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Strong correlation was found between maximum sorption of acid on chitosan and its pK value in aqueous solution with the only exception - isovaleric acid - Fig. Taking into account that this acid has a branched hydrocarbon radical we suggested that structure and length of the radical can also effect carbonic acids sorption on chitosan.
But if we plot maximum sorption versus hydrocarbon radical length, we observe increase of sorption with increase of radical length Fig.
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It is obvious that hydrophobic interaction between chitosan and carbonic acids will be stronger with increase of the acid hydrocarbon radical length. Nevertheless, isovaleric acid with the same number of carbon atoms has the smallest value of sorption. This effect can be explained by space hindrances during penetration of a branched hydrocarbon radical inside chitosan helices. Initially, the clay particles are dispersed and occur in a parallel arrangement, due to their negative surface charge and positively charged cation shells repelling each other. There are two divisions of flocculators: As a result of flocculation , soils gain improved engineering performances, specifically by increasing the plastic limit, increasing shear strength and the development of a granular texture.
Srivastava, in Encyclopedia of Separation Science , Coagulation and flocculation are often considered as a pretreatment step in DAF processes. Favourable conditions for bubble attachment to particles requires coagulation conditions that reduce particle charge and produce hydrophobic particles.
Coagulant dosages and pH conditions that satisfy these criteria depend on the coagulant type and raw water characteristics, including particle concentration, hardness, and concentration and type of natural organic matter NOM. Unlike in sedimentation, large floc particles are not needed in DAF.
John Gregory, in Interface Science and Technology , A flocculation process involves dosing a coagulant and then allowing collisions to occur see Fig.https://guqowybajo.tk/map.php
Read e-book online Coagulation and Flocculation: Theory and Applications: 47 PDF
Both the rapid and slow mixing stages can have important influences on the effectiveness of the flocculation process. Rapid mixing should not be too intense or prolonged, since the high shear rate involved can result in poorer floc growth in the subsequent slow mixing stage . The results in Fig. The flocculation was monitored in the same way as for the results in Fig.
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The PACl was added after 60 s and rapid mixing rpm was applied for between 5 and 60 s. There then followed a period of slow stirring 50 rpm during which FI values reached plateau values. The largest increase in FI occurs for 10 s of rapid mix and longer times give significantly smaller flocs. It is noteworthy that in the 60 s rapid mix case a plateau value of FI is apparent before the slow stirring begins.
This shows that small flocs are formed in this stage, but floc growth is severely limited by the high shear. During the slow stirring phase further floc growth is possible, but to smaller limiting sizes than for shorter rapid mix times.
The effective shear rate in the slow mixing stage also needs to be carefully controlled. If the shear rate is high, the flocculation rate can be increased, according to Eq. However, floc growth is restricted by the applied shear, giving a limiting floc size see Figs. The question of floc strength and limiting floc size will be considered further in 4.
In this way, fairly rapid floc growth can occur in the early stages and large flocs can be formed in the low-shear regions. Harcum, in Biologically Inspired Textiles , Coagulation and flocculation are used in conjunction with filtration and centrifugation to improve the efficiency of these other processes.
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For example, if the cells to be removed from a culture broth are very small, it is possible that the filter media can become fouled or clogged owing to the cells filling the void space in the filter media. However, if the cells can be made to aggregate into larger more rigid particles, filtration becomes more efficient because of the lower pressure drops required across the filter media.
The same principle can be applied to centrifugation, an agent can be added to the culture broth that causes the cells to aggregate with this agent, such that the cell aggregate has a higher density.
Centrifugation efficiencies increase proportionally based on the density difference. Coagulation and flocculation agents are normally relatively inexpensive; however, the fate of the cells may preclude some agents. Typically, diatomaceous earth and calcium chloride can be used as flocculation agents. High-molecular-weight, water-soluble organic compounds can also be used; however, waste disposal costs may be higher.
Thus, for extracellular biologically inspired textile proteins, coagulation and flocculation may be appropriate alternatives, since the cells are normally discarded. In Studies in Interface Science , During the flocculation , the surfactant affects most significantly the kinetics of thinning of the liquid interlayer which are formed due to the mutual approach of drops, in which case the crucial role is played by the localisation of the surfactant in the phases only the surfactant dissolved in the dispersion medium can lead to tangential immobility of the adsorption layers , on the long-range intermolecular interaction, and the electrostatic repulsion forces.
And finally, for the coalescence, the effect of the surfactant is most evident in providing the prerequisites for the formation of equilibrium thin films, whose thickness and stability depend on the molecular, electrostatic and steric adsorption interaction energy, and also on the rigidity of the adsorption layers with respect to the formation of holes in the film .
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Check Access Check Access. Author links open overlay panel Luuk K. Publisher Summary In general, a mineral oxide surface in contact with an electrolyte solution of a given pH, outside the pzc, will develop a primary surface charge. Recommended articles Citing articles 0.
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