殷志平,吳義鋒,呂錫武
(東南大學(xué)能源與環(huán)境學(xué)院,江蘇 南京 210096)
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景觀(guān)型與蔬菜型水平潛流濕地除磷動(dòng)力學(xué)模型
殷志平,吳義鋒,呂錫武
(東南大學(xué)能源與環(huán)境學(xué)院,江蘇 南京 210096)
利用景觀(guān)型和蔬菜型水平潛流濕地凈化經(jīng)生化處理后的生活污水尾水,進(jìn)行濕地除磷動(dòng)力學(xué)模型研究。對(duì)比分析不同濕地單元的除磷效率。為優(yōu)化濕地除磷設(shè)計(jì),采用一級(jí)動(dòng)力學(xué)模型和Monod模型模擬除磷效果,對(duì)比模擬準(zhǔn)確性,討論水溫、水力負(fù)荷與模型反應(yīng)速率常數(shù)間關(guān)系,并建立濕地除磷模型構(gòu)建式。結(jié)果表明,景觀(guān)型濕地除磷能力順序:美人蕉單元>再力花單元>鳶尾單元,蔬菜型濕地:空心菜單元>茭白單元>番茄單元,除磷效果差異歸因于不同類(lèi)植物的生物量區(qū)別。Monod模型(模型效率值ME:0.76~0.86)對(duì)濕地除磷的預(yù)測(cè)較一級(jí)動(dòng)力學(xué)模型(ME:0.53~0.72)具有更高準(zhǔn)確性。總磷面積去除率隨水溫的降低而減小,Arrhenius擬合結(jié)果表明,美人蕉(?=1.006)、再力花(?=1.008)和空心菜(?=1.006)單元Kmax對(duì)水溫變化不敏感,水溫對(duì)鳶尾(?=1.015)和茭白(?=1.014)單元除磷效率有較大影響。Kmax20與水力負(fù)荷間存在顯著正相關(guān)性,兩者符合乘冪方程(R2:0.657;0.805)關(guān)系??紤]了水溫和水力負(fù)荷因素的Monod模型構(gòu)建式,對(duì)試驗(yàn)濕地除磷預(yù)測(cè)具備準(zhǔn)確性。
景觀(guān)型、蔬菜型水平潛流濕地;總磷;動(dòng)力學(xué)模型;Monod模型構(gòu)建式;優(yōu)化設(shè)計(jì)
DOI:10.11949/j.issn.0438-1157.20151445
人工濕地作為一種環(huán)境友好型生態(tài)技術(shù),其低投資、低能耗和維護(hù)管理簡(jiǎn)便的特點(diǎn)使其在工農(nóng)業(yè)廢水、小城鎮(zhèn)及農(nóng)村生活污水處理和水環(huán)境修復(fù)中具有獨(dú)特優(yōu)勢(shì)[1-2]。目前,人工濕地已成功應(yīng)用于生活污水、暴雨徑流和工農(nóng)業(yè)廢水等的處理凈化[3-4]。各類(lèi)濕地中,景觀(guān)型和蔬菜型潛流濕地具備良好水質(zhì)凈化功能的同時(shí),可產(chǎn)生一定的景觀(guān)效益與經(jīng)濟(jì)價(jià)值,是實(shí)現(xiàn)污水中營(yíng)養(yǎng)鹽去除與資源化利用的重要途徑。在營(yíng)養(yǎng)鹽中,磷是湖泊、水庫(kù)等水體富營(yíng)養(yǎng)化的主要限制因子[5],控制磷污染物進(jìn)入水體是防治水體富營(yíng)養(yǎng)化的主要途徑[6]。國(guó)內(nèi)外大量研究表明,景觀(guān)型和蔬菜型人工濕地均表現(xiàn)出良好的除磷效果[7-11]。但同時(shí)進(jìn)行兩類(lèi)濕地除磷研究的相關(guān)報(bào)道較少。
人工濕地的廣泛應(yīng)用和愈發(fā)嚴(yán)格的水質(zhì)標(biāo)準(zhǔn)對(duì)濕地設(shè)計(jì)方法提出了更高的要求[12]。目前,人工濕地的設(shè)計(jì)通?;诮?jīng)驗(yàn)公式,如負(fù)荷法等。采用經(jīng)驗(yàn)方法得到的濕地面積通常比一級(jí)動(dòng)力學(xué)模型的計(jì)算結(jié)果高出10%~30%[13]。增加了工程造價(jià),削弱了濕地的低成本優(yōu)勢(shì)。對(duì)此國(guó)內(nèi)外進(jìn)行了不同的濕地動(dòng)力學(xué)模型研究,但多集中于有機(jī)物的去除[14-18],對(duì)營(yíng)養(yǎng)鹽去除模型的研究較少,景觀(guān)型和蔬菜型濕地除磷模型的研究也鮮有報(bào)道。建立合適的濕地除磷模型可增強(qiáng)對(duì)復(fù)雜濕地系統(tǒng)除磷動(dòng)力學(xué)和功能的理解,提高濕地設(shè)計(jì)的合理性,實(shí)現(xiàn)除磷效率的最大化和濕地尺寸、造價(jià)的最小化。同時(shí),Rousseau等[12]指出需特別關(guān)注模型中參數(shù)的不確定性。模型中的速率常數(shù)常假定為恒定常數(shù),而實(shí)際研究表明其受水力負(fù)荷、進(jìn)水濃度、溫度等因素影響[17,19-21]。而國(guó)內(nèi)對(duì)濕地除磷速率常數(shù)的影響研究關(guān)注較少。
本文通過(guò)構(gòu)建景觀(guān)型和蔬菜型水平潛流濕地兩類(lèi)濕地,開(kāi)展?jié)竦叵到y(tǒng)的除磷效果和動(dòng)力學(xué)研究。采用一級(jí)動(dòng)力學(xué)模型和Monod模型模擬除磷效果,并對(duì)比模擬準(zhǔn)確性。在模型速率常數(shù)的影響因素上,研究水溫、水力負(fù)荷與速率常數(shù)間的關(guān)系,并建立濕地除磷模型構(gòu)建式。為濕地除磷模型的選擇、模型參數(shù)的完善和濕地系統(tǒng)的優(yōu)化設(shè)計(jì)提供理論依據(jù)。
1.1試驗(yàn)材料與方法
試驗(yàn)于東南大學(xué)無(wú)錫太湖水環(huán)境工程研究中心實(shí)驗(yàn)室進(jìn)行。試驗(yàn)裝置(圖1)由6組平行的水平潛流人工濕地單元構(gòu)成,其中3組為景觀(guān)型濕地,分別種植美人蕉(canna)、再力花(thalia dealbata)和常綠鳶尾(iris tectorum),另外3組為蔬菜型濕地,分別種植空心菜(water spinach)、茭白(zizania)和番茄(tomato)。景觀(guān)型濕地栽植密度為20株·m-2,蔬菜型濕地栽植密度為26 株·m-2,試驗(yàn)期間植物長(zhǎng)勢(shì)良好。單元尺寸:長(zhǎng)L=2.0 m;寬B=0.30 m;高H=0.6 m;長(zhǎng)寬比=6.67;水深H=0.40 m;基質(zhì)高度=0.45 m;單元表面積=0.60 m2,單元長(zhǎng)度方向上間隔0.5 m設(shè)置一取樣口。單元內(nèi)折流板構(gòu)造形式:水流下行板距池底15 cm,水流上行板距基質(zhì)表面15 cm。單元床體內(nèi)由下至上填料配置:10 cm粗礫石(粒徑30~50 mm),25cm陶粒(粒徑10~15 mm),10 cm細(xì)礫石(粒徑10~20 mm)?;|(zhì)平均孔隙率約40%。
圖1 水平潛流人工濕地裝置示意圖(標(biāo)高單位:米)Fig.1 Schematic representation of horizontal subsurface flow wetlands(unit: m)
開(kāi)展本試驗(yàn)之前,各組濕地已穩(wěn)定運(yùn)行1年,濕地微生態(tài)系統(tǒng)趨于穩(wěn)定。系統(tǒng)進(jìn)水為經(jīng)水解池+好氧接觸氧化池處理后的宿舍區(qū)生活污水,進(jìn)水水質(zhì)見(jiàn)表1。控制濕地進(jìn)水水力負(fù)荷于0.18~0.30 m3·m-2·d-1間,進(jìn)行濕地除磷性能研究及動(dòng)力學(xué)模型研究。
表1 R濕地進(jìn)水水質(zhì)Table 1 Influent quality of wetlands
2014年8月~11月期間,每次取樣時(shí)間間隔為3 d,每個(gè)單元的取樣點(diǎn):進(jìn)水、出水及長(zhǎng)度方向上的3個(gè)中間取樣點(diǎn)(0.5 m,1.0 m,1.5 m)。測(cè)試指標(biāo)包括:水溫、pH、ORP和總磷(TP)等。
1.2除磷動(dòng)力學(xué)模型
采用兩種方法描述濕地除磷動(dòng)力學(xué),一是假定濕地除磷遵循一級(jí)反應(yīng)動(dòng)力學(xué),二是假定濕地除磷遵循Monod反應(yīng)動(dòng)力學(xué)。在濕地動(dòng)力學(xué)模型中,一級(jí)動(dòng)力學(xué)模型是應(yīng)用最廣泛的模型。對(duì)于Monod模型,Saeed等[22]指出Monod模型可用于構(gòu)造更真實(shí)的濕地預(yù)測(cè)模型,McNevin等[18]提倡將Monod模型用于濕地的設(shè)計(jì)。
水平潛流濕地系統(tǒng)中,污水主要以水平流動(dòng)方式流經(jīng)基質(zhì)。Sun等[23]通過(guò)對(duì)比平推流和完全混合流兩種假設(shè)下的水平潛流濕地模擬結(jié)果,指出平推流更符合實(shí)際結(jié)果。本文將試驗(yàn)濕地單元內(nèi)的水流流態(tài)視為理想推流。
研究表明,考慮污染物背景濃度C?可增強(qiáng)動(dòng)力學(xué)模型預(yù)測(cè)的準(zhǔn)確性。對(duì)磷而言,C?接近于零值[19]。本文中C?取0 mg·L-1。
1.2.1基于推流的一級(jí)動(dòng)力學(xué)模型理想推流一級(jí)動(dòng)力學(xué)模型(考慮C?)-KC?模型式如下
式中,Cout為出水TP濃度,mg·L-1;Cin為進(jìn)水TP濃度,mg·L-1;C?為T(mén)P背景濃度,0 mg·L-1;K為一級(jí)反應(yīng)速率常數(shù),d-1;t為水力停留時(shí)間,d。
一級(jí)反應(yīng)速率常數(shù)公式
1.2.2基于推流的Monod模型Monod模型式如下
式中,Cout為出水TP濃度,mg·L-1;Chalf為T(mén)P半飽和速率常數(shù),mg·L-1,取0.2 mg·L-1[24];Kmax為T(mén)P最大體積去除速率常數(shù),g·m-3·d-1。
基于理想推流,式(3)在邊界條件下t=0( C=Cin;t=t,C=Cout)的積分形式
由式(4)得,最大體積去除速率常數(shù)公式
K和Kmax的求解滿(mǎn)足誤差平方和最小(誤差=出水測(cè)量值-出水預(yù)測(cè)值)。
Tanner等[25]提出了Arrhenius方程,用以表示溫度對(duì)反應(yīng)速率常數(shù)的影響,公式如下
式(6)等價(jià)線(xiàn)性公式
式中,KT為T(mén)(℃)下的反應(yīng)速率常數(shù),d-1;K20為20℃下的反應(yīng)速率常數(shù),d-1;?為量綱1溫度系數(shù);T為水溫,℃。式(7)的斜率與截距用以計(jì)算式(6)的參數(shù)。
模型預(yù)測(cè)的準(zhǔn)確性通過(guò)模型效率(ME)比較,ME反映實(shí)測(cè)值與預(yù)測(cè)值間的整體偏差。ME數(shù)值范圍-∞~1,數(shù)值越高表明預(yù)測(cè)值與實(shí)測(cè)值間越接近,ME公式
2.1景觀(guān)型和蔬菜型濕地的除磷效率
景觀(guān)型濕地TP平均面積去除率順序:美人蕉單元0.286 g·m-2·d-1>再力花單元0.270 g·m-2·d-1>常綠鳶尾單元0.177 g·m-2·d-1。蔬菜型濕地:空心菜單元0.265 g·m-2·d-1>茭白單元0.221 g·m-2·d-1>番茄單元0.165 g·m-2·d-1。6組單元順序?yàn)槊廊私秵卧驹倭▎卧究招牟藛卧拒讍卧境>G鳶尾單元>番茄單元。試驗(yàn)濕地未填加強(qiáng)化除磷基質(zhì),植物與微生物的耦合作用是濕地除磷的主要途徑之一[26]。有研究指出,不同植物的除磷效果差異較大[27-28]。本試驗(yàn)濕地除磷效果的差異歸因于植物種類(lèi)的區(qū)別,美人蕉、再力花和空心菜濕地較大的植物生物量獲得了較好除磷效果。Jing等[9]通過(guò)對(duì)不同植物類(lèi)型潛流濕地的研究,指出茭白、蘆葦和千屈菜濕地TP平均面積去除率分別為0.253、0.297和0.248 g·m-2·d-1。
圖2 不同月份的濕地TP面積去除率Fig.2 Monthly changes of areal removal efficiency of TP in different wetland units [mass-removal rate=(Cin-Cout)Q/A,where Q is influent flow, A is wetland area]
表2 R景觀(guān)型和蔬菜型濕地除磷速率常數(shù)及METable 2 Reaction coefficient values of landscape type and vegetable type wetlands , and ME
不同月份TP面積去除率存有差異(圖2)。8月~11月間,6組單元總體表現(xiàn)為8月面積去除率最大,隨著溫度降低,面積去除率逐漸減小,在11月份出現(xiàn)最低值。植物同化磷存有季節(jié)差異,與植物的生長(zhǎng)周期性相關(guān)[29-30]。張巖等[31-32]指出水平潛流濕地的TP面積去除率隨月份(溫度)變化。
2.2濕地除磷動(dòng)力學(xué)分析
由表2得,水力負(fù)荷0.24 m3·m-2·d-1條件下,景觀(guān)型和蔬菜型濕地單元K、Kmax值順序結(jié)果與2.1節(jié)中一致。表2中,K值范圍:0.83~1.87 d-1,Kmax值范圍:1.20~2.07 g·m-3·d-1。Ngo等[33]指出,潛流濕地TP一級(jí)面積速率常數(shù)k為0.112~0.230 m·d-1,本試驗(yàn)結(jié)果為0.133~0.299 m·d-1。
除番茄單元外,Monod模型ME值(0.760~ 0.860)均較一級(jí)動(dòng)力學(xué)模型ME值(0.530~0.718)更接近1,Monod模型在預(yù)測(cè)試驗(yàn)濕地出水TP濃度上具有更高的準(zhǔn)確性。下文中,溫度和水力負(fù)荷對(duì)除磷速率常數(shù)的影響分析均以Monod 模型為基礎(chǔ)。
2.3Kmax隨水溫變化特征
圖3和表3中R2(0.625~0.904)結(jié)果表明,以Arrhenius方程擬合溫度與Kmax間關(guān)系是適宜的。表3中?結(jié)果指出,6組單元Kmax隨水溫的降低而減小,歸因于植物吸收磷存有季節(jié)差異[29],6種試驗(yàn)植物在低溫下磷吸收速率降低。其中,美人蕉(?=1.006)、再力花(?=1.008)和空心菜(?=1.006)單元Kmax受水溫影響不敏感,水溫對(duì)鳶尾(?=1.015)和茭白(?=1.014)單元的Kmax存在較大影響。
2.4水力負(fù)荷對(duì)Kmax20的影響
水力負(fù)荷(q)控制為0.18,0.24和0.30 m3·m-2·d-1。Kmax20依據(jù)2.3節(jié)中Arrhenius方程計(jì)算。圖4表明,Kmax20與q間存有明顯正相關(guān)性,Kmax20隨q值增大而增大,與Kadlec[19]和Rousseau等[12]的研究發(fā)現(xiàn)一致。需指出,Kmax20隨q值變化有否閾值及閾值的大小需進(jìn)一步研究。
圖3 Arrhenius方程擬合水溫與Kmax的關(guān)系Fig.3 Dependence of Kmaxon water temperature, and evaluation of Arrhenius-type equations for facilities(a) canna; (b) thalia dealbata; (c) iris tectorum; (d) water spinach; (e) zizania; (f) tomato
表3 RArrhenius方程擬合結(jié)果Table 3 Results of Arrhenius-type equations
選取乘冪方程[19]和指數(shù)方程[17]擬合Kmax20與q間關(guān)系,利用乘冪回歸與指數(shù)回歸獲得最適方程參數(shù)
式中,q為水力負(fù)荷,m3·m-2·d-1;m和n為量綱1負(fù)荷系數(shù)。
乘冪回歸擬合結(jié)果[式(11)、式(12)分別對(duì)應(yīng)再力花和空心菜濕地]
指數(shù)回歸擬合結(jié)果[式(13)、式(14)分別對(duì)應(yīng)再力花和空心菜濕地]
其中,乘冪方程(R2:0.657;0.805)較指數(shù)方程(R2:0.639;0.787)的相關(guān)性更高。
2.5Monod模型構(gòu)建式
基于2.3和2.4節(jié),Kmax是溫度的函數(shù),符合Arrhenius方程,同時(shí)Kmax20與水力負(fù)荷相關(guān)。結(jié)合式(3)、式(6)和式(9)構(gòu)建式(15)
圖4 Kmax20與水力負(fù)荷間的關(guān)系Fig.4 Relations for dependence of Kmax20on hydraulic loading(a)thalia dealbata unit; (b) water spinach unit
式中,H為濕地內(nèi)水深,m;ε為基質(zhì)孔隙率,%。式(15)用于水力負(fù)荷已知時(shí)的出水濃度預(yù)測(cè),或出水濃度限制值下的水力負(fù)荷計(jì)算。
Monod模型構(gòu)建式[式(16)、式(17)分別對(duì)應(yīng)再力花和空心菜濕地]
表4 RMonod模型構(gòu)建式預(yù)測(cè)結(jié)果Table 4 Prediction results of constructed Monod models
(1)景觀(guān)型濕地除磷能力順序?yàn)槊廊私秵卧娣e去除率:0.286 g·m-2·d-1;Kmax20:2.083 g·m-3·d-1)>再力花單元(0.270 g·m-2·d-1;1.972 g·m-3·d-1)>鳶尾單元(0.177 g·m-2·d-1;1.283 g·m-3·d-1)。蔬菜型濕地:空心菜單元(0.265 g·m-2·d-1;2.042 g·m-3·d-1)>茭白單元(0.221 g·m-2·d-1;1.659 g·m-3·d-1)>番茄單元(0.165 g·m-2·d-1;1.209 g·m-3·d-1)。美人蕉、再力花、空心菜和茭白單元具備較強(qiáng)的除磷能力。
(2)除番茄單元外,Monod模型ME值(0.760~0.860)均較一級(jí)動(dòng)力學(xué)模型ME值(0.530~0.718)更趨近1。Monod模型對(duì)試驗(yàn)濕地除磷效果的預(yù)測(cè)具備更高的準(zhǔn)確性。
(3)8月~11月間,濕地TP面積去除率隨溫度下降而降低。Arrhenius擬合結(jié)果指出,美人蕉(?=1.006)、再力花(?=1.008)和空心菜(?=1.006)單元Kmax受水溫影響不敏感,水溫對(duì)鳶尾(?=1.015)和茭白(?=1.014)單元除磷有較大影響。Kmax20隨水力負(fù)荷的提高而增大。較指數(shù)方程(R2:0.639;0.787),乘冪方程(R2:0.657;0.805)對(duì)Kmax20與水力負(fù)荷關(guān)系的擬合度更高。Monod模型構(gòu)建式可提升模型的準(zhǔn)確性和適用性。
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Kinetic modelling of total phosphorus removal in landscape type and vegetable type horizontal subsurface-flow constructed wetlands
YIN Zhiping, WU Yifeng, Lü Xiwu
(School of Energy & Environment, Southeast University, Nanjing 210096, Jiangsu, China)
The studies on total phosphorus (TP) removal in landscape type and vegetable type horizontal subsurface flow wetlands were conducted. The raw water was domestic sewage which has been treated by biochemical treatment processes. The TP removal efficiency of different wetland units were compared and analysed. To optimize the design of wetlands, the first order reaction kinetics model and the Monod model were used to simulate the TP removal results and their accuracy were compared. Meanwhile, the relationship between water temperature, hydraulic loading rate (q) and the reaction coefficients were discussed. The results showed that in landscape type wetlands, the order of TP removal capacity was canna unit>thalia dealbata unit>iris tectorum unit, while it was water spinach unit>zizania unit>tomato unit in vegetable type wetland units, which was attributed to the biomass difference of different plants. The comparative evaluation between the first order kinetics model (ME: 0.53—0.72) and the Monod model (ME: 0.76—0.86) showed that the Monod model had higher accuracy in predicting the TP removal results. Decreased values of areal removal efficiency of TP were observed at lower water temperature. The Kmaxof canna (?=1.006), thalia dealbata (?=1.008) and water spinach units(?=1.006) were insensitive to the change of water temperature. The water temperature had a great influence on TP removal efficiency of iris tectorum (?=1.015) and zizania (?=1.014) units. The increased values of Kmax20were observed at higher q values. The power equations (R2: 0.657; 0.805) can well reflected the relationship between Kmax20and q. The constructed Monod model, which had considered the influence of water temperature and q on Kmax, gave a certain accuracy in predicting TP removal of experimental wetlands.
date: 2015-09-14.
WU Yifeng, shinfun@seu.edu.cn
supported by the National Science and Technology Support Program (2013BAJ10B13).
landscape type, vegetable type horizontal subsurface flow wetlands; total phosphorus; kinetic model; constructed Monod model; optimal design
X 171
A
0438—1157(2016)05—2048—08
2015-09-14收到初稿,2015-11-10收到修改稿。
聯(lián)系人:吳義鋒。第一作者:殷志平(1991—),男,碩士研究生。
國(guó)家科技支撐項(xiàng)目(2013BAJ10B13)。