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İçme sularında koagülasyon ile organik madde giderimi

Organics removal by coaqulation in drinking waters

  1. Tez No: 83021
  2. Yazar: İSMAİL AYDIN
  3. Danışmanlar: DOÇ. DR. LÜTFİ AKÇA
  4. Tez Türü: Yüksek Lisans
  5. Konular: Çevre Mühendisliği, Environmental Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1999
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Çevre Mühendisliği Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 111

Özet

ÖZET Son yıllarda organik maddelerin ve bunların oluşturdukları bileşiklerin insan sağlığı üzerindeki etkilerinin daha belirgin anlaşılmasıyla, bu kirletici maddeleri daha iyi tanımlamak ve bunları gerek mevcut arıtma tesisleri, gerekse ilave arıtma üniteleriyle sulardan tasfiye etmek elzem olmuştur. Tasfiye imkanları araştırılırken eldeki mevcut sistemlerden azami şekilde istifade etmek gerekmektedir. Bu çalışmada, içmesularında bulunan organik maddelerin ve yan ürünlerinin klasik arıtma sistemleriyle tasfiye şartları ince!enmiştir,ayrıca mevcut arıtma tesisleriyle tasfiye verimlerinin arttırılması hedeflenmiştir. Birinci bölümde çalışma konusunun genel bir değerlendirilmesi yapılmış, çalışmanın amaç ve kapsamına değinilmiştir. İkinci bölümde içmesularında bulunması muhtemel organik maddelerin yapı ve özellikleri, standartları incelenmiştir. Üçüncü bölümde, bu organik maddelerin koagülasyon ve flokülasyon gibi klasik arıtma metodlarıyla tasfiye şartları ve bunları etkileyen durumlar gözden geçirilmiştir. Dördüncü bölümde, yapılan deneysel çalışmalar, deney programı ve ölçüm yöntemleri anlatılmış, çalışılan ham su kaynağının özelliklerine değinilmiştir. Beşinci bölümde yapılan deneysel çalışmalar sonucunda elde edilen bulgular tartışılmış, veriler grafiklerle de desteklenmiştir. Altıncı bölümde çalışmalar sonunda elde edilen sonuçlar değerlendirilmiş ve öneriler sunulmuştur.

Özet (Çeviri)

ORGANICS REMOVAL BY COAGULATION IN DRINKING WATERS SUMMARY The organic content of water is troublesome for a number of reasons: 1. The organic content of natural water is largely responsible for problems associated with color. 2. Certain organic compound contribute to taste and odor problems in drinking water supplies. 3. The presence of organic compounds in treated water may foster problems associated with biological quality changes in the distrubition system. 4. The presence of organic compounds in drinking water has been reported to aggravate corrosion problems in the distribution system 5. The presence of organic compounds may interfere with demineralization processes by fouling anion exchange resins or membrans. 6. Organic compounds in water have been shown to interfere with the oxidation and removal of iron and manganese. 7. Haloforms and other halogenated organic compounds can be formed when chlorine is added to water at the levels required for disinfection. The chlorine may react either with natural humic substances or with certain anthropogenic compounds or both. 8. Certain organic compounds are known to be toxic or carcinogenic and these may be harmful even at the very low concentration at which they are present in water supplies. While humic subtances themselves are thougt to be harmles, these compounds may have other materials associated with them such as pesticides, phthalates, and heavy metals. The growing concern over the organic content of natural waters and its public health significance has highligthed the need for improved purification procedures. In 1978 the USEPA proposed a standart of 100 \xg/\ for total trihalomethanes in finished drinking water. Recognizing the goal of minimizing the organic content of drinking water as a treatment objective requires that the control process for existing treatment processes be reevaluated. Processes that have been finely tuned for particulate removal, for example, may not efficiently remove the water organic content. Coagulation is traditionally considered a pretreatment processes for particulate removal. However, the processes is instrumental in reducing the organic content of treated waters. If activated carbon must be used to reduce the organic content of the product water to an acceptable level, the pretratment processes become extremly important. Activated carbon is an expensive unit processes ; assuming the coagulation processes can be optimized for organics removal, the reduced load the carbon column will extend the expected life of the carbon while improwing product water quality and reducing treatment cost. The organic content of natural waters derives in part from naturally occuring products of biological activity in the aquatic and terrestrial environments and in xipart from human activities. The naturally occuring organics are frequently referred to as humic substances. Humic substances are amorphous, acidic, predominantly aromatic, hydrophilic, chemically complex polyelectrolyt.es that range in molecular weight from a few hundred to tens of thousands. Humic materials are negativly charged macromolecules under the ph conditions of most natural waters. Althoug these macromolecules may be truly dissolved, they can be classified as colloids because of their colloidal dimensions. Originally, humic substances were classified according to their solubilities under different conditions. However, many investigators consider only fulvic acid and humic acid and tend not to seperate the hymatomelanic acid component from the humic acid fraction. The three acidic fractions are structurally similar, but differ in molecular weight, ultimate an analysis, and functional group content, with fulvic acid havinga lower molecular weight. Fulvic acids contain more oxygen but less carbon and nitrogen, and have a higher content of oxygen-contain functional groups (COOH, OH, C=0) Per unit weight. Humic substances contain the following functional groups in varying quantities that affect their stability in water: carboxyl, phenolic, alcoholic, ketonic, quinonoid and methoxyl. For the pH of most natural waters, humic materials are the negativly charged macromolecules (anionic polymers). As the pH is increased, steabilitiy will increase because of the dissociation of the functional groups. The configuration of the humic molecule in solution will depend upon ionic strengt and pH. An extended configuration would be expected with increasing pH as a resault of repulsion between charged functional groups. Clay minerals dispersed in natural waters adsorb humic substances. The extent of adsorption depends upon the type of clay, the cationic form of the clay, and the solution pH. The presence of multivalent cations is important in this adsorbtion mechanism, since they act in a bridging capacity between the negativly charged clays and the negativly charged organics. Like exchange reactions, this mode of adsorption is reversible and influenced strongly by the electrolyte concentration. The maximum adsorption occurs at or near the pH corresponding to the pK of the humic material. The coagulation of humic substances with inorganic coagulants can be accomplished through two mechanism of destabilization-charge neutralization or precipitation. For the purposes of this discussion alum will be considered the coagulant. Destabilization may be accomplished by charge neutralization resulting from a spesific chemical interaction between positivly charged alumunium species and the negativly charged groups on the humic colloids. The fixation of multivalent cations onto ionized groups on hydrophilic colloids may be caused by electrostatic or chemical interaction, reducing the charge of the particles and altering their solubility. Destabilization by this mechanism would be accomplished over a narrow pH range (pH 4-6), and a stoichiometric relationship between the raw water humic concentration and the optimum cuagulant dosage would be obserbed. Humic substances can form water-soluble and water- insoluble complexes with metal ions. As the alum dosage is increased, precipitation may occur; however, destabilization by these mechanism may XIIincorparate humic material within alumunium hydroxide floe or coprecipatate it is alumunium humate. These destabilization mechanism were indicates an optimum region of operation for water treatment plants. In water treatment practice the parameters significantli affecting the operation of a coagulation process for color removal using ion or alumunium salts include pH, coagulant dosage and raw water humic concentration. Color removal to be dependent upon pH and coagulant dosage, with a. stoichiometric relationship between raw water color and the optimum coagulant dosage. Coagulation of natural organics or humic substances, the cationic polyelectrolytes can be used to destabilize humic acids. The cationic polyelectrolyte destabilizes the humics by charge neutralization involving a chemical reaction with carboxylate and phenolate groups on the humics. The removal of humics where polymers are used as coagulant aids with alum is an effective method of coagulation. The presence of organic matter in solution or as a complex on clay surfaces to inhibit coagulation. The cationic polielectrolyt.es reacts first with humate or fulvate on the clay surface before destabilizing by interparticle bridging. The best conditions for organics removal in a natural water may or may not coincide with the conditions required for good turbity removal. If the alum dosage is sufficiently high, good removals of turbidity may be achieved over a broad pH range, and the optimum pH may be selected for the best organics removal. At lower coagulant dosages the best operation pH must be determined by comparing the benefits of improved turbidity removal against the benefits of improved organic removal. Effective removal of natural organic matter from raw water can be achieved by aluminium coagulation provided due attention is paid to micro-floc formation (coagulation) and macro-floc development (flocculation). In this study; the effect of pH, coagulant dosages and the using of cationic polyelecrolytes as a coagulant aid on the coagulation conditions and how these parameters should be controlled to maximise organic matters is investigated. The removal of the organic matters by conventional coagulation and flocculation processes was examinated for the influent raw water to the Büyükçekmece Water Treatment Plant in istanbul. The general purposes and research need are given in the first chapter. In the second chapter, the structure and properties of the organic matters were examinated. These organics were classified of their effects and chemical properties. The organic matters were examinated three main group. Firstly volatail organic chemicals are referred. The affect of these chemicals on the human health were examinated. Maximum contaminant level and gools are given. After these senthetic organic chemicals were examinated. The affect of these chemicals on the human health were examinated. Maximum contaminant level and gools are given. After these senthetic polinucleer aromatic hydrocarbons were examinated. The affect of these chemicals on the human health were examinated. Maximum contaminant level and gools are given also. The sources of these contaminants are given at the same time. In the third chapter, the general mechanism of coagulation and flocculation and conventional removal of organics by these mechanism were examinated. Chemical coagulation with metallic salts has traditionally been used for turbidity removal; however coagulation is also capable of some organic matters removal. Aluminium (or iron) coagulation can remove organics via one of two general XIIImechanism: adsorption onto aluminium (or iron) hydroxide floe or formationof insoluble complexes in a manner anogous to charge neutralization. Generally the former mechanism is a more dominant at a higher coagulant dosages and higher pH, wheras the latter is relativly more dominant at a lower dose and lower pH. Several mechanism are referred to when describing the removal of natural organic matters, and each mechanism is favoured by a particular set of operational conditions. In practice, it is likely that these operational conditions will overlap and that more than one mechanism will be responsible for natural organic matters removal. The three mechanism of NOM removal most commonly referred to are charge neutralisation, entrapment, and adsorption. Charge neutralisation is the mechanism used to explain the precipitation of NOM in operational regions where aluminium hydroxide precipitation is minimal. Cationic aluminium interacts electrostatically with anionic NOM to form insoluble charge-neutral products. The concept of enhanced coagulation involves a broadening of coagulation objectives from turbitidy removal to include natural organic matter (NOM) removal. These dual objectives require modifying coagulation conditions, with the three principal alternatives being (1) type of coagulant, (2) coagulant dosage, and (3) coagulation pH. pH control of coagulation is one of the most important factors governing NOM removal. For many water treatment plants, the pH of coagulation, flocculation is usually the consequence of variable coagulant addition responding to variable water turbitiy, rather than the result of deliberate pH adjustment. This practice leads to variable removal efficiency of NOM. Removal of NOM can be achieved by providing additional unit processes, such as granular activated carbon (GAC) and nanofiltration, or by enhancing existing coagulation, flocculation and sedimentation processes. Enhanced coagulation is a valuable means of controlling the organic matters without requiring significant capital investments. In the forth chapter, the experimental studies are explained. The raw water characteristics and properties are given. The using chemicals and mesuring system are explained and listed also in the tables. Coagulation and flocculation experiments were carried out using smale scale jar testing. To evaluate the optimum coagulant dosages and the treatment pH's, standart“Jar-test”experiments were performed. The solutions were stirred rapidly at 100 rpm for 2 min during coagulant addition, followed by slow stirring at 30 rpm for 30 min. The pH was adjusted with dropwise addition of a %5 lime slurry or 1 N sulphuric acid to selected walues between pH 4 and 9 during a second 2-min rapid stir and finally the solutions were stirred slowly for 30 min. At the end of each experiment, samples were removed and filtered through a 0.45 - |am membrane before being analysed for absorbance at 270 nm. The floe settling experiments required 1000- ml samples of water. The results of these experiments were susceptible to slight variations in physical conditions of jar test stirring. xivFor coagulation aluminium sulphate [Aİ2(S04)3İ8H20] and several catyonic and anionic polimer (for coagulant aid) are used. The alum doses used include 20, 30, 40, 50, 60, 70, and 80 mg/l. The coagulation pH was carry out in the range of 4 - 9. The turbidity measurings were measured by digital turbidimeter (Dr.Lange Model). Dissolved organic matter concentration was measured in term of ultraviolet absorbance (UVA) at 270 nm by spectrophotometer (Jenway 6105 UV/Vis) with 1 cm. quartz cell. To decrease the measurings error every measurment was recurrenced two times. In the fifth chapter the experimentel results and their criticals on the coagulations with alum; alum and polyelectrolyte; and alum, polyelectrolyte, sepyolit are discussed. The first stage of experiments the coagulations pH was changed from 4 to 9 and the best operation pH was determined for turbidity and organics removal. The optimum pH of aluminium sulphate coagulation appeared as 6-7. The lower pH was obtained to the organics removal than turbidity removal. The best pH was 6 for the organics removal also 6.5-7 for the turbidity removal. In the second stage the best aluminium sulfate dosage was determined for the organics and turbidity removal. The best dosage was determined as 50 mg/l for turbidity and organics removal also. At the upper dosages restabilisation was appered. After determining the best coagulation pH and coagulant dosage the polyelectrolytes was used as a coagulant aid. When the cationic polyelectrolytes was used to increasing of the removal of organics was occured specially. In these chapter changing of the ultraviole absorbance(UVA), TOC and turbidity with alum dosages and operational pH are presented in the graphics. At the end of these chapter the coreiation curves are given between UVA/NTU, UVA/KMn04 and UVA/TOC. in the sixth chapter the results of the experiments are discussed. It was found that in the lower pH conditions (pH 4, pH 5) organic and turbidity reductions is very limited. In these conditions floe formations were observed higly weak. The best organics removal was occured at pH 6 while for turbidity removal at about pH 6.5-7. The best coagulant dosages also turbidity and organics removal were observed at 50 mg/l. In these conditions the UV absorbance removal was obtained about 50-60 %. The turbidity removal was obtained about 80-85 %. When cationic polyelectrolytes were used the removal efficiencys were increased. In these conditions the UV absorbance removal was obtained about 70 %. The turbidity removal efficiency was obtained about 90-95 %. xv

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