强化混凝与优化混凝:必要性、研究进展和发展方向

混凝是一个恒久的话题,一个引人人胜的课题,一个亟待解决的难题.水质的急剧恶化与科学技术的日趋发展,对混凝研究提出了严峻的挑战,而同时也给研究以一定的发展机遇.在简略地回顾混凝研究历史的基础上,对水体颗粒物、无机高分子絮凝剂、混凝作用机理以及混凝工艺研究的进展进行了概括性介绍.重点论述了强化混凝/优化混凝的必要性与目标.并进一步对若干主要研究进展与发展方向加以评述.     

不同水体溶解性有机物的混凝去除特性

采用硫酸铝、工业氯化铁、无机高分子絮凝剂(PAC)3种无机混凝剂,对广州珠江、北京密云、天津滦河不同原水进行了混凝实验,分析了不同混凝剂去除水体有机物的特性以及不同水体溶解性有机物(DOM)的内在分级特征与其混凝去除率的关系.实验结果表明,①珠江水体由于碱度低,pH较易下降,高投药浓度下此水体DOM更易被氯化铁去除;中低投药下,在南方水体中,PAC与盐类絮凝剂对去除DOM的混凝性能差别不如在北方水体中明显,表明南北方水体DOM的内在特性存在一定差异,即北方水体DOM中可混凝去除部分的有机物易发生电中和作用,带有较多负电基团,南方珠江水体DOM含带电基团的有机物相对较少,而中性有机物含量相对较高,这与进一步分级结果一致.②所有水体从混凝收敛点看,总溶解性有机碳(DOC)去除率都是工业PAC最高,显示电中和(憎水化)-沉淀(吸附)可能为这些水体DOM的主要去除机理.③从不同水体的DOC平均去除率看,珠江水体高于密云水体,它们又明显高于滦河水体.对水体DOM进一步的化学分级研究结果表明,DOC去除率越高的水体,其中的憎水中性物质(HoN)含量也越高.这表明,除了碱度、总有机碳(TOC)外,原水DOM的内在化学分级特征也是影响水体DOC混凝去除率的重要因素.     

高锰酸钾预氧化强化混凝去除绿藻的研究

以小球藻为对象,研究不同高锰酸钾投加量下小球藻胞外有机物分子量的分布、Zeta电位和胞外有机物浓度变化,并观察细胞结构,探讨预氧化强化混凝的机理.研究发现,当高锰酸钾浓度≤2 mg·L-1时,氧化前后藻液中的有机物组成基本不变,胞外分泌物(EOM)部分被氧化;在预氧化初期,EOM在高锰酸钾诱导下释放,胞外有机物浓度升高;藻的表面电位先下降后上升,藻活性由于高锰酸钾氧化受到抑制,但藻细胞结构保持完整,氧化后生成的MnO2附着在藻细胞表面,增加了藻细胞的比重,有利于后续的混凝沉降除藻.高锰酸钾浓度≥3 mg·L-1时,细胞壁被破坏,藻液中出现大分子的有机物,胞外有机物浓度上升,Zeta电位下降,这些都不利于后续的混凝除藻.结果表明,当高锰酸钾投加量为2 mg·L-1,预氧化1h后,PAC投加量为40 mg.L-1时,除藻效率达到92％,去除效果远好于直接混凝除藻.     

Effects of pre-ozonation on organic matter removal by coagulation with IPF-PACI

Ozone plays an important role as a disinfectant and oxidant in potable water treatment practice and is increasingly being used as a pre-oxidant before coagulation. The purpose of this study is to obtain insight into the mechanisms that are operative in pre-ozonized coagulation. Effects ofpre-ozonation on organic matter removal during coagulation with IPF-PAC1 were investigated by using PDA （photometric disperse analysis）, apparent molecular weight distribution and chemical fractionation. The dynamic formation of flocs during coagulation process was detected. Changes of aquatic organic matter （AOM） structure resulted from the influence of pre-ozonation were evaluated. Results show that dosage of O3 and characteristics of AOM are two of the major factors influencing the performance of O3 on coagulation. No significant coagulation-aid effect of O3 was observed for all experiments using either A1C13 or PAC1. On the contrary, with the application of pre-ozonation, the coagulation efficiency of A1C13 was significantly deteriorated, reflected by the retardation of floc formation, and the removal decreases of turbidity, DOC, and UV254. However, if PACl was used instead of AlCl3, the adverse effects of pre-ozonation were mitigated obviously, particularly when the O3 dosage was less than 0.69 （mg O3/mg TOC）. The difference between removals of UV254, and DOC indicated that pre-ozonation greatly changed the molecular structure of AOM, but its capability of mineralization was not remarkable. Only 5% or so DOC was removed by pre-ozonation at 0.6--0.8 mg/L alone. Fractionation results showed that the organic products of pre-ozonation exhibited lower molecular weight and more hydrophilicity, which impaired the removal of DOC in the following coagulation process.     

典型北方高碱度微污染水体强化混凝的示范研究

以高碱度、受有机物污染的典型北方水体为例,探索适宜的强化混凝技术.在水质调查的基础上,提出适合水质特征的强化混凝目标.研究了高碱度水体强化混凝技术方法.研究表明,可以通过3条技术途径提高水体中有机物的去除效率.其一在混凝前优化pH,促进絮凝剂水解形成中聚体,AlCl3在pH 6左右,FeCl3在pH 5左右时,有机物去除率可以提高一倍左右;其二是强化沉淀软化;其三是絮凝剂优化.结合我国实际情况,通过对传统絮凝剂进行改性,研制出了适合我国北方水质特征的高效絮凝剂,能较传统絮凝剂将有机物去除率提高30%以上.     

Effects of pre-ozonation on organic matter removal by coagulation with IPF-PACl

Introduction Ozonation as one of pre-oxidation techniques has complicated influences on coagulation in terms of turbidity and organic matter removals (Edwards and Benjamin, 1992a, b). Many studies have been carried out on the effects of ozone on coagulation, however there still exists some discrepancies among different researches. The mechanisms involved in the interac- tions between pre-ozonation and coagulation remain unclear. Reckhow and Singer (1984) reported that UV254, TOC, and TOX …     

优化混凝工艺及操作规范的研究与进展

水质的急剧恶化、科学技术的迅速发展与日趋严格的水质标准,对传统混凝工艺提出了严峻的挑战,同时也赋予其新的发展机遇.基于水源微污染现状和消毒副产物控制及安全供水的目标,针对性地提出优化混凝工艺及其操作规范成为目前推动水工业发展的重点所在.本文从评估体系、混凝剂优化、混凝过程优化、絮体结构形成优化以及系统优化控制等角度对优化混凝技术加以综合介绍,并进一步对若干主要研究进展与发展方向加以评述,以推动优化混凝工艺及操作规范的建立与发展.     

强化絮凝法去除水中DBP先质研究

采用强化絮凝的方法，实验研究和探明了混合反应强度，浊度，ＰＨ值等因素对去除水中ＤＢＰ先质的影响规律，进一步揭示了强化絮凝条件下除浊与除ＤＢＰ先质的相互关系，求得了不同水质条件下的最佳ＰＨ值和最佳投药量。     

混凝微界面过程研究与进展:AOM颗/粒物-IPF水-溶液相互作用的重要性

颗粒物微界面的物理化学过程在混凝工艺中起着十分重要的决定作用.有关界面过程化学的研究构成了混凝技术研究与发展的重要内容和理论基础.本文仅以颗粒物/AOM-IPF-水溶液的相互作用为例,从水体颗粒物的稳定性、高效纳米絮凝剂的研究、微界面形态与过程以及混凝作用机理等诸方面,对该领域的研究与进展加以系统介绍.     

强化混凝对二级处理出水中溶解性有机物特性的影响

以沈阳市B污水处理厂二级处理出水为研究对象,采用FeCl3.6H2O作为混凝剂,研究了强化混凝对二级处理出水中溶解性有机物(DOM)的卤代活性和荧光特性的影响.按照DOM在XAD树脂上的吸附特性将其分为5个部分:疏水性有机酸(HPO-A)、疏水性中性有机物(HPO-N)、过渡亲水性有机酸(TPI-A)、过渡亲水性中性有机物(TPI-N)和亲水性有机物(HPI).结果表明,强化混凝(混凝剂投加量为80mg.L-1,pH=5.00)对DOC的去除率为55.3%.强化混凝对HPO-A的去除率最高,而对HPI的去除率最低.强化混凝后,HPO-N的三卤甲烷生成活性(STHMFP)上升,而其他4种DOM组分的STHMFP下降.强化混凝能够有效去除类富里酸荧光物质和具有高环数和高聚合度的稠环类芳香性荧光物质.强化混凝对DOM组分的去除率和DOM组分的荧光强度下降率的相关性不显著.     

磁混凝工艺处理市政废水中的污染物去除特征研究

本研究对2个磁混凝站点进行了水质分析与溶解性有机物（DOM）的系统表征，考察了市政废水在磁混凝过程中的污染物去除效果与DOM去除特征，分析了强化磁混凝过程关键作用.研究发现：磁混凝可显著去除浊度、悬浮态有机物和磷，2个站点TCOD和TP去除率分别为52.53%/76.78%和64.41%/81.59%.市政废水DOM组成复杂，内源性DOM占比较高，两个站点DOM种类相似，但B站点进水有机物含量略少，且芳香类DOM占比较低.磁混凝对DOM具有显著的去除效果，主要去除高腐殖化程度、芳香性、聚合度、疏水性的大分子有机物，络氨酸类蛋白是主要的去除物质.B站点强化药剂的投加显著提升DOM和氨氮的去除效果，TOC和氨氮的去除率可达40.01%和36.08%，同时磷和TCOD的混凝效果也得到一定强化.本研究揭示了磁混凝过程污染物去除特征，促进了磁混凝过程的理解，为磁混凝在水处理中的推广应用提供了有效支撑.     

Effects of ozonation and coagulation on effluent organic matter characteristics and ultrafiltration membrane fouling

Effluent organic matter （EfOM） is the major cause of fouling in the low pressure membranes process for wastewater reuse. Coagulation and oxidation of biological wastewater treatment effluent have been applied for the fouling control of microfiltration membranes. However, the change in EfOM structure by pre-treatments has not been clearly identified. The changes of EfOM characteristics induced by coagulation and ozonation were investigated through size exclusion chromatography, UV/Vis spectrophotometry, fluorescence spectrophotometry and titrimetric analysis to identify the mechanisms in the reduction of ultrafiltration （UF） membrane fouling. The results indicated that reduction of flux decline by coagulation was due to modified characteristics of dissolved organic carbon （DOC） content. Total concentration of DOC was not reduced by ozonation. However, the mass fraction of the molecules with molecular weight larger than 5 kDa, fluorescence intensity, aromaticity, highly condensed chromophores, average molecular weight and soluble microbial byproducts decreased greatly after ozonation. These results indicated that EfOM was partially oxidized by ozonation to low molecular weight, highly charged compounds with abundant electron- withdrawing functional groups, which are favourable for alleviating UF membrane flux decline.     

Disinfection byproduct precursor removal by enhanced coagulation and their distribution in chemical fractions

Raw water from the Songhua River was treated by four types of coagulants, ferric chloride(FeCl3), aluminum sulfate(Al2(SO4)3),polyaluminum chloride(PACl) and composite polyaluminum(HPAC), in order to remove dissolved organic matter(DOM). Considering the disinfection byproduct(DBP) precursor treatability, DOM was divided into five chemical fractions based on resin adsorption.Trihalomethane formation potential(THMFP) and haloacetic acid formation potential(HAAFP) were measured for each fraction. The results showed that hydrophobic acids(HoA), hydrophilic matter(HiM) and hydrophobic neutral(HoN) were the dominant fractions.Although both HoN and HoA were the main THM precursors, the contribution for THMFP changed after coagulation. Additionally,HoA and HiM were the main HAA precursors, while the contribution of HoN to HAAFP significantly increased after coagulation.HoM was more easily removed than HiM, no matter which coagulant was used, especially under enhanced coagulation conditions.DOC removal was highest for enhanced coagulation using FeCl3 while DBPFP was lowest using PACl. This could indicate that not all DOC fractions contained the precursors of DBPs. Reduction of THMFP and HAAFP by PACl under enhanced coagulation could reach51% and 59% respectively.     

The impact of preozonation on the coagulation of cellular organic matter produced by Microcystis aeruginosa and its toxin degradation

Ozonation pretreatment is typically implemented to improve algal cell coagulation. However, knowledge on the effect of ozonation on the characteristics and coagulation of associated algal organic matter, particularly cellular organic matter (COM), which is extensively released during algal bloom decay, is limited. Hence, this study aimed to elucidate the impact of ozonation applied before the coagulation of dissolved COM from the cyanobacteria Microcystis aeruginosa. Additionally, the degradation of microcystins (MCs) naturally present in the COM matrix was investigated. A range of ozone doses (0.1–1.0 mg O₃/mg of dissolved organic carbon – DOC) and ozonation pH values (pH 5, 7 and 9) were tested, while aluminium and ferric sulphate coagulants were used for subsequent coagulation. Despite negligible COM removal, ozonation itself eliminated MCs, and a lower ozone dose was required when performing ozonation at acidic or neutral pH (0.4 mg O₃/mg DOC at pH 5 and 7 compared to 0.8 mg O₃/mg DOC at pH 9). Enhanced MC degradation and a similar pattern of pH dependence were observed after preozonation-coagulation, whereas coagulation alone did not sufficiently remove MCs. In contrast to the benefits of MC depletion, preozonation using ≥ 0.4 mg O₃/mg DOC decreased the coagulation efficiency (from 42%/48% to 28%–38%/41%–44% using Al/Fe-based coagulants), which was more severe with increasing ozone dosage. Coagulation was also influenced by the preozonation pH, where pH 9 caused the lowest reduction in COM removal. The results indicate that ozonation efficiently removes MCs, but its employment before COM coagulation is disputable due to the deterioration of coagulation.     

Study on the effects of organic matter characteristics on the residual aluminum and flocs in coagulation processes

Characteristics of organic matter may affect the residual aluminum after the coagulation process. This study reported the results of a survey for one drinking water treatment plant and measured the concentration of residual aluminum species with different molecular weights.Survey results indicated that humic acid or organic matter whose molecular weight was smaller than 1500 Da had significant effects on residual aluminum. All the treatment processes were ineffective in removing dissolved organic matter whose molecular weight was smaller than1500 Da. These results also indicated that the addition of sand or polyacrylamide in the coagulation process could greatly decrease the concentration of humic acid, and the concentration of residual aluminum also decreased. These results revealed that for all water samples after filtration, the majority of total residual aluminum existed in the form of total dissolved aluminum, accounting for 70%–90%. The concentration of residual aluminum produced in bovine serum albumin solutions indicated that when the DOC was larger than4.0 mg/L, there were still significant differences when the solution p H value varied from 4.0 to 9.0.     

Study on the effects of organic matter characteristics on the residual aluminum and flocs in coagulation processes

Characteristics of organic matter may affect the residual aluminum after the coagulation process. This study reported the results of a survey for one drinking water treatment plant and measured the concentration of residual aluminum species with different molecular weights. Survey results indicated that humic acid or organic matter whose molecular weight was smaller than 1500 Da had significant effects on residual aluminum. All the treatment processes were ineffective in removing dissolved organic matter whose molecular weight was smaller than 1500 Da. These results also indicated that the addition of sand or polyacrylamide in the coagulation process could greatly decrease the concentration of humic acid, and the concentration of residual aluminum also decreased. These results revealed that for all water samples after filtration, the majority of total residual aluminum existed in the form of total dissolved aluminum, accounting for 70%–90%. The concentration of residual aluminum produced in bovine serum albumin solutions indicated that when the DOC was larger than 4.0 mg/L, there were still significant differences when the solution pH value varied from 4.0 to 9.0.     

水中天然有机物混凝过程的光学在线监测及控制

以腐殖酸为去除对象，用光散射颗粒分析仪（PDA）对水中天然有机物的混凝过程进行在线监测，结果表明PDA输出信号（FI曲线）的特征值与絮凝体粒径和有机物去除率之间具有相关性，在弱酸性（pH=5.0)T和中性（pH=7.0)条件下，通过合理控制混凝剂投量，腐殖酸的TOC去除率可达50％，UV254去除率可达80％－90％，但pH=7.0时的投量为pH=5.0的5倍以上，在pH＝5．0的条件下，吸附电和中是有机物混凝的主要机理，但在混凝剂投量非常高的情况下，卷扫絮凝也起重要作用。在pH=7.0条件下，卷扫絮凝则是有机物混凝的主要机理。     

胞外物质影响铁盐混凝除铜绿微囊藻的效能与机制

藻及其代谢产物严重威胁着饮用水质的安全.混凝是饮用水处理工艺中去除藻细胞最为重要的单元,而藻细胞的胞外有机物(EOM)是影响藻细胞脱稳和去除的重要因素.本文以铜绿微囊藻为研究对象,对比混凝对原始藻细胞和经离心去除EOM的藻细胞(裸藻)的去除效果.结果发现,在pH为6.0、7.0和8.0的条件下,铁盐混凝对裸藻细胞(去除EOM的藻细胞)的去除率比原始藻细胞分别提高了5.01%、29.24%和27.45%,证实EOM对铁盐混凝除藻具有抑制作用.此外,絮体粒径动态分析表明,在pH分别为6.0、7.0和8.0下,裸藻细胞对应的最大絮体粒径均比原始藻细胞要高.Zeta电位分析表明,裸藻比原始藻的Zeta电位更高,因此,更容易通过压缩双电层脱稳.三维荧光分析结果表明,EOM易与金属发生络合反应,生成螯合物,从而抑制混凝除藻.     

Effect of bioflocculants on the coagulation activity of alum for removal of trihalomethane precursors from low turbid water

Reactivity of chlorine towards hydrophobic groups present in natural organic matter(NOM)provokes the formation of carcinogenic disinfection byproducts such as trihalomethanes in chlorinated water. The present study aimed to investigate the variations in coagulant activity of alum using two different bioflocculants(coagulant aid) namely, Moringa oleifera and Cyamopsis tetragonoloba for the removal of hydrophobic fractions of NOM and subsequent chlorine consumption by treated water. Effect of dual coagulants on trihalomethane surrogate parameters such as total organic carbon, dissolved organic carbon, UV absorbing materials and prominent hydrophobic species such as phenolic groups along with aromatic chromophores, polyhydroxy aromatic moiety have also been studied. The concept of differential spectroscopy and absorbance slope index has been employed to understand the combined effects of alum-bioflocculants on the reactivity of NOM with chlorine. Our result shows that the combination of alum and C. tetragonoloba is more efficient for reducing trihalomethane surrogates from chlorinated water as compared to M. oleifera. C. tetragonoloba elicited synchronized effects of sweep coagulation and particle bridging-adsorption which eventually facilitated efficient removal of hydrophobic fractions of NOM. The variation in the mechanistic approach of bioflocculants was due to the presence of cationic charge on M. oleifera and adhesive property of C. tetragonoloba.     

Preferential binding between intracellular organic matters and Al13 polymer to enhance coagulation performance

Coagulation is the best available method for removing intracellular organic matter (IOM), which is released from algae cells and is an important precursor to disinfection by-products in drinking water treatment. To gain insight into the best strategy to optimize IOM removal, the coagulation performance of two Al salts, i.e., aluminum chloride (AlCl₃) and polyaluminum chloride (PACl, containing 81.2% Al₁₃), was investigated to illuminate the effect of Al species distribution on IOM removal. PACl showed better removal efficiency than AlCl₃ with regard to the removal of turbidity and dissolved organic carbon (DOC), owing to the higher charge neutralization effect and greater stability of pre-formed Al₁₃ species. High pressure size exclusion chromatography analysis indicated that the superiority of PACl in DOC removal could be ascribed to the higher binding affinity between Al₁₃ polymer and the low and medium molecular weight (MW) fractions of IOM. The results of differential log-transformed absorbance at 254 and 350?nm indicated more significant formation of complexes between AlCl₃ and IOM, which benefits the removal of tryptophan-like proteins thereafter. Additionally, PACl showed more significant superiority compared to AlCl₃ in the removal of < 5?kDa and hydrophilic fractions, which are widely viewed as the most difficult to remove by coagulation. This study provides insight into the interactions between Al species and IOM, and advances the optimization of coagulation for the removal of IOM in eutrophic water.