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题名: 水质特征对铝盐混凝剂混凝过程的影响 —残余铝生成及沉后水过滤特性
作者: 焦茹媛
学位类别: 博士
答辩日期: 2016-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 王东升
关键词: 混凝剂形态,水质特性,溶解性有机物,絮体可过滤性,残余铝 ; coagulants species,water characteristics,dissolved organic matter,flocs filterability,residual aluminum
其他题名: Influence of Water Characteristics on the Coagulation Process by Al-based coagulants —Residual Aluminum Concentration and the Floc Filterability
学位专业: 环境工程
中文摘要:     水是人类赖以生存及发展的宝贵资源。随着社会的发展及人类活动的影响,水污染日益严重,水质安全不断受到威胁。混凝工艺是饮用水处理工艺中应用最为广泛的工艺之一,迄今为止仍为各种工艺中不可或缺的前置环节。本论文通过对我国主要城市饮用水原水及出厂水水质进行大规模调查,全面了解了我国饮用水原水水质特性及其对混凝处理过程的影响。此外,根据调查结果,针对我国饮用水混凝处理过程中常出现的问题,研究了水质特性、铝系混凝剂不同形态等对混凝过程中絮体生成、絮体的可过滤性以及处理后残余铝的影响。
通过对我国23个城市的52个饮用水水厂的原水及出厂水进行调查,首次全面地了解了我国饮用水原水特点。调查发现我国饮用水原水的DOC和UV254值与其他国家相差不大,但原水SUVA值相对较低,且含有较多的低分子量有机物和蛋白类物质。相比于长江、珠江及沿海地区,黄河流域水源中DOM中含有的腐殖质类物质及高分子量有机物最少。对于不同的地理位置,气候和人为因素对水质影响显著,其中,北方比南方原水的pH及有机物含量要高,且其有机物分子量相对较低。对比饮用水处理前后水质变化发现,所有处理后水中分子量在1000Da~2000Da范围的有机物含量有显著的增加。根据原水水质特征,本论文将我国各地区进行分类。与此同时,发现原水DOM的去除率与有机物的来源有显著的关系。腐植酸、富里酸及微生物代谢产物等天然来源有机物去除率的高低决定了整体有机物的去除。
    针对不同形态铝系混凝剂(Al2(SO4)3,Al13和Al30)对不同分子量有机物(0-1kDa, 800Da-6kDa和6kDa-70kDa)的混凝去除特性进行了研究,并考察了其对残余铝浓度及形态分布的影响。通过对比,发现Al13对低分子量有机物水样的DOC及浊度去除能力有限,但对中等及高分子量有机物水样的DOC及浊度去除效果较其他两种混凝剂要好,特别是在低投加量情况下。随着有机物分子量的增多,Al2(SO4)3需要更多的投加量使浊度降至最低。而Al30在低投加量条件下比Al2(SO4)3更能有效降低低分子量及高分子量有机物水样的DOC。对不同形态混凝剂,混凝后总残余铝浓度随着有机物分子量的增高而呈下降趋势,其中,电中和机理下残余铝浓度相对较低。中性条件下Al2(SO4)3形成絮体较大,但絮体的密实度较差。相比而言,Al13形成絮体较小,但密实度较高(除了低分子量有机物水样)。絮体的分形维数相比于絮体的大小更能反映残余铝的浓度变化趋势。Al13和Al30混凝剂处理后单体态铝(0-1kDa)及胶体态铝(30k-100kDa)是水中残余铝的主要形态,特别是单体态铝。
    针对不同水体特性下絮体的形成及其可过滤性,选择实际水体,研究了同一有机物浓度下,不同原水浊度对混凝机理及形成絮体可过滤性的影响,研究发现,最大化去除浊度的混凝剂最佳投加量低于最大化絮体可过滤性的最佳混凝剂投加量,而与最大化去除DOC的混凝剂投加量基本一致。因此,在实际水处理过程中,需要高于浊度最大化去除的混凝剂投加量,或最大化去除DOC的混凝剂投加量以达到提高絮体可过滤性的目的。浊度去除及絮体可过滤性指数的最佳pH范围一致。对比不同浊度原水的混凝结果发现,高浊度原水形成絮体的速度及尺寸大于低浊度原水。同时,考察了不同混凝机制下絮体特性与其可过滤性的关系。卷扫网捕机理下,提高原水浊度促进了水体DOC的去除并提高了絮体的可过滤性。对不同浊度水体,电中和机理下DOC的去除及絮体的过滤性都优于卷扫网捕机理。卷扫网捕机理下,提高絮体沉降性有助于提升过滤过程中絮体的可过滤性。而在电中和机理下,提高絮体尺寸分布的均匀性有助于提升过滤过程中絮体的可过滤性。
    选择具有典型铝形态的Al2(SO4)3及Al13两种混凝剂,考察了不同混凝剂形态对实际水体絮体形成及其可过滤性的影响。结果表明,最优投加量下,Al13絮体的可过滤性强于Al2(SO4)3。在中性条件下(pH6.5~7.5),Al2(SO4)3形成絮体尺寸大于Al13,然而Al13形成絮体密实度更强且尺寸分布更为均匀。因此,Al13在pH6.5和7.0条件下浊度去除率更高,同时絮体的可过滤性更好。此外,通过ESI-TOF-MS检测发现,中性pH条件下,Al13中铝形态比Al2(SO4)3更丰富,尤其是高聚合态铝,而在电中和作用机理下,Al13铝形态越丰富其混凝效果越好,絮体的可过滤性越强。同时研究了两种混凝剂的絮体强度及絮体破碎前后对絮体可过滤性的影响,对比发现,Al13絮体的抗破碎能力及破碎后的再生能力较强,尤其在高破碎强度下。相比卷扫网捕,电中和机理形成絮体彻底破碎后絮体再生能力更强。
英文摘要:     Water is the precious resources that determine the survival and development of human. However, with the development of the society and the influence of human activities, water pollution becomes more and more serious, and the safety of drinking water is threatened. Coagulation treatment is one of the most widely used technologies in water treatment process. So far, it is still the indispensable pretreatment process for all kinds of technologies. In this study, both source and treated waters from the full-scale drinking water treatment plants (DWTPs) in the main cities in China were investigated, and the comprehensive understanding to link the water characteristics to its treatability by coagulation in drinking water treatment was got. Based on the investigation, the influences of water characteristics and the coagulants species on the formation and treatability of flocs, and the residual aluminum were also studied.
    By the investigation of the water characteristics in both source and treated waters from 52 full-scale DWTPs of 23 cities in China, the comprehensive understanding to link the character to the treatability of dissolved organic matter (DOM) in drinking water treatment was the first time to be obtained. From the results, it was found that similar dissolved organic carbon (DOC) concentration and UV254 values were observed as compared with the other countries; however, low SUVA value and more low molecular weight organic matters and protein-like matters were observed in our country. Compared with the Yangtze River, Pearl River and the coastal area, the humic-like matters and the high molecular weight organic matters in the Yellow River were the lowest. The influence of climatic variation and human activities on the water characteristics was significant. The results showed the molecular weight of organic matters of the south part of China was larger than that of north; while the concentration of organic matter of the south part was lower than that of north. By comparing the differences between before and after the treatment, the significant increase of the middle molecular weight fraction (1000Da ~ 2000Da) was found. Based on the principal component analysis result of source water characteristics, the areas in China were grouped. In addition, the assessment confirmed the origin of DOM is the key factor influencing DOM removal.
    The effects of organic matter molecular weight (0-1kDa, 800Da-6kDa and 6kDa-70kDa) and coagulants species (Al2(SO4)3, Al13 and Al30) on the concentration and aluminium distribution in residual aluminium were investigated. In general, Al13 had relative poor ability to remove turbidity and DOC for low MW OM water samples, but it had good performance for mid and high MW OM water samples, especially at the low dosage. The higher of the MW, the more Al2(SO4)3 dosage was needed to reach the lowest turbidity. For the DOC removal, Al30 had better performance for the low and higher molecular weight (MW) organic matter water samples at lower dosage than Al2(SO4)3. For all the water samples, the residual Al concentration decreases as the organic matter MW rises. Charge neutralization mechanism showed better effects on the reducing of residual Al. Df is more important to reflect the dissolved residual Al rather than the flocs size. Al2(SO4)3 tended to form largest flocs but lowest Df for all the water samples at neutral pH condition. However, Al13 formed smallest flocs but highest Df (except the low MW OM water sample). The total dissolved residual Al concentration of Al13 and Al30weremainly contributed by the fractions with low (0-1kDa) and/or high MW (30k-100kDa), especially in the fraction with range of 0-1kDa.
    The impacts of physical characteristics of flocs formed using aluminium sulphate on filtration treatment of two comparative water samples were investigated. In general, the optimum dosage for maximizing filterability was higher than that for minimizing turbidity under neutral pH conditions; while the optimum dosage for both DOC removal and floc filterability was similar. In addition, the optimum pH for both turbidity removal and floc filterability was the same. Generally, floc formed from water with higher turbidity grew faster and larger. In addition, under sweep flocculation mechanism, higher turbidity contributed to greater DOC removal and better filterability of flocs. Charge neutralization mechanism showed better performance compared to sweep flocculation mechanism in DOC removal and floc filterability improvement for both waters, and showed superiority in turbidity removal only when raw water had high turbidity. Under sweep flocculation, improving the settling ability of flocs and reducing the residual flocs after the sedimentation process is an alternative means to promote the filtration efficiency. However, when charge neutralization mechanism is predominant, decreasing the floc size distribution will be favorable for floc removal by filtration processes.
    Aluminium sulphate (alum) and Al13 were investigated to understand the influence of coagulant species on the formation and filterability of flocs. At pH6.5 and pH7.0, it was found that Al13, a high MW polymer, showed better floc filterability than alum. This is because of the densely compacted and well-distributed size flocs from Al13, even though floc sizes of alum were generally bigger. Al specie distributions of the two coagulants at different pH levels were compared by using electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). It was found that Al species from Al13were more abundant than that from alum, especially for the high molecular weight (MW) oligomers. Under the charge neutralisation mechanism, higher MW Al species was found to improve coagulation performance and floc filterability. In addition, breakage resistance and regrowth ability of Al13 was better than alum. Comparing with flocs formed by sweep flocculation mechanism, flocs formed by the charge neutralisation mechanism readily regenerated after being thoroughly broken up.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/36871
Appears in Collections:环境水质学国家重点实验室_学位论文

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Recommended Citation:
焦茹媛. 水质特征对铝盐混凝剂混凝过程的影响 —残余铝生成及沉后水过滤特性[D]. 北京. 中国科学院研究生院. 2016.
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