生物炭對(duì)篩選菌株去除水中硝酸鹽和N2O排放的影響

王朝旭,李元坤,劉勇超

生物炭對(duì)篩選菌株去除水中硝酸鹽和N2O排放的影響

王朝旭1,2*,李元坤1,劉勇超1

(1.太原理工大學(xué)環(huán)境科學(xué)與工程學(xué)院,山西 晉中 030600；2.山西省市政工程研究生教育創(chuàng)新中心,山西 晉中 030600)

為探究改性生物炭對(duì)微生物去除水中低濃度硝酸鹽和N2O排放的影響, 以稻殼生物炭(BC)為基礎(chǔ)材料, 分別制備并表征FeCl3、H2O2和NaOH改性生物炭(BC-Fe、BC-H2O2和BC-NaOH), 同時(shí)從活性污泥中篩選一株反硝化細(xì)菌strain KK1. 將BC、BC-Fe、BC-H2O2和BC-NaOH分別加入含有該菌株的培養(yǎng)體系, 同時(shí)設(shè)置不添加生物炭的對(duì)照處理, 開展微生物去除模擬廢水中低濃度硝酸鹽(約10mg/L, 以N計(jì))的室內(nèi)培養(yǎng)實(shí)驗(yàn), 分析培養(yǎng)體系N2O排放速率、氮素和溶解性有機(jī)碳含量的動(dòng)態(tài)變化. 結(jié)果表明, 所篩選菌株120h內(nèi)的NO3--N平均降解速率為0.10mg/(L?h). 與BC相比, BC-Fe和BC-H2O2的羧基和內(nèi)酯基含量顯著增加, 氧化性增強(qiáng); 而BC-NaOH的酚羥基含量顯著增加, 還原性增強(qiáng). BC-Fe和BC-H2O2的總酸性含氧官能團(tuán)含量較BC分別顯著增加57.17%和22.86%, 而BC-NaOH的總堿性含氧官能團(tuán)含量顯著增加91.67%. 與BC相比, BC-Fe和BC-H2O2促進(jìn)反硝化細(xì)菌對(duì)NO3--N的還原, N2O累積排放量分別為添加BC處理的3.11和2.17倍; 而BC-NaOH抑制反硝化細(xì)菌對(duì)NO3--N的還原, N2O累積排放量?jī)H為添加BC處理的49.63%. 生物炭對(duì)微生物反硝化作用和N2O排放的影響歸因于改性引起的生物炭pH值、溶解性有機(jī)碳含量和氧化還原性的差異.

改性生物炭；低濃度硝酸鹽；深度脫氮；N2O排放

2020年,全國(guó)污水排放總量約570億m3,其中約42.6%的污水處理廠尾水經(jīng)深度處理后再生利用,其余尾水則可能直接排入受納水體,給我國(guó)的水生態(tài)環(huán)境帶來(lái)嚴(yán)重危害[1].《城鎮(zhèn)污水處理廠污染物排放標(biāo)準(zhǔn)》(GB 18918—2002)中的一級(jí)A標(biāo)準(zhǔn)總氮限值15mg/L,相比《地表水環(huán)境質(zhì)量標(biāo)準(zhǔn)》(GB 3838— 2002)中的Ⅴ類水質(zhì)標(biāo)準(zhǔn)總氮限值2.0mg/L,污水處理廠尾水總氮濃度仍較高,且尾水中總氮以NO3--N為主.水中過(guò)量NO3--N不僅影響人類身體健康,還會(huì)導(dǎo)致水體富營(yíng)養(yǎng)化[2-3].因此,以污水處理廠尾水深度脫氮為背景的水中硝酸鹽去除成為研究熱點(diǎn).

生物炭是由農(nóng)業(yè)廢棄物、植物或畜禽糞便等生物質(zhì)在無(wú)氧條件下熱解產(chǎn)生的固體富碳物質(zhì)[4].生物炭不僅具有較強(qiáng)的吸附性能[5],而且其表面的氧化還原活性官能團(tuán)具有類似“電子穿梭體”的得失電子能力[6],同時(shí)其也可以利用自身的π電子離域和類石墨片狀結(jié)構(gòu)進(jìn)行電子轉(zhuǎn)移[7-8].反硝化作用是氮循環(huán)的關(guān)鍵步驟,而生物炭對(duì)反硝化作用影響顯著.300℃熱解生物炭的溶解性芳香基團(tuán)(如酚羥基),可作為電子供體促進(jìn)NO3--N還原[9].另外,低溫?zé)峤馍锾靠商岣叻聪趸?xì)菌豐度,并促進(jìn)反硝化作用[10].

采用物理化學(xué)手段對(duì)生物炭進(jìn)行改性,可以生產(chǎn)具有不同特性的生物炭[11].改性生物炭對(duì)反硝化作用有顯著影響.將FeCl3改性竹炭加入水平潛流人工濕地基質(zhì),可顯著提高反硝化細(xì)菌豐度和NO3--N去除效率[12-13].H2O2改性可顯著提高生物炭表面氧化性官能團(tuán)(如醌基)含量,并降低還原性官能團(tuán)(如酚羥基)含量;其庫(kù)侖效率計(jì)算結(jié)果表明,H2O2改性生物炭削弱了反硝化過(guò)程中生物炭的“電子穿梭體”作用,并抑制NO3-還原[14].然而,也有研究表明, H2O2改性生物炭可促進(jìn)反硝化細(xì)菌sp.XL4對(duì)NO3-的降解,去除率高達(dá)97.9%[15].另外,NaOH改性可顯著提高生物炭的pH值和表面堿性含氧官能團(tuán)含量[16].將NaOH改性玉米秸稈生物炭按一定比例加入人工濕地,可提高其反硝化脫氮效能,主要原因?yàn)楦男詢?yōu)化了生物炭的孔結(jié)構(gòu)、比表面積和表面含氧官能團(tuán)含量等[17].目前,改性生物炭對(duì)反硝化作用的影響結(jié)果不一,尤其是FeCl3、H2O2和NaOH改性生物炭在低濃度硝酸鹽廢水深度脫氮和N2O排放中的作用尚不清楚.

因此,本研究首先制備并表征了FeCl3、H2O2和NaOH改性稻殼生物炭,并從活性污泥中篩選一株反硝化細(xì)菌.然后,采用室內(nèi)培養(yǎng)實(shí)驗(yàn)方法,探究改性生物炭對(duì)微生物去除模擬廢水中低濃度硝酸鹽(NO3--N質(zhì)量濃度為10mg/L)和N2O排放的影響.研究結(jié)果可為污水處理廠尾水深度脫氮提供技術(shù)參考和理論支撐.

1 材料與方法

1.1 生物炭改性與特性表征

實(shí)驗(yàn)所用稻殼生物炭(BC)購(gòu)自中國(guó)大連九成物產(chǎn)有限公司,使用前過(guò)1mm篩.分別采用FeCl3、H2O2和NaOH 3種改性劑對(duì)BC進(jìn)行改性.具體方法如下:將BC以1:10(g:mL)的比例加入1mol/L的FeCl3溶液中,攪拌30min后,轉(zhuǎn)入瓷坩堝,于馬弗爐中煅燒2h(400℃),冷卻至室溫,最后用超純水將混合物淋洗至濾液澄清且pH值恒定,并烘干至恒重(60℃),記為BC-Fe[18];類似地,將BC分別與濃度30%的H2O2或2mol/L的NaOH溶液以1:50(g:mL)的比例混合,振蕩12或24h后(150r/min,(25±1)℃),將混合物淋洗烘干,分別記為BC-H2O2或BC-NaOH[14,19]. BC、BC-Fe、BC-H2O2和BC-NaOH的理化性質(zhì)測(cè)定方法同文獻(xiàn)[20,51],含氧官能團(tuán)類型用傅立葉變換紅外光譜儀(SpectrumTwo,美國(guó))測(cè)定.

1.2 反硝化細(xì)菌的培養(yǎng)和鑒定

1.2.1 富集、分離和純化 實(shí)驗(yàn)菌種來(lái)源于山西省太原市某污水處理廠缺氧池活性污泥.采用與文獻(xiàn)[21,51]相同的方法富集反硝化細(xì)菌.富集后采用平板涂布法分離并初篩反硝化細(xì)菌[22].所有培養(yǎng)基在配制過(guò)程中,首先通入高純氮?dú)?99.999%)驅(qū)氧30min,同時(shí)向培養(yǎng)基中加入還原劑-半胱氨酸(0.5g/L),利用其還原性去除氧,使培養(yǎng)基處于無(wú)氧狀態(tài),然后滅菌20min備用(121℃)[23].

1.2.2 生物化學(xué)和分子生物學(xué)鑒定 從溴百里酚藍(lán)初篩培養(yǎng)基表面挑取呈藍(lán)色的單菌落[22],接種至150mL模擬廢水[組成及質(zhì)量濃度(g/L):檸檬酸鈉0.18, KNO30.07(NO3--N質(zhì)量濃度為10mg/L),其余同反硝化液體培養(yǎng)基][21],連續(xù)培養(yǎng)120h(150r/min, (25±1)℃),分別于培養(yǎng)0, 4, 8, 12, 24, 36, 48, 60, 72, 84和96h時(shí)采樣,測(cè)定其NO3--N、NO2--N、NH4+-N和TN濃度.選取NO3--N和TN濃度明顯降低的菌株作為后續(xù)實(shí)驗(yàn)所用反硝化細(xì)菌(DB).將該菌株接種至反硝化液體培養(yǎng)基培養(yǎng)72h后, 4℃保存?zhèn)溆?

將含有DB的反硝化液體培養(yǎng)基離心(10000r/ min,5min)收集菌體后,由生工生物工程(上海)股份有限公司進(jìn)行菌種鑒定.將所獲菌株序列通過(guò)BLAST檢索,與GenBank中的核酸序列進(jìn)行同源性比對(duì),利用MEGA 7軟件,以鄰接法構(gòu)建16S rDNA基因系統(tǒng)發(fā)育樹.

1.3 室內(nèi)培養(yǎng)實(shí)驗(yàn)

為探究BC、BC-Fe、BC-H2O2和BC-NaOH對(duì)篩選菌株去除水中低濃度硝酸鹽和N2O排放的影響及機(jī)理,在模擬廢水中添加所篩選菌株和生物炭,分析該體系對(duì)低濃度硝酸鹽的去除效果.模擬廢水的水質(zhì)同1.2.2節(jié).本實(shí)驗(yàn)共設(shè)5個(gè)處理:①模擬廢水+細(xì)菌種子液(DB);②模擬廢水+細(xì)菌種子液+未改性稻殼生物炭(DB+BC);③模擬廢水+細(xì)菌種子液+FeCl3改性稻殼生物炭(DB+BC-Fe);④模擬廢水+細(xì)菌種子液+H2O2改性稻殼生物炭(DB+BC-H2O2);⑤模擬廢水+細(xì)菌種子液+NaOH改性稻殼生物炭(DB+BC-NaOH).

將5mL細(xì)菌種子液(細(xì)菌種子液制備方法同文獻(xiàn)[21,51])與1g生物炭(BC、BC-Fe、BC-H2O2或BC-NaOH)添加至裝有100mL模擬廢水的培養(yǎng)瓶(300mL)中;同時(shí)設(shè)置不添加生物炭的對(duì)照處理.充分混勻后,用連接有兩個(gè)三通閥的瓶蓋密封培養(yǎng)瓶口.為了在培養(yǎng)過(guò)程中保持無(wú)氧狀態(tài),培養(yǎng)瓶的頂部空間用高純氮?dú)?99.999%)充分置換.所有培養(yǎng)瓶置于搖床(150r/min,(25±1)℃)中避光連續(xù)培養(yǎng)96h.每個(gè)處理設(shè)置6個(gè)培養(yǎng)瓶,平均分成兩組.第1組培養(yǎng)瓶進(jìn)行N2O排放速率測(cè)定;分別于培養(yǎng)第4,8,12, 24,36,48,60,72,84和96h時(shí),測(cè)定培養(yǎng)瓶中N2O濃度,并計(jì)算N2O排放速率和累積排放量(均以100mL培養(yǎng)液為計(jì)量單位).第2組培養(yǎng)瓶用于測(cè)定培養(yǎng)體系的理化性質(zhì);分別于培養(yǎng)0,4,8,12,24,36,48,60,72,84和96h時(shí),在培養(yǎng)體系混勻狀態(tài)下采樣,并測(cè)定培養(yǎng)過(guò)程中pH值、電導(dǎo)率以及NO3--N、NO2--N、NH4+-N、TN和溶解性有機(jī)碳(DOC)濃度[24].

1.4 數(shù)據(jù)分析

采用Microsoft Excel 2019處理數(shù)據(jù),數(shù)據(jù)形式為(平均值±標(biāo)準(zhǔn)偏差)(=3).采用Origin 2018軟件繪圖.采用IBM SPSS Statistics 25進(jìn)行方差分析和多重比較,顯著性水平設(shè)為=0.05.

2 結(jié)果與分析

2.1 所篩選菌株降解能力及分子生物學(xué)鑒定

整個(gè)培養(yǎng)過(guò)程中,NO3--N濃度逐漸降低,并在培養(yǎng)的第120h降至0mg/L.NO3--N的120h平均降解速率為0.10mg/(L×h).NO2--N在培養(yǎng)的36～84h產(chǎn)生明顯積累,導(dǎo)致該階段TN濃度較高(圖1(a)).

將該菌株的16S rDNA序列與GenBank中的核酸序列進(jìn)行同源性比對(duì),所構(gòu)建系統(tǒng)發(fā)育樹如圖1(b)所示.結(jié)果表明,該菌株與strain H113(MH671626)、strain RT1902(MT568560)和strain B2-E-2(OK271540)的進(jìn)化距離較近,相似性均為99.93%,從而確定該菌株為解鳥氨酸拉烏爾菌,命名為strainKK1(OP159448).

本研究所篩選strain KK1的NO3--N降解速率(0.10mg/(L×h))高于江興龍等[25]從水產(chǎn)養(yǎng)殖場(chǎng)尾水中篩選的PN-1(0.07mg/(L×h)),但低于其他反硝化菌屬,如strain N31(0.59mg/(L×h))[26]和Y-11(1.99mg/(L×h))[27]等,主要原因?yàn)椴煌N屬反硝化細(xì)菌的特性不同.

2.2 改性對(duì)生物炭性質(zhì)的影響

與BC相比,BC-Fe的羧基和內(nèi)酯基含量分別增加128.89%和5.84%,酚羥基含量減少31.71%; BC-H2O2的羧基和內(nèi)酯基含量分別增加4.44%和29.03%,酚羥基含量減少9.76%,表明BC-Fe和BC- H2O2的氧化性增強(qiáng).然而,BC-NaOH的酚羥基含量增加41.46%,羧基和內(nèi)酯基含量分別減少8.89%和22.58%,表明BC-NaOH的還原性增強(qiáng).另外,與BC相比,BC-Fe和BC-H2O2的總酸性含氧官能團(tuán)含量分別顯著增加57.17%和22.86%,總堿性含氧官能團(tuán)含量分別顯著減少96.67%和26.67%;而BC-NaOH的總堿性含氧官能團(tuán)含量顯著增加91.67%,總酸性含氧官能團(tuán)含量顯著減少12.86%.相應(yīng)地,BC-Fe和BC-H2O2的pH值較BC分別顯著降低5.32和2.40,而BC-NaOH的pH值則顯著升高2.54.

BC-Fe和BC-H2O2的DOC含量較BC分別顯著降低92.58%和24.53%,主要由于FeCl3和H2O2對(duì)DOC的氧化作用;而BC-NaOH的DOC含量是BC的4.57倍,主要由于NaOH對(duì)大分子有機(jī)物的堿解作用.與BC相比,BC-Fe和BC-H2O2的NH4+-N含量分別顯著增加59.57%和42.48%,NO3--N含量分別顯著增加425.71%和47.46%;BC-NaOH的NO3--N含量顯著增加179.32%.FeCl3改性顯著提高稻殼生物炭的電導(dǎo)率(達(dá)BC的8.53倍)(表1).

表1 改性前后生物炭的基本性質(zhì)

注: BC、BC-Fe、BC-H2O2和BC-NaOH分別為未改性、FeCl3改性、H2O2改性和NaOH改性稻殼生物炭; DOC為溶解性有機(jī)碳. 數(shù)值是(平均值±標(biāo)準(zhǔn)偏差)(=3), 同一行不同字母表示處理間差異顯著(<0.05).

2.3 改性生物炭對(duì)反硝化過(guò)程N(yùn)2O排放的影響

DB和DB+BC處理的N2O排放速率峰值均在第24h出現(xiàn)(分別為678.00和514.95ng N/h),但DB+BC處理的N2O累積排放量比DB處理高7.53%,且差異顯著(<0.05).另一方面,與DB+BC處理相比,DB+BC-Fe和DB+BC-H2O2處理的N2O排放速率峰值(分別為1823.23和2313.28ng N/h)分別提前至第8h和第12h出現(xiàn),且N2O累積排放量分別為DB+BC處理的3.11和2.17倍;然而,DB+BC-NaOH處理的N2O排放速率峰值(244.70ng N/h)則延后至第48h出現(xiàn),N2O累積排放量?jī)H為DB+BC處理的49.63%(圖2).

2.4 改性生物炭對(duì)反硝化過(guò)程氮含量變化的影響

隨培養(yǎng)時(shí)間延長(zhǎng),各處理NO3--N濃度均呈下降趨勢(shì),第48h時(shí)NO3--N濃度降至零.NO3--N主要在培養(yǎng)的前36h內(nèi)降解,該時(shí)段內(nèi)DB+BC處理NO3--N濃度降低94.26%,而DB+BC-Fe和DB+BC-H2O2處理NO3--N濃度降低約100%,DB+BC-NaOH處理NO3--N濃度降低86.23%,整體呈DB+BC-Fe/DB+ BC-H2O2> DB+BC> DB+BC-NaOH的趨勢(shì)(圖3(a)).

與DB+BC處理相比,DB+BC-Fe和DB+BC- H2O2處理中NO3--N提前12h完全降解,而DB+ BC-NaOH處理則無(wú)此現(xiàn)象.同時(shí),0～8和0～12h時(shí)段,DB+BC-Fe和DB+BC-H2O2處理的NO3--N平均降解速率(0～8h:0.97和0.91mg/(L×h);0～12h:0.75和0.67mg/(L×h))顯著高于DB+BC處理(0～8h:0.62mg/(L×h);0～12h:0.64mg/(L×h)),而DB+BC-NaOH處理的NO3--N平均降解速率(0～ 8h:0.50mg/(L×h);0～12h: 0.43mg/(L×h))則顯著低于DB+ BC處理.0～24h時(shí)段,不同處理的NO3--N平均降解速率也呈上述規(guī)律,但差異不顯著(<0.05).另一方面,0～4,0～8和0～12h時(shí)段,添加生物炭處理的NO3--N平均降解速率顯著高于DB處理(<0.05)(圖4).

整個(gè)培養(yǎng)過(guò)程中,各處理NO2--N濃度均呈先上升后下降的趨勢(shì).DB和DB+BC處理NO2--N濃度在第36h達(dá)到峰值(分別為6.03和6.52mg/L),DB+ BC-Fe和DB+BC-H2O2處理NO2--N濃度峰值(分別為9.31和8.34mg/L)提前至第24h,而DB+BC- NaOH處理NO2--N濃度峰值(7.30mg/L)則在第48h才出現(xiàn)(圖3(b)).在培養(yǎng)過(guò)程中,各處理NH4+-N濃度變化不大,表明未發(fā)生明顯的硝化作用.DB+BC-Fe處理的NH4+-N濃度略高(5.49～6.89mg/L),可能由BC-Fe本身較高的NH4+-N含量所致;而其他處理的NH4+-N濃度均保持在較低水平(0.71～2.71mg/L)(圖3(c)).整個(gè)培養(yǎng)過(guò)程中,各處理TN濃度呈逐漸下降的趨勢(shì).值得注意的是,由于改性后生物炭本身的NH4+-N和NO3--N含量均不同程度增加,導(dǎo)致添加改性生物炭處理的TN濃度較高(圖3(d)).

添加生物炭處理的DOC濃度在培養(yǎng)的前12h內(nèi)均不同程度增加,且達(dá)到峰值,隨后逐漸降低.整個(gè)培養(yǎng)過(guò)程中,各處理DOC濃度呈DB+BC-NaOH> DB+BC/DB+BC-H2O2> DB+BC-Fe> DB的趨勢(shì),主要與生物炭本身的DOC含量有關(guān)(圖3(e)).

圖4 不同時(shí)段各處理NO3--N平均降解速率

2.5 改性生物炭對(duì)反硝化過(guò)程pH值和電導(dǎo)率的影響

由于BC-Fe和BC-H2O2的pH值較BC低,而BC-NaOH的pH值較BC高,在0～12h內(nèi),DB+BC-Fe和DB+BC-H2O2處理的pH值急劇降低,而DB+ BC-NaOH處理的pH值急劇升高.第12h之后,各處理pH值均有所增大,表明發(fā)生了不同程度的反硝化作用;然而,由于BC-Fe的pH值僅為1.96,導(dǎo)致DB+BC-Fe處理培養(yǎng)過(guò)程中pH值持續(xù)降低.各處理間pH值的差異主要由所添加生物炭本身的pH值引起,整體呈如下趨勢(shì):DB+BC-NaOH> DB+BC> DB> DB+BC-Fe/DB+BC-H2O2(圖5(a)).DB+BC-Fe處理的電導(dǎo)率最高,而DB+BC-H2O2處理的電導(dǎo)率最低,主要與生物炭本身的電導(dǎo)率有關(guān)(圖5(b)).

3 討論

在0～4,0～8和0～12h時(shí)段,添加生物炭處理的NO3--N平均降解速率顯著高于DB處理;而在0～24和0～36h時(shí)段,二者之間無(wú)顯著差異(<0.05)(圖4),表明生物炭添加一定程度上促進(jìn)了培養(yǎng)體系的反硝化作用,尤其是BC-Fe和BC-H2O2.潛在原因可能為,生物炭是多孔碳材料,其孔隙可為附著的反硝化細(xì)菌提供適宜的生長(zhǎng)環(huán)境,提高其豐度和活性,從而加速NO3--N降解[28].另外,生物炭表面的氧化還原活性官能團(tuán)具有類似腐殖質(zhì)的“電子穿梭體”功能,且生物炭的共軛π-電子系統(tǒng)具有較強(qiáng)的電子轉(zhuǎn)移能力,有利于NO3--N還原去除[6,29].

與DB+BC處理相比,DB+BC-Fe和DB+BC- H2O2處理的NO3--N降解速率顯著增大,其N2O累積排放量也分別增加210.68%和117.27%,表明BC-Fe和BC-H2O2促進(jìn)反硝化細(xì)菌對(duì)NO3--N的還原,并增加N2O排放;而DB+BC-NaOH處理的NO3--N降解速率顯著減小,其N2O累積排放量則減少50.37%,表明BC-NaOH抑制反硝化細(xì)菌對(duì)NO3--N的還原,并減少N2O排放.主要原因有:

第一,反硝化作用是產(chǎn)堿過(guò)程,每還原1mol NO3-會(huì)消耗2mol H+[30].因此,培養(yǎng)體系較低的pH值更利于反硝化作用進(jìn)行.FeCl3和H2O2改性使生物炭表面總酸性含氧官能團(tuán)含量增加[31-32],pH值降低,進(jìn)而使培養(yǎng)體系的pH值處于較低水平(分別為6.25～ 6.61和7.06～7.23,12h之后).因此,DB+BC-Fe和DB+ BC-H2O2處理更利于NO3--N還原.相反,NaOH改性使生物炭表面總堿性含氧官能團(tuán)含量增加[16],pH值升高,進(jìn)而使培養(yǎng)體系的pH值處于較高水平(8.14～8.39,12h之后),不利于NO3--N還原.另外,本研究所篩選strain KK1攜帶N2O還原酶,具有N2O還原能力,培養(yǎng)12h之后的N2O/(N2O+N2)比值最大僅為0.025.較低的pH值可抑制N2O還原酶活性,增加N2O排放[33].李鵬章等[34]研究了相同碳氮比條件下,pH值對(duì)N2O累積排放量的影響,發(fā)現(xiàn)低pH值有利于N2O積累,pH=6時(shí)的N2O累積排放量為pH=7.8時(shí)的800倍.因此,DB+ BC-Fe和DB+BC-H2O2處理中,N2O還原酶活性可能受到抑制,進(jìn)而增加N2O排放.

第二,當(dāng)碳生物有效性較低時(shí),與其他異化還原酶相比,N2O還原酶的電子競(jìng)爭(zhēng)能力較弱,導(dǎo)致N2O排放增加[34].生物炭除含有大量芳香碳之外,還含有一些微生物易利用的DOC,可作為反硝化細(xì)菌的碳源[35].與BC相比,BC-Fe和BC-H2O2的DOC含量分別顯著降低92.58%和23.53%,而BC-NaOH的DOC含量則顯著增加356.94%.因此,BC-Fe和BC-H2O2的添加可使培養(yǎng)體系的碳生物有效性降低,N2O排放增加;而BC-NaOH的添加可使培養(yǎng)體系的碳生物有效性提高,N2O排放減少.Senbayram等[36]研究也發(fā)現(xiàn),農(nóng)田土壤施用富含DOC的有機(jī)肥,可提高其反硝化速率并降低N2O排放.

第三,生物炭表面醌類基團(tuán)和酚羥基含量顯著影響生物炭的得失電子能力[11].與BC相比,BC-Fe和BC-H2O2的羧基和內(nèi)酯基(醌類基團(tuán)、C=O)含量顯著增加,氧化性增強(qiáng);而BC-NaOH的酚羥基含量顯著增加,還原性增強(qiáng).C=O/C-OH電對(duì)的標(biāo)準(zhǔn)氧化還原電位為113mV,而NO3-/NO2-電對(duì)的標(biāo)準(zhǔn)氧化還原電位為430mV(pH=7)[37],NO3-的氧化性強(qiáng)于醌類基團(tuán).因此,反硝化過(guò)程中醌類基團(tuán)不與NO3-競(jìng)爭(zhēng)電子.但是,醌類基團(tuán)的氧化性可抑制N2O還原,使N2O排放增加;酚羥基的還原性可促進(jìn)N2O還原,使N2O排放減少.Yuan等[38]研究也表明,H2O2改性生物炭表面增加的醌類基團(tuán)可作為電子受體與N2O競(jìng)爭(zhēng)電子,導(dǎo)致N2O排放增加.

培養(yǎng)的0～36h為NO3--N的主要去除階段.在此期間,與DB+BC處理相比,DB+BC-Fe和DB+ BC-H2O2處理的NO3--N累積去除量分別增加0.87%和3.25%,而N2O累積排放量分別顯著增加264.01%和199.27%;相反,DB+BC-NaOH處理的NO3--N累積去除量減少12.36%,而N2O累積排放量顯著減少66.94%.在石灰性農(nóng)田土壤中的研究也發(fā)現(xiàn),與施用未改性生物炭處理相比,施用FeCl3改性生物炭處理的NO3--N還原量增加9.83%,而N2O累積排放量顯著增加465.98%[39].類似地,在污水生物脫氮過(guò)程中,同步硝化反硝化工藝的總氮去除率(90.39%)高于順序式硝化反硝化工藝(63.78%),而其N2O釋放量則是順序式硝化反硝化工藝的5倍[40].因此,在氮污染物去除和N2O排放相關(guān)研究中,經(jīng)常出現(xiàn)二者同步增大的情況.本研究中,鑒于不同生物炭對(duì)培養(yǎng)體系N2O排放的影響強(qiáng)于對(duì)NO3--N去除的影響.綜合考慮生物炭的水質(zhì)凈化效能和N2O排放效應(yīng),在污水處理廠尾水等含硝酸鹽水體深度脫氮方面,可優(yōu)選NaOH改性生物炭.

4 結(jié)論

4.1 從活性污泥中篩選一株反硝化細(xì)菌strain KK1(OP159448),其120h內(nèi)的NO3--N平均降解速率為0.10mg/(L×h).

4.2 與BC相比, BC-Fe和BC-H2O2的羧基和內(nèi)酯基含量顯著增加,氧化性增強(qiáng);而BC-NaOH的酚羥基含量顯著增加,還原性增強(qiáng). BC-Fe和BC-H2O2的總酸性含氧官能團(tuán)含量較BC分別顯著增加57.17%和22.86%, 而BC-NaOH的總堿性含氧官能團(tuán)含量顯著增加91.67%;相應(yīng)地, BC-Fe和BC- H2O2的pH值分別顯著降低5.32和2.40,而BC- NaOH的pH值則顯著升高2.54.

4.3 與BC相比,BC-Fe和BC-H2O2促進(jìn)反硝化細(xì)菌對(duì)NO3--N的還原,并增加N2O排放,而BC-NaOH抑制反硝化細(xì)菌對(duì)NO3--N的還原,并減少N2O排放.

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Effect of biochar on the removal of nitrate and N2O emission from water by a screened denitrifying bacterium.

WANG Chao-xu1,2*, LI Yuan-kun1, LIU Yong-chao1

(1.College of Environmental Science and Engineering, Taiyuan University of Technology, Jinzhong 030600,China；2.Innovation Center for Postgraduate Education in Municipal Engineering of Shanxi Province, Jinzhong 030600, China)., 2023,43(11)：5728～5736

To investigate the effect of modified biochar on microbial removal of nitrate with low concentration and N2O emission from water, FeCl3-, H2O2- and NaOH-modified biochars (BC-Fe, BC-H2O2, and BC-NaOH) were prepared by utilizing the pristine rice husk-derived biochar (BC) and characterized further. Meanwhile, a strain of denitrifying bacteria,strain KK1, was screened from activated sludge. Then BC, BC-Fe, BC-H2O2, and BC-NaOH were incorporated into the incubation system containing the strain, respectively and a control treatment without any biochar addition was also setup. The indoor incubation experiment on the microbial removal of nitrate (about 10mg/L, in terms of N) from simulated wastewater was carried out and the dynamic changes of N2O emission rate and NO3--N, NO2--N, NH4+-N, TN, and dissolved organic carbon (DOC) concentrationsduring incubation were analyzed. Results showed that the average NO3--N degradation rate of the screened strain was 0.10mg/(L×h) within 120h. Compared with BC, the carboxyl and lactone contents of BC-Fe and BC-H2O2significantly increased and their oxidizing ability was enhanced, while the phenolic hydroxyl content of BC-NaOH significantly increased and its reducing ability was enhanced. Meanwhile, the total acidic oxygen-containing functional group contents of BC-Fe and BC-H2O2significantly increased by 57.17% and 22.86%, respectively compared with BC, while the total basic oxygen-containing functional group content of BC-NaOH significantly increased by 91.67%. Compared with BC, BC-Fe and BC-H2O2promoted the reduction of NO3--N by denitrifier, and the cumulative N2O emissions were 3.11 and 2.17 times higher than that of the treatment with BC addition, respectively; while BC-NaOH inhibited the reduction of NO3--N by denitrifier, and the cumulative N2O emission was only 49.63% that of the treatment with BC addition. The impact of biochar on microbial denitrification and N2O emission is attributed to the differences in pH value, DOC content, and redox property of biochar caused by modification.

modified biochar；nitrate with low concentration；advanced denitrogenation；N2O emission

X52

A

1000-6923(2023)11-5728-09

王朝旭(1981-),男,河南鄭州人,副教授,博士,主要從事生物質(zhì)炭的水土環(huán)境效應(yīng)研究.發(fā)表論文20篇.cxwang127@126.com.

王朝旭,李元坤,劉勇超.生物炭對(duì)篩選菌株去除水中硝酸鹽和N2O排放的影響 [J]. 中國(guó)環(huán)境科學(xué), 2023,43(11):5728-5736.

Wang C X, Li Y K, Liu Y C. Effect of biochar on the removal of nitrate and N2O emission from water by a screened denitrifying bacterium [J]. China Environmental Science, 2023,43(11):5728-5736.

2023-03-19

山西省自然科學(xué)基金資助項(xiàng)目(201901D111066)

*責(zé)任作者, 副教授, cxwang127@126.com