污泥超高溫好氧發(fā)酵去除氟喹諾酮類抗生素及其降解產(chǎn)物

宋相通,楊明超,張 俊,郭亞麗,董 濱,*

污泥超高溫好氧發(fā)酵去除氟喹諾酮類抗生素及其降解產(chǎn)物

宋相通1,楊明超1,張 俊2.3,郭亞麗2,董 濱1,2*

(1.同濟(jì)大學(xué)環(huán)境科學(xué)與工程學(xué)院,上海 200092；2.中國長江三峽集團(tuán)有限公司長江生態(tài)環(huán)境工程研究中心,北京 100038；3.長江生態(tài)環(huán)保集團(tuán)有限公司,湖北 武漢 430070)

對(duì)比分析了污泥傳統(tǒng)高溫好氧發(fā)酵(TC)和超高溫好氧發(fā)酵(HTC)對(duì)諾氟沙星(NOR)、氧氟沙星(OFL)及其降解產(chǎn)物的去除性能.結(jié)果表明,超高溫好氧與高溫好氧發(fā)酵25d時(shí)NOR去除率分別為91.8%,92.1%,產(chǎn)物諾氟沙星脫乙基(NORP)殘留含量分別為628,668μg/kg;OFL去除率分別為92.1%、88.1%,產(chǎn)物氧氟沙星脫乙基(OFLP)殘留含量分別為191,675μg/kg,相較于傳統(tǒng)高溫好氧發(fā)酵,超高溫好氧發(fā)酵使得NOR、OFL的生態(tài)風(fēng)險(xiǎn)分別降低3.1%、30.5%,這表明超高溫好氧發(fā)酵可以更有效地去除氧氟沙星及其降解產(chǎn)物,降低發(fā)酵產(chǎn)物中OFL的環(huán)境暴露風(fēng)險(xiǎn).同時(shí),超高溫好氧發(fā)酵產(chǎn)物DOC/DON更低,種子發(fā)芽指數(shù)高,發(fā)酵產(chǎn)物植物毒性小,有利于污泥的安全土地利用.

污泥；超高溫；好氧發(fā)酵；氟喹諾酮；抗生素；降解產(chǎn)物

氟喹諾酮類(FQs)是最常用的抗生素之一,目前普遍使用的是第三代藥物,包括諾氟沙星(NOR)、環(huán)丙沙星(CIP)、氧氟沙星(OFL)等.研究表明長江中下游的65個(gè)湖泊的水和沉積物中檢測(cè)到5種氟喹諾酮類抗生素,對(duì)湖泊中的藻類、細(xì)菌構(gòu)成中等風(fēng)險(xiǎn)[1].Wang等[2]研究表明,吸附是活性污泥污水處理過程中FQs的主要去除途徑,占不同F(xiàn)Qs總?cè)コ康?0%～91%.大量抗生素的聚集與殘留使得污泥已成為環(huán)境中抗生素最重要的歸宿之一[3],隨著污泥土地利用過程,對(duì)土壤生態(tài)造成威脅.

好氧發(fā)酵是一個(gè)傳統(tǒng)且經(jīng)濟(jì)的技術(shù),將污泥等有機(jī)固廢轉(zhuǎn)化為土壤改良劑.前期研究表明好氧發(fā)酵能夠去除基質(zhì)中FQs,去除效果與發(fā)酵堆體溫度密切相關(guān)[4].Yang等[5]研究指出,雞糞好氧發(fā)酵過程中OFL等5種FQs去除率可達(dá)45.3%～75.4%, Ja?owiecki等[6]研究表明,NOR與OFL在好氧發(fā)酵過程中去除率分別達(dá)到80%、60%,Selvam等[7]研究豬糞好氧發(fā)酵過程中CIP去除率最高達(dá)到82.9%, Zhang等[8]研究城市污水污泥好氧發(fā)酵過程中NOR與OFL去除率均達(dá)85%以上.近年來研究也發(fā)現(xiàn),多地牛、豬糞便的發(fā)酵產(chǎn)物殘留高濃度FQs[9],這表明傳統(tǒng)高溫好氧發(fā)酵無法充分去除氟喹諾酮類抗生素.

超高溫好氧發(fā)酵(HTC)是利用極端嗜熱菌群使發(fā)酵過程中最高溫度達(dá)到80℃以上,并維持3d以上的新型發(fā)酵工藝[10].與傳統(tǒng)高溫好氧發(fā)酵(TC)相比,最高溫度提高20℃以上,Liao等[11]研究表明,HTC過程中抗生素耐藥基因的去除率顯著提高.前期研究中,Paul等[12]觀察到CIP中哌嗪環(huán)轉(zhuǎn)化使得抗菌活性降低, Zhu等[13]認(rèn)為FQs降解產(chǎn)物對(duì)DNA拓?fù)洚悩?gòu)酶的結(jié)合親和力相比母體較低,因此抗菌活性降低.但是目前關(guān)于FQs好氧發(fā)酵過程中降解產(chǎn)物的定量研究較少.參考Prieto等[14]提出的FQs生物降解路徑,本研究選取NOR、OFL及其哌嗪環(huán)脫乙基產(chǎn)物,使用LC/MS-MS定量檢測(cè)NOR、OFL在HTC、TC兩種發(fā)酵過程中的殘留含量及其哌嗪環(huán)脫乙基產(chǎn)物含量,以期從降解產(chǎn)物層面解釋FQs在不同好氧發(fā)酵過程中的降解行為,為污泥的安全土地利用提供理論參考.

1 材料與方法

1.1 實(shí)驗(yàn)材料

生污泥取自上海某養(yǎng)殖業(yè)污水處理廠,使用前生污泥儲(chǔ)存在4℃冰箱中.稻谷殼取自某農(nóng)產(chǎn)品加工廠,平均直徑約0.9mm,作為發(fā)酵輔料以調(diào)節(jié)含水率.超高溫好氧發(fā)酵腐熟料來自實(shí)驗(yàn)室運(yùn)行的超高溫發(fā)酵堆體,原材料的理化性質(zhì)如表1所示.

表1 生污泥、腐熟料、稻谷殼的理化性質(zhì)(%)

注:*以干基重量計(jì),數(shù)據(jù)以平均值±3個(gè)重復(fù)的標(biāo)準(zhǔn)差表示.

1.2 實(shí)驗(yàn)方法

發(fā)酵反應(yīng)器如圖1所示,容積為15L(高31cm,直徑25cm),外層為厚2cm的恒溫水浴層,在距反應(yīng)器底部7cm處設(shè)置氣流均布板,發(fā)酵堆體由安裝在距反應(yīng)器底部12cm的不銹鋼格柵支撐.采樣時(shí)在分別距反應(yīng)器頂部10,20和30cm的堆體中心取樣.

本研究預(yù)實(shí)驗(yàn)中確定了各發(fā)酵原料的最佳配比,本研究中HTC組添加生污泥、稻谷殼與超高溫好氧發(fā)酵腐熟料干重比為2.0:1.0:0.8,TC組添加生污泥與稻谷殼干重比為2.0:1.0,2組均添加10mg/kg的NOR與OFL.HTC堆體總質(zhì)量濕重10.4kg,干重5.7kg,TC堆體總質(zhì)量濕重8.2kg、干重4.5kg,在啟動(dòng)發(fā)酵之前確保堆體的均質(zhì)性.

2組發(fā)酵堆體初始水分含量調(diào)節(jié)至55％左右,發(fā)酵過程持續(xù)40d,空氣泵持續(xù)運(yùn)行,通風(fēng)量為0.50L/(min·kg).每天10:00記錄3個(gè)采樣位置的溫度,并從3處采樣位置各取10g子樣本并混勻,收集重量為30g的代表性樣本.樣品分為3部分,其中一部分立即分析,一部分經(jīng)風(fēng)干研磨,過50目篩后保存,另一部分儲(chǔ)存在-80℃冰箱中,冷凍干燥后用于FQs及其產(chǎn)物分析.

圖1 發(fā)酵反應(yīng)器示意

(1)反應(yīng)器;(2)氣體出口;(3)不銹鋼格柵;(4)氣流均布板;(5)保溫層;(6)恒溫水循環(huán)泵;(7)氣體流量計(jì);(8)曝氣風(fēng)機(jī)

1.3 檢測(cè)分析方法

取樣前在分別距反應(yīng)器頂部10,20和30cm的堆體中心取樣位置,采用Pt100型電子溫度計(jì)監(jiān)測(cè)堆體溫度.預(yù)先在105℃下干燥至恒重的樣品在馬弗爐中600℃燃燒4h,確定揮發(fā)分含量(VS/TS).準(zhǔn)備新鮮樣品的水提取液(1:10/樣品:水),使用TOC分析儀(日本島津SSM-5000A)測(cè)定溶解性有機(jī)碳(DOC)與溶解性有機(jī)氮(DON),種子發(fā)芽指數(shù)(GI)試驗(yàn)用于評(píng)估發(fā)酵產(chǎn)物的植物毒性,參考Gao等[15]提出的方法.

根據(jù)Yuan等[16]的方法,分析了發(fā)酵產(chǎn)物中NOR、OFL殘留含量及其降解產(chǎn)物含量:稱取均質(zhì)試樣1.0g,置于50mL聚丙烯離心管中,分別用20, 20,10mL,0.1mol/L EDTA-Mcllvaine緩沖液冰水浴超聲提取3次,每次渦旋混合10min,冰水浴超聲10min,10000r/min離心5min,合并上清液.取5mL上清液以2.5mL/min的速度過預(yù)先用6mL甲醇,6mL水活化的SAX-HLB串聯(lián)固相萃取柱(200mg,6mL),將小柱抽干,用6mL甲醇+乙酸乙酯洗脫,收集洗脫液用氮?dú)獯蹈?用2mL初始流動(dòng)相溶解,過0.45μm尼龍濾膜,轉(zhuǎn)移至2mL琥珀色玻璃小瓶中,待液相色譜/串聯(lián)質(zhì)譜(LC/MS-MS, ThermoFisher)測(cè)定.色譜柱:Eclipse Plus C18柱(4.6mm×150mm,3.5μm),流動(dòng)相為體積比70:30的質(zhì)量分?jǐn)?shù)為0.2％甲酸和乙腈,流速為0.5mL/min,柱溫40℃,進(jìn)樣體積20μL.質(zhì)譜條件為多反應(yīng)監(jiān)測(cè)模式(MRM),正離子模式,其余質(zhì)譜參數(shù)采用儀器微量進(jìn)樣優(yōu)化結(jié)果,各化合物質(zhì)譜參數(shù)如表2所示.

表2 諾氟沙星、氧氟沙星及其降解產(chǎn)物測(cè)定質(zhì)譜參數(shù)

1.4 諾氟沙星與氧氟沙星生態(tài)風(fēng)險(xiǎn)評(píng)估

本研究采用風(fēng)險(xiǎn)熵權(quán)法(RQ)評(píng)估發(fā)酵產(chǎn)物中氟喹諾酮類抗生素的生態(tài)風(fēng)險(xiǎn).RQ值通常表示為特定污染物的測(cè)量濃度(MEC),與預(yù)測(cè)無影響濃度(PNEC)之比,具體計(jì)算公式為:

式中:PNECSoil為氟喹諾酮類抗生素土壤預(yù)測(cè)無影響濃度,μg/kg;PNECWater為氟喹諾酮類抗生素水預(yù)測(cè)無影響濃度,μg/L;d為土壤-水分配系數(shù);EC50為半最大效應(yīng)濃度,mg/L.EC50為急性毒性時(shí), AF取1000;EC50為慢性毒性時(shí),AF取100.NOR及OFL相關(guān)參數(shù)如表3所示.

表3 NOR與OFL生態(tài)風(fēng)險(xiǎn)評(píng)估參數(shù)

2 結(jié)果與討論

2.1 溫度變化曲線

溫度是好氧發(fā)酵過程中重要參數(shù),與微生物活動(dòng)密切相關(guān),不僅影響微生物的代謝速率與群落結(jié)構(gòu),而且影響發(fā)酵產(chǎn)物的理化特性[19].根據(jù)溫度變化,本研究將發(fā)酵過程分為4個(gè)階段(圖2):升溫階段0～4d;超高溫/高溫階段5～10d;降溫階段11～23d;腐熟階段24～40d. 1d時(shí)開啟50℃水浴保溫,11d時(shí)堆體溫度出現(xiàn)明顯下降趨勢(shì),將水浴保溫下降至35℃, 24d時(shí)堆體溫度開始接近水浴溫度,認(rèn)為堆體進(jìn)入腐熟階段,進(jìn)一步將水浴保溫下調(diào)至30℃,40d時(shí),HTC與TC組堆體溫度降低至水浴溫度,發(fā)酵結(jié)束.HTC發(fā)酵開始時(shí)有機(jī)物快速分解,溫度迅速升高,在4d達(dá)到80℃,在6d達(dá)到最高溫度83.3℃, 80℃以上維持了6d,17d時(shí)溫度快速下降,進(jìn)行翻堆維持發(fā)酵過程.TC組6d達(dá)到最高溫度60.3℃,在22d時(shí)翻堆維持發(fā)酵過程.

圖2 HTC和TC過程溫度變化曲線

2.2 VS總量與VS/TS變化曲線

圖3 HTC和TC過程VS總量與VS/TS變化曲線

有機(jī)質(zhì)含量是評(píng)估好氧發(fā)酵腐熟度的重要參數(shù)通常用揮發(fā)分含量(VS/TS)來表示.有機(jī)質(zhì)含量通常在發(fā)酵末期達(dá)到相對(duì)穩(wěn)定的狀態(tài),表示好氧發(fā)酵進(jìn)入腐熟階段[20],發(fā)酵堆體中有機(jī)質(zhì)總量采用VS總量表示,VS總量=堆體總質(zhì)量′(1-含水率)′(VS/TS).

如圖3所示, HTC與TC過程有機(jī)質(zhì)含量均呈下降趨勢(shì), HTC在超高溫階段有機(jī)質(zhì)的分解速率高于降溫和腐熟階段,而TC過程中各階段有機(jī)質(zhì)分解速率差異較小.HTC和TC發(fā)酵過程中VS/TS分別降低了24.9%和20.3%,考慮取樣對(duì)堆體總質(zhì)量的影響后,發(fā)酵完成時(shí)HTC與TC堆體干重分別為3.5kg與3.1kg,有機(jī)質(zhì)總量分別降低了53.8%與44.6%.值得注意的是HTC過程中, 24d時(shí)VS/TS值已趨于穩(wěn)定,而TC組此時(shí)VS/TS值仍略有下降,表明HTC過程堆體達(dá)到穩(wěn)定狀態(tài)較快,發(fā)酵周期更短.

2.3 DOC、DON及DOC/DON變化曲線

溶解性有機(jī)碳是有機(jī)固廢中活性最強(qiáng)的組分之一,研究指出DOC可作為反映好氧發(fā)酵穩(wěn)定性的一個(gè)重要參數(shù)[21-22].如圖4所示,HTC過程中DOC呈持續(xù)下降趨勢(shì),尤其是前11天DOC快速下降,TC組有機(jī)物分解速率低于HTC組,HTC組發(fā)酵過程中,第24天DOC趨于穩(wěn)定,與此同時(shí),TC過程DOC仍有小幅降低,表明HTC過程堆體較快趨于穩(wěn)定,發(fā)酵周期更短.

圖4 HTC和TC過程DOC與DON變化曲線

溶解性有機(jī)氮主要由低分子量的化合物,如氨基酸、氨基糖、尿素和嘌呤,以及高分子量的化合物,如蛋白質(zhì)、葉綠素、DNA 和多酚等組成[23].2種發(fā)酵過程初期,堆體中DON含量均呈上升趨勢(shì).這表明溶解性有機(jī)物快速分解,使得堆體的干基質(zhì)量下降,同時(shí)堆體中有機(jī)氮水解活性高,使得發(fā)酵初期DON含量增加.之后DON含量逐漸下降,一方面DON易于被微生物同化利用,另一方面,硝化和反硝化等過程使得DON含量下降[21].值得注意的是,由于HTC過程啟動(dòng)時(shí)添加超高溫好氧發(fā)酵腐熟料,相當(dāng)于進(jìn)行微生物接種,而TC過程未接種,微生物活性較低,DON利用速率小于有機(jī)氮水解速率,使得TC過程前期DON含量上升.

DOC和DON容易被微生物利用,與常規(guī)C/N相比,DOC/DON更能充分說明發(fā)酵產(chǎn)物的穩(wěn)定性.如圖5所示,HTC與TC過程中DOC/DON均呈現(xiàn)出逐漸下降趨勢(shì),Said-Pullicino等[21]研究指出,當(dāng)DOC/DON比值約為5～6時(shí),發(fā)酵達(dá)到了腐熟穩(wěn)定.發(fā)酵完成時(shí),HTC組與TC組均達(dá)到腐熟穩(wěn)定的標(biāo)準(zhǔn),不過HTC組發(fā)酵周期顯著短于TC組.

圖5 HTC和TC過程DOC/DON變化曲線

2.4 發(fā)芽指數(shù)變化曲線

圖6 HTC和TC過程GI變化曲線

通常,未完全腐熟的發(fā)酵產(chǎn)物會(huì)產(chǎn)生有植物毒性的物質(zhì)抑制植物生長,此外有研究指出,抗生素的存在會(huì)顯著抑制植物根系生長[24-25].GI不僅是一個(gè)腐熟化程度指標(biāo),也是一個(gè)評(píng)估發(fā)酵產(chǎn)物植物毒性變化的指標(biāo),具體計(jì)算公式為:

式中對(duì)照組為新鮮樣品水提取液,空白組為無菌水.2種發(fā)酵過程初期,GI值均低于20%(圖6),表明生污泥具有較強(qiáng)的植物毒性,HTC組與TC組穩(wěn)定產(chǎn)物GI分別為136.7%和119.5%,發(fā)酵過程不僅消除了植物毒性,而且對(duì)植物根系生長有促進(jìn)作用.值得注意的是,HTC過程中在16d已經(jīng)滿足GI不低于80%的閾值范圍,而TC過程28d時(shí)GI才超過80%.這個(gè)事實(shí)符合2.2與2.3節(jié)中HTC發(fā)酵周期較短的結(jié)論.

2.5 NOR與OFL殘留含量變化與生態(tài)風(fēng)險(xiǎn)評(píng)估

如圖7a所示,HTC與TC過程中NOR與OFL含量均顯著下降.HTC與TC組初始NOR含量分別為9210,9750μg/kg,25d時(shí)NOR殘留含量為752, 775μg/kg,去除率分別達(dá)到91.8%,92.1%,兩者去除率無顯著差別.如圖7b所示,HTC與TC組初始OFL含量分別為8181,7815μg/kg,25d時(shí)OFL殘留含量為645,929μg/kg,去除率分別達(dá)到92.1%、88.1%, HTC過程對(duì)OFL去除率更高.有研究表明是因?yàn)楦邷仄茐牧薕FL分子結(jié)構(gòu),或是高溫促進(jìn)了OFL的生物降解活性[26].TC過程中,OFL比NOR更加難以去除,這與Ja?owiecki等[6]研究結(jié)果相符.本研究生態(tài)風(fēng)險(xiǎn)評(píng)估中MEC值采用25d時(shí)NOR與OFL殘留含量,PNECSoil采用表3中數(shù)據(jù),如圖8所示,HTC相較于TC,NOR生態(tài)風(fēng)險(xiǎn)下降3.1%,OFL生態(tài)風(fēng)險(xiǎn)下降30.5%.將含有FQs的發(fā)酵產(chǎn)物施用進(jìn)土壤需格外關(guān)注,因?yàn)镕Qs可能被蔬菜吸收和積累[27],對(duì)人類健康構(gòu)成潛在的風(fēng)險(xiǎn),且FQs殘留可促使污染的土壤中FQs耐藥基因的產(chǎn)生.這項(xiàng)研究中的風(fēng)險(xiǎn)評(píng)估是根據(jù)細(xì)菌的毒性數(shù)據(jù)進(jìn)行的,未考慮FQs降解產(chǎn)物的毒性作用,風(fēng)險(xiǎn)水平可能被高估或低估.

圖8 發(fā)酵產(chǎn)物中NOR與OFL風(fēng)險(xiǎn)熵值

2.6 諾氟沙星與氧氟沙星降解產(chǎn)物含量變化

研究指出在FQs氧化過程中形成的各種氧化中間體與產(chǎn)物,極有可能保留其母體化合物的生態(tài)毒性,甚至發(fā)展出新的可遺傳毒性[28].Zhu等[13]研究表明,與FQs母體化合物相比,氧化后的FQs對(duì)綠藻表現(xiàn)出相同甚至更高的毒性.因此,好氧發(fā)酵過程應(yīng)該盡可能降低FQs降解產(chǎn)物的含量.如圖9a所示,HTC與TC過程中由于前期NOR快速分解,NORP產(chǎn)生積累,導(dǎo)致含量上升,NORP含量最高點(diǎn)分別出現(xiàn)在4d與5d,最終濃度分別為628,668μg/kg.如圖9b所示,由于HTC與TC組在OFL去除速率方面的差異, HTC過程OFLP含量最高點(diǎn)在4d,最終含量191μg/ kg,TC過程OFLP含量最高點(diǎn)出現(xiàn)在10d,最終含量675μg/kg.這表明HTC能有效降低污泥中氧氟沙星脫乙基降解產(chǎn)物的含量,相比較TC而言,HTC穩(wěn)定產(chǎn)物的土地利用更安全.

3 結(jié)論

3.1 超高溫好氧與高溫好氧發(fā)酵25d時(shí)NOR去除率分別為91.8%,92.1%,降解產(chǎn)物NORP殘留含量分別為628,668μg/kg;OFL去除率分別為92.1%、88.1%,降解產(chǎn)物OFLP殘留含量分別為191,675μg/ kg.超高溫好氧發(fā)酵可以顯著提高OFL的去除率,對(duì)中間降解產(chǎn)物OFLP的降解效果顯著優(yōu)于傳統(tǒng)高溫好氧發(fā)酵.

3.2 相較于傳統(tǒng)高溫發(fā)酵,超高溫好氧發(fā)酵穩(wěn)定產(chǎn)物中NOR、OFL的生態(tài)風(fēng)險(xiǎn)分別降低3.1%、30.5%,同時(shí)DOC/DON更低、腐熟度更高、種子發(fā)芽指數(shù)較高,有利于安全土地利用.

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Removal of fluoroquinolone antibiotics generated from the sludge using hyper-thermophilic composting and its degraded products.

SONG Xiang-tong1, YANG Ming-chao1, ZHANG Jun2,3, GUO Ya-li2, DONG Bin1,2*

(1.College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China；2.China Three Gorges Corporation Yangtze Ecology and Environment Engineering Research Center, Beijing 100038, China；3.Yangtze Ecology and Environment Corporation Limited, Wuhan 430070, China)., 2022,42(1)：220～226

The removal performance of NOR, OFL and their degradation products from traditional thermophilic composting (TC) and from hyper-thermophilic composting (HTC) were compared. The results showed that after 25 days’ hyper-thermophilic composting, the removal rate of NOR with TC and HTC was 91.8% and 92.1% with the residual NORP of 628 and 668μg/kg, respectively, while the removal rate of OFL was 92.1% and 88.1%, respectively with the residual OFLP and 191 and 675μg/kg, respectively. Compared with TC, HTC reduced the ecological risk of NOR and OFL by 3.1% and 30.5%, respectively, indicating that HTC could more effectively remove the ofloxacin and its degradation products and thus reduced the risk of environmental exposure to OFL in composting products. At the same time, the DOC/DON of hyper-thermophilic composting products was lower with the higher seed germination index and the plant toxicity of composting products was also lower, which is must be beneficial to the safe land use of sludge.

sludge；hyper-thermophilic；composting；fluoroquinolone；antibiotic；degradation product

X705

A

1000-6923(2022)01-0220-07

宋相通(1996-),男,同濟(jì)大學(xué)碩士研究生,研究方向?yàn)楣腆w廢棄物資源化利用.

2021-06-03

中國長江三峽集團(tuán)有限公司資助項(xiàng)目(202003080);國家重點(diǎn)研發(fā)計(jì)劃(2020YFC1908702);國家重點(diǎn)研發(fā)計(jì)劃(2021YFC3200704)

* 責(zé)任作者, 教授, dongbin@#edu.cn