郭曉婭，年躍剛*，閆海紅,3，殷勤,3，高鵬，陳光偉

1.環(huán)境基準(zhǔn)與風(fēng)險(xiǎn)評(píng)估國(guó)家重點(diǎn)實(shí)驗(yàn)室，中國(guó)環(huán)境科學(xué)研究院，北京 100012 2.中國(guó)環(huán)境科學(xué)研究院水污染控制技術(shù)研究中心，北京 100012 3.北京師范大學(xué)水科學(xué)研究院，北京 100875 4.中藍(lán)連海設(shè)計(jì)研究院，上海 201204 5.中糧生化能源(公主嶺)有限公司，吉林 四平 136100

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玉米淀粉廢水強(qiáng)化混凝與反硝化脫氮除磷技術(shù)研究

郭曉婭1,2，年躍剛1,2*，閆海紅1,2,3，殷勤1,2,3，高鵬4，陳光偉5

1.環(huán)境基準(zhǔn)與風(fēng)險(xiǎn)評(píng)估國(guó)家重點(diǎn)實(shí)驗(yàn)室，中國(guó)環(huán)境科學(xué)研究院，北京 100012 2.中國(guó)環(huán)境科學(xué)研究院水污染控制技術(shù)研究中心，北京 100012 3.北京師范大學(xué)水科學(xué)研究院，北京 100875 4.中藍(lán)連海設(shè)計(jì)研究院，上海 201204 5.中糧生化能源(公主嶺)有限公司，吉林 四平 136100

針對(duì)現(xiàn)行玉米淀粉廢水處理工藝出水氮、磷易超標(biāo)的問(wèn)題，提出2種提高脫氮除磷潛能的解決方案：在預(yù)處理階段設(shè)置混凝工藝強(qiáng)化去除部分污染物；在反硝化階段引入部分豎流沉淀池(初沉池)出水作為補(bǔ)充碳源。通過(guò)設(shè)計(jì)單因素混凝試驗(yàn)，對(duì)比氯化鐵、硫酸鋁、殼聚糖、海藻酸鈉4種絮凝劑對(duì)污染物的去除效果。結(jié)果表明：氯化鐵較適合作玉米淀粉廢水處理絮凝劑，當(dāng)氯化鐵投加量為0.40 gL，pH為4，溫度為35 ℃時(shí)，TP、SS、TN和CODCr的去除率分別為93.5%、94.8%、10.8%和10.7%。采用序批式反應(yīng)器，研究了以淀粉廢水處理過(guò)程中的初沉池出水作為反硝化碳源的污染物降解特性與動(dòng)力學(xué)特性；分別采用基于Monod方程的微分方程模型和分段零級(jí)反應(yīng)動(dòng)力學(xué)模型擬合試驗(yàn)數(shù)據(jù)。結(jié)果表明：反硝化過(guò)程中存在-N積累現(xiàn)象，-N最大積累率為61%；采用基于Monod方程的微分方程模型，能夠很好地?cái)M合水解酸化段廢水作為碳源的反硝化過(guò)程中-N以及-N與-N當(dāng)量總和)濃度的變化趨勢(shì)，-N以及的最大降解速率分別為24.21、12.78和15.97 mg(g·h)(以MLVSS計(jì))；分段零級(jí)動(dòng)力學(xué)模型能較好擬合-N濃度隨時(shí)間的變化趨勢(shì)，階段1和階段2的反硝化速率分別為16.09和8.71 mg(g·h)(以MLVSS計(jì))。

玉米淀粉廢水；混凝；反硝化碳源；動(dòng)力學(xué)模型

目前關(guān)于淀粉廢水的預(yù)處理技術(shù)包括泡沫分離法[2]、酸沉法[3]、絮凝法[4]等，主要以回收廢水中的蛋白質(zhì)為主，而以除磷為目的研究較少，因?yàn)樵陬A(yù)處理階段進(jìn)行化學(xué)除磷成本較高，且易引起生物處理磷元素的缺失。針對(duì)外加碳源，國(guó)內(nèi)外研究者多以降低脫氮成本，資源化利用廢物為主要研究方向，開(kāi)發(fā)了多種新型外加碳源，如厭氧產(chǎn)酸發(fā)酵液[5-6]、天然或人工緩釋碳源[7-8]、高濃度有機(jī)廢水[9-10]等。玉米淀粉廢水的主要成分為淀粉和蛋白質(zhì)，廢水的CODCr為8 000～30 000 mgL，BOD5為5 000～20 000 mgL，其本身屬于可生化的高濃度有機(jī)廢水，如能將預(yù)處理過(guò)程中的部分廢水作為其脫氮工藝的外加碳源，不僅能夠提高脫氮工藝的碳氮比，也能減輕來(lái)水水質(zhì)對(duì)生物處理的壓力，同時(shí)為混凝處理后的廢水提供部分磷元素，可極大地降低廢水的處理成本。

1 材料與方法

1.1 混凝試驗(yàn)廢水來(lái)源及試驗(yàn)方法

廢水取自吉林省某大型玉米深加工企業(yè)，該企業(yè)廢水處理系統(tǒng)采用豎流沉淀預(yù)處理水解酸化EGSBAO工藝。取豎流沉淀池(初沉池)出水作為混凝試驗(yàn)用水，由于該企業(yè)廢水水質(zhì)不穩(wěn)定，為比較不同絮凝劑的混凝效果，采用12組水質(zhì)較為相近的廢水進(jìn)行試驗(yàn)。混凝試驗(yàn)用水水質(zhì)如表1所示。試驗(yàn)所用絮凝劑為殼聚糖、硫酸鋁、氯化鐵、海藻酸鈉，試劑均購(gòu)自國(guó)藥集團(tuán)化學(xué)試劑有限公司。

表1 混凝試驗(yàn)用水水質(zhì)

Table 1 Water quality of coagulation experiments mgL

Table 1 Water quality of coagulation experiments mgL

CODCrSS濃度TN濃度TP濃度pH6881～7428246～290329～38988～10336～39

注：pH無(wú)單位。

水樣加酸堿調(diào)整pH，取6個(gè)1 L燒杯，分別放入同水質(zhì)的淀粉廢水1 L，投加一定量的絮凝劑，置于六聯(lián)攪拌機(jī)上，快速攪拌1 min(轉(zhuǎn)速為250 rmin)，慢速攪拌20 min(轉(zhuǎn)速40 rmin)，靜置沉淀30 min，取表面1～2 cm處上清液測(cè)定混凝效果。

1.2 反硝化脫氮試驗(yàn)碳源與污泥來(lái)源及試驗(yàn)方法

碳源為該企業(yè)豎流沉淀池出水，該次試驗(yàn)水質(zhì)指標(biāo)：CODCr為12 234 mgL；TN濃度為531 mgL；TP濃度為161 mgL；濃度為24 mgL；濃度為2.3 mgL；濃度為4.9 mgL；pH為3.98。接種污泥為二沉池濃縮污泥[11]。

反應(yīng)器為柱狀有機(jī)玻璃反應(yīng)器，有效容積為7 L(圖1)。以廢水作為反硝化碳源，對(duì)污泥進(jìn)行馴化，得到穩(wěn)定的反硝化脫氮系統(tǒng)。取出部分活性污泥，用超純水淘洗3次并曝氣30 min，使污泥處于內(nèi)源呼吸階段。根據(jù)正交試驗(yàn)設(shè)計(jì)進(jìn)行批式試驗(yàn)：分別向9個(gè)250 mL錐形瓶?jī)?nèi)加入不同體積的廢水碳源、150 mL活性污泥和50 mL自配水，再加入自來(lái)水補(bǔ)足至250 mL。通過(guò)1 molL的NaOH和HCl調(diào)節(jié)廢水pH，用封口膜將錐形瓶密封，以消除外界環(huán)境因素對(duì)反硝化作用的影響。自配水配置方法：將一定量的硝酸鉀、磷酸二氫鉀加入自來(lái)水中，控制各錐形瓶硝態(tài)氮濃度約為100 mgL，磷酸鹽及其他微量元素充足。

1—pH計(jì)電極；2—恒溫加熱棒；3—機(jī)械攪拌棒；4—取樣口及排水口；5—反應(yīng)器。圖1 試驗(yàn)裝置Fig.1 The schematic diagram of experimental setup

1.3 試驗(yàn)儀器

主要試驗(yàn)儀器包括ZR-6型混凝試驗(yàn)攪拌機(jī)(深圳中潤(rùn))；CTL-12型化學(xué)需氧量速測(cè)儀(承德華通)；UV-2100紫外可見(jiàn)分光光度計(jì)(上海尤尼柯)；ICS-1000離子色譜儀(美國(guó)戴安)；FG2便攜式pH計(jì)(瑞士梅特勒)。

1.4 分析方法

1.5 數(shù)據(jù)處理

根據(jù)硝酸鹽還原電子傳遞體系當(dāng)量關(guān)系，將每1 g亞硝酸鹽還原為氮?dú)馑璧碾娮赢?dāng)量與將0.6 g硝酸鹽氮還原為氮?dú)馑璧碾娮赢?dāng)量相同，采用硝酸鹽和亞硝酸鹽當(dāng)量總和表征比反硝化速率[13]：

(1)

(2)

(3)

(4)

(5)

當(dāng)碳源充足且硝酸鹽濃度比較高時(shí)，比反硝化速率只與反硝化菌的活性和數(shù)量有關(guān)，與硝酸鹽氮的濃度無(wú)關(guān)，反硝化過(guò)程呈零級(jí)反應(yīng)動(dòng)力學(xué)[17]，反硝化速率可表示為：

vd=ΔCcor(Δt×X)

式中：vd為反硝化速率，mg(mg·d)；t為時(shí)間，d。

2 結(jié)果與分析

2.1 混凝試驗(yàn)及其結(jié)果分析

影響混凝效果的因素有投加量、轉(zhuǎn)速、pH、溫度等，綜合考慮各影響因素對(duì)工程運(yùn)行的影響，選取絮凝劑投加量、pH以及溫度3種因素進(jìn)行單因素試驗(yàn)，對(duì)比分析氯化鐵、硫酸鋁、海藻酸鈉和殼聚糖4種絮凝劑對(duì)污染物尤其是TP和SS的去除效果。試驗(yàn)設(shè)計(jì)如表2所示。

表2 混凝單因素試驗(yàn)設(shè)計(jì)Table 2 Design table of single factor experiments of coagulation

4種絮凝劑最佳混凝效果及去除成本如表3所示。從表3可以看出，氯化鐵和硫酸鋁除TP和SS效果顯著，考慮到原水的pH(3.5～3.9)和溫度(30～35 ℃)，認(rèn)為氯化鐵絮凝劑較適宜，且有市售的氯化鐵水溶液，省去了企業(yè)增設(shè)溶藥池等問(wèn)題，因此建議使用氯化鐵作為玉米淀粉廢水的絮凝劑。吳昊等[18]研究了不同絮凝劑對(duì)淀粉廢水生化處理出水中TP的去除效果表明，4種絮凝劑中氯化鐵的除磷效果最佳，但由于處理后出水pH呈酸性，達(dá)不到國(guó)家排放標(biāo)準(zhǔn)要求，需和氯化鈣聯(lián)合使用。將氯化鐵絮凝劑置于預(yù)處理階段既可以避免此類(lèi)問(wèn)題的發(fā)生，同時(shí)也可以緩解反應(yīng)器管道堵塞問(wèn)題。

表3 4種絮凝劑最佳混凝效果及成本Table 3 The best coagulation effects and costs of 4 kinds of flocculants

2.2 以初沉池出水為碳源的正交試驗(yàn)設(shè)計(jì)及直觀分析表

表4 因素水平表Table 4 Experimental conditions

表5 極差直觀分析Table 5 Intuitionistic range analysis

注：K1，K2，K3為不同影響因子在不同水平下硝態(tài)氮去除率和的平均值；R為極差，表明各因子對(duì)結(jié)果的影響程度。

由表5可知，以淀粉廢水處理過(guò)程中的初沉池出水作為碳源可獲得較高的脫氮率。其中，溫度為反硝化過(guò)程的顯著影響因子，各因子對(duì)硝態(tài)氮去除率的影響程度為：溫度>pH>CN。最優(yōu)反應(yīng)條件：溫度為40 ℃，pH為7，CN為9。同時(shí)試驗(yàn)發(fā)現(xiàn)，系統(tǒng)在20 ℃可發(fā)生明顯的-N積累現(xiàn)象。

2.3 反硝化過(guò)程中氮濃度變化規(guī)律

在正交最優(yōu)操作條件下，設(shè)定反應(yīng)器溫度為40 ℃，pH為7，CN為9，設(shè)計(jì)以初沉池出水為碳源和以乙酸鈉為碳源作為對(duì)照的2個(gè)系統(tǒng)，獲取反硝化反應(yīng)周期內(nèi)氮濃度的變化，如圖2所示。由圖2可知，硝態(tài)氮降解過(guò)程呈明顯的階段變化(階段Ⅰ、Ⅱ、Ⅲ)。以初沉池出水為碳源的反硝化過(guò)程在前60-N濃度呈直線下降，去除率為-N逐步積累至最高點(diǎn)；60 min后，系統(tǒng)內(nèi)主要進(jìn)行以-N為電子受體的反硝化，-N濃度逐漸降低。-N濃度在整個(gè)反應(yīng)過(guò)程中呈逐漸下降趨勢(shì)。以乙酸鈉為碳源的反硝化過(guò)程在前40 min對(duì)-N的去除率達(dá)到98.59%。隨著反硝化反應(yīng)的進(jìn)行，2個(gè)系統(tǒng)內(nèi)pH不斷上升，均出現(xiàn)折點(diǎn)A和折點(diǎn)B。折點(diǎn)A恰好與-N濃度接近零)及-N濃度的峰值)同時(shí)出現(xiàn)；折點(diǎn)B與+0.6-N濃度轉(zhuǎn)折點(diǎn))同時(shí)出現(xiàn)，指示反硝化的結(jié)束。其與王少坡等[19-21]的試驗(yàn)結(jié)果相同，因此可根據(jù)pH的變化判斷反硝化進(jìn)行的程度。

注：A和B為pH變化轉(zhuǎn)折點(diǎn)；C、D、E為硝態(tài)氮濃度變化轉(zhuǎn)折點(diǎn)。圖2 2種反硝化碳源氮濃度的變化Fig.2 Variation of nitrogen concentration with two kinds of denitrification carbon sources

圖3 Monod動(dòng)態(tài)模型擬合Fig.3 Simulation of nitrogen compounds by Monod model

2.4 Monod動(dòng)態(tài)模型擬合

表6 反硝化過(guò)程動(dòng)態(tài)模型動(dòng)力學(xué)參數(shù)Table 6 The kinetic parameter values of denitrification process

注：KD為半飽和常數(shù)。

2.5 分段零級(jí)動(dòng)力學(xué)擬合

圖4 分段零級(jí)動(dòng)力學(xué)擬合Fig.4 Simulation of nitrogen compounds by piecewise zero-order kinetic model

從表7可以看出，分段零級(jí)反應(yīng)方程能夠較好

表7 反硝化碳源試驗(yàn)Ccor-時(shí)間擬合結(jié)果Table 7 Fitting results of Ccor against time with two denitrification carbon sources

從擬合優(yōu)度來(lái)看，利用分段零級(jí)反應(yīng)方程擬合數(shù)據(jù)的R2低于利用改進(jìn)的Monod方程擬合的R2，但同樣可以達(dá)到較高的擬合水平。Monod經(jīng)驗(yàn)方程適用于較廣的基質(zhì)濃度，已得到廣泛的驗(yàn)證和應(yīng)用，對(duì)于反硝化工藝的合理設(shè)計(jì)以及過(guò)程的正確控制具有重要意義，但Monod方程中的vmax只能獲知微生物利用碳源的最大降解速率。分段動(dòng)力學(xué)方程除簡(jiǎn)化了計(jì)算過(guò)程外，還可以觀察到反硝化速率隨時(shí)間的變化情況，能夠直觀地了解碳源性能及污染物隨時(shí)間的降解規(guī)律。

3 結(jié)論

(1)強(qiáng)化混凝預(yù)處理工藝可以去除部分污染物，減輕玉米淀粉廢水來(lái)水水質(zhì)對(duì)后續(xù)生物處理，尤其是對(duì)厭氧反應(yīng)器的影響，氯化鐵絮凝劑投加量為0.40 gL，pH為4，溫度為35 ℃時(shí)，TP、SS、TN、CODCr的去除率分別為93.5%、94.8%、10.8%和10.7%。

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Enhanced coagulation and nitrification for nitrogen and phosphorus removal from corn starch wastewater

GUO Xiaoya1,2, NIAN Yuegang1,2, YAN Haihong1,2,3, YIN Qin1,2,3, GAO Peng4, CHEN Guangwei5

1.State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences,Beijing 100012, China 2.Research Center of Water Pollution Control Technology, Chinese Research Academy of Environmental Sciences, Beijing 100012, China 3.College of Water Science, Beijing Normal University, Beijing 100875, China 4.China Bluestar Lehigh Engineering Corporation, Shanghai 201204, China 5.COFCO Bio-chemical Energy(Gongzhuling)Company Limited, Siping 136100, China

Considering the limit-exceeding problems of nitrogen and phosphorus in current cornstarch wastewater treatment, two solutions were put forward: one is to remove some pollutants by enhanced flocculation at the pretreatment stage; the other is to utilize the effluent of primary sedimentation tank as a carbon source for denitrification. The wastewater was treated by ferric chloride, aluminum sulfate, chitosan, and sodium alginate as flocculants, and optimum conditions were determined by single factor coagulation tests. The results showed that the ferric chloride was the suitable flocculant for treatment of cornstarch wastewater. When the dosing quantity of ferric chloride coagulant was 0.40 gL, pH was 4, temperature was 35 ℃, the removal rates of TP, SS, TN and CODCrwere 93.5%, 94.8%, 10.8% and 10.7%, respectively. The pollutant degradation characteristics and dynamic characteristics were studied by sequencing batch reactor with the effluent of primary sedimentation tank as the carbon source for denitrification, and Monod equation and piecewise zero-order kinetic model were used to fit the experimental data. The results showed that-N accumulation was found in the denitrification process, and the accumulation rate was 61%. The predicted values of simulation parameters using Monod equation fit well with the measured data, and the maximum degradation rates of-N and-N were 24.21, 12.78 and 15.97 mg(g MLVSS·h) respectively. The concentrations of-N was also fit well by piecewise zero-order kinetic model and the denitrification rates of stage 1 and 2 were 16.09 and 8.71 mg(g MLVSS·h) respectively.

cornstarch wastewater; coagulation; carbon source for denitrification; kinetic model

2016-03-21

國(guó)家水體污染控制與治理科技重大專(zhuān)項(xiàng)(2012ZX07202-009-01)

郭曉婭(1990—)，女，碩士研究生，主要從事水污染控制與資源化技術(shù)研究，xiaoyaguo1990@163.com

*責(zé)任作者：年躍剛(1963—)，男，研究員，博士，主要從事生態(tài)修復(fù)、中水回用技術(shù)研究，nianyg@craes.org.cn

X703

1674-991X(2017)01-0007-08

10.3969j.issn.1674-991X.2017.01.002