Flocculation adsorption

Where MU water silica is high (say, more than 20-30 ppm Si02), action probably is needed to reduce the silica level at source. This may be achieved in several ways, for example, by the use of anion exchange or flocculation-adsorption processes using ferric sulfate or magnesium hydroxide. 

Bioelimination is detected by BOD, which is rather low BOD, compared to the COD. In such cases the polymer is removed from the waste stream in the WWT/CWWT by flocculation, adsorption, hydrolysis, and, to a certain degree, by biodegradation. Representatives are PVA, CMC, and acrylate sizes [16,17]. 

Chemical—Volatilization, neutralization, precipitation, flocculation, adsorption, desorption, dissolution, oxidation. 

Flocculation Adsorption, precipitation, formation of complexes Decolorization, elimination of organic carbon... 

The most common processes today are sedimentation, filtration, flocculation, adsorption, distillation, and solvent evaporation. These treatment methods are used for phase or component separation purposes. 

This book covers the latest advances in oxidation technologies, ozonation, membrane technology, micropollutant removal, and filtration processes including biological filtration, membrane filtration, and ultrafiltration. Also covered are fundamental processes such as coagulation, flocculation, adsorption, ozonation, preozonation, and granular activated carbon. 

Others are aimed at separation of the dyes by physico-chemical means (precipitation, flocculation, adsorption) to give an unobjectionable bulk effluent and a relatively small quantity of separated dye sludge which is suitable for further treatment or direct disposal as chemical waste. 

These and others experimental facts have been theoretically analyzed with the use of the methods of the self-consistent field and scaling [7i-17], The results of an analysis can be lined in the following simplified model in the flocculent adsorption layer (a distance between the centers of the adsorptive molecules I > 2Rj, the polymeric chain is in practically the same conformational state as in the solution in dripless adsorptive layer (/ < 27 an interaction between the adsorbed chains compresses the pol5mieric bdls in the adsorption plate and stretches them in a form of the chain by blobs [76], cylinders [72] or rotation ellipsoids [75] along the normal to the surface. 

In recent years, a variety of methods, including flocculation, adsorption, filtration, oxidation, and electrolysis, have been carried out to remove contaminant from wastewater [28-32]. Therein, flocculation is one of the most widely applied methods in primary purification due to its low cost and easy operation [33-35]. 

U. Goren, A. Aharoni, M. Kummel, R. Messalen, I. Mukmenev, A. Brenner, V. Gitis, Role of membrane pore size in tertiary flocculation/adsorption/ultrafiltration treatment of municipal wastewater. Separation and Purification Technology 2008,61, 193-203. 

Jyh-Ping Hsu is the dean of the College of Engineering, National Ilan University (on leave from the Department of Chemical Engineering, National Taiwan University). Among his research interests are flocculation, adsorption, and electrokinetic phenomena. 

Conventional methods of As removal from drinking water include oxidation/precipitation, coagulation/flocculation, adsorption, ion-exchange and membrane technologies. Similar approaches can be used also for defluoridation (Meenakshi and Maheshwari, 2006) and removal of U from driiiking water (Katsoyiannis and Zouboulis, 2013) although some of these methods have been tested at laboratory or pilot scale only. 

The physical chemist is very interested in kinetics—in the mechanisms of chemical reactions, the rates of adsorption, dissolution or evaporation, and generally, in time as a variable. As may be imagined, there is a wide spectrum of rate phenomena and in the sophistication achieved in dealing wifli them. In some cases changes in area or in amounts of phases are involved, as in rates of evaporation, condensation, dissolution, precipitation, flocculation, and adsorption and desorption. In other cases surface composition is changing as with reaction in monolayers. The field of catalysis is focused largely on the study of surface reaction mechanisms. Thus, throughout this book, the kinetic aspects of interfacial phenomena are discussed in concert with the associated thermodynamic properties. 

For example, van den Tempel [35] reports the results shown in Fig. XIV-9 on the effect of electrolyte concentration on flocculation rates of an O/W emulsion. Note that d ln)ldt (equal to k in the simple theory) increases rapidly with ionic strength, presumably due to the decrease in double-layer half-thickness and perhaps also due to some Stem layer adsorption of positive ions. The preexponential factor in Eq. XIV-7, ko = (8kr/3 ), should have the value of about 10 " cm, but at low electrolyte concentration, the values in the figure are smaller by tenfold or a hundredfold. This reduction may be qualitatively ascribed to charged repulsion. 

An interesting example of a large specific surface which is wholly external in nature is provided by a dispersed aerosol composed of fine particles free of cracks and fissures. As soon as the aerosol settles out, of course, its particles come into contact with one another and form aggregates but if the particles are spherical, more particularly if the material is hard, the particle-to-particle contacts will be very small in area the interparticulate junctions will then be so weak that many of them will become broken apart during mechanical handling, or be prized open by the film of adsorbate during an adsorption experiment. In favourable cases the flocculated specimen may have so open a structure that it behaves, as far as its adsorptive properties are concerned, as a completely non-porous material. Solids of this kind are of importance because of their relevance to standard adsorption isotherms (cf. Section 2.12) which play a fundamental role in procedures for the evaluation of specific surface area and pore size distribution by adsorption methods. 

The carboxylated units, ionized, decrease adsorption on subterranean substrates (23), ia proportion to the number of units, an important parameter ia petroleum recovery processes. In waste treatment processes cationic acrylamide comonomer units are often used (31) to iacrease adsorption and thereby flocculation of soHds ia wastewater (see Acrylamide POLYMERS Flocculating agents). The favorable and characteristics of acrylamide facilitate the... 

Cationic monomers are used to enhance adsorption on waste soHds and faciHtate flocculation (31). One of the first used in water treatment processes (10) is obtained by the cyclization of dimethyldiallylammonium chloride in 60—70 wt % aqueous solution (43) (see Water). Another cationic water-soluble polymer, poly(dimethylarnine-fi9-epichlorohydrin) (11), prepared by the step-growth... 

Dilution. In many appHcations, dilution of the flocculant solution before it is mixed with the substrate stream can improve performance (12). The mechanism probably involves getting a more uniform distribution of the polymer molecules. Since the dosage needed to form floes is usually well below the adsorption maximum, a high local concentration is effectively removed from the system at that point, leaving no flocculant for the rest of the particles. A portion of the clarified overflow can be used for dilution so no extra water is added to the process. 

There are two general theories of the stabUity of lyophobic coUoids, or, more precisely, two general mechanisms controlling the dispersion and flocculation of these coUoids. Both theories regard adsorption of dissolved species as a key process in stabilization. However, one theory is based on a consideration of ionic forces near the interface, whereas the other is based on steric forces. The two theories complement each other and are in no sense contradictory. In some systems, one mechanism may be predominant, and in others both mechanisms may operate simultaneously. The fundamental kinetic considerations common to both theories are based on Smoluchowski s classical theory of the coagulation of coUoids. 

For color removal, ozonization has achieved the greatest practical importance as seen by the plethora of articles and patents on this method (147—163). Ozonization in combination with treatments such as coagulation, flocculation, carbon adsorption, uv irradiation, gamma radiation, and biodegradation significantly and successfully remove dye wastes and reduce costs (156,164—170). 

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