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外文資料 2009 International Conference on Energy and Environment Technology Study on Coagulation-Microfiltration Combination Process for Treating Luan River Water Liang Wang, Yueqi Zhu Department of Environmental Engineering Tianjin Polytechnic University Tianjin, China e-mail: mashi7822@163.com Abstract—Study on coagulation-microfiltration combination process for treatment of Luan river water was carried out. The experimental results showed that when the dosage of FeCl3 was 35mg/L, the removal of turbidity was above 95%, the organic matter was above 50%, and recovery of membrane flux reached 81% for the combination process. On the other hand, among the four coagulants (FeCl3, Polymeric Ferric Sulfate, Al2(SO4)3, Polymeric Aluminum Chloride) the iron-based coagulant is superior to Al-based coagulant not only in the removal of turbidity but also the organic matter, and the effect of coagulation was affected by pH. The results also suggested that coagulation could mitigate membrane fouling, and the influent water quality of MF membrane process which followed coagulation could be improved. Keywords-Coagulation; Membrane filtration; Membrane fouling I. INTRODUCTION With more and more serious pollution of water resources and implementation of the new Sanitary Standard for Drinking Water (GB 5749-2006) in China, conventional treatment process (e.g. coagulation-sedimentation-sand filtration- disinfection) which most existing water plants adopt could not provide satisfied drinking water[1]. In recent years, Membrane Technology has been widely applied in water treatment for its prominent advantages, such as higher separation efficiency, more stable and reliable effluent water quality, shorter processes, and small occupation area, etc. Therefore, Membrane Technology has been considered as an important guarantee for the safety of drinking water at present. Nowadays microfiltration (MF) and ultrafiltration (UF) processes are main application techniques in water plants, but their removal ability of dissolved organic matter (DOM) are very poor (only about 5%~10%) because the diameter of DOM in water is much smaller than the pore size of micro-filtration membrane or ultra-filtration membrane. So combined processes of enhanced coagulation, granular activated carbon (GAC) adsorption or photochemical oxidation with MF (or UF) were considered to be effective technologies to remove DOM in water [2]. Moreover, many studies have demonstrated that removal of DOM could be improved and membrane fouling could be alleviated when coagulation was used as pretreatment of membrane filtration process [3]. The objective of this study was to discuss the influence of different coagulants and dosing methods on removal efficiency of DOM and the influence of coagulation on membrane flux for combined process of coagulation-MF in treatment of Luan River water. II. MATERIAL AND METHOD Experimental Methods At first, raw water was pumped into a coagulation reactor where coagulant was dosed and the water was agitated with blender. Then two types of water samples were taken from the reactor, one was supernatant from coagulation-sedimentation followed by membrane filtration, another was mixed liquor from the coagulation reactor followed by membrane filtration. MF membrane used in the experiment was PVDF hollow fiber membrane with film holes diameter 0.22μm, and fiber inside and outside diameter were 0.6mm and 1.0mm respectively, provided by MOTIANMO Company of Tianjin Polytechnic University. Self-made membrane module in U pattern, with length 40cm, 20 pieces and membrane surface in one set. III. SELECTION OF COAGULANTS A. The influence of different coagulants on removal effect of pollutants Four coagulants were considered in the experiment: ferric chloride (FeCl3), Polymeric Ferric Sulfate (PFS), aluminum sulfate (Al2(SO4)3) and Polymeric Aluminum Chloride (PAC). The experimental design was as follows: FeCl3, PFS, Al2(SO4)3, and PAC were used as coagulants in beaker test, dosage of which were 20mg/L, 25mg/L, 30mg/L, 35mg/L,40mg/L and 45 mg/L respectively. Removal of turbidity, TOC and UV254 were used to evaluate coagulation performance. 1) The influence of coagulants under different dosing conditions on removal of turbidity It was showed that removal of turbidity increased with the increase of coagulants’ dosage, especially for aluminium coagulants. Among the four coagulants the best removal efficiency of turbidity was when PFS was added and the poorest removal of turbidity was obtained when Al2(SO4)3 was added. When the dosage was set at 45 mg/L, removal rate of turbidity for the four coagulants were separately 93.87% (PFS), 91.21% (FeCl3), 86.15% (PAC) and 82.9% (Al2(SO4)3). However, in view of efficiency disparities among them,due to the main aluminium species in aluminium coagulant solutions are monomeric species as well as polymeric species which make up of flocculating form with small in size. Exactly opposite, ferric coagulants in which the flocculation exists as iron hydroxides created with great density are effective for being precipitated faster, as well as a relatively high degree of polymerization 2~900 under critical pH of aluminium coagulant. PFS, on the other hand, are multi-hydroxyl- complexes, existed a class of intermediates produced by the hydrolysis-polymerization-precipitation process of ferric salts under a certain condition that can be good neutralization of the colloid charge and “bridge” adsorption of the particles, coarse flocculation with fast formation, large size and good sedimentation effect produced in it. So the conclusion is that ferric coagulants performed very well in water treatment for low turbidity and PFS has high removal efficiency for SS or turbidity. 2) The influence of different coagulants on removal of TOC The TOC removal of ferric coagulants were better than that of aluminum coagulants. When dosage of PFS and FeCl3 were both 45mg/L, TOC removal were separately 55.6% and 51.4%. Equally, adding both of them under the condition of 35mg/L, we can achieve the best outcome as 46.14% and 48.38%. On the other hand, there was a similar change for aluminium coagulants between TOC removal and turbidity removal. 3) The influence of different coagulants on removal of UV254 The results showed that removal of UV254 was approximately identical with removal of TOC, which indicated that there was a positive correlation between UV254 and to some extent TOC can be substituted by UV254 to represent NOM in water. B. The effect of pH on TOC removal This part is devoted to the distribution of TOC removal with variation of pH, a detailed arrangement is as follows:coagulant dosage is 35mg/L respectively and pH is 5.0, 6.0,6.5, 7.0, 7.5 and 8.0 respectively. It is shown that, pH 7.0 is the optimum of ferric coagulants as well as pH 6.5 for aluminium coagulants under the same dosage 35mg/L. This is possible because NOM (e.g humic acid) in Water is negatively charged under neutral condition, and hydrolyzates of metal salt coagulants have plenty of positive charge, so a neutralization reaction was occurred easily and quickly between them, forming the precipitates then. This result showed that a correct selection of pH can effectively decrease DOM in water [3]. C. Product water quality analysis of coagulation-MF process Raw water, mixed liquor of coagulation and supernatant of coagulation-sedimentation were separately filtrated by MF membrane to compare their removal effect of pollutants with a dosage of 35mg/L FeCl3. It was suggested that over 95% of removal for turbidity can be obtained when raw water was filtrated by MF membrane, but its removal of TOC and UV254 were only 6.82% and 15.56% respectively, which indicated that the removal ability of DOM in raw water for MF was very limited. That is to say, MF can not be considered as the main DOM-removing process because of colloid impurities in raw water, the major factor causing resistance in membrane filtration [4]. The study on adsorption-coexistence relationship between organic matters and clay impurities in the water, reported by CH Kim, found that organic matters in raw water captured by MF membrane, most of which are adsorbed by small colloidal particles of clay, and then removed with these particles. So organic matters captured strictly by MF membrane for only a tiny portion of total DOM, in addition, the removal rate of organic pollutants increased by 8~10%, comparing coagulation effluent water with membrane filtration ones. Consequently, strive to improve the removal efficiency of DOM in raw water, pre-coagulation with membrane filtration technology can be convinced. In that way, coagulation and adsorption act on processing together toward a better performance. D. The influence of coagulation on the filtration performance of membrane 1) Characterization of filtration performance of membrane Constant flux filtration was adopted in the experiment. With continuous running of MF, trans-membrane pressure (TMP) of MF increases gradually. In order to characterize the membrane flux decline rule with extension of running time and membrane flux recovery, analyses are computed between time and flux attenuation ratio, to state as a formula [5]: r-- Flux attenuation or recovery rate Jq(x)--Flux of fouled or washed membrane Jp(T)--Water flux T--Room temperature 2) The influence of coagulation pretreatment methods on membrane filtration performance Coagulation, coagulation-sedimentation and sand filtration were three types of pretreatment methods of MF in the experiment [6]. And filtrates of raw water, supernatant liquid of coagulation-sedimentation, mixed liquor of Coagulation and sand filtration effluent were compared (35mg/L FeCl3 was dosed for coagulation or coagulation-sedimentation pretreatment). A filtration cycle included membrane filtration 60mins and five-minute washing was set. The pressure of washing is 1.2 times greater than that of filtration. PVDF hollow fiber membrane and self-made membrane module in U pattern were adopted. The time-dependent curves of flux attenuation ratio were showed. After 5-cycles filtration, the membrane flux declined rapidly to 36%, and after washing its recovery rate arrived at 52% of the initial flux, which suggested that it was very easy to result in membrane fouling when raw water was directly filtrated. Compared with direct filtration, membrane flux can be obviously increased for other three pretreatment methods, and filtrating mixed liquor was the best, its recovery rate of membrane flux after washing can reach to 81% or more, and the effect of filtrating supernatant liquid was second. The greatest influence on retention of membrane flux was obtained when sand filtration effluent was filtrated. Therefore, the process of coagulation-sand filtration should not be considered as pretreatment of MF, and the others (coagulation pretreatment and coagulation-sedimentation pretreatment) can be chosen according actual situation. CONCLUSION 1) In general, the removal performance of pollutants for ferric coagulants was superior to that of aluminium coagulants in the process of Luan water coagulation treatment. The optimal dosage of ferric coagulants was determined to be 35mg/L combining experimental results and economic benefit. For aluminium coagulants PAC has a higher removal ability for pollutants than that of Al2(SO4)3 under the same conditions, which was associated with its own products of hydrolysis, and the conclusion also was consistent with the works of others. 2) from the experimental results it can be consluded that the optimal pH of raw water was 7.0 for ferric coagulants and 6.5 for aluminium coagulants with a dosage of 35mg/L. since dosing of ferric coagulants has a great influence on pH of water, the coagulation system still can reach the expected pH standard without additional adjustment under the condition of 35mg/L dosage. 3) Three effluent water qualities of UF membrane filtration: raw water, coagulated water and supernatant liquid are compared, which indicated that effluent turbidity of less than 0.2NTU can be guaranteed because of the excellent retention performance of MF membrane. But removal of dissolved organic pollutants was only 8%-15% after MF filtration, which was lower than that of traditional coagulation process. 4) Coagulation pretreatment can effectively alleviate membrane fouling [7, 8]. When FeCl3 coagulation with a dosage of 35mg/L was used to be pretreatment of MF filtration, 80% of membrane flux can be maintained after a filtration cycle, which suggested membrane fouling has been effectively alleviated. Among the three kinds of pretreatment methods, membrane fouling was most serious when MF membrane was used to filtrate sand filtration effluent, and the smallest membrane fouling was obtained when MF membrane was used to filtrate mixed liquor of coagulation. REFERENCES [1] J. P. Croue, “Isolation, fractionation, characterization and reactive properties of natural organic matter,” IWA Publishing, Greece, vol.2, pp. 126–129, September 2002. [2] S. Judd and B. Jefferson, “Membrane for Industrial Wastewater Recovery and Re-use,” Elsevier Science Ltd., Oxford, UK, vol.2, pp. 51–62, May 2003. [3] M. Clara, B. Strenn, E. Saracevic and N. Kreuzinger, “Feed–water pretreatment: methods to reduce membrane fouling by natural organic matter,” J. Aachen, Germany, vol.1, pp. 43–57, June 2004. [4] P. Songprasert, B.R. Lim and K.H. Ahn, “A model for membrane system in the treatment of wastewater containing high-molecular-weight compounds,” J. Am. Water Works Assoc., vol. 90, pp. 108–115, June 2001. [5] C. H. Kim, M. Hosomi and M. Okada, “Characteristics of fouling due to clay–organic substances in potable water treatment by ultrafiltration,” in Water Science and Technology, vol.38, pp. 243–250, October 2003. [6] C. Wallis-Lage, “Coagulation–Sedimentation Systems: similarities and difference between manufactures,” in Proceedings of WEF 76th Annual Conference and Exposition, Los Angeles, CA, October 2003. [7] B. Jefferson, A. Brookes and P. Le Clech, “Methods for understanding organic fouling in MBRs,” in Water Res., pp. 237–244, September 2004. [8] L. Defrance, M.Y. Jaffrin, “Reversibility of fouling formed in activated sludge filtration,” J. Membr. Sci.,vol.157, pp. 373–384, June 2002. 中文譯文 對灤河水質混凝微濾膜處理工藝的研究 Liang Wang, Yueqi Zhu 環(huán)境工程學系 天津工業(yè)大學 天津，中國 摘要：對灤河水處理的混凝微濾組合工藝進行了研究。實驗結果表明，當FeCl3的用量35mg/ L時，濁度去除率95％以上，有機質含量在50％以上，膜通量恢復達到81％。另一方面，四個混凝劑（氯化鐵，聚合硫酸鐵，硫酸鋁，聚合氯化鋁）鐵鹽混凝劑優(yōu)于鋁鹽混凝劑，不僅表現(xiàn)在除濁，而且在有機質，混凝效果和pH值影響方面。研究結果還表明，混凝可以減輕膜污染，還改善MF膜處理過程中進水水質。 關鍵詞：混凝，膜過濾，膜污染 一 導言 隨著越來越多的嚴重污染水資源和飲用水（國標5749-2006）新衛(wèi)生標準在中國的實施，其中大多數(shù)現(xiàn)有的自來水廠采用常規(guī)處理工藝（如混凝沉淀砂濾，消毒），已經(jīng)不能提供較滿意的飲用水為人們服務。[1]. 近年來，膜技術已廣泛應用于水的處理工藝，他具有更高的分離效率，更穩(wěn)定和可靠的出水水質，流程短，占地面積小等突出優(yōu)點。因此，膜技術處理工藝已被認為是目前飲用水水質安全的重要保證。 如今微濾（MF）和超濾（UF）工藝在自來水廠已經(jīng)開始應用，但他們對溶解有機物的去除能力（DOM）非常差（只有約5％?10％），因為在水中的DOM直徑比微濾膜或超濾膜孔徑小，因此，結合了強化混凝過程中顆?；钚蕴浚℅AC）吸附氧化或光化學與MF這些被認為是有效的技術，用來去除水中的DOM[2].。 此外，許多研究已經(jīng)表明，當混凝作為膜過濾工藝預處理采用時，去除DOM工藝可以改進，可以減輕膜污染[3] 這項研究的目的是討論不同混凝劑對去除效率的影響，及混凝對膜通量和DOM的影響，還有混凝-微膜處理組合工藝在處理灤河水時的可行性。 二 材料與方法 實驗方法 首先，將原水注入混凝反應器，加入一定量的混凝劑，并攪拌。然后，分別從反應器中取兩組液體，一組是經(jīng)過膜過濾的混凝后的上清液，另一組是經(jīng)過膜過濾的混凝反應器混合后的混合液。 MF膜實驗中所用的是膜孔直徑為0.22μm的聚偏氟乙烯中空纖維膜，光纖內(nèi)外徑分別為0.6mm和1.0mm，分別由天津工業(yè)大學MOTIANMO公司提供。自制的U型膜組件，長度為40厘米，20件，集于0.04平方米的膜表面。 三 混凝劑的選擇 A: 不同混凝劑對污染物去除效果的影響 試驗中采用的混凝劑有：三氯化鐵，聚合硫酸鐵，硫酸鋁，和聚合氯化鋁四種。實驗設計如下：三氯化鐵，聚合硫酸鐵，硫酸鋁，和PAC分別加入燒杯做混凝劑試驗，其中每種混凝劑分為六組，每組用量分別為20mg / L，25mg/ L，30mg/ L，35mg/ L，40mg / L，45 mg/ L。通過對TOC和UV254的檢測，確定水中混濁度，以評價各混凝劑的混凝性能。 1）不同加藥量條件下，混凝劑對濁度去除率的影響 結果顯示：渾濁度的去除率隨藥劑投加量的增加而增加。尤其是加入鋁鹽混凝劑的效果更為明顯。這四種混凝劑對濁度的去除效果最好的是隨著聚合硫酸鐵量增加而濁度減小時，加入硫酸鐵混凝劑。當混凝劑用量為45mg/ L時，四種混凝劑去除率分別為： 93.87％（聚合硫酸鐵），91.21％（三氯化鐵），86.15％（聚合氯化鋁）和82.9％（硫酸鋁）。但是，在它們之間的效率差距，不是由于鋁鹽混凝劑在聚合過程中形成了單體較小的絮凝體。恰好相反，其中絮凝在存在氫氧化鐵的混凝劑中沉淀較快，鋁鹽混凝劑只有當達到臨界PH值時達到較高的混凝效果。聚合硫酸鐵，另一方面，是多羥基化合物，存在膠體電荷，在一定條件下有良好的吸附作用，在鐵鹽類的水解聚合沉淀過程中產(chǎn)生中間體類粒子，快速形成較大的絮凝體，達到良好的絮凝沉淀效果。 所以結論是，鐵混凝劑的表現(xiàn)相當不錯，在低濁度水的處理中，聚合硫酸鐵對懸浮顆?；驖岫热コ矢?。 2）不同混凝劑對TOC去除率的影響 鐵鹽混凝劑對TOC的去除率均高于鋁鹽混凝劑。當聚合硫酸鐵和三氯化鐵用量均為45mg/ L時，TOC去除率分別為55.6％和51.4％。同樣條件下，當聚合硫酸鐵和三氯化鐵用量均為35mg/ L時，可達到最好的效果，去除率分別為46.14％和48.38％。另一方面， TOC去除率和濁度的去除率在加入鋁鹽混合劑時也有類似變化。 3）不同混凝劑對UV254去除率的影響 結果表明，混凝劑對UV254的去除率和TOC的去除率大約相同，這表明，有一些混凝劑對UV254與TOC的去除量可互相替代，在水中有機物去除程度呈正相關。 B： pH值對TOC去除效果的影響 TOC去除率隨pH變化的分布，詳細安排如下：混凝劑投加量為35mg/ L時，pH值分別為5.0，6.0, 6.5，7.0，7.5和8.0。 結果表明，當混凝劑的用量均為35mg/ L時， pH值為7.0，鐵鹽混凝劑效果最佳；pH值為6.5時，鋁鹽混凝劑效果最佳。這種情況是可能的，因為天然有機物（如腐殖酸）在水中性條件下是帶負電荷的，金屬鹽類混凝劑的水解產(chǎn)物帶有大量的正電荷，所以發(fā)生中和反應，然后，它們之間快速聚合，形成沉淀物。這一結果表明，pH值的正確的選擇可以有效地降低水中的DOM[3]。 C.產(chǎn)品水混凝微濾過程的質量分析 原水，混合液的上清液分別采用微濾過濾膜過濾，比較三氯化鐵混凝劑投加量為35mg/ L時對污染物的去除效果。 結果顯示，當使用微濾膜過濾時，原水濁度的去除率可超過95％，但是，其對TOC和UV254的去除率分別只有6.82％和15.56％，這表明，用微濾膜過濾時，對原水中DOM的去除率非常有限。這就是說，微濾過濾膜對水中DOM的去除起關鍵性作用。主要原因是去除原水膠體雜質的過程中對膜造成了很大的過濾阻力[4]。 粘土中有機質和雜質在水中的吸附共存關系的研究，CH報告發(fā)現(xiàn)，被微濾膜攔截的原水有機物，其中大部分是較小的粘土吸附膠體顆粒，并隨著移動。 因此，嚴格的說，微濾過濾膜只攔截了一小部分DOM.此外，原水混凝后再過濾，有機污染物的去除率比之增加了8?10％。 因此，努力改善原水DOM的去除效率，需要預先混凝再過濾才能更有效。這樣一來，只有絮凝和吸附共同使用，才能達到更高的去除率，得到較好的水質。 D. 絮凝影響膜過濾性能 1）表面過濾膜的性能 過濾技術通過了不斷的實驗，隨著微濾連續(xù)運行，膜壓力有增大的趨勢，為了使運行時間延長，膜通量恢復，分析計算流量和衰減率之間的關系。用標準公式表示[5]。 式中： r——衰減通量或回收率 Jp(T)——水通量 T——室內(nèi)溫度 2)混凝預處理方法對膜過濾性能的影響 混凝，混凝沉淀和砂濾是在實驗中的三種微濾預處理方法[6]。與原水，混凝沉淀，混凝砂濾出水混合液的上清液濾液進行了比較（35mg/ L的氯化鐵是為絮凝或混凝沉淀預處理劑量）。一個過濾膜過濾周期包括60分鐘和五分鐘的洗滌，壓力的洗滌是過濾的1.2倍多。 聚偏氟乙烯中空纖維膜和U型自制膜組件被采用。通量衰減率的時間依賴曲線顯示，初始通量經(jīng)過5次過濾，膜通量迅速下降到36％，洗滌后其回收率在52％。這結果表明，原水直接過濾，很容易造成膜污染。與直接過濾相比，其他三種預處理方法可明顯增加其膜通量，其中過濾混合是最好的，其清洗后膜通量恢復率達到81％以上，而過濾上清液效果次之，當采用砂濾出水過濾時，對膜通量的影響最大。因此，混凝砂濾過程不應被視為微濾預處理，其他預處理（混凝預處理及混凝沉淀預處理）可根據(jù)實際情況選擇。 結論 1）在一般情況下，在灤河水的處理中，鐵鹽混凝劑對污染物的去除效果明顯優(yōu)于鋁鹽混凝劑混凝處理效果。結合實驗結果，鐵鹽混凝劑的最佳投藥量被確定為35mg/ L時，有最大經(jīng)濟效益。在相同條件下，對于鋁鹽的混凝劑PAC比硫酸鋁具有較高的去除污染物的能力。最后得出的結論與別人的結論相符。 2）從實驗結果可以得出結論，原水中混凝劑的最適投加量為3.5mg/ L，原水PH值為7.0時，鐵鹽混凝劑混凝效果最佳；PH值為6.5時，鋁鹽混凝劑的混凝效果最佳。由于PH值對鐵鹽混凝劑的投加影響很大，在無額外條件調(diào)整下，絮凝系統(tǒng)在35mg/ L的劑量條件下，仍能達到預計pH標準。 3）三種超濾膜過濾出水水質：原水，凝結水和上清液進行了比較，表明，出水濁度小于0.2NTU，微濾膜截留性能具有良好的保證。但微濾過濾后去除溶解的有機污染物只有8％-15％，比傳統(tǒng)的混凝效果低。 4）混凝預處理可以有效緩解膜污染[7, 8]。當三氯化鐵的混凝劑使用量為35mg/ L時，過濾預處理后，膜通量為80％，可維持一個過濾周期，這表明膜污染得到了有效緩解。在預處理的三種方法中，采用砂濾過濾出水時，膜污染是最嚴重。采用混凝沉淀過濾時，膜污染程度最小。 參考文獻 [1] J. P. Croue, “Isolation, fractionation, characterization and reactive properties of natural organic matter,” IWA Publishing, Greece, vol.2, pp. 126–129, September 2002. [2] S. Judd and B. Jefferson, “Membrane for Industrial Wastewater Recovery and Re-use,” Elsevier Science Ltd., Oxford, UK, vol.2, pp. 51–62, May 2003. [3] M. Clara, B. Strenn, E. Saracevic and N. Kreuzinger, “Feed–water pretreatment: methods to reduce membrane fouling by natural organic matter,” J. Aachen, Germany, vol.1, pp. 43–57, June 2004. [4] P. Songprasert, B.R. Lim and K.H. Ahn, “A model for membrane system in the treatment of wastewater containing high-molecular-weight compounds,” J. Am. Water Works Assoc., vol. 90, pp. 108–115, June 2001. [5] C. H. Kim, M. Hosomi and M. Okada, “Characteristics of fouling due to clay–organic substances in potable water treatment by ultrafiltration,” in Water Science and Technology, vol.38, pp. 243–250, October 2003. [6] C. Wallis-Lage, “Coagulation–Sedimentation Systems: similarities and difference between manufactures,” in Proceedings of WEF 76th Annual Conference and Exposition, Los Angeles, CA, October 2003. [7] B. Jefferson, A. Brookes and P. Le Clech, “Methods for understanding organic fouling in MBRs,” in Water Res., pp. 237–244, September 2004. [8] L. Defrance, M.Y. Jaffrin, “Reversibility of fouling formed in activated sludge filtration,” J. Membr. Sci.,vol.157, pp. 373–384, June 2002.