赤泥對(duì)堆肥腐熟度及其產(chǎn)品對(duì)稻米Cd阻控效果

周紅燕,陳 喆,2*,李侃麒,冷為貴,王宗抗

赤泥對(duì)堆肥腐熟度及其產(chǎn)品對(duì)稻米Cd阻控效果

周紅燕1,陳 喆1,2*,李侃麒1,冷為貴3,王宗抗3

(1.桂林理工大學(xué)環(huán)境科學(xué)與工程學(xué)院,廣西 桂林 541004；2.廣西師范大學(xué),珍稀瀕危動(dòng)植物生態(tài)與環(huán)境保護(hù)教育部重點(diǎn)實(shí)驗(yàn)室,廣西 桂林 541004；3.貴港市芭田生態(tài)有限公司,廣西 貴港 537000)

以赤泥作為堆肥添加劑進(jìn)行雞糞好氧堆肥試驗(yàn),分析了堆肥過(guò)程中赤泥對(duì)溫度、pH值、電導(dǎo)率(EC)及種子發(fā)芽指數(shù)(GI)的影響.通過(guò)三維熒光與紫外-可見(jiàn)光光譜特征解析堆肥過(guò)程中腐殖酸(HA)組分的演變特征.并利用盆栽實(shí)驗(yàn)探索堆肥產(chǎn)品對(duì)礦區(qū)土壤中稻米鎘的阻隔效果.結(jié)果表明,赤泥的添加提高了堆體高溫期的溫度.EC較堆肥前均顯著降低,但赤泥堆肥EC(4.29mS/cm)顯著高于雞糞堆肥EC(3.59mS/cm).雞糞堆肥與赤泥堆肥的GI隨著堆肥時(shí)間的增長(zhǎng)而升高,在堆肥結(jié)束時(shí)分別達(dá)到100.2%和96.44%,說(shuō)明2種堆肥產(chǎn)品均未表現(xiàn)出植物毒性.2種堆肥HA中類蛋白質(zhì)等物在堆肥過(guò)程中均轉(zhuǎn)化為較為穩(wěn)定的類腐殖質(zhì)物質(zhì),HA的SUVA254、SUVA280和A226～400在堆肥結(jié)束后也顯著提高,表明堆肥的腐殖化程度升高.此外,赤泥的添加提高了腐殖化參數(shù)數(shù)值,證明赤泥的加入能夠加速堆肥腐殖化進(jìn)程.在盆栽實(shí)驗(yàn)中,雞糞堆肥與赤泥堆肥均提高了土壤的pH值,降低了土壤中DTPA-Cd和糙米中Cd的含量.其中,施用2g/kg赤泥堆肥后,糙米Cd含量降低幅度最大,為58.68%,水稻糙米中Cd的含量由未施用堆肥的0.42mg/kg降低至0.17mg/kg.因此,赤泥的添加可以在一定程度上提高堆肥效率,同時(shí)施加堆肥產(chǎn)品對(duì)土壤Cd的生物有效性及水稻植株內(nèi)Cd起到抑制與阻隔作用,且施加赤泥堆肥效果更為顯著.

赤泥；雞糞；堆肥；水稻；鎘污染；重金屬

赤泥是制鋁工業(yè)提取氧化鋁時(shí)排出的工業(yè)固體廢棄物,廣西平果鋁是中國(guó)特大型鋁土礦,年產(chǎn)氧化鋁高達(dá)200萬(wàn)t,年排放赤泥量也高達(dá)約200萬(wàn)t[1].鋁礦開(kāi)采造成赤泥的露天隨意堆放不僅占用礦區(qū)大量耕地資源,而且雨水對(duì)赤泥堆場(chǎng)的不斷沖刷與淋溶作用已造成礦區(qū)大面積重金屬污染,其中以鎘(Cd)污染耕地超標(biāo)問(wèn)題尤為突出.目前,赤泥的主要利用途徑包括生產(chǎn)水泥、混凝土[2],提取有價(jià)金屬[3]等.研究表明,赤泥因其堿性可有效增加土壤pH值,有利于鐵錳氧化物的形成[4],能夠降低金屬的溶解度和生---物有效性.同時(shí),由于赤泥中富含的鋁硅酸鹽可吸附或絡(luò)合重金屬[5],使得赤泥可被作為土壤鈍化劑[6]使用,但仍需通過(guò)預(yù)處理與無(wú)害化等手段確保赤泥投加的安全性.通過(guò)堆肥可將畜禽糞便中的病原體、抗生素和重金屬等物質(zhì)無(wú)害化,使之成為優(yōu)質(zhì)的肥料[7].堆肥過(guò)程中通常添加秸稈、粉煤灰[8]和石灰[9]等作為膨脹劑和鈍化劑,加速堆肥發(fā)酵,鈍化重金屬,提升堆肥品質(zhì).土壤中施用有機(jī)肥不僅可以調(diào)節(jié)土壤養(yǎng)分含量和pH值,還可以固定、吸附土壤中的重金屬離子.Wang等[10]研究表明,施用有機(jī)-無(wú)機(jī)復(fù)混肥可以增加土壤pH值2～3個(gè)單位,并降低玉米植株各部位中Cd的濃度;Zhang等[11]的研究也表明,豬糞堆肥可以代替化肥施用于土壤,并能夠顯著降低小麥籽粒中重金屬鎳、銅、鋅、鎘和鉛的含量,且低于我國(guó)小麥?zhǔn)称窐?biāo)準(zhǔn)限值.赤泥對(duì)土壤中的重金屬也可以起到較好的鈍化作用[12].

本研究以雞糞與米糠為基質(zhì),以赤泥為輔料進(jìn)行雞糞好氧堆肥試驗(yàn),通過(guò)三維熒光和紫外-可見(jiàn)光光譜,分析堆肥腐殖酸中有機(jī)物質(zhì)的變化,探究赤泥對(duì)堆肥效率與質(zhì)量的影響;并對(duì)水稻進(jìn)行盆栽實(shí)驗(yàn)探索堆肥產(chǎn)品對(duì)礦區(qū)Cd污染土壤中水稻稻米Cd的阻隔效果,為利用赤泥提高堆肥效率與品質(zhì)提供參考.

1 材料與方法

1.1 供試材料

堆肥實(shí)驗(yàn)采用雞糞與米糠為原料,以赤泥為輔料.雞糞取自廣西桂林豐悅農(nóng)業(yè)科技發(fā)展有限公司,米糠取自廣西賀州農(nóng)豐寶公司,赤泥取自廣西平果鋁業(yè)公司.盆栽實(shí)驗(yàn)供試土壤采自某礦區(qū)周邊Cd污染耕地土壤.堆肥原輔材料及供試土壤的基礎(chǔ)理化性質(zhì)如表1所示.

表1 堆肥原輔料與供試土壤的基礎(chǔ)理化性質(zhì)

1.2 堆肥實(shí)驗(yàn)

1.2.1 實(shí)驗(yàn)設(shè)計(jì) 堆肥發(fā)酵桶有效體積為50L,堆肥桶高為41cm,上口直徑為40cm,下口直徑為33cm,桶底鋪一層多面空心球,上覆雙層紗網(wǎng).根據(jù)研究目的共設(shè)置2個(gè)處理,雞糞堆肥(CM):將雞糞:米糠以質(zhì)量比5:1均勻混合;赤泥堆肥(RM):將雞糞:米糠:赤泥以質(zhì)量比5:1:0.75均勻混合,每個(gè)處理設(shè)置3個(gè)重復(fù).調(diào)節(jié)含水率和碳氮比分別為60%和25/1,采用強(qiáng)制通風(fēng)好氧堆肥方式,使用氧氣泵由下部篩網(wǎng)向上通風(fēng)供氧,通氣量為2L/min.

1.2.2 采樣與前處理 堆肥歷時(shí)約45d,分別在堆肥的第0,5,11,19,28,36,45d采集樣品各約600g,采用五點(diǎn)法[13]對(duì)堆體中心部位進(jìn)行取樣,混合均勻后采用四分法[13]將樣品分為3份各200g,樣品于４℃冰箱保存,測(cè)定pH值、電導(dǎo)率(EC)、含水率及種子發(fā)芽指數(shù)(GI).一份樣品經(jīng)－54℃凍干后研磨過(guò)100目篩,用于重金屬分析與腐殖質(zhì)的提取實(shí)驗(yàn).另一份樣品保存于－20℃冰箱中.

1.2.3 基礎(chǔ)理化性質(zhì)測(cè)定 每天早(08:00)、晚(18:00)分別對(duì)堆體進(jìn)行溫度測(cè)定,從上到下依次測(cè)定5,15,25,35,40cm等5個(gè)層次的溫度,取其算術(shù)平均值為當(dāng)天測(cè)量溫度,同時(shí)記錄環(huán)境溫度.取不同時(shí)期新鮮堆肥并按固液比1:10(/)加入超純水[14],150r/min混合振蕩浸提30min,取出并靜置30min,待測(cè)pH值.取不同時(shí)期新鮮堆肥樣品并按固液比1:10(/)加入超純水[14],混合振蕩浸提30min,取出在4000r/min,25℃條件下離心10min,待測(cè)電導(dǎo)率.

1.2.4 種子發(fā)芽指數(shù)(%) 取新鮮堆肥樣品并按固液比1:10(/)加入超純水,混合振蕩浸提30min,取出并靜置浸提1h,在4000r/min,25℃條件下離心10min后,用定性濾紙過(guò)濾,吸取10mL 濾液于墊有濾紙的培養(yǎng)皿內(nèi),均勻放入20粒小白菜種子(種子需先置于蒸餾水中浸泡2h,挑選飽滿種子),蓋上皿蓋,在25℃培養(yǎng)箱中避光培養(yǎng)72h后測(cè)定發(fā)芽率和根長(zhǎng)[15].每個(gè)樣品3次重復(fù),同時(shí)以去離子水做空白試驗(yàn).GI(%)=(處理種子發(fā)芽率′處理種子根長(zhǎng))/(對(duì)照種子發(fā)芽率′對(duì)照種子根長(zhǎng))′100%.

1.2.5 堆肥腐殖酸(HA)的提取 堆肥腐殖酸提取按照國(guó)際腐殖質(zhì)協(xié)會(huì)提供的方法[16]進(jìn)行提取.

1.2.6 HA三維熒光(3D-EEM)測(cè)定與分析[17]3D-EEM采用儀器Perkin Elmer Lumines-cence Spectrometer LS50B測(cè)定.激發(fā)光源:150W氙弧燈;PMT電壓:700V;信噪比>110;帶通(Bandpass):激發(fā)波長(zhǎng)(x)＝10nm;發(fā)射波長(zhǎng)(m)＝10nm;掃描速度:1200nm/min.激發(fā)發(fā)射波長(zhǎng)范圍x:300～ 450nm,m:350～600nm.平行因子分析(PARAFAC)采用MATLAB7.11中DOMFluor工具包分析.

1.2.7 HA紫外-可見(jiàn)光光譜(UV-Vis)測(cè)定[18]UV-Vis采用UV-8000a光度計(jì)測(cè)定.以純水作為空白對(duì)照,在紫外吸收區(qū),掃描波長(zhǎng)范圍為190～ 700nm,掃描間距為1nm.首先將待測(cè)樣品的TOC調(diào)整為20mg/L以下,掃描全譜.

1.3 盆栽實(shí)驗(yàn)

1.3.1 實(shí)驗(yàn)設(shè)計(jì) 本實(shí)驗(yàn)共設(shè)7個(gè)處理,不添加堆肥為對(duì)照(CK),施加純雞糞0.5,1和2g/kg風(fēng)干土壤(CM0.5、CM1和CM2),施加赤泥堆肥0.5,1和2g/kg風(fēng)干土壤(RM0.5、RM1和RM2).每個(gè)處理設(shè)3個(gè)重復(fù).將15kg風(fēng)干土裝入25L培養(yǎng)桶,桶高為30cm,上口直徑為32cm,下口直徑為29cm,在淹水狀態(tài)下(土面水深 3～4cm)平衡30d后移苗.本實(shí)驗(yàn)采用的水稻品種均為陸兩優(yōu)996(Lu Liang You996).每盆移栽4株水稻秧苗,移栽后90d(抽穗期)收獲.整個(gè)生育期保持土面水深3～4cm.實(shí)驗(yàn)期間水稻無(wú)病蟲害發(fā)生.在移苗21d后施入堆肥.

1.3.2 采樣與預(yù)處理 水稻收獲后,將水稻籽粒脫殼,用不銹鋼粉碎機(jī)粉碎至約1mm的粉末,測(cè)定Cd的含量.水稻收獲后,采集培養(yǎng)桶中土樣,風(fēng)干,混勻,過(guò)20目篩,測(cè)定有效態(tài)Cd的含量.

1.3.3 有效硅的測(cè)定[19]采用0.025mol/L檸檬酸緩浸提,進(jìn)行鉬藍(lán)比色.

1.3.4 重金屬總量的測(cè)定[20]重金屬總量采用三酸(HNO3-HF-HClO4)消解法進(jìn)行消解,使用ICP- OES待測(cè)(ICP-OES,Opetima 7000DV).

1.3.5 重金屬有效態(tài)的測(cè)定[21]稱取風(fēng)干土壤樣品并按固液比1:10(/)加入DTPA溶液,在180r/min條件下室溫振蕩反應(yīng)2h,然后在4000r/min,25℃條件下離心10min,過(guò)0.45μm濾膜,使用 ICP-OES待測(cè).

1.4 數(shù)據(jù)統(tǒng)計(jì)與分析

數(shù)據(jù)統(tǒng)計(jì)分析用Microsoft Excel 2010以及SPSS11.5完成,用Duncan法進(jìn)行顯著性多重比較分析,用Pearson系數(shù)法(<0.05)進(jìn)行相關(guān)性分析.數(shù)據(jù)繪圖用Origin 8.0完成.

2 結(jié)果與討論

2.1 赤泥對(duì)雞糞堆體溫度、pH值、EC、GI的變化

如圖1a所示,堆肥初期溫度迅速升高,CM與RM這2個(gè)處理的溫度均在堆肥第1天達(dá)到50℃以上,維持5d,即已達(dá)到堆肥無(wú)害化衛(wèi)生要求[22].其中,CM最高溫度平均達(dá)到62.1℃,RM最高溫度平均達(dá)到66.8℃,說(shuō)明赤泥的添加可以顯著提高堆體在高溫期的溫度(<0.05),這可能是因?yàn)樵诙逊蔬^(guò)程中,赤泥的堿性避免了pH值的降低并為微生物提供了足夠的鈣,增強(qiáng)了微生物的代謝活性[23].

如圖1b所示,CM與RM處理的pH值均呈先上升后下降的趨勢(shì),這與前人研究[24]結(jié)果一致.在堆肥結(jié)束時(shí),CM與RM的pH值分別為8.14和8.27.由于微生物分解蛋白質(zhì)類有機(jī)物,含氮物質(zhì)在微生物作用下被分解并產(chǎn)生大量氨氮,在堆體內(nèi)積累使 pH值上升.隨著堆肥的進(jìn)行,堆體有機(jī)物分解并產(chǎn)生小分子有機(jī)酸,導(dǎo)致pH值下降[25].

如圖1c所示,在堆肥過(guò)程中,CM處理的EC從6.13mS/cm降到3.59mS/cm;RM處理由5.25mS/cm降到4.29mS/cm.2種堆肥的EC值在堆肥過(guò)程中均呈現(xiàn)先上升,再下降的趨勢(shì).堆肥完成時(shí),RM的EC值要顯著高于CM的EC值(<0.05),表明赤泥的添加會(huì)增加堆體的EC值[26].

如圖1d所示,在堆肥初期,2種堆肥處理的GI增長(zhǎng)速率較慢.隨著堆肥時(shí)間延長(zhǎng),兩種處理堆肥過(guò)程中GI增長(zhǎng)迅速.CM與RM堆肥的GI最終分別達(dá)到100.21%和96.44%,這可能是由于RM的EC值大于CM的所導(dǎo)致.堆肥完成時(shí),CM與RM這2種堆肥的GI均超過(guò)80%,表明隨著堆肥的進(jìn)行,堆肥產(chǎn)品均已完成無(wú)害化并達(dá)到腐熟,對(duì)植物的毒害作用逐漸減少,且赤泥的投加并未造成堆肥產(chǎn)品的植物毒性[27].

圖1 不同處理在堆肥過(guò)程中溫度、pH值、EC與GI的動(dòng)態(tài)變化

CM:雞糞堆肥;RM:含赤泥的雞糞堆肥

2.2 赤泥對(duì)堆肥HA組分的平行因子分析

2.2.1 堆肥HA組分特征 如圖2所示,經(jīng)過(guò)PARAFAC得出兩組HA的組分均主要有3種,分別為組分1(C1:x=395nm,m=480nm)、組分2(C2:x=380nm,m=420nm)和組分3(C3:x=285nm,m=340nm).HA的成分主要以C1和C2為主.C1和C2均屬于類腐殖質(zhì)物質(zhì),C1反映了長(zhǎng)波類腐殖酸物質(zhì),C2反映了類富里酸物質(zhì)[28];C3則反映了類色氨酸類物質(zhì)(類蛋白物質(zhì))[29].CM與RM堆肥HA的熒光組分與已報(bào)道的市政污泥堆肥的熒光物質(zhì)組成相似[30].

2.2.2 不同分子量熒光組分演變規(guī)律 如圖3所示,CM處理中,堆肥初期的HA組分主要以C3為主,占比64.15%,隨著堆肥進(jìn)行,C3含量逐漸減少,堆肥結(jié)束時(shí)C3為22.52%,C1的含量則從13.89%增長(zhǎng)至35.84%,C2從21.10%增長(zhǎng)至41.64%.RM處理中,堆肥初期HA組分也以C3為主,但顯著低于CM中C3含量(<0.05),僅為51.29%,隨著堆肥進(jìn)行,C3含量逐漸下降至20.43%.C1的含量從22.90%增長(zhǎng)為38.97%,C2從25.81%增長(zhǎng)至40.60%,與CM結(jié)果相似.從以上3種組分的含量變化可以得知有機(jī)物的降解由難到易為C1>C2>C3,即最易降解的為類蛋白質(zhì)物質(zhì),這可能是由于C3的成分及結(jié)構(gòu)簡(jiǎn)單,生物利用性較高導(dǎo)致.此外,由于類腐殖酸中含有大量的芳香基團(tuán),C1含量的增長(zhǎng)說(shuō)明HA中芳香官能團(tuán)大量增長(zhǎng)[31].而赤泥的添加導(dǎo)致初始C3含量減少,初始C1含量增加,說(shuō)明赤泥不僅促進(jìn)了不穩(wěn)定C3含量的快速降低,還促進(jìn)更穩(wěn)定的C1含量增加,從而加速了堆體的解毒過(guò)程[32].然而,在該研究中進(jìn)行PARAFAC分析的樣品僅為14個(gè),存在一定的局限性,在后續(xù)研究中應(yīng)使用更多的樣品數(shù)量進(jìn)行PARAFAC分析以保證數(shù)據(jù)的代表性.

圖2 三維熒光平行因子分析解析出不同HA的3種組分

圖3 堆肥不同階段中HA組分百分含量變化

2.3 堆肥HA的紫外特征分析

2.3.1 SUVA254和SUVA280不飽和C=C鍵會(huì)引起有機(jī)質(zhì)在254nm波長(zhǎng)下的紫外吸收,SUVA254(=254′100/TOC)被認(rèn)為與芳香族化合物的含量呈正比[33].如圖4a、b所示,CM與RM中HA的SUVA254初始值分別為0.76和1.65,堆肥結(jié)束時(shí)分別為2.50與2.32.SUVA254一直呈增長(zhǎng)趨勢(shì),說(shuō)明HA的C=C含量在堆肥過(guò)程中逐漸增加,HA物質(zhì)穩(wěn)定化程度得到了提高.同樣,SUVA280(=280′100/TOC)也可以表征堆肥的腐殖化程度,在相同TOC濃度下,SUVA280值越大,表示堆肥過(guò)程中非腐殖物質(zhì)向腐殖質(zhì)轉(zhuǎn)化,堆肥產(chǎn)品的穩(wěn)定程度越高[34].CM與RM中HA的SUVA280初始值分別為0.67和1.51,堆肥結(jié)束時(shí)分別為2.35與2.30,進(jìn)一步說(shuō)明HA腐殖化程度提高.

2.3.2253/203和226-400253/203(有機(jī)物分子在紫外-可見(jiàn)光光譜的253nm和203nm處的吸光度之比)與芳香環(huán)上取代基的種類和取代程度相關(guān),當(dāng)芳香環(huán)取代基的脂肪鏈增加,該值將減小,若芳香環(huán)中羰基、羧基、羥基等取代基增多時(shí),該值便隨之增加[35].如圖4c、d所示,CM與RM中HA的253/203(=253/203)初始值分別為0.14和0.17,在堆肥結(jié)束時(shí)分別為0.27和0.24.在堆肥過(guò)程中,CM與RM的253/203總體呈上升趨勢(shì),這是由于在堆肥前期,HA物質(zhì)的耗氧反應(yīng)劇烈,苯環(huán)取代基上的含氧基團(tuán)相對(duì)含量快速升高,苯環(huán)上的脂肪鏈發(fā)生聚合反應(yīng)轉(zhuǎn)化為羥基、羧基等[36].據(jù)報(bào)道[37],堆肥物質(zhì)的苯環(huán)結(jié)構(gòu)是體現(xiàn)堆肥穩(wěn)定化程度重要指標(biāo),226～400nm吸收帶具有很強(qiáng)紫外吸收,與有機(jī)質(zhì)中的多個(gè)共軛體系的苯環(huán)相關(guān),CM與RM中HA的226-400(226～ 400nm吸收帶的區(qū)域積分)初始值分別為2.11和5.22,堆肥結(jié)束后分別為8.30和7.82.226～400呈上升趨勢(shì),說(shuō)明有機(jī)質(zhì)的分子縮合程度增高,芳香化程度增高,HA物質(zhì)的穩(wěn)定程度提高,堆肥產(chǎn)品逐漸穩(wěn)定.以上結(jié)果說(shuō)明,由于赤泥的加入使得RM中各腐殖化參數(shù)初始值顯著高于CM的初始值(<0.05),以此加速腐殖化過(guò)程.

2.4 堆肥HA不同光譜特征參數(shù)相關(guān)性分析

如表2所示.CM與RM的C1、C2均在<0.05水平上與C3呈負(fù)相關(guān)性顯著,這說(shuō)明C3減小會(huì)引起C1和C2的增加,而C3可能是C1和C2的來(lái)源.CM與RM的SUVA254、SUVA280及226～400兩兩呈正相關(guān)性極顯著(<0.01),說(shuō)明HA中一些含有苯環(huán)的有機(jī)物可能在254nm及280nm處有極強(qiáng)的吸收峰,進(jìn)一步驗(yàn)證了堆肥過(guò)程中芳香性增加,聚合度升高.此外,CM的SUVA254、SUVA280及226～400均與C1呈正相關(guān)性顯著(<0.05),RM的SUVA254、SUVA280及226～400均與C2呈正相關(guān)性顯著(<0.05),且相關(guān)性強(qiáng)度由大到小依次為226～400>SUVA280> SUVA254,226～400顯示相關(guān)性更大的原因可能是該參數(shù)為堆肥有機(jī)物在226～400nm這一波段的紫外吸收區(qū)域積分,它包含了SUVA254及SUVA280的相關(guān)信息,雖然這3個(gè)參數(shù)均可在一定程度上反映堆肥腐熟度,但226～400能較為全面地反映堆肥腐殖化程度的紫外特征參數(shù).在CM中,253/203與以上3個(gè)紫外參數(shù)呈現(xiàn)出正相關(guān)性極顯著(<0.01),卻與C1未達(dá)到顯著性水平(>0.05),而在RM中,253/203與以上3個(gè)參數(shù)均未呈現(xiàn)出顯著性水平(>0.05),卻與C2正相關(guān)性顯著(<0.05),表明該參數(shù)與SUVA254、SUVA280及226～400相比,不能較好地反映堆肥的腐熟程度.

表2 堆肥HA的熒光組成與光譜特征參數(shù)的相關(guān)性

注:*,<0.05:相關(guān)性顯著;**,<0.01:相關(guān)性極顯著.

2.5 堆肥對(duì)水稻植株內(nèi)Cd的積累效果

表3 雞糞堆肥與赤泥堆肥的理化性質(zhì)

由表3可知,經(jīng)過(guò)堆肥處理后,CM和RM處理中重金屬的總量均未超過(guò)有機(jī)無(wú)機(jī)復(fù)合肥料(GB/T 18877-2020)[38]的限量標(biāo)準(zhǔn).

由表4可知,隨著2種堆肥施加劑量增加,土壤pH值逐漸增加.施加雞糞堆肥與赤泥堆肥后顯著降低了土壤中DTPA-Cd含量,土壤中Cd的活性隨著施加劑量的增加而降低.未改良土壤中DTPA-Cd的含量為1.10mg/kg,施加雞糞堆肥與赤泥堆肥后土壤中DTPA-Cd的降低幅度分別為11.92%～20.91%和14.09%～33.59%.施加赤泥堆肥后顯著增加了土壤中有效Si的含量,且隨著施加劑量的增加而增加,增加幅度為49.07%～75.21%.而施加雞糞堆肥后對(duì)土壤中有效Si影響不顯著.施加2種堆肥后,與CK相比,水稻糙米中Cd含量均顯著降低,降低幅度為17.97%～58.68%.糙米Cd的含量在0.17～0.42mg/kg之間,水稻糙米Cd含量由大到小為:CK>CM0.5> CM1>CM2>RM0.5>RM1>RM2,其中RM2處理下的糙米Cd含量低于國(guó)家《食品安全國(guó)家標(biāo)準(zhǔn)食品中污染物限量》中的規(guī)定值(0.2mg/kg,GB 2762- 2017)[39].

表4 不同劑量的雞糞堆肥與赤泥堆肥對(duì)土壤性質(zhì)及糙米中Cd含量的影響

注:同列不同小寫字母表示不同處理間存在顯著差異(<0.05,=3).

土壤中有效態(tài)Cd與糙米Cd含量的降低,可能是由于堆肥的堿性有效增加了pH值,有利于重金屬氫氧化物復(fù)合物沉淀的生成[40].而赤泥中還含有硅酸鹽礦物,SiO32-水解產(chǎn)生的OH-對(duì)中和土壤酸性、提高土壤pH值有著至關(guān)重要的作用.此外,硅酸鹽礦物中的有效硅可與土壤中移動(dòng)態(tài)Cd2+形成CdSiO3沉淀物,使重金屬沉積在土壤和植物根系表面[41].

同時(shí),因堆肥過(guò)程中形成大量腐殖質(zhì),腐殖質(zhì)和土壤中重金屬離子發(fā)生螯合與絡(luò)合反應(yīng)[42].腐殖質(zhì)中的羧基、酚羥基以及羰基等活性功能基團(tuán)增加,促進(jìn)腐殖質(zhì)提供更多可絡(luò)合重金屬的吸附點(diǎn)位[43],形成有機(jī)金屬配合物.其中,氨基和巰基基團(tuán)對(duì)Cd2+的絡(luò)合與羥基對(duì)Cd2+的共沉淀均起重要作用.可見(jiàn),施加堆肥對(duì)土壤Cd的生物有效性有抑制作用,對(duì)水稻植株內(nèi)Cd起到有效的阻隔效果,且施加赤泥堆肥效果更為顯著.

3 結(jié)論

3.1 雞糞堆肥與赤泥堆肥高溫期均維持5d,已達(dá)到無(wú)害化衛(wèi)生要求,且添加赤泥后,提高了堆體高溫期的溫度.2種堆肥的EC較堆肥前均顯著降低,堆肥完成時(shí),RM的EC要顯著高于CM的EC,表明赤泥的添加會(huì)增加堆體的EC.雞糞堆肥與赤泥堆肥的GI在堆肥結(jié)束時(shí)分別達(dá)到100.21%和96.44%,說(shuō)明兩種堆肥產(chǎn)品均沒(méi)有植物毒性,且達(dá)到腐熟狀態(tài).

3.2 隨著堆肥的進(jìn)行,2個(gè)處理的腐殖酸中類蛋白質(zhì)等物逐漸轉(zhuǎn)化為較為穩(wěn)定的類腐殖質(zhì)物質(zhì),腐殖酸的SUVA254和SUVA280、253/203、226～400在堆肥結(jié)束后也均得到提高,說(shuō)明堆肥的芳香性與腐殖化程度升高,且赤泥的添加會(huì)加速堆體的腐殖化進(jìn)程.

3.3 雞糞堆肥與赤泥堆肥提高了土壤的pH值,顯著降低了土壤中DTPA-Cd的含量,施加2g/kg赤泥堆肥后,土壤中DTPA-Cd的含量降低了33.59%,且顯著增加了土壤中有效Si的含量.施加2種堆肥后,糙米中Cd含量降低幅度為17.97%～58.68%,且施用2g/kg赤泥堆肥時(shí),水稻糙米種Cd的含量降低至0.17mg/kg,并達(dá)到中國(guó)的食用安全標(biāo)準(zhǔn).

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Effects of red mud on compost maturity and Cd resistance control of rice.

ZHOU Hong-yan1,CHEN Zhe1,2*,LI Kan-qi1,LENG Wei-gui3,WANG Zong-kang3

(1.College of Environmental Science and Engineering,Guilin University of Technology,Guilin 541004,China；2.Key Laboratory of Ecology and Environmental Protection of Rare and Endangered Plants,Ministry of Education,Guangxi Normal University,Guilin 541004,China；3.Guigang Patan Ecology Co.,LTD.,Guigang 537000,China).,2022,42(8)：3812～3821

Red mud was used as an additive to conduct aerobic composting experiments of chicken manure for evaluating effects of red mud on temperature,pH,electrical conductivity (EC),and seed germination index (GI) during composting. The evolution characteristics of humic acid (HA) components during composting were analyzed by combining three-dimensional fluorescence with ultraviolet-visible light spectrum; and the pot experiments were also conducted to explore the barrier effect of compost products on rice cadmium in the mining soil. The results showed that red mud increased the temperature of the compost during the high temperature period. The EC of both groups decreased significantly after composting,however,the EC of red mud compost (4.29mS/cm) was much higher than that of chicken manure compost (3.59mS/cm).The GI of chicken manure compost and red mud compost increased with composting time by; 100.2% and 96.44%,respectively,at the end of composting,indicating that the products of neither red mud compost nor chicken manure compost exhibited phytotoxicity. The protein-like substances in the HA of the two kinds of composts were converted into relatively stable humus-like substances throughout the composting process. A significant increase in SUVA254,SUVA280,and A226-400of HA indicates the elevated humification degree of compost. In addition,red mud could optimize the humification parameters,implying that the addition of red mud can accelerate the humification process of the heap. In pot experiments,both chicken manure compost and red mud compost increased soil pH and reduced the concentration of DTPA-Cd in soil and total Cd in brown rice. After applying 2g/kg red mud compost,the Cd content in brown rice decreased significantly (by 58.68%) from 0.42mg/kg to 0.17mg/kg after composting. Therefore,red mud can accelerate the composting efficiency to a certain extent. The application of compost products can inhibit the bioavailability of Cd in both soil and rice plants,and an addition of red mud can lead to a higher composting efficiency.

red mud；chicken manure；composting；rice；cadmium pollution；heavy metals

X705

A

1000-6923(2022)08-3812-10

2022-01-24

廣西創(chuàng)新研究團(tuán)隊(duì)項(xiàng)目(2018GXNSFGA281001);廣西科技基地和人才專項(xiàng)(桂科AD19110012);貴港市科技研發(fā)項(xiàng)目(貴科攻2021019);桂林市重大科技專項(xiàng)(20190219-3)

* 責(zé)任作者,講師,ldchenzhe@qq.com

周紅燕(1997-),女,四川廣安人,桂林理工大學(xué)碩士研究生,主要從事固體廢物資源化研究.