Hot Spot Theory

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When the negative pressure applied on the liquid is sufficiently high, the average distance between the molecules would exceed the critical molecular distance necessary to maintain the intact liquid and the liquid will break down to form cavities in vapor and gas-filled micro bubbles. The gases and vapors are compressed inside the heat generating cavity which ultimately produces a localized hot spot of short duration, creating local pressures and high temperatures (101, 102, 103). Among the sonochimie theories, the hot spot theory is widely accepted to explain the sonochemical reactions in the field of environment, which suggests that the collapse is so rapid and that the compression of the gas and steam inside the bubble is an adiabatic process.…show more content…
For example, polyaluminium ferric chloride, a new type of composite coagulant, was reported to have the advantages of high stability and good coagulating effect of hydrophobic and hydrophilic dyes. The discoloration capacity exceeded that of the poly polyferric sulfate and aluminum chloride. On the other hand, to avoid any problem of the disposal of solid sludge, different innovative approaches have been proposed. These include clotting separate volume low dye bath alum sludge recycling, recovery of chemical coagulant textile sludge, reuse of sludge in textile building materials, and processes such as vermicomposting textile mill sludge, coagulation followed by carbon adsorption. The coagulation followed by adsorption has been reported to produce effluent reuse standardcompared with the shoot coagulant consumption by 50%, thereby lowering the formed sludge volume compared to induce coagulation alone (11-115). Coagulation in combination with AOP, whether sequential or simultaneously, has been reported for dyeing wastewater. For example, simultaneous application of coagulation and Fenton oxidation showed improved performance over one of their autonomous…show more content…
The activated carbon, either in the powder or granular form is the most widely used adsorbent due to its extensive surface micro porous structure, high adsorption capacity and high surface reactivity. It is very effective to adsorb cationic, mordant and acid dyes and to a lesser extent dispersed, direct, vat, pigment and reactive dyes. The use of carbon adsorption for decolorization of the crude wastewater is impractical as a consequence of the competition between the colored molecules, and other organic / inorganic compounds. Hence, its use is recommended as a polishing step or used at the end of an emergency unit treatment stage to meet the discharge color duration. The weight loss is inevitable during its expensive onsite regeneration and hampers its widespread use. The use of non-conventional, economical sources as precursors for activated carbon has been proposed to achieve the cost-effectiveness in the application. As previously stated, adsorption is a non-destructive method in which there is only the change in the phase of the removed impurities and, therefore impose further problems in the form of sludge (121-124). The high cost also necessitates the adsorbent regeneration. On the contrary, some catalytic oxidation /reduction systems seem to be more effectively focused on the treatment of the small volume dyes. So it seems attractive to combine other adsorption process in a

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