含生物質(zhì)炭城市污泥堆肥中溶解性有機(jī)質(zhì)的光譜特征

閆金龍,江 韜,2,*,趙秀蘭,2,魏世強(qiáng),2,王定勇,2,李璐璐,郭 念,孫文彬(.西南大學(xué)資源環(huán)境學(xué)院,重慶 40076；2.重慶市農(nóng)業(yè)資源與環(huán)境研究重點(diǎn)實(shí)驗(yàn)室,重慶 40076)

含生物質(zhì)炭城市污泥堆肥中溶解性有機(jī)質(zhì)的光譜特征

閆金龍1,江 韜1,2,*,趙秀蘭1,2,魏世強(qiáng)1,2,王定勇1,2,李璐璐1,郭 念1,孫文彬1(1.西南大學(xué)資源環(huán)境學(xué)院,重慶 400716；2.重慶市農(nóng)業(yè)資源與環(huán)境研究重點(diǎn)實(shí)驗(yàn)室,重慶 400716)

以外源添加生物質(zhì)炭的城市污泥堆肥過(guò)程中溶解性有機(jī)質(zhì)(DOM)為研究對(duì)象,討論了其紫外-可見(jiàn)和熒光光譜特征變化.結(jié)果表明:與對(duì)照組相比,外源添加生物質(zhì)炭的處理其堆肥 DOM的芳香性和腐殖化程度更高,有利于提高堆肥的腐熟度,且外源添加花生殼炭的處理較添加小麥秸稈炭的處理更有利于堆肥腐熟度的提高.外源添加花生殼炭的處理在堆肥21d后,其堆肥腐熟度可能達(dá)到峰值,而外源添加小麥秸稈炭的處理其堆肥腐熟度則隨著堆肥時(shí)間的進(jìn)行而增加.對(duì)照組和處理組堆肥DOM的FI>0.7,BIX>0.8,表明其來(lái)源為自生源,可能與微生物對(duì)有機(jī)物的降解有關(guān).因此,通過(guò)對(duì)城市污泥堆肥過(guò)程中DOM的光譜特征分析,能較好地評(píng)估城市污泥堆肥腐熟度的情況.

生物質(zhì)炭；堆肥；溶解性有機(jī)質(zhì)(DOM)；紫外光譜；熒光光譜

隨著我國(guó)城市經(jīng)濟(jì)的高速發(fā)展,城市污水處理帶來(lái)的城市污泥產(chǎn)量急劇增加[1].城市污泥是潛在的有機(jī)肥原料,同時(shí)污泥中還含有病原微生物、重金屬等污染物,極易造成二次污染,因此,對(duì)污泥的處置一直是研究的熱點(diǎn)[2-3].其中,堆肥是污泥處置及實(shí)現(xiàn)無(wú)害化、資源化利用的重要方法之一[4-5].近年來(lái),為提高堆肥效率,常采用外源添加生物質(zhì)炭的方式改善堆體條件(例如C/N比,含水率,孔隙度,堆肥養(yǎng)分等),提升堆體有機(jī)質(zhì)穩(wěn)定性和腐殖化程度[6-7].

堆肥中有機(jī)質(zhì)轉(zhuǎn)化是評(píng)估堆肥腐熟程度和環(huán)境安全性的重要基礎(chǔ).堆肥過(guò)程中溶解性有機(jī)質(zhì)(DOM)的變化被認(rèn)為是能靈敏反映堆肥腐熟狀況的重要指標(biāo),且較堆肥的固相組分更具代表性[8-9].

目前,針對(duì)DOM定性研究,應(yīng)用較多的是紫外-可見(jiàn)光譜和同步熒光技術(shù),因其靈敏度高和分析便捷,被廣泛應(yīng)用于自然有機(jī)質(zhì)(NOM)研究中,尤其是水體DOM歸趨[10].相比之下,針對(duì)堆肥DOM 性質(zhì)的研究較少[11-12].目前,已有報(bào)道表明添加外源生物質(zhì)炭有利于堆肥固炭,而高C/N比下堆肥腐熟度也相應(yīng)提高[13-14],而在該過(guò)程中對(duì)DOM 的探討還相對(duì)不足,且以前研究的結(jié)論也并不一致[15-16],尤其是對(duì)不同調(diào)理劑處理方式下堆肥 DOM 的性質(zhì)光譜表征缺少關(guān)注[17-18].基于此,本研究采用紫外-可見(jiàn)光譜及三維熒光光譜對(duì)添加不同生物質(zhì)炭的城市污泥堆肥過(guò)程中DOM 的光譜特征進(jìn)行表征,并通過(guò)特征參數(shù)的計(jì)算,進(jìn)一步了解不同處理堆肥在堆肥過(guò)程中的差異,為進(jìn)一步提高堆肥效率、正確評(píng)估堆肥腐熟程度和環(huán)境安全性提供一定的理論依據(jù).

1 材料與方法

1.1 不同堆肥處理及樣品采集

圖1 堆肥試驗(yàn)示意Fig.1 The sketch map of compost

以污水處理廠污泥和小麥秸稈作為堆肥基質(zhì),以生物質(zhì)炭(完全炭化)為調(diào)理劑.污泥取自重慶市某污水處理廠的脫水車(chē)間,小麥秸稈取自學(xué)校農(nóng)場(chǎng),破碎至 2～3cm,生物質(zhì)炭購(gòu)于商丘市三利新能源有限公司.將污泥與小麥秸稈按一定量混合,使混合堆肥物料的C/N比達(dá)到18,然后向堆體添加生物質(zhì)炭.以未加生物質(zhì)炭的污泥為對(duì)照(以下簡(jiǎn)稱(chēng)“CK”).生物質(zhì)炭的類(lèi)型為小麥秸稈炭(以下簡(jiǎn)稱(chēng)“+麥”)、花生殼炭(以下簡(jiǎn)稱(chēng)“+花”),添加量為堆肥基質(zhì)的 6%(按堆體的重量記).將各堆體分別放入容積為26.4L (80cm× 55cm×60cm)的泡沫箱中,箱的底部打一個(gè)小孔,接入通氣泵,采用強(qiáng)制通風(fēng)與人工翻堆相結(jié)合的方式進(jìn)行高溫好氧堆肥(圖 1).堆肥過(guò)程中每周翻堆1次,堆體的水分保持在60%～70%,根據(jù)堆肥期間溫度變化情況,分別于堆肥初始(第0d)、堆肥21d、42d后取樣進(jìn)行分析.不同堆肥處理的初始物料基本性質(zhì)見(jiàn)表1.

表1 不同處理堆肥的初始物料基本性質(zhì)Table 1 Basic characteristics of different composting treatments

1.2 堆肥DOM提取

采用去離子水提取堆肥 DOM[19].將所采集的堆肥樣品自然風(fēng)干后,磨細(xì),過(guò)2mm篩.按土:水=1:6(W/V),采用去離子水與堆肥固體混合后, 25℃下200r/min振蕩16h,然后400r/min下離心20min,上清液過(guò) 0.45μm濾膜后,濾液即為堆肥DOM樣品.DOM測(cè)定TOC和TON(德國(guó),Yena Multi N/C 3000)后,濃度以DOC(mg/L)計(jì).所有樣品在進(jìn)行光譜測(cè)定前,均稀釋相同倍數(shù)(0.6mLDOM定容到100mL棕色容量瓶).

1.3 光譜測(cè)定

紫外-可見(jiàn)光譜在 Hitachi U-1800紫外-可見(jiàn)分光光度計(jì)上進(jìn)行測(cè)定.掃描波長(zhǎng)為 200～800nm,程序自動(dòng)繪制掃描曲線(xiàn).根據(jù)光譜數(shù)據(jù),計(jì)算特征紫外吸光系數(shù) SUVA254nm[SUVA254nm= A254/(b·c)]、SUVA280nm[SUVA280nm=A280/(b·c)],單位:L/(mg C·m); A254為波長(zhǎng)254nm時(shí)吸光度;b為石英吸收池厚度(0.01m);c為DOM濃度(mg/L).同時(shí)計(jì)算E2/E3(250nm及365nm時(shí)吸光度比值)和E4/E6(465nm和665nm時(shí)吸光度比值).

采用Hitachi F-7000熒光光譜儀對(duì)DOM樣品進(jìn)行三維熒光掃描.激光光源 150W 氙弧燈, PMT電壓為700V,信噪比>110;狹縫寬度Ex=5nm, Em=2nm;響應(yīng)時(shí)間為自動(dòng).掃描范圍:Ex=200～450nm,Em=200～600nm,掃描速度1200nm/min.測(cè)定前,保持樣品溫度恒定,以去離子水做熒光測(cè)定空白.Origin 8.0繪制三維熒光光譜圖.同時(shí)提取相關(guān)熒光特征,并計(jì)算熒光指數(shù)(FI)、自生源指數(shù)(BIX)及腐殖化指數(shù)(HIX),具體計(jì)算方法為:FI為Ex=370nm時(shí),Em波長(zhǎng)分別為450和500nm時(shí)的熒光強(qiáng)度比值[20-21];BIX為Ex=310nm時(shí),Em波長(zhǎng)分別為 380和 430nm 時(shí)的熒光強(qiáng)度比值[22-23]; HIX=ΣI434→480/(ΣI300→344+ΣI434→480),式中 ΣIx→y表示在 Ex=255nm時(shí),連續(xù)發(fā)射波長(zhǎng)范圍熒光強(qiáng)度的積分面積[21,23-24].

2 結(jié)果與討論

2.1 不同處理堆肥過(guò)程中DOM的紫外-可見(jiàn)光譜特征變化

圖2 不同堆肥處理過(guò)程中DOM的紫外-可見(jiàn)吸收光譜曲線(xiàn)Fig.2 UV-VIS spectrum of DOM extracted from different composting treatment progresses

2.1.1 不同處理堆肥過(guò)程中DOM的紫外-可見(jiàn)光譜 紫外-可見(jiàn)吸收光譜是由于分子中的價(jià)電子,特別是有機(jī)質(zhì)中不飽和鍵和芳香性結(jié)構(gòu)中π-π*電子躍遷而產(chǎn)生的.實(shí)際上,堆肥作為有機(jī)質(zhì)的一種特殊形式,其結(jié)構(gòu)和功能基團(tuán)較為復(fù)雜,不同生色團(tuán)較多,并不具有明顯的易被鑒定的光譜特征.從不同處理堆肥過(guò)程中 DOM的紫外可見(jiàn)光譜圖(圖2)可知,在200～800nm全波長(zhǎng)范圍內(nèi),并未發(fā)現(xiàn)有任何特征吸收峰,在可見(jiàn)光長(zhǎng)波段,幾乎無(wú)任何吸收.這和很多自然有機(jī)質(zhì)(NOM)的紫外-可見(jiàn)光譜特征是一致的[25].但隨著堆肥過(guò)程的進(jìn)行,處理組污泥堆肥其 DOM的紫外可見(jiàn)光譜發(fā)生了明顯的紅移現(xiàn)象,且隨著堆肥時(shí)間的進(jìn)行其紅移現(xiàn)象越來(lái)越明顯.造成這種現(xiàn)象的原因可能是在堆肥過(guò)程中,處理組堆肥的腐熟度較對(duì)照組有大幅度的提高,DOM 共軛結(jié)構(gòu)和芳香結(jié)構(gòu)增多,腐殖化程度增強(qiáng).其次,表明添加小麥秸稈和花生殼外源生物有機(jī)質(zhì)炭后,有利于提高城市污泥堆肥的腐熟度.

2.1.2 堆肥過(guò)程中 DOM 的紫外特征參數(shù) SUVA254nm是研究天然有機(jī)質(zhì)的重要特征參數(shù),其大小可間接表征有機(jī)質(zhì)的芳香性程度, SUVA254nm越高,有機(jī)質(zhì)芳香度越高[26-27].從表 2可知,對(duì)照組和添加小麥秸稈炭的處理組隨堆肥時(shí)間進(jìn)行,其SUVA254nm值不斷增加,表明隨著堆肥的進(jìn)行,污泥堆肥的腐熟度不斷增加,芳香性結(jié)構(gòu)不斷增多.而添加花生殼炭的處理組在 42d后其值小于堆肥21d后的SUVA254nm值,可能是由于添加花生殼炭的污泥在堆肥 21d達(dá)到了腐熟的峰值,之后有機(jī)質(zhì)在微生物的作用下開(kāi)始分解.另外,各堆肥過(guò)程中對(duì)照組的 SUVA254nm值總體上小于處理組的值,進(jìn)一步說(shuō)明了添加小麥秸稈和花生殼的外源有機(jī)質(zhì)炭有利于提高城市污泥堆肥的腐熟度.此外,DOM在280nm摩爾吸光系數(shù)(SUVA280nm)與相對(duì)分子質(zhì)量存在顯著正相關(guān)

[26,28].由表2可知,處理組和對(duì)照組的SUVA280和 SUVA254的變化趨勢(shì)基本一致,反映了不同處理堆肥過(guò)程中 DOM 芳香性增強(qiáng)可能與大分子物質(zhì)的增加有關(guān).

Dorado等[29]研究表明E2/E3與E4/E6和有機(jī)質(zhì)的腐殖化程度、芳香性及相對(duì)分子質(zhì)量成負(fù)相關(guān),其值越高,腐殖化程度越低.本試驗(yàn)中,堆肥過(guò)程中對(duì)照組DOM的E2/E3與SUVA254nm呈負(fù)相關(guān) (r=0.89),而E4/E6與SUVA254nm未呈現(xiàn)負(fù)相關(guān)關(guān)系,添加小麥秸稈炭的堆肥DOM的SUVA254nm與 E2/E3,E4/E6均未呈現(xiàn)負(fù)相關(guān)關(guān)系,但添加花生殼炭的堆肥DOM的SUVA254nm與E2/E3,E4/E6均呈現(xiàn)負(fù)相關(guān)關(guān)系(r=0.93和0.95),結(jié)果表明E2/E3可能較適合用于堆肥過(guò)程中腐殖化程度的表征.

表2 不同處理堆肥過(guò)程中DOM的紫外-可見(jiàn)光譜特征參數(shù)Table 2 Specific UV-Vis parameters of DOM extracted from different composting treatment processes

2.2 不同處理堆肥過(guò)程中DOM熒光光譜特征變化

2.2.1 不同處理堆肥過(guò)程中 DOM 三維熒光光譜 目前,針對(duì)三維熒光光譜熒光峰的辨析大多還集中在淡水及海洋DOM的研究,事實(shí)上,土壤及堆肥中DOM的熒光特征和自然水體的DOM并沒(méi)有本質(zhì)區(qū)別,因此,可采用水體DOM的熒光峰鑒別范圍對(duì)堆肥 DOM 進(jìn)行劃分[30-32],具體為紫外區(qū)類(lèi)腐殖酸峰 A(230～250nm/426～466nm);可見(jiàn)光區(qū)類(lèi)腐殖酸峰C(300～305nm/408～456nm);類(lèi)蛋白熒光峰 B(270～280/326～348nm)及類(lèi)蛋白質(zhì)熒光峰D(225～230/320～360nm).

從不同處理堆肥過(guò)程 DOM 的熒光光譜圖(圖3)中可得,除添加小麥秸稈炭的處理組在堆肥開(kāi)始時(shí)僅有D峰外,對(duì)照組和添加花生殼炭的處理組在堆肥開(kāi)始都有B峰和D峰,且堆肥開(kāi)始均未發(fā)現(xiàn)C峰,除對(duì)照組外,兩個(gè)處理組也未發(fā)現(xiàn)A峰.但隨著堆肥的進(jìn)行,對(duì)照組和處理組的B峰均消失,C峰強(qiáng)度隨堆肥時(shí)間增加而增強(qiáng),D峰強(qiáng)度則表現(xiàn)出總體上隨堆肥時(shí)間增強(qiáng)而減小,而A峰強(qiáng)度的變化則為:對(duì)照組隨堆肥時(shí)間增加先減小后增加,而處理組則剛好相反,先增加后減小.結(jié)果表明,堆肥開(kāi)始時(shí),堆肥腐殖化程度不高,主要以類(lèi)蛋白峰為主,但隨著堆肥過(guò)程的進(jìn)行,堆肥腐殖化程度逐漸提高,類(lèi)腐殖酸峰逐漸增強(qiáng),而類(lèi)蛋白峰逐漸減弱.且處理組和對(duì)照組相比,A峰強(qiáng)度的變化相反,說(shuō)明添加外源有機(jī)質(zhì)有利于提高堆肥的腐殖化程度.

2.2.2 不同處理堆肥過(guò)程中 DOM 熒光特征參數(shù) 熒光A峰和熒光C峰強(qiáng)度的比值r(A,C)是一個(gè)與有機(jī)質(zhì)結(jié)構(gòu)和腐殖化程度相關(guān)的指標(biāo).由表3可知,堆肥21d后,對(duì)照組和添加小麥秸稈炭的處理組均隨著堆肥過(guò)程的進(jìn)行,r(A,C)值逐漸減小,而添加花生殼炭的處理組r(A,C)值逐漸增大,說(shuō)明在堆肥 21d左右添加花生殼炭的堆肥腐熟度可能達(dá)到了峰值,且處理組在堆肥過(guò)程中 r(A,C)值基本上小于對(duì)照組.而有研究報(bào)道,大分子量、相對(duì)穩(wěn)定的芳香性結(jié)構(gòu)是C峰的主要貢獻(xiàn)者,而A峰的主要來(lái)源是低分子量但熒光效率高的物質(zhì)[33],本研究熒光圖譜也發(fā)現(xiàn)隨著堆肥時(shí)間的進(jìn)行,C峰強(qiáng)度逐漸增大,r(A,C)值減小.說(shuō)明隨著堆肥時(shí)間的進(jìn)行,堆肥腐殖化程度增加,添加外源有機(jī)質(zhì)炭有利于堆肥的腐殖化提高,進(jìn)一步形成穩(wěn)定的腐殖質(zhì).

腐殖化指數(shù)(HIX)是評(píng)價(jià)DOM腐殖化程度的重要指標(biāo)[34-35].由于有機(jī)質(zhì)芳香性越強(qiáng),熒光發(fā)射出現(xiàn)紅移(向長(zhǎng)波方向轉(zhuǎn)移),因此HIX值范圍在0～1之間,HIX越高意味著DOM中碳?xì)浠衔锝M分越少,腐殖化程度越高.間接水提取或直接抽濾的土壤間隙水 DOM 的 HIX在0.6～0.9[21,36];而自然水體中 DOM 的 HIX一般為:<0.6(海水)和>0.7(淡水).不同處理堆肥過(guò)程中DOM的HIX和海水DOM的值更為接近,這可能和兩種來(lái)源的 DOM都有著明顯的自生源特征有關(guān).研究認(rèn)為BIX在0.6～0.7之間時(shí),DOM主要為陸源輸入,外源輸入特征明顯[22],而本研究中 BIX 均>0.8,進(jìn)一步證明了堆肥過(guò)程中DOM主要來(lái)源為自生源[23].

圖3 不同處理堆肥過(guò)程中DOM的三維熒光圖譜Fig.3 3D-EEMs of DOM extracted from different composting treatment processes

進(jìn)一步,FI是評(píng)價(jià) DOM 來(lái)源的依據(jù):FI= 1.7～2.0時(shí)來(lái)自于微生物分解,芳香度不高;FI<1.4來(lái)源于陸地輸入,具有較高芳香度[21,37].對(duì)照組和處理組FI均大于1.7(表3),和以自生源(微生物活動(dòng)產(chǎn)生)為主的DOM熒光指數(shù)相近,表明微生物和堆肥中DOM的形成有密切相關(guān),同時(shí)也證明微生物對(duì)有機(jī)物的降解也是堆肥形成的主要原因[38-39].

由于有機(jī)質(zhì)的腐殖化程度提高,具有熒光特性的分子結(jié)構(gòu)增多,發(fā)射光譜出現(xiàn)紅移[34,40].在EX=240nm時(shí),發(fā)射光譜中后1/4波段熒光強(qiáng)度積分面積與前 1/4波段熒光強(qiáng)度積分面積比值(A4/A1)可以用來(lái)作為有機(jī)質(zhì)腐殖化的表征指標(biāo),比值增加意味有機(jī)質(zhì)芳香結(jié)果增加,腐殖化程度提高[34,41].本研究也得到類(lèi)似結(jié)論,隨著堆肥過(guò)程的進(jìn)行,處理組和對(duì)照組的 A4/A1值均增加,且前者大于后者,其中添加花生殼炭的處理組的A4/A1值最大,結(jié)果說(shuō)明隨著堆肥過(guò)程的進(jìn)行,堆肥DOM 的芳香程度不斷提高,添加外源有機(jī)質(zhì)炭后,能提高堆肥的芳香度,且添加花生殼炭的處理對(duì)堆肥腐殖化程度的提高效果更好.

表3 不同處理堆肥過(guò)程DOM的相關(guān)熒光參數(shù)Table 3 Fluorescence parameters of DOM extracted from different composting treatment processes

3 結(jié)論

3.1 對(duì)照組和外源添加生物質(zhì)炭的處理組城市污泥堆肥中DOM的HIX與海水DOM值接近,FI均>1.7,同時(shí)BIX均>0.8,表明其來(lái)源以自生源為主,可能與微生物對(duì)有機(jī)物的降解有關(guān).

3.2 外源添加小麥秸稈炭的處理隨堆肥時(shí)間的進(jìn)行,堆肥DOM的SUVA254nm、SUVA280nm以及r(A,C)值等不斷增加,表明堆肥腐熟度不斷提高,而外源添加花生殼炭的處理在堆肥 21d,其對(duì)應(yīng)值均達(dá)到最大值,表明其堆肥腐熟度可能達(dá)到峰值,繼續(xù)堆肥其腐熟度減小.

3.3 外源添加花生殼和小麥秸稈炭的處理組堆肥DOM的E2/E3、r(A,C)值等指標(biāo)總體上均大于對(duì)照組,表明外源添加生物質(zhì)炭有利于提高堆肥腐熟度,且外源添加花生殼炭的處理堆肥DOM的A4/A1值最大,說(shuō)明其對(duì)堆肥腐熟度的提高效果更好.

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Spectral characteristics of dissolved organic matter in co-composting process of municipal sludge with biochar.

YAN Jin-long1, JIANG Tao1,2*, ZHAO Xiu-lan1,2, WEI Shi-qiang1,2, WANG Ding-yong1,2, LI Lu-lu1, GUO Nian1, SUN Wen-bin1(1.College of Resources and Environment, Southwest University, Chongqing 400716, China；2.Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing 400716, China). China Environmental Science, 2014,34(2)：459～465

Changes in the UV-visible and fluorescence characteristics of DOM from the co-composting process of municipal sludge with two types of biochars were discussed. The results showed the aromaticity and humification of DOM from the co-composting with biochars significantly increased compared with control, which indicated in favor of improving the maturity of compost. The treatment with biochar from peanut shell showed the highest maturity, followed by wheat straw biochar. After 21days, compost treated with biochar from peanut shell reached its maximum maturity, while that treated with biochar from wheat straw continued to increase over the whole time. Meanwhile, the DOM from the compost with or without treatment was found to be autochthonous, FI>0.7, BIX>0.8, mainly attributed to the microbial decomposition of compost. Thus, the spectral characteristics of DOM are capable of assessing the degree of maturity of compost during the co-composting process with biochars from different source.

biochar；compost；dissolved organic matter (DOM)；UV-visible spectrum；fluorescence spectrum

X705

：A

：1000-6923(2014)02-0459-07

閆金龍(1989-),男,四川渠縣人,西南大學(xué)資源環(huán)境學(xué)院博士研究生,主要從事環(huán)境污染化學(xué)研究.

2013-05-10

中國(guó)博士后科學(xué)基金資助項(xiàng)目(2013M542238);中央高?；究蒲袠I(yè)務(wù)費(fèi)(XDJK2013C151);西南大學(xué)博士基金(SWU112098);重慶市科委科技攻關(guān)項(xiàng)目(CSTC-2008AC7013)

* 責(zé)任作者, 講師, Jiangtower666@163.com