張 強,李詠梅.投加Na2S對化學(xué)強化除磷污泥厭氧發(fā)酵釋磷的影響 [J]. 中國環(huán)境科學(xué),2021,41(3):1219-1227.

Zhang Q,Li Y M. Effects of dosing sodium sulfide on phosphorus release during the anaerobic fermentation of waste sludge produced by chemical enhanced phosphorus removal [J]. China Environmental Science,2021,41(3):1219-1227.

[37] 康曉榮.超聲聯(lián)合堿促進剩余污泥水解酸化及產(chǎn)物研究 [D]. 哈爾濱:哈爾濱工業(yè)大學(xué),2013.

Kang X R. Study on hydrolysis and acidification of activated sludge enhanced by ultrasound combined with alkaline [D]. Harbin: Harbin Institute of Technology,2013.

[38] Donachie S P,Bowman J P,Stephen L W,et al. Arcobacter halophilus sp. nov.,the first obligate halophile in the genus Arcobacter [J]. International Journal of Systematic and Evolutionary Microbiology,2005,55:1271-1277.

[39] Gerritsen J,Fuentes S,Grievink W,et al. Characterization of..,sp..,isolated from the gastro- intestinal tract of a rat,and proposal for the reclassification of five closely related members of the genusinto the genera..,..,.. and.[J]. International Journal of Systematic and Evolutionary Microbiology,2014,64(Pt 5):1600-1616.

[40] 賀張偉.預(yù)處理方法對污泥厭氧耦合微生物電解及厭氧消化產(chǎn)能的影響 [D]. 哈爾濱:哈爾濱工程大學(xué),2014.

He Z W. Study on influence factor and mechanisms of organic matters conversion and phosphorus release during waste activated sludge anaerobic fermentation process [D]. Harbin: Harbin Engineering University,2014.

[41] Mielczarek A T,Kragelund C,Eriksen P S,et al. Population dynamics of filamentous bacteria in Danish wastewater treatment plants with nutrient removal [J]. Water Research,2012,46(12):3781-3795.

[42] He Q C,Feng C P,Chen N,et al. Characterizations of dissolved organic matter and bacterial community structures in rice washing drainage (RWD)-based synthetic groundwater denitrification [J]. Chemosphere,2019,215:142-152.

[43] Simona ?,Jakub K,Tomá?J. Biological water denitrification-A review [J]. Enzyme and Microbial Technology,1992,14(3):170-183.

[44] Pervin H M,Batstone D J,Bond P L. Previously unclassified bacteria dominate during thermophilic and mesophilic anaerobic pre-treatment of primary sludge [J]. Systematic and Applied Microbiology,2013,36(4):281-290.

[45] Wang J,Lou Y,Feng K,et al. Enhancing the decomposition of extracellular polymeric substances and the recovery of short-chain fatty acids from waste activated sludge: Analysis of the performance and mechanism of co-treatment by free nitrous acid and calcium peroxide [J]. J Hazard Mater,2022,423(Pt A):127022.

[46] Chislett M,Guo J H,Bond P L,et al. Structural changes in cell-wall and cell-membrane organic materials following exposure to free nitrous acid [J]. Environmental Science and Technology,2020,54(16): 10301-10312.

[47] Wang J S,Zhang Z J,Ye X,et al. Performance and mechanism of free nitrous acid on the solubilization of waste activated sludge [J]. RSC Advances,2018,8(29):15897-15905.

[48] Sang S Y,Coakley R,Lau G W,et al. Anaerobic killing of mucoid Pseudomonas aeruginosa by acidified nitrite derivatives under cystic fibrosis airway conditions [J]. Journal of Clinical Investigation,2006,116(2):436-446.

[49] Huang Y,Kong M,Westerman D,et al. Effects of HCO3-on degradation of toxic contaminants of emerging concern by UV/NO3(.) [J]. Environmental Science and Technology,2018,52(21):12697- 12707.

[50] 徐慧敏,秦衛(wèi)華,何國富,等.超聲聯(lián)合熱堿技術(shù)促進剩余污泥破解的參數(shù)優(yōu)化 [J]. 中國環(huán)境科學(xué),2017,37(9):3431-3436.

Xu H M,Qin W H,He G F,et al. Optimization of combined ultrasonic and thermo-chemical pretreatment of waste activated sludge for enhanced disintegration [J]. China Environmental Science,2017,37(9): 3431-3436.

[51] Thorn K A,Cox L G. Ultraviolet irradiation effects incorporation of nitrate and nitrite nitrogen into aquatic natural organic matter [J]. Journal of Environmental Quality,2012,41(3):865-881.

[52] Zheng M,Daniels K D,Park M,et al. Attenuation of pharmaceutically active compounds in aqueous solution by UV/CaO2process: Influencing factors,degradation mechanism and pathways [J]. Water Research,2019,164:114922.

[53] Yang J,Liu X,Wang D,et al. Mechanisms of peroxymonosulfate pretreatment enhancing production of short-chain fatty acids from waste activated sludge [J]. Water Research,2019,148:239-249.

[54] Arshad Z,Maqbool T,Shin K H,et al. Using stable isotope probing and fluorescence spectroscopy to examine the roles of substrate and soluble microbial products in extracellular polymeric substance formation in activated sludge process [J]. Science of the Total Environment,2021,788:147875.

[55] 孫珮石,江映翔,劉安文,等.紫外線輻射對活性污泥除磷性能的增強作用 [J]. 中國環(huán)境科學(xué),2003,23(2):184-188.

Sun P S,Jiang Y X,Liu A W,et al. Enhancement of phosphorus removal property of activated sludge with UV ray irradiation [J]. China Environmental Science,2003,23(2):184-188.

[56] 黃 芳.高溫?zé)崴膺^程中污泥腐殖酸的演變及其對厭氧消化效果的影響研究 [D]. 無錫:江南大學(xué),2021.

Huang F. Evolutions of humic acids during slusge thermal hydrolysis and their effects on anaerobic digestion [D]. Wuxi: Jiangnan University,2021.

[57] Luo J Y,Huang W X,Zhang Q,et al. Effects of different hypochlorite types on the waste activated sludge fermentation from the perspectives of volatile fatty acids production,microbial community and activity,and characteristics of fermented sludge [J]. Bioresource Technology,2020,307:123227.

[58] Zahedi S,Icaran P,Yuan Z,et al. Effect of free nitrous acid pre- treatment on primary sludge at low exposure times [J]. Bioresource Technology,2017,228:272-278.

[59] 韓 興.污水紫外消毒裝置設(shè)計及工藝參數(shù)優(yōu)化研究[D]. 長春:吉林農(nóng)業(yè)大學(xué),2006.

Han X. Research on the design of sewage ultraviolet disinfection equipment and optimization of the craft parameter [D]. Changchun: Jilin Agricultural University. 2006.

致謝：感謝山西省太原市楊家堡污水處理廠的工作人員協(xié)助完成.

Enhancement of acidification from waste activated sludge via anaerobic fermentation by free nitrous acid (FNA) pretreatment assisted by ultraviolet.

YIN Xiao-yun,LIU Zhi-hong*,ZHOU Ai-juan,LI Ya-nan,YUE Xiu-ping,CUI Zhi-xuan

(College of Environmental Science and Engineering,Taiyuan University of Technology,Taiyuan 030024,China).,2022,42(8)：3770～3779

In order to break the bottleneck of the limited hydrolysis performance and low short chain fatty acids (SCFAs) production efficiency from waste activated sludge (WAS) during the traditional anaerobic fermentation,this work investigated the effect of the ultraviolet (UV) assisted free nitrous acid (FNA) pretreatment on WAS disintegration and acidification,and compared with thermal (H) and ultrasonic (US) coupled with FNA pretreatment. Results revealed that UV assisted FNA co-pretreatment (FNA-UV) had a synergistic effect on disruption of both extracellular polymeric substances and cell envelope.?OH and?O2-,as the main reaction intermediates,their intensities in FNA-UV group were much stronger than that obtained in other pretreatment groups (FNA-US and FNA-H). Moreover,these two free radicals,with the intermediates such as ?NO,?NO2andONOO-,further promoting the release of soluble organics.The contents of soluble carbohydrates and protein were 60% and 90% higher than that obtained in FNA group respectively,which served more soluble substrates for SCFAs generation. Accordingly,SCFAs concentration peaked at 4d in FNA-UV group (201.8±4.8)mg COD/g VSS with 56.8% acetic acid (HAc)),which was 67% higher than that of FNA group. Carbon balance analysis at the final stage of the fermentation showed that UV assisted FNA pretreatment played an important role in sludge reduction,release and transformation of soluble substrates,and finally SCFAs production. The functional microbial consortia analysis indicated the anaerobic fermentation bacteria and nitrate-reducing bacteria were obviously enriched in FNA-UV group,which were 23.7%～270.6% higher than that obtained in other groups.

free nitrous acid (FNA)；waste activated sludge (WAS)；short chain fatty acids (SCFAs)；anaerobic fermentation；physical method；high-throughput sequencing

X703.1

A

1000-6923(2022)08-3770-10

2021-12-28

國家自然科學(xué)基金資助項目(52100155,52070139);山西省基礎(chǔ)研究計劃項目(20210302124347);山西省重點研發(fā)項目(社發(fā)領(lǐng)域) (201903D321055)

* 責(zé)任作者,講師,liuzhihong0227@163.com

殷霄云(1998-),女,河南漯河人,太原理工大學(xué)碩士研究生,主要從事廢棄生物質(zhì)資源化.