李 蕓,熊向陽(yáng),李 軍*,陳 剛,張美雪,張彥灼,姚 遠(yuǎn),李 強(qiáng)(.北京工業(yè)大學(xué)建筑工程學(xué)院,北京市水質(zhì)科學(xué)與水環(huán)境恢復(fù)工程重點(diǎn)實(shí)驗(yàn)室,北京 004；.中國(guó)城市建設(shè)研究院有限公司,北京 000)

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膜生物反應(yīng)器處理晚期垃圾滲濾液亞硝化性能及其抑制動(dòng)力學(xué)分析

李 蕓1,熊向陽(yáng)2,李 軍1*,陳 剛2,張美雪1,張彥灼1,姚 遠(yuǎn)2,李 強(qiáng)2(1.北京工業(yè)大學(xué)建筑工程學(xué)院,北京市水質(zhì)科學(xué)與水環(huán)境恢復(fù)工程重點(diǎn)實(shí)驗(yàn)室,北京 100124；2.中國(guó)城市建設(shè)研究院有限公司,北京 100012)

摘要：采用連續(xù)流MBR反應(yīng)器處理晚期垃圾滲濾液,考察其亞硝化性能;并探討底物、產(chǎn)物和毒性物質(zhì)對(duì)亞硝化性能的抑制及其動(dòng)力學(xué)特性.結(jié)果表明,在進(jìn)水N H4+-N濃度為(280±20)mg/L時(shí),通過(guò)控制DO為0.5～1mg/L,pH值為7.8～8.2和溫度為(30±1)℃,成功啟動(dòng)MBR的亞硝化工藝,在第32d時(shí), NO2--N積累率為84.27％;后逐步升高進(jìn)水負(fù)荷,并提高DO至2～3mg/L,逐漸實(shí)現(xiàn)MBR系統(tǒng)中以晚期垃圾滲濾液原液為進(jìn)水的亞硝化,在第112d時(shí),系統(tǒng)出水NO2--N濃度為889mg/L, NO2--N積累率為97.23％.底物、產(chǎn)物和毒性物質(zhì)的抑制實(shí)驗(yàn)表明,毒性物質(zhì)對(duì)微生物的抑制作用強(qiáng)于底物和產(chǎn)物;當(dāng)毒性物質(zhì)濃度(以COD計(jì))為1600.2mg/L時(shí),氨氧化速率下降了22.15％,而相應(yīng)條件下若以FA為單因子抑制時(shí),氨氧化速率下降了4.74％～6.49％,若以FNA為單因子抑制時(shí),氨氧化速率相比下降了14.46％～15.86％.分別采用Haldane底物抑制模型、Aiba產(chǎn)物抑制模型以及修正后的毒性物質(zhì)抑制模型對(duì)實(shí)驗(yàn)數(shù)據(jù)進(jìn)行非線性擬合,相關(guān)系數(shù)R2分別為0.9821、0.9961和0.9924,并得到底物、產(chǎn)物和毒性物質(zhì)的抑制動(dòng)力學(xué)模型.

關(guān)鍵詞：晚期垃圾滲濾液；膜生物反應(yīng)器(MBR)；亞硝化；抑制動(dòng)力學(xué)

* 責(zé)任作者, 教授, jglijun@bjut.edu.cn

垃圾填埋場(chǎng)所產(chǎn)生的垃圾滲濾液成分復(fù)雜、氨氮濃度大,并且含有毒性有機(jī)物和重金屬等毒害物質(zhì)[1-2].在脫氮方面,新鮮的垃圾滲濾液中的有機(jī)物可生化性較好,可利用其自身碳源通過(guò)常規(guī)的硝化反硝化,或短程硝化反硝化等工藝進(jìn)行脫氮;而晚期垃圾滲濾液中的有機(jī)物往往可生化性較差,為典型的高氨氮低碳氮比污水,在采用常規(guī)硝化反硝化工藝脫氮過(guò)程中需要補(bǔ)充大量碳源,造成處理成本增高,故應(yīng)尋求更經(jīng)濟(jì)節(jié)能的脫氮方法.

亞硝化與厭氧氨氧化的自養(yǎng)組合脫氮技術(shù)已經(jīng)成為高氨氮低碳氮比廢水的研究熱點(diǎn).亞硝化與厭氧氨氧化的組合工藝有兩種,一是亞硝化階段實(shí)現(xiàn)NO2--N積累后與原液配成ρ(NO2--N)/ ρ(NH4+-N)為1:1的進(jìn)水進(jìn)行厭氧氨氧化脫氮,二是在亞硝化階段控制出水ρ(NO2--N)/ρ(NH4+-N) 為1:1,后進(jìn)行厭氧氨氧化脫氮.不管是前者還是后者都需實(shí)現(xiàn)穩(wěn)定的亞硝化,才能滿足后續(xù)脫氮要求,而實(shí)現(xiàn)穩(wěn)定的亞硝化關(guān)鍵是氨氧化菌(AOB)的截留,及亞硝酸氧化菌(NOB)的淘汰; AOB為自養(yǎng)菌,其生長(zhǎng)緩慢,世代周期較長(zhǎng)[3]. MBR可實(shí)現(xiàn)系統(tǒng)污泥的高效截留,對(duì)于繁殖速度較慢的AOB來(lái)說(shuō),采用該工藝可實(shí)現(xiàn)AOB菌群的快速富集,從而縮短實(shí)現(xiàn)亞硝化的時(shí)間.目前,采用MBR實(shí)現(xiàn)亞硝化的研究較少[4-5],且處理的廢水均為氨氮濃度較低的模擬配水.而晚期垃圾滲濾液原液中氨氮一般大于1000mg/L,采用MBR反應(yīng)器處理晚期垃圾滲濾液原液的亞硝化也鮮有報(bào)道.

因此,本研究以實(shí)際晚期垃圾滲濾液原液為處理對(duì)象,通過(guò)控制運(yùn)行條件,并逐步增加進(jìn)水負(fù)荷以實(shí)現(xiàn)MBR反應(yīng)器處理晚期垃圾滲濾液原液的亞硝化.此外,晚期垃圾滲濾液具有高氨氮和有微生物毒性作用的特點(diǎn),在處理過(guò)程中,高氨氮環(huán)境會(huì)形成較高濃度的游離氨(FA)從而對(duì)微生物產(chǎn)生抑制,亞硝化會(huì)導(dǎo)致NO2--N逐漸積累所產(chǎn)生的游離亞硝酸(FNA)也會(huì)形成產(chǎn)物抑制[6-7],晚期垃圾滲濾液中所含的有毒害作用的有機(jī)物及重金屬等也會(huì)形成毒性抑制[8-9].故通過(guò)批試實(shí)驗(yàn)分別對(duì)亞硝化過(guò)程中底物、產(chǎn)物及毒性物質(zhì)的抑制作用及其抑制動(dòng)力學(xué)進(jìn)行探討,以分析晚期垃圾滲濾液亞硝化過(guò)程中底物、產(chǎn)物及毒性物質(zhì)的抑制特性并得出其抑制動(dòng)力學(xué)方程,以期為MBR亞硝化工藝處理晚期垃圾滲濾液的實(shí)際應(yīng)用提供指導(dǎo).

1 材料與方法

1.1 實(shí)驗(yàn)裝置

實(shí)驗(yàn)采用MBR反應(yīng)器(圖1),反應(yīng)器由有機(jī)玻璃制成,其有效容積為25L,內(nèi)置膜組件(聚偏氟乙烯中空纖維膜,膜孔徑為0.1μm,膜面積為0.5m2).進(jìn)水由蠕動(dòng)泵泵入,出水通過(guò)膜組件由蠕動(dòng)泵排出,通過(guò)可編程邏輯控制器系統(tǒng)控制,采用恒通量過(guò)濾間歇抽吸方式進(jìn)行產(chǎn)水,膜通量為2.28L/(m2·h),抽吸周期為10min,8min抽吸,停2min.曝氣裝置置于膜組件下,通過(guò)轉(zhuǎn)子流量計(jì)控制曝氣量,曝氣量為40～160L/h,曝氣產(chǎn)生的水力剪切作用可形成錯(cuò)流過(guò)濾以減緩膜污染并對(duì)反應(yīng)器內(nèi)液相形成擾動(dòng).通過(guò)真空表(津制00000578型,天津)來(lái)顯示過(guò)膜壓力(TMP),以此判斷膜污染程度.溫控裝置控制溫度為(30±1)℃左右,HRT為22h,除了定期取100mL水樣測(cè)MLSS外,未進(jìn)行排泥.

圖1　MBR反應(yīng)器示意Fig.1 Schematic diagram of MBR reactor

1.2 實(shí)驗(yàn)種泥和滲濾液

實(shí)驗(yàn)所用種泥取自北京某污水處理廠活性污泥,為全程硝化污泥,硝化性能良好.接種初始污泥濃度MLSS為3104mg/L,MLVSS為2540mg/L.

實(shí)驗(yàn)所用滲濾液取自北京某垃圾填埋廠(填埋年限大于5a),為晚期滲濾液,取回后密閉貯存于塑料桶中,平均每月更新一次.具體水質(zhì)如下: NH4+-N為900～1500mg/L, NO2--N為0～2mg/L, NO3--N為0～8mg/L, COD為2000～4000mg/L, pH 值7.5～8.5,堿度6000～10000mg/L.

1.3 抑制動(dòng)力學(xué)批試實(shí)驗(yàn)

取第71d時(shí)MBR中亞硝化活性污泥,用自來(lái)水和PBS緩沖液各清洗3～5遍,后進(jìn)行濃縮,濃縮液MLSS約為5.04g/L,批試實(shí)驗(yàn)各取150mL污泥濃縮液加入至1L的燒杯中并稀釋至1L進(jìn)行,底物和產(chǎn)物抑制實(shí)驗(yàn)中NH4+-N和NO2--N根據(jù)所設(shè)梯度配成相應(yīng)濃度,毒性物質(zhì)抑制以氯化銨調(diào)節(jié)各梯度NH4+-N濃度統(tǒng)一以消除底物抑制的影響.以碳酸氫鈉和鹽酸調(diào)節(jié)堿度和pH值恒定,在恒溫培養(yǎng)箱中進(jìn)行實(shí)驗(yàn),每間隔30min取樣測(cè)定,計(jì)算氨氧化速率、NO2--N生成速率和硝態(tài)氮生成速率,所有測(cè)試設(shè)3個(gè)平行并求平均值.

1.4 測(cè)試分析方法

NH4+-N:納氏試劑光度法;NO2--N:N-(1-萘基)-乙二胺分光光度法;NO3--N:麝香草酚分光光度法;懸浮固體(MLSS)、揮發(fā)性懸浮固體(MLVSS):重量法;pH值、DO、溫度: WTW/ Multi3420便攜式測(cè)定儀.

NO2--N積累率(R)、游離氨(FA)和游離亞硝酸(FNA)分別按照以下公式計(jì)算:

式中:ρ[NO2--N]為出水NO2--N濃度, mg/L; ρ[NO3--N]為出水NO3--N濃度, mg/L; ρ[NH4+-N] 為NH4+-N濃度, mg/L; T為溫度,℃.

2 結(jié)果與討論

2.1 低溶解氧條件下亞硝化的啟動(dòng)

一般認(rèn)為,通過(guò)控制合適的溫度、pH值以及溶解氧(DO)可以抑制亞硝酸氧化菌(NOB),促使氨氧化菌(AOB)的富集,從而實(shí)現(xiàn)亞硝化.多數(shù)研究表明,能夠快速富集AOB并且對(duì)NOB產(chǎn)生抑制的條件是:溫度為30～35℃[10],pH值為8.0左右[11],DO小于1mg/L[12-13].因此在本實(shí)驗(yàn)中,為了快速啟動(dòng)亞硝化反應(yīng),反應(yīng)器在啟動(dòng)期的運(yùn)行條件為:溫度控制在(30±1)℃,pH值維持在7.8～8.2, DO控制在0.5～1mg/L,HRT為22h.啟動(dòng)期分為兩個(gè)階段,第一階段(0～18d)是采用無(wú)機(jī)配水啟動(dòng)短程硝化,進(jìn)水NH4+-N濃度為280±20mg/L;第二階段(19～32d)通入稀釋后的垃圾滲濾液,同樣控制進(jìn)水NH4+-N濃度為280±20mg/L.MBR亞硝化系統(tǒng)啟動(dòng)的運(yùn)行性能如圖2所示.

圖2　啟動(dòng)階段MBR亞硝化運(yùn)行性能Fig.2 Performance of nitritation during startup

由圖2可以看出,在第一階段,經(jīng)過(guò)3～5d的適應(yīng)期后,出水NO3--N呈逐漸降低趨勢(shì),而出水NO2--N濃度則逐漸升高.說(shuō)明通過(guò)控制實(shí)驗(yàn)溫度、溶解氧和pH值,NOB活性受到明顯抑制,而AOB活性則逐漸提高,系統(tǒng)在由全程硝化向亞硝化轉(zhuǎn)變.在第15d和17d時(shí),系統(tǒng)NO2--N積累率分別為50.7％和53.5％,說(shuō)明此時(shí)系統(tǒng)中AOB已經(jīng)為優(yōu)勢(shì)種群;通常認(rèn)為,NO2--N積累率大于50％即發(fā)生了短程硝化反應(yīng).因此,在第19d開始通入稀釋后的垃圾滲濾液,該開始時(shí),系統(tǒng)因?yàn)檫M(jìn)水水質(zhì)發(fā)生變化,并且垃圾滲濾液中含有大量毒害物質(zhì),微生物活性受到抑制,從而導(dǎo)致系統(tǒng)受到干擾,出水水質(zhì)發(fā)生變化,出水NH4+-N升高(由5.14mg/L升至74.20mg/L), NH4+-N去除率由98.17％降至75.53％.后經(jīng)過(guò)14d的運(yùn)行,系統(tǒng)硝化性能得到恢復(fù),直至32d時(shí), NH4+-N去除率恢復(fù)至93.59％,說(shuō)明系統(tǒng)中微生物已經(jīng)逐步適應(yīng)該進(jìn)水水質(zhì).而在整個(gè)啟動(dòng)過(guò)程中, NO2--N積累率呈逐漸增長(zhǎng)的趨勢(shì),在第32d時(shí),其值為84.27％,說(shuō)明反應(yīng)器亞硝化啟動(dòng)成功.

2.2 MBR反應(yīng)器負(fù)荷提高階段亞硝化性能

隨著系統(tǒng)亞硝化的成功啟動(dòng),系統(tǒng)中的亞硝化細(xì)菌已經(jīng)逐漸取代硝化細(xì)菌成為優(yōu)勢(shì)菌種, NO2--N逐漸在系統(tǒng)中積累.此時(shí)系統(tǒng)中對(duì)NOB的抑制因子包括有溫度、pH值、FA、FNA和DO.然而,較低的溶解氧不僅會(huì)抑制NOB,同時(shí)也會(huì)影響AOB的活性[14].有研究表明,當(dāng)系統(tǒng)中存在其他的抑制因素時(shí),即使在DO較高的情況下仍然能夠維持亞硝化[15].因此,此時(shí)控制其他條件不變,將DO提高至2～3mg/L,并開始提高進(jìn)水負(fù)荷,負(fù)荷提高期共歷時(shí)72d,分為3個(gè)階段逐漸提升至垃圾滲濾液原液,第一階段(33～58d)進(jìn)水NH4+-N濃度為550～600mg/L;第二階段(59～80d)進(jìn)水NH4+-N濃度為750～850mg/L;第三階段(81～112d)為滲濾液原液,其進(jìn)水NH4+-N濃度為950～1050mg/L.負(fù)荷提高期系統(tǒng)亞硝化性能如圖3所示,可以看出,每次負(fù)荷的提高都會(huì)導(dǎo)致出水NH4+-N濃度升高,第一階段初始時(shí)NH4+-N去除率由93.59％降至50.63％,第二階段初始時(shí)NH4+-N去除率由92.53％降至66.47％,第三階段初始時(shí)NH4+-N去除率由86.17％降至65.17％.這是因?yàn)橐皇敲看呜?fù)荷提高時(shí)系統(tǒng)中微生物生物量未相應(yīng)升高,二是進(jìn)水負(fù)荷提高使得系統(tǒng)中水質(zhì)環(huán)境發(fā)生改變,從而影響系統(tǒng)中微生物活性,并且滲濾液中毒性物質(zhì)濃度的升高也會(huì)對(duì)系統(tǒng)中微生物活性造成抑制.負(fù)荷提高后經(jīng)過(guò)一段時(shí)間運(yùn)行, NH4+-N出水逐漸降低,去除率逐漸升高,其原因?yàn)橐皇窍到y(tǒng)中微生物的增殖,處理負(fù)荷增強(qiáng),二是微生物逐漸對(duì)負(fù)荷提高后水質(zhì)的適應(yīng),活性有所提高. NO2--N出水濃度隨著進(jìn)水負(fù)荷的提高也呈先降低后升高的趨勢(shì),但是整體來(lái)看, NO2--N出水濃度隨系統(tǒng)運(yùn)行時(shí)間而逐步升高, NO2--N積累率在第45d時(shí)為90.18％,在運(yùn)行至112d時(shí),系統(tǒng)出水NO2--N濃度高達(dá)889mg/L, NO2--N積累率為97.23％;說(shuō)明通過(guò)連續(xù)運(yùn)行,系統(tǒng)中AOB大量富集,并且逐漸適應(yīng)高負(fù)荷下的垃圾滲濾液.而盡管在負(fù)荷提高期將溶解氧提高至2～3mg/L,但是整個(gè)過(guò)程中并未見有NO3--N的大量積累,出水NO3--N基本維持在30～ 50mg/L的范圍,說(shuō)明該過(guò)程中DO不是NO2--N積累的關(guān)鍵因素.

圖3　負(fù)荷提高階段亞硝化運(yùn)行性能Fig.3 Performance of nitritation during load increase stage

2.3 亞硝化過(guò)程中膜污染及污泥特性

一般通過(guò)過(guò)膜壓力(TMP)來(lái)表征膜組件運(yùn)行過(guò)程中的污染程度[16].在恒通量運(yùn)行情況下,TMP會(huì)隨著膜污染程度的加劇而升高.亞硝化過(guò)程中,共分為啟動(dòng)期和負(fù)荷提高期(圖4),而負(fù)荷提高期又分為3階段進(jìn)行.不同運(yùn)行階段的TMP如圖4所示,可以看出,隨著垃圾滲濾液進(jìn)水負(fù)荷的提高,膜污染速率逐漸加快,其原因?yàn)橥砥诶鴿B濾液中含有較高濃度的有機(jī)物和金屬離子等會(huì)加快膜污染速率,此外有研究表明,外界條件的改變會(huì)導(dǎo)致微生物釋放大量的胞外聚合物(EPS)和溶解性微生物產(chǎn)物(SMP)[17],EPS和SMP的存在也會(huì)加快膜污染速率,說(shuō)明本實(shí)驗(yàn)中垃圾滲濾液進(jìn)水負(fù)荷的提高對(duì)膜污染的影響起一定作用.

圖4同時(shí)也反映了系統(tǒng)中污泥濃度的變化,在亞硝化啟動(dòng)期,MLSS呈逐漸降低趨勢(shì),其原因是系統(tǒng)在啟動(dòng)前期進(jìn)水為無(wú)機(jī)配水,通過(guò)限氧、高溫及適宜pH值等條件的控制,系統(tǒng)逐漸向亞硝化轉(zhuǎn)變,部分NOB裂解死亡;啟動(dòng)后期進(jìn)入可生化性較差的晚期垃圾滲濾液,滲濾液中的毒性物質(zhì)也會(huì)導(dǎo)致系統(tǒng)中微生物的死亡而分解.而進(jìn)入負(fù)荷提高期后,系統(tǒng)中MLSS逐漸升高,其原因?yàn)橐皇墙?jīng)過(guò)啟動(dòng)后期微生物對(duì)垃圾滲濾液的適應(yīng)馴化,其逐漸適應(yīng)滲濾液的水質(zhì);二是滲濾液中微量的可降解有機(jī)物促進(jìn)好氧異養(yǎng)菌的生長(zhǎng)繁殖;三是AOB在系統(tǒng)中逐漸積累.

圖4　亞硝化過(guò)程中TMP和MLSS的變化Fig.4 Evolution of TMP and MLSS during the operation phases

2.4 底物、產(chǎn)物和毒性物質(zhì)對(duì)亞硝化的抑制及其動(dòng)力學(xué)

實(shí)驗(yàn)所處理的廢水為晚期垃圾滲濾液,具有高氨氮和有微生物毒性作用的特點(diǎn),在通過(guò)MBR反應(yīng)器亞硝化過(guò)程中會(huì)產(chǎn)生抑制作用,包括底物、產(chǎn)物及毒性物質(zhì)的抑制作用.通過(guò)批試實(shí)驗(yàn),對(duì)MBR反應(yīng)器中亞硝化活性污泥進(jìn)行不同抑制因子的抑制動(dòng)力學(xué)測(cè)定并建立抑制動(dòng)力學(xué)模型.

2.4.1 底物、產(chǎn)物和毒性物質(zhì)的抑制 底物、產(chǎn)物和毒性物質(zhì)對(duì)亞硝化的影響如表1所示,FA濃度在2.88～42.38mg/L,隨著FA濃度的升高,氨氧化速率和NO2--N生成速率呈現(xiàn)出先升高后降低的趨勢(shì),而NO3--N生成速率則在逐漸降低.在FA濃度為11.75mg/L時(shí),氨氧化速率為1.436g/ (g·d),而當(dāng)FA濃度上升至42.38mg/L時(shí),氨氧化速率降低至1.248mg/L,為最高時(shí)的86.88％; NO2--N生成速率和NO3--N生成速率分別降低至最高時(shí)的88.84％和53.97％.NH4+-N為硝化菌的底物,硝化細(xì)菌利用NH4+-N氧化成NO2--N和NO3--N,并從中獲得其自身生長(zhǎng)繁殖所需的能量. 高NH4+-N形成的FA可以抑制NOB的活性,從而致使AOB逐漸取代NOB成為優(yōu)勢(shì)菌群,從而實(shí)現(xiàn)亞硝化[18];然而過(guò)高的FA也會(huì)對(duì)AOB形成抑制,一般認(rèn)為,FA對(duì)NOB的抑制作用強(qiáng)于AOB.Vadivelu等[19]的研究認(rèn)為0.1～1mg/L的FA就會(huì)對(duì)NOB產(chǎn)生抑制,當(dāng)FA達(dá)到6mg/L時(shí)幾乎可完全抑制NOB的生長(zhǎng),而對(duì)AOB抑制范圍一般在10～150mg/L[20].本實(shí)驗(yàn)中最高氨氧化速率和NO2--N生成速率時(shí)的FA濃度處于9.45～ 11.75mg/L,稍微高于Vadivelu等的研究;此外盡管FA濃度高達(dá)42.38mg/L,但是仍然有少量的NO3--N產(chǎn)生,并未完全抑制NOB的活性,這可能是由于實(shí)驗(yàn)中的活性污泥長(zhǎng)期處于高NH4+-N水質(zhì)條件下運(yùn)行,從而對(duì)FA產(chǎn)生一定的適應(yīng)性,此現(xiàn)象在Villaverde等[21]和Fux等[22]的研究中也有所體現(xiàn).

AOB將NH4+-N氧化成NO2--N, NO2--N的存在以及大量的集聚會(huì)形成游離亞硝酸(FNA),而當(dāng)FNA達(dá)到一定濃度時(shí)會(huì)對(duì)AOB和NOB都產(chǎn)生抑制作用.實(shí)驗(yàn)結(jié)果表明,FNA濃度在0.008～0.1036mg/L之間,隨著FNA濃度的升高,氨氧化速率、NO2--N生成速率和NO3--N生成速率與FA呈現(xiàn)出相同的變化規(guī)律,當(dāng)FNA為0.1036mg/L時(shí),氨氧化速率、NO2--N生成速率和NO3--N生成速率分別降至最高時(shí)的84.14％、86.59％和54.23％. Vadivelu等的研究認(rèn)為,當(dāng)FNA濃度為0.011mg/L時(shí),NOB的活性即受到抑制,而當(dāng)FNA濃度為0.023mg/L時(shí),NOB活性則被完全抑制;而FNA完全抑制AOB的濃度為0.4mg/L[23-25].本實(shí)驗(yàn)中FNA濃度小于AOB完全抑制濃度(0.40mg/L),在濃度為0.0317mg/L時(shí),開始對(duì)AOB活性產(chǎn)生抑制;而在該范圍內(nèi),也未見NOB活性被完全抑制,其原因也可能是其對(duì)FNA有一定的適應(yīng)性.

垃圾滲濾液成分復(fù)雜,含有大量具有毒害作用的有機(jī)物、鹽離子和重金屬,這些因素均會(huì)對(duì)反應(yīng)器中微生物產(chǎn)生抑制[26],從而影響亞硝化性能.垃圾滲濾液中毒性物質(zhì)的濃度以COD計(jì), 實(shí)驗(yàn)考察了其濃度在0～2667mg/L時(shí)的亞硝化情況,隨著毒性物質(zhì)濃度的升高,氨氧化速率、NO2--N生成速率和NO3--N生成速率都受到抑制,呈逐步降低的趨勢(shì),當(dāng)COD為2667mg/L時(shí),氨氧化速率、NO2--N生成速率和NO3--N生成速率分別降低至44.36％、45.12％和44.03％.

由表2可知,當(dāng)COD為1600.2mg/L時(shí),氨氧化速率為0.9848g/(g·d),與最大氨氧化速率相比下降了22.15％.同時(shí)相應(yīng)條件下滲濾液中氨氮對(duì)應(yīng)的FA為27.78mg/L,若以FA為單因子抑制,此時(shí)氨氧化速率為1.3432～1.3684mg/L之間,與最大氨氧化速率相比下降了4.74％～6.49％.假設(shè)NH4+-N完全轉(zhuǎn)化成NO2--N,則相應(yīng)條件下滲濾液中NO2--N對(duì)應(yīng)的FNA為0.09638mg/L,若以FNA為單因子抑制,此時(shí)氨氧化速率為1.1875～ 1.2072mg/L之間,與最大氨氧化速率相比下降了14.46％～15.86％.通過(guò)對(duì)比發(fā)現(xiàn),晚期垃圾滲濾液中的毒性物質(zhì)對(duì)亞硝化的抑制作用強(qiáng)于FNA和FA.

表2　晚期垃圾滲濾液中COD與氨氮、FA和FNA對(duì)應(yīng)關(guān)系Table 2 Corresponding relation of COD and NH4+-N, FA and FNA in the old landfill leachate

2.4.2 抑制動(dòng)力學(xué)模型及分析 底物抑制動(dòng)力學(xué)可采用Haldane模型[27-28]來(lái)進(jìn)行描述,Haldane模型其方程為:

式中:ν為底物轉(zhuǎn)化速率,g/(g·d);νmax為最大轉(zhuǎn)化速率,g/(g·d);S為底物濃度, mg/L; kS為半飽和常數(shù),mg/L;kh為Haldane抑制動(dòng)力學(xué)常數(shù), mg/L.

Aiba模型[29]最初是描述乙醇發(fā)酵產(chǎn)物抑制的模型,也有將其應(yīng)用于硝化反應(yīng)的基質(zhì)抑制動(dòng)力學(xué)模擬[30],并得出了較好的擬合相關(guān)度.其方程可以描述為:

式中:ν為底物轉(zhuǎn)化速率,g/(g·d);νmax為最大底物轉(zhuǎn)化速率,g/(g·d);S為基質(zhì)濃度,mg/L; kS為半飽和常數(shù),mg/L; ka為Aiba抑制動(dòng)力學(xué)常數(shù), mg/L.

表3　抑制動(dòng)力學(xué)模型參數(shù)Table 3 Constants for inhibition kinetics model

毒性物質(zhì)抑制的動(dòng)力學(xué)模型引用乙酸降解時(shí)氯酚抑制作用的動(dòng)力學(xué)模型[31],其方程如下:

式中:ν為底物轉(zhuǎn)化速率,g/(g·d);νmax為最大底物轉(zhuǎn)化速率,g/(g·d);S為基質(zhì)濃度, mg/L;kS為半飽和速率常數(shù),mg/L;k0和k1為抑制系數(shù).

抑制系數(shù)k0和k1按以下公式計(jì)算:

式中:α為毒毒性物質(zhì)濃度, mg/L;β為毒性物質(zhì)完全抑制濃度, mg/L;m和n為常數(shù).

通過(guò)引入速率比λ對(duì)上式進(jìn)行經(jīng)修正,得出反映毒性物質(zhì)對(duì)基質(zhì)轉(zhuǎn)化速率的抑制方程為[32]:

其中λ= ν/ν0,λ為速率比;ν為毒性物質(zhì)在各濃度下基質(zhì)轉(zhuǎn)化速率,g/(g·d);ν0為未投加毒性物質(zhì)條件下基質(zhì)轉(zhuǎn)化速率,g/(g·d).該式可描述毒性物質(zhì)濃度對(duì)基質(zhì)轉(zhuǎn)化速率的抑制作用,其中,β值越大說(shuō)明需要更高濃度的毒性物質(zhì)才能完全抑制微生物活性,其毒性越弱.當(dāng)β值相近時(shí),m和n值越大說(shuō)明毒性物質(zhì)的抑制作用越弱.用修正的抑制方程式(9)對(duì)實(shí)驗(yàn)結(jié)果進(jìn)行擬合.

通過(guò)Origin8.0分別對(duì)表1中數(shù)據(jù)進(jìn)行非線性擬合(圖5),可得出底物、產(chǎn)物和毒性物質(zhì)對(duì)亞硝化抑制的動(dòng)力學(xué)方程.擬合曲線與實(shí)驗(yàn)數(shù)據(jù)的相關(guān)系數(shù)R2分別為0.9821、0.9961和0.9924,說(shuō)明3個(gè)模型均可較好的描述本實(shí)驗(yàn)中各抑制因子對(duì)亞硝化的抑制動(dòng)力學(xué)行為.其中,通過(guò)FA抑制動(dòng)力學(xué)模型可得在FA單因子控制下的最大氨氧化速率為2.087g/(g·d),對(duì)FA的半飽和常數(shù)為3.185mg/L,Haldane抑制動(dòng)力學(xué)常數(shù)為67.234mg/L;最大反應(yīng)速率時(shí)的底物濃度可通過(guò)式(10)求得,為14.62mg/L.通過(guò)FNA抑制動(dòng)力學(xué)模型可得在FNA單因子控制下的最大氨氧化速率為1.484g/(g·d), 對(duì)FNA的半飽和常數(shù)為0.001mg/L,Aiba抑制動(dòng)力學(xué)常數(shù)為0.432mg/L.通過(guò)毒性物質(zhì)抑制動(dòng)力學(xué)模型可得在毒性物質(zhì)控制下毒性物質(zhì)完全抑制濃度為4054.02mg/L (以COD計(jì)),動(dòng)力學(xué)常數(shù)m和n分別為2.19和2.32.

圖5　亞硝化抑制動(dòng)力學(xué)模型Fig.5 The inhibition kinetics model of nitritation　a.底物抑制 b.產(chǎn)物抑制 c.毒性物質(zhì)抑制

3 結(jié)論

3.1 通過(guò)控制DO為0.5～1mg/L,pH值為7.8～8.2和溫度為(30±1)℃,在進(jìn)水NH4+-N濃度為(280±20)mg/L時(shí)成功啟動(dòng)MBR的亞硝化工藝.后逐步升高進(jìn)水負(fù)荷,并提高DO至2～3mg/L,逐漸實(shí)現(xiàn)MBR系統(tǒng)中以晚期垃圾滲濾液原液為進(jìn)水的亞硝化,實(shí)現(xiàn)了垃圾滲濾液原液的亞硝化.

3.2 MBR亞硝化系統(tǒng)在運(yùn)行過(guò)程中,微生物會(huì)受到底物、產(chǎn)物和垃圾滲濾液中的毒性物質(zhì)的抑制,其中毒性物質(zhì)對(duì)微生物的抑制作用強(qiáng)于底物和產(chǎn)物.當(dāng)毒性物質(zhì)濃度(以COD計(jì))為1600.2mg/L時(shí),氨氧化速率下降了22.15％,而相應(yīng)條件下若以FA為單因子抑制時(shí),氨氧化速率下降了4.74％～6.49％,若以FNA為單因子抑制時(shí),氨氧化速率相比下降了14.46％～15.86％.

3.3 分別采用Haldane底物抑制模型、Aiba產(chǎn)物抑制模型以及修正后的毒性物質(zhì)抑制模型對(duì)實(shí)驗(yàn)數(shù)據(jù)進(jìn)行擬合,FA抑制的半飽和常數(shù)為3.185mg/L,抑制動(dòng)力學(xué)常數(shù)為67.234mg/L;FNA抑制的半飽和常數(shù)為0.001mg/L,抑制動(dòng)力學(xué)常數(shù)為0.432mg/L;毒性物質(zhì)完全抑制濃度為4054.02mg/L (以COD計(jì)),動(dòng)力學(xué)常數(shù)m和n分別為2.19和2.32.

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Performance of nitritation process in membrane bioreactor for old landfill leachate and analysis of inhibition kinetics.

LI Yun1, XIONG Xiang-yang2, LI Jun1*, CHEN Gang2, ZHANG Mei-xue1, ZHANG Yan-zhuo1, YAO Yuan2, LI>Qiang2(1.College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 1000124, China；2.China Urban Construction Design and Research Institute Corporation Limited, Beijing 100012, China). China Environmental Science, 2016,36(2)：419～427

Abstract：The performance of nitritation were investigated in continuous flow MBR fed with old landfill leachate, the inhibition of substrate, product and toxicant on nitritation process and the inhibition kinetics were analyzed. The results show that: the nitritation process was started up in MBR which controlled the NH4+-N concentration of inflow was (280±20)mg/L, the DO was 0.5～1.0mg/L, pH was 7.8～8.2 and temperature was (30±1)℃; and at 32d, the nitrite accumulation rate was 84.27％. Influent load was increase gradually and improved the DO to 2～3mg/L in the next period, nitritation process was realized gradually in MBR system which the inflow was the old landfill leachate completely, the ρ (NO2--N) of effluent from system was 889mg/L and the nitrite accumulation rate was 97.23％ at 112d. The inhibition experiments of substrate, product and toxicant showed that, the inhibition of toxicant surpass substrate and product, when the concentration of toxicant (calculated by COD) was 1600.2mg/L, the ammonia oxidation rate declined by 22.15％, and if inhibition factor was FA only in corresponding conditions, ammonia oxidation rate decreased by 4.74％～6.49％, and if inhibition factor was FNA only in corresponding conditions, ammonia oxidation rate decreased by 14.46％～15.86％. Haldane model, Aiba model and the revised toxicant inhibiting model were adopted for nonlinear fitting on the experimental data respectively, the correlation coefficient R2were 0.9821, 0.9961 and 0.9924 respectively, and the inhibition kinetics models of substrate, product and toxicant were obtained.

Key words：old landfill leachate；membrane bioreactor (MBR)；nitritation；inhibition kinetics

作者簡(jiǎn)介：李 蕓(1985-),男,江西宜春人,北京工業(yè)大學(xué)博士研究生,主要研究方向?yàn)槲鬯幚砝碚撆c技術(shù).發(fā)表論文2篇.

基金項(xiàng)目：國(guó)家水體污染控制與治理科技重大專項(xiàng)(2014ZX07201-011);中國(guó)城市建設(shè)研究院院級(jí)課題(Y07H13074)

收稿日期：2015-08-02

中圖分類號(hào)：X703.5

文獻(xiàn)標(biāo)識(shí)碼：A

文章編號(hào)：1000-6923(2016)02-0419-09