臭氧氧化对饮用水原水中NOM的影响及改进处理方法

天然有机物(NOM)是普遍存在于自然水体中的一类复杂的有机混合物,不同处理方法对原水中NOM的去除情况不同,这对饮用水的安全性也有较大影响。臭氧氧化是近年来饮用水处理中常用的消毒方法,因此,研究臭氧氧化对饮用水原水中NOM的影响有着重要的意义。介绍了NOM的分类方法以及臭氧氧化对每种NOM组分的作用,分析了臭氧氧化NOM对饮用水消毒副产物生成的影响。同时,总结了一些以臭氧氧化为基础的改进处理方法,对比分析了它们的优缺点,并为以后的研究工作提出了建议和展望。     

饮用水中天然有机物去除技术的研究进展

水中存在的天然有机物(NOM)在饮用水处理过程中不仅会增加消毒副产物(DBPs)的数量，影响后续工艺处理，还会和水中的其他物质结合生成毒性更强的物质(有机金属络合物),严重危害人类身体健康。因此，研究NOM的去除对水质安全意义重大。文中介绍了NOM的种类及其危害，根据国内外去除NOM技术的研究现状，综述了混凝、吸附、高级氧化、膜处理和离子交换等技术去除NOM的效果及机理，重点阐述了以混凝为核心单元的耦合工艺对NOM去除的研究进展，分析了各种耦合工艺的优势与局限性，并对今后混凝技术的研究方向进行了展望。     

天然有机物提取及表征技术近期发展动态

在阐述天然有机物(NOM)来源和危害的基础上,对NOM的提取、分离和表征技术的近期发展动态进行了全面综述。介绍了NOM的各种提取和分离方法,对各种提取方法的优缺点和产率进行了分析比较,指出以反渗透、大孔树脂和膜分离为核心的工艺为目前最主要的提取分离手段。此外,详细列举了包括光谱、色谱、核磁共振、原子力显微成像等在内的NOM表征方法,对各分析结果所对应的NOM的结构特征和物化性质进行了阐述。     

原水天然有机物化学特性与消毒副产物关系

原水氯消毒过程中,氯会与水中的天然有机物(NOM)反应,生成三卤甲烷、卤乙酸等消毒副产物(DBPs).为了选择有效的饮用水净化工艺,控制消毒副产物的生成,研究天然有机物的化学特性及与消毒副产物的关系,是十分必要的.在总结NOM相似组分化学分离方法的基础上,概括了不同水源中NOM及各组分溶解性有机砌(DOC)的含量,对消毒副产物的贡献,化学组成以及可能生成DBPs的化学结构.不同水源中NOM及各组分DOC含量不同,相同组分对消毒副产物的贡献也有很大的差别,且NOM各组分的化学组成有一定的重叠,对生成DBPs的化学结构需继续研究.     

在使用铝系混凝剂的饮用水混凝期间铜离子（Ⅱ）对天然有机物去除的影响

混凝处理已经被证明在饮用水处理期间是控制天然有机物（NOM）最适合的技术。水源中重金属如铜（Ⅱ）（其能够形成铜．天然有机物络合物和／或与混凝剂相互作用）的存在对NOM的混凝造成干扰。在本研究中,检验了使用明矾或PAX．18（一种Kemiron Inc．,／3arrow,Florida销售的聚合氯化铝）去除NOM过程中铜离子（Ⅱ）的影响。结果显示在分别使用明矾混凝和PAx．18混凝的模拟水中,1～10mg／L的铜离子（Ⅱ）能够将总有机碳（TOC）的去除率提高25％和22％。存在铜离子（Ⅱ）的水中NOM去除率的提高很可能归因于铜．NoM络合物的形成,他们会更易于吸附在铝沉淀上,同时与铜离子（Ⅱ）形成共沉淀,这种共沉淀物还可以吸附NOM。     

活性炭对典型水源地NOM吸附特性的影响

利用修正后的Freundlich吸附等温线研究水源地水体中天然有机物(NOM)溶出pH、活性炭种类及活性炭粒径等对NOM吸附强度的影响。结果表明,典型水源地土壤溶出NOM吸附特性可以用修正后的Freundlich吸附等温线很好地表征;中性条件下溶出NOM的吸附强度明显高于酸性和碱性;活性炭对NOM的吸附具有选择性,且吸附强度呈现AR>HS->CP>AK-703的趋势;NOM的吸附强度随活性炭粒径的减小而增大。     

纳滤膜的制备与应用

目前,纳滤膜应用于饮用水处理行业已引起业界广泛的关注与研究。纳滤膜是一种介于反渗透膜与超滤膜之间的水处理膜,有着较高的渗透和截留性能;纳滤膜一方面能截留水体中大部分的微量污染物质,另一方面保留水体中对人体有益的矿物质。文中主要讨论了纳滤膜的制备方法、分离机理、表征方法、污染以及在饮用水方面的应用和所面临的瓶颈,并探讨了纳滤膜技术今后的发展工作。可以看出,纳滤膜在饮用水处理领域有着广阔的应用前景。     

使用深度氧化处理去除消毒副产物的前体物的试验室初步研究

天然有机物（NoM）普遍存在于世界各地的地表水和地下水中。在饮用水处理期间,仍留在处理后水中的NOM可以与氯反应形成消毒副产物。之前的研究已经显示,二氧化钛光催化剂对于UV254吸光物质可以获得超过96％的去除率,如疏水NOM,对于溶解有机碳（DOC）可以获得超过80％的去除率。但是,在适于用作市政饮用水之前,需要另外的过滤步骤回收悬浮催化剂。为了解决这个问题,我们使用了固载化催化剂,该催化剂使用溶胶凝胶制备而成,同时在台架试验中评估了其性能。在本研究中,二氧化钛溶胶凝胶已经被涂在底材上。结果显示制备的各种涂料对于DOC和UV254吸光率具有不同的去除效果。最大去除率分别是1．336g／m^2和89％。     

生活饮用水处理及化学清洗

介绍了直接饮用水对人体的危害,叙述了生活饮用水处理工艺的目的和应用特点,在二次供水设施清洗工艺流程中应注意的事项及要点,饮用水在处理前后的差异和处理后水质的标准及评价。对全面了解清洗技术在生活饮用水质中的应用具有重要意义。     

不同吸附模型分析天然有机物的吸附特征

为探讨活性炭吸附土壤溶出天然有机物(NOM)的最佳模型,利用Langmuir模型、Freundlich模型和Modified Freundlich模型分别对活性炭吸附不同浓度土壤(农田和森林)溶出NOM的数据进行拟合分析,发现与前两种模型相比,Modified Freundlich模型更适合用于对土壤溶出非均质复杂混合物NOM吸附过程的描述。用UV260表征溶出NOM的浓度的情况下,当农田和森林土壤溶出NOM的浓度范围分别在53.4～109.2/m和50.6～185.9/m时,低浓度的土壤溶出NOM更适合用于NOM吸附特性的分析。此外,在三种模型中与吸附强度相关参数(b、K和k)的分析中,K与b线性关系的具有高度相关性(R2=0.9857),而k与K(R2=0.0775)和k与b(R2=0.1429)的相关性较低,即Langmuir模型和Freundlich模型在描述NOM单层吸附过程中具有较好的一致性。     

Characterization of anion exchange membranes with natural organic matter (NOM) during electrodialysis

Natural organic matter (NOM) is thought to be a major source of fouling during membrane filtration of natural waters. The organic matter present in surface waters was characterized in terms of its molecular weight distribution, acidity and electrokinetic properties. The fouling potentials of anion exchange membranes were predicted by the characterization. Changes in the physicochemical properties of anion exchange membranes were also examined during electrodialysis (ED) process of solutions containing NOM. The ED performances were evaluated for the three anion exchange membranes (AMX, AM-1 and ACM) in the presence of NOM. Fouling phenomena in terms of current efficiency and NaCl flux were in good agreement with the fouling potentials predicted by the characterization results. Observations of the molecular weight distribution and the constituents of NOM revealed that the hydrophobic NOM fraction with high molecular weights deposited mainly on the membrane surface, providing fouling effects on the anion exchange membrane.     

Effects of Ozonation on Natural Organic Matter Reactivity in Adsorption and Biodegradation Processes – A Case Study: The Úzquiza Reservoir Water

In this paper the influences of preozonation on the effectiveness of NOM adsorption and biodegradation processes are studied. Three different types of water have been used in this study: A natural water from the Úzquiza Reservoir (Burgos, Spain), synthetics waters prepared using natural humic substances (fulvic and humic acids extracted from the Úzquiza Reservoir) and a synthetic water prepared using a commercially supplied humic acid. The effect of preozonation on NOM adsorption by activated carbon is evaluated: adsorption of humic acids (hydrophobic, high molecular weight compounds) is improved following preozonation; however, for the fulvic acids (hydrophilic, low molecular weight compounds), no net appreciable effect of preozonation on adsorption was observed. Preozonation increases the biodegradability of NOM: biodegradable dissolved organic carbon (BDOC), which was determined using two different bioassays (Billen-Servais method and Joret-Lévi method), increases with increasing ozone dosage. A characterization of humic substances based on their adsorption and biodegradability properties is also reported, showing the effect of ozone.     

Effect of hydrophilic/hydrophobic fractions of natural organic matter on irreversible fouling of membranes

Natural organic matter (NOM) has been identified as a major factor affecting membrane processes performances, but its impact is difficult to quantify from global parameters such as organic carbon content. The extent of fouling due to the different fractions of NOM from surface water has been examined in dead-end ultrafiltration using criteria such as flux decline and irreversibility in regard with organic matter rejection. The most important flux decline was observed during the filtration of the hydrophilic acids fraction whereas fulvic acids led to the most irreversible fouling. Furthermore, the hydrophilic fraction lost its fouling character when mixed with other fractions underlining that interactions between numerous components are possibly more important than the composition itself.     

Behaviour of natural organic mater during ultrasonic irradiation

Ultrasonic irradiation has been one of the advanced oxidation methods for natural organic matter (NOM) removal. Its application simplicity and no production of toxic by-products make the system attractive. It has been shown that high power ultrasound produces strong cavitation in aqueous solution causing shock wave and reactive free radicals by the violent collapse of the cavitation bubble. These effects should contribute to the physical disruption and inactivation of microbial structures as well as to the decomposition of toxic chemicals in the water. The objective of this research was to investigate the effectiveness of low frequency – high power sonication for NOM removal (measured by both means of UV₂₅₄ absorbance and TOC) as well as controlling DBPs formation by varying irradiation time, light intensity, NOM concentration. Temperature, pH, conductivity, redox potential, and turbidity were monitored to evaluate the experimental study. The results indicate a strong capacity of sonication for NOM removal. The preliminary experiments showed that NOM removal is influenced by the intensity and time of sonication. Ultrasound, applied under such conditions, may be a realistic possibility for large-scale treatment; however, further studies should be performed to evaluate its effectiveness on different water sources.     

Ozone Cleaning of Fouled Poly(Vinylidene) Fluoride/Carbon Nanotube Membranes

This research demonstrates for the first time that ozone is an effective cleaning agent for polyvinylidene fluoride (PVDF) membranes fouled by natural organic matter (NOM). Bare PVDF membranes as well as PVDF impregnated with CNTs (pristine (CNTs–P) and oxidized (CNTs–O)) at 0.3% mass membranes were used. Three different methods were investigated for cleaning the fouled membranes including; A: 10-min cleaning by pure water, B: 5-min water followed by 5-min ozonated water, and C: 10-min fully ozonated water. It was found that the application of fully ozonated water for 10 min was very effective to reinstate the flux to almost its original value of unfouled membrane. The CNTs–P/PVDF membrane exhibited the highest fouling with a total fouling ratio of 81%, while for the bare PVDF and the CNTs–O/PVDF membranes, the fouling ratios were 76% and 74%, respectively. The full ozonated water cleaning method gave the highest removal of fouling leaving the lowest irreversible fouling on the membrane as compared to the other cleaning methods. On the other hand, the highest removal of NOM fouling was obtained for CNTs–O/PVDF membranes indicating that fouling on CNTs–O/PVDF membrane was less bound than the other membranes. Contact angle measurements of the fouled membranes showed that all membranes exhibited increased contact angles due to the NOM deposition but after cleaning, particularly with ozonated water, the membrane contact angles returned to almost their original values. FTIR analysis of the membranes corroborated the results obtained.     

Characterizations of NOM included in NF and UF membrane permeates

The characteristic changes in the natural organic matter (NOM), from the feed to the permeate, due to nanofiltration (NF) and tight-ultrafiltration (UF), were investigated in terms of size (molecular weight), structure (hydrophobic and hydrophilic fractions), and functionality (charge density in terms of carboxylic acidity). These characteristic changes were expected to be associated with the reactivity of the disinfection by-products (DBP), fractions of biodegradable dissolved organic carbon (BDOC), and assimilable organic carbon (AOC) relative to the total organic carbon. The BDOC and AOC analyses demonstrated that the NOM included in the NF and tight-UF permeates were more biodegradable than those included in the feed waters, which were relatively hydrophilic and smaller, than those in the feed waters. The influence of the hydrodynamic operating condition in terms of the J₀/k ratio on the characteristics of the NOM included in the NF and tight-UF permeates was also demonstrated. In addition, the effects of the pH, ionic strength, and calcium ions on the specific UV absorbance (SUVA) values of the NOM in each of the feed and permeate waters, were demonstrated for a better understanding of the above characteristic changes, and to determine the applicability of the SUVA analysis for the characterization of the NOM.     

Simultaneous adsorption of MIB and NOM onto activated carbon. I. Characterisation of the system and NOM adsorption

The objective of this work was to increase the understanding of the adsorption competition between an odour compound, 2-methylisoborneol, and natural organic material (NOM). Part I describes the characterisation of six commercially available activated carbons, undertaken using nitrogen gas adsorption, surface titrations, and Fourier transform infrared spectroscopy. The natural organic material (NOM) from one raw water and four fractions obtained from an isolation and fractionation procedure undertaken on the same raw water, were characterised using ¹³C NMR, high-performance size exclusion chromatography, UV-visible absorbance and elemental analysis. Simultaneous adsorption of NOM and MIB indicated that the adsorption of the NOM was largely dependent on the pore volume distribution of the activated carbons, and less influenced by the variation in surface chemistry. Larger NOM molecules showed greater relative rates of adsorption where the access to the internal structure of the carbon was restricted by size exclusion, due to the shorter diffusion distances to adsorption sites travelled by the larger molecules. As the concentration of MIB was extremely low compared with that of the NOM in these experiments, no effect of MIB on NOM adsorption was seen. Part II reports the significant effect of the NOM solutions on the adsorption of MIB.