摘要：强化混凝技术目前在给水领域主要应用于控制饮用水中消毒副产物的含量，以求达到更高的饮用水水质要求。依据国内外进行过的试验研究及应用，综述了强化混凝技术的研究进展及结果，在此基础上探讨了强化混凝在给水处理工程特别是电站净水系统中的应用前景。

 

关键词：给水处理 强化混凝 水质

 

 　目前严重影响净水水质进一步提高的问题之一是水中有机物的控制与去除。数十年来，国内外水处理工作者在有机物去除问题上已做过大量研究，探索过多种去除有机物的材料和方法。近年来美国环境保护局(USEPA)为达到饮用水消毒/消毒副产物(D/DBP)第一阶段的控制目标——饮用水中总三卤甲烷(THMs)≤0.08mg/L，卤乙酸(HAAs)≤0.06mg/L，推荐采用的工艺有：强化混凝(enhanced coagulation)、粒状活性炭吸附(GAC adsorption)和膜过滤(membrane filtration)，而且将强化混凝列为控制天然有机物(NOM)的最佳方法。　　

 

　　水的混凝处理是常规给水处理系统中最常用的一种工艺，通常其主要作用是去除水中悬浮颗粒和胶体微粒，同时也可以去除水中一部分有机物，但去除有机物的效率不高且波动范围较大，这主要与水中有机物的种类、形态有关。目前给水处理工艺中常用的混凝剂是Al2(SO4)3、FeCl3、PFS(聚合硫酸铁)、PAC(聚合铝)，由于水的pH值直接影响到混凝剂的水解形态和水中微粒的表面特性，进而影响到混凝效果，因此对大多数原水而言，最佳混凝效果并不发生在微粒ζ电位为0时。事实上，当混凝剂用量低时，获得较好混凝效果所发生的作用机理主要是电性中和、吸附架桥；而当混凝剂用量高时，获得较好混凝效果所发生的作用机理主要是吸附架桥、网捕沉淀。

 

天然水体中的有机物(通常主要为腐殖酸类有机物，其分子结构上常含有较多的-COOH和-OH基团)，按其在水中存在的形态可分为悬浮态(包括单独存在的有机颗粒和吸附在水中微粒表面的有机质)、胶态和溶解态三种，悬浮态、胶态部分通常是些分子质量较大、溶解度较小的有机物组分，天然水中的有机物有相当一部分被微小固体颗粒所吸附。混凝、澄清是常规给水处理系统中第一个处理单元，而天然水体中悬浮态、胶态部分有机物的性质与水体中存在的微粒很相似，如通常条件下带有负电荷(有机物在水中有离解趋向)，因此在混凝处理过程中，它们的去除机理应该是相似的，即通过电性中和、吸附架桥、网捕沉淀得以去除，而且去除率较高(可达80%～90%)。而水中分子质量较小、溶解度较大的有机物(主要是腐殖酸类中的富里酸等)，在一般混凝条件下去除率很低，主要原因是由于其具有良好的亲水性而不易被混凝剂的水解产物——金属氢氧化物所吸附。但是，如果通过改善混凝处理条件，即在低pH、高混凝剂用量的强化混凝条件下形成大量金属氢氧化物，改善混凝剂水解产物的形态且使其正电荷密度上升，同时低pH条件会影响有机物离解度和改变水中有机物

存在形态，有机物质子化程度提高，电荷密度降低，进而降低其溶解度及亲水性，成为较易被吸附的形态，吸着到大量存在的金属氢氧化物颗粒上共沉淀，这样可提高水中溶解态有机物的去除率，进而提高水中有机物总的去除率。所以，理论上通过改善混凝条件(强化混凝)是提高给水处理工程中有机物去除率的可行且有效的途径。　

 

　　强化混凝处理工艺试验研究较多的是美国，而且主要是在饮用水处理行业，其主要目标是提高饮用水中D/DBP先质的去除率。Thomas R. Hundt等人的研究表明，水中富里酸(FA)类有机物主要通过电性中和沉淀、吸附共沉淀得以去除，且主要与铝盐的水解形态有关；低pH条件，聚合氯化铝对FA的去除效果优于AlCl3。Gil Grozes等人对Sacramenta等河水进行的强化混凝试验发现，混凝的pH控制是获得NOM最大去除率的决定因素，在pH≈6的条件下，强化混凝可增加65%的NOM去除率。过量加入相近剂量的混凝剂，铁盐对NOM的去除效果明显优于铝盐，其解释是：①铁盐的酸化能力比铝盐强，所以其混凝时pH值比铝盐低，较低的pH条件会增加腐殖酸类物质的质子化程度，增加混凝剂水解产物上的正电荷密度，减少混凝剂需求量，有利于有机物吸附到金属氢氧化物上；②尽管铝盐水解产物的比表面积［200～400m2/gAl(OH)3］大于铁盐水解产物的比表面积［160～230m2/gFe(OH)3］，但相近剂量的铁盐水解产生Fe(OH)3的量是铝盐水解产生Al(OH)3量的2.8倍。另外还发现了高分子聚合物作混凝剂对溶解态NOM的去除效果较差，这是由于它们不能产生对有机质具有较好吸附作用的水解产物，也说明了水中NOM的混凝去除机理主要是被吸附在混凝剂水解产物(金属氢氧化物)上而从水中分离出来。F.Julien等人的研究也表明，铁盐对NOM的去除效果优于铝盐，有机物上有一个或没有功能基时，不能同时被典型的混凝—絮凝和吸附在金属氢氧化物絮体上而去除，而含有至少两个相邻功能基(-COOH和-OH)的化合物可同时由混凝—絮凝和吸附去除，有机物的去除取决于其上的功能基-COOH和-OH的多少及分子质量，且有机物最大去除率并不发生在ζ电位为0时。Joseph G.等人对腐殖酸类物质较多的原水进行混凝试验时，发现混凝剂量与TOC去除率关系曲线上出现突变点，而相对腐殖酸类物质较少的原水，混凝剂量与TOC去除率关系曲线比较平缓，这说明水中NOM的去除主要依靠沉淀和共沉淀。Joseph G.等人还比较了几个主要的有机物去除工艺特征认为强化混凝是去除天然水中有机物较经济、实用的一种工艺。Eric M.Vrijenhoek等人研究发现，去除THMS先质的最佳pH值为5.5，去除机理可能是：在混凝剂用量低时，形成金属—有机物的复合物；而在混凝剂用量较高时，有机物吸附到金属氢氧化物上而被去除，腐殖酸类成分多的原水，NOM去除率较高。试验还表明，在低pH条件下能维持原有的浊度去除效果。

 

 

丁桓如等人用聚合硫酸铁和聚合氯化铝对黄浦江水进行的混凝试验表明，在最佳pH条件下(聚合硫酸铁为5.6，聚合氯化铝为5.5)，聚合硫酸铁和聚合氯化铝混凝剂对水中总的、溶解态的和紫外吸收部分的有机物去除率分别达到70%、52%、55%和70%、52%、33%，去除该水体中有机物的最佳pH范围在5.5～6.5。铁盐的pH适用范围比铝盐大，在低pH混凝条件下，水体中有机物的去除率明显提高，而且聚合硫酸铁优于聚合氯化铝。黄廷林用Al2(SO4)3作混凝剂对腐殖酸水样和兴庆湖水样进行的强化混凝试验表明，混合搅拌强度对TOC去除效果有影响，在较低的混合搅拌强度下，通过延长絮凝反应时间可获得稍好的TOC去除效果。但是，混合强度对TOC去除效果的影响远没有pH和混凝剂用量的影响大，去除TOC的最佳pH值均在5.5左右，TOC去除率分别可达80%和70%以上，且浊度变化不影响DBP先质去除。

 

　　国内外的试验研究得到了几个较一致的结论：①水中有机物主要依靠吸附共沉淀得以去除；②去除水中有机物的最佳pH值在5.5～6.5，加大混凝剂用量是有利的；③NOM在混凝条件下去除的主要影响因素是pH值和混凝剂；④强化混凝对腐殖酸类有机物的去除特别有效。

 

化混凝是在常规混凝处理基础上发展起来的去除水中有机物特别是富含腐殖酸类有机物的一种处理工艺，相对其他处理工艺，其成本较低且在原有处理设备上稍作改造就可实施。国内外的试验研究均表明混凝处理的pH值控制在6左右，并且适当提高混凝剂用量，对大多数源水中的有机物具有较好的去除效果，关键是pH的调节问题。pH调节可通过加酸、用酸化能力强的混凝剂(如FeCl3)或用离子交换除盐系统中的阳床酸性出水调节，这样的工艺条件在工业给水工程中实施是可行的，特别是在电站给水处理中。因为一般的电站给水处理系统中都有离子交换除盐系统辅助的酸碱系统，所以混凝的pH调节更易实现，而对含有

反渗透(RO)预除盐装置的系统，为降低RO膜的水解率和防止结垢，其进水pH值一般均要调节到酸性范围内，这对实施强化混凝而言，实质上是将pH调节点前移了。强化混凝主要增加了水处理系统中相关设备的防腐需求、pH调节等费用，但对有机物含量不高的源水可省去GAC吸附设备的投资及运行费用，而对有机物含量较高的源水，通过强化混凝处理也可进一步提高GAC吸附设备的运行效率(降低进水pH值，对GAC吸附去除水中NOM更有效，最根本的是要在较低的成本和充分利用现有工艺的条件下，实现给水质量的明显提高。因此，对源水进行强化混凝试验以确定去除水中有机物的最佳pH范围及混凝剂用量，进一步研究强化混凝与其他工艺(如GAC吸附处理)的配合使用，这在我国水源水普遍受到微污染的情况下很有现实意义，并相信混凝强化技术在给水处理工程中也有较大的应用推广价值。

 

 

Enhanced Coagulation in Water Treatment Project 

 

 Abstract: The enhanced coagulation technology is currently mainly used in the field of control of drinking water disinfection by-products in the content, in order to achieve a higher quality of drinking water requirements. Test conducted according to international research and application of enhanced coagulation technology, reviewed research progress and results, on the basis of the enhanced coagulation in water treatment projects, especially water purification systems in power plant applications. 

 

Keywords: water treatment water by enhanced coagulation 

 

  

 

     Seriously affect the water quality is currently one of the issues to further improve the control and removal of organic matter in water. For decades, foreign workers in organic matter removal treatment has done extensive research on the issue, explore a variety of materials and methods to remove organic matter. In recent years, the U.S. Environmental Protection Agency (USEPA) to meet drinking water disinfection / disinfection byproducts (D / DBP) the first phase of the control objectives - total trihalomethanes in drinking water

(THMs) ≤ 0.08mg / L, haloacetic acids ( HAAs) ≤ 0.06mg / L, recommended process include: enhanced coagulation (enhanced coagulation), granular activated carbon adsorption (GAC adsorption) and membrane filtration (membrane filtration), but also as the control of enhanced coagulation of natural organic matter (NOM) the best way. 

 

    Coagulation treatment of water, conventional water treatment system is the most commonly used technique, its main role is usually to remove suspended particles and colloidal particles in water, but also able to remove part of the organic matter, but it is not efficient removal of organic matter and a larger range, mainly with the type of organic matter in water, form related. Present a common coagulant in water treatment is Al2 (SO4) 3, FeCl3, PFS (PFS), PAC (PACl), due to the water directly affects the pH value of the Hydrolysis of coagulant and water particles surface properties, thereby affecting coagulation, so most of the raw water, the best place in the coagulation effect is not ζ potential of particles 0. In fact, when the coagulant dosage is low, get a better effect occurring coagulation mechanism is charge neutralization, adsorption bridging; and when the coagulant dosage is high, get a better coagulation effect occurred The adsorption mechanism is mainly bridges netting precipitation. 

 

     Organic matter in natural waters (usually mainly humic acid organic compounds, the molecular structure often contains more-COOH and-OH groups), their presence in water can be divided into the suspended form (including the separate existence adsorption of organic particles and organic matter in the surface of the particles in the water), three kinds of colloidal and dissolved, suspended, colloidal part of the larger molecular weight is usually more, the smaller the solubility of organic components of natural water a considerable portion of organic matter is Adsorption of small solid particles.Coagulation, clarification conventional water treatment system is the first processing unit, while the natural water suspended, colloidal organic part of the nature and existence of the particles is very similar to water, such as a negative charge under normal conditions (organic matter in water, dissociation tend to), so the coagulation process, their removal mechanism should be similar, namely, by charge neutralization, bridging adsorption, precipitation to remove the netting, and the removal rate is higher (up to 80 % ~ 90%). The smaller molecular weight in water, solubility of the larger organic matter (mainly humic acid fulvic acid in the class, etc.), in general, the removal rate is very low under the conditions of coagulation, mainly due to its good and not susceptible to hydrophilic coagulant hydrolysis product - the adsorption of metal hydroxide. However, if by improving the conditions of coagulation, ie at low pH, high coagulant dosage form of enhanced coagulation conditions, a large number of metal hydroxide, to improve the shape and coagulant hydrolysis to increase the positive charge density, while low pH conditions, organic matter will affect the degree of dissociation and change existing form of organic matter in water, organic matter increased the degree of protonation, charge density is reduced, thereby reducing the solubility and hydrophilic properties, a form more easily adsorbed, adsorption to the abundance of metal hydroxides precipitation particles, which can increase the water removal rate of dissolved organic matter, thereby increasing the removal rate of total organic matter in water. So, in theory, by improving the conditions of coagulation (coagulation) to the water treatment works to improve the removal of organic matter and effective way possible. 

 

     Experimental study of enhanced coagulation treatment process more the United States, but mainly in the water treatment industry, the main objective is to improve the drinking water in the D / DBP precursors removal. Thomas R. Hundt, who studies have shown that the water fulvic acid (FA) class of organic compounds, mainly through charge neutralization and precipitation, adsorption to remove the precipitation and hydrolysis of mainly the morphology of aluminum; low pH conditions, chloride polymerization the removal of aluminum on the FA is better than AlCl3. Gil Grozes, who carried on the Sacramenta coagulation and other water tests found that coagulation pH control is to obtain the maximum removal rate of the determinants of NOM, the pH ≈ 6 conditions, the enhanced coagulation can increase to 65% of the NOM In addition to rates.Excessive dose of coagulant added similar, iron salts on the removal of NOM is better than aluminum, and its interpretation is: ① iron salt of the acidification capacity than aluminum strong, so when the coagulation pH value lower than the aluminum, low pH, humic substances will increase the level of protons, increasing coagulant hydrolysis products on the density of positive charge to reduce the coagulant demand is conducive to the metal hydroxide on the adsorption of organic compounds; ② Although the aluminum Hydrolysis specific surface area [200 ~ 400m2/gAl (OH) 3] ferric hydrolysis products is greater than the specific surface area [160 ~ 230m2/gFe (OH) 3], but similar doses of iron salts hydrolysis of Fe (OH) 3 is the amount of aluminum hydrolysis Al (OH) 3 and 2.8 times the amount. Also found for the coagulant polymer removal of dissolved NOM less effective, it is because they can not produce good adsorption of organic matter in the hydrolysis products, and also shows the coagulation water NOMmechanism is to be adsorbed on the coagulant hydrolysis products (metal hydroxide) rather isolated from the water. F. Julien et al study also showed that the effect of iron salt on the removal of NOM than aluminum, organic or not, there is a functional, you can not also be typical of coagulation - flocculation and adsorption in the metal hydroxide flocbody and removal, which contain at least two adjacent functional groups (-COOH and-OH) compounds at the same time the coagulation - flocculation and adsorption to remove organic matter removal depends on the functional groups-COOH and -OH of the number and molecular weight, and the maximum removal rate of organic matter does not occur in the ζ potential is 0. Joseph G. et al humic substances on higher raw water coagulation tests, found that the amount of coagulant and appear on the TOC removal curve mutation, and relatively less humic substances in raw water, mixed TOC removal efficiency of coagulation dose and relatively gentle curve, indicating that the removal of NOM in water mainly depends on precipitation and total precipitation. Joseph G., who also compared the main characteristics of the organic removal process that enhanced coagulation to remove natural organic matter in water is more economical and practical a process. Eric M. Vrijenhoek et al study found that the best removal THMS precursors pH 5.5, removal mechanism may be: in the coagulant dosage is low, the formation of the metal - organic complex; in coagulant dosage high, the organic compounds adsorbed on the metal hydroxides were removed more humic acid composition of raw water, NOM removal rate is higher. The results also show that at low pH conditions to maintain the original turbidity removal. 

 

     Ding Huan, such as other people use PFS and PAC on the Huangpu River to the coagulation tests showed that the optimum pH conditions (PFS, 5.6, 5.5 PAC), ferric sulfate and chloride polymerization of the total aluminum coagulant in water, and UV absorption of dissolved organic matter removal rates of some 70%, 52%, 55% and 70%, 52%, 33%, removal of most of the organic matter in water best pH range of 5.5 to 6.5. Iron salt, pH range than alum for larger coagulation at low pH conditions, the water removal rate was significantly improved, and PFS than PAC. HUANG Ting-lin with Al2 (SO4) 3 as coagulant Xingqing humic acid lake water samples and samples of the enhanced coagulation tests showed that mixing intensity on TOC removal influence, mixing at low intensity, flocculation obtained by extending the reaction time slightly better TOC removal. However, the mixing intensity on TOC removal effect of pH and coagulant dosage is far from the impact, the optimum pH value of TOC removal were around 5.5, TOC removal rates were 80% and 70% or more, and the turbidity does not affect the removal of DBP precursors. 

 

    Study abroad has been some of the more consistent conclusion: ① rely mainly on organic matter in water to remove adsorbed precipitation; ② best to remove organic matter in water pH value of 5.5 ~ 6.5, is beneficial to increase the amount of coagulant ; ③ NOM removal in the coagulation conditions, the main factor is the pH value and coagulant; ④ enhanced coagulation of humic acid organic removal particularly effective.

 

     Of coagulation in the conventional coagulation developed on the basis of the removal of organic compounds in water rich in humic acid organic compounds, especially a treatment process, compared with other treatment processes, and its low cost and processing equipment in the original brief transformation can be implemented. Study at home and abroad show that the pH value of the control of coagulation in the 6 or so, and appropriately increasing the coagulant dosage, the source of most of the organic matter in water removal with a good, the key issue is the regulation of pH. pH adjusted by adding acid, with the acidification ability of the coagulant (such as FeCl3) or by ion exchange demineralization system Yang bed Suanxing water regulation, such conditions implemented in the industrial water supply project is feasible, especially in the power plant to the water treatment. Because most of the power plant water treatment system, desalination system has assisted ion exchange acid-base system, so more likely to achieve coagulation pH regulation, while containing reverse osmosis (RO) desalination plant of the system pre-order to reduce the RO membrane hydrolysis rate and the prevention of fouling, the pH value of water generally have to be adjusted to the acidic range, which is the implementation of enhanced coagulation, the pH regulation is essentially a point forward. Coagulation treatment system mainly increased corrosion in the demand for related equipment, pH adjustment and other costs, but the source is not high organic content of water can save GAC adsorption equipment investment and operating costs, and higher levels of organic matter source water, through enhanced coagulation treatment can further improve the operating efficiency of GAC adsorption equipment (lowering water pH, NOM on GAC Adsorption removal of more effective, the most fundamental is to lower costs and take advantage of existing technologyconditions, to achieve water quality has improved significantly. Therefore, the source water coagulation tests to determine the best removal of organic matter in water pH and coagulant dosage range, further enhanced coagulation and other processes (such as GAC adsorption processing) with the use, which in our micro-polluted source water in general case by the great practical significance, and that enhanced coagulation in water treatment projects also have a greater application value.