Dyes, removal

Analysis of certain papers requires special treatment before they can be disintegrated properly. Papers containing synthetics, tars, asphalt, mbber, viscose, or wet-strength resins must be analyzed individually (see TAPPI T401) (20). Dyes or colors must be removed from highly colored papers before examination. The method of dye removal depends on the type of dye. 

Nitro-substituted indolino spiroben2opyrans or indolino spironaphthopyrans are photochromic when dissolved in organic solvents or polymer matrices (27). Absorption of uv radiation results in the colorless spiro compound [1498-88-0], C22H2gN202, being transformed into the colored, ring-opened species. This colored species is often called a photomerocyanine because of its stmctural similarity to the merocyanine dyes (see Cyanine dyes). Removal of the ultraviolet light source results in thermal reversion to the spiro compound. 

Baiju, K.V., Shukla, S., Biju, S., Reddy, M.L.P., and Warrier, K.G.K. (2009) Morphology-dependent dye-removal mechanism as observed for anatase-titania photocatalyst. Catalysis Letters,... 

Reactive Orange 96 Anaerobic culture of sulfate-reducing bacteria, methanogens, and fermentative bacteria Sulfate-reducing bacteria removed 95% of the dye in 40 h. Methane producing bacteria did not contribute in dye removal. Fermentative bacteria could remove only 30% of the dye in 90 h [186]... 

The assessment of reaction kinetics by means of batch tests may be strongly affected by dye adsorption on the biophase and supports. The relevance of the adsorption phenomena of dyes on biophase has been addressed in studies regarding free cells [41], granular support biofilm [24], entrapped cells [11, 18], anaerobic sludge [10,24,31,34] and biological activated carbon (BAC) [42,45,47,48]. They have pointed out that the kinetics may be overestimated if the assessment of the adsorption contribution to the dye removal is not taken into account. Under batch conditions, the dye is fastly split between the liquid phase and the biophase, resulting in a sharp reduction of the dye concentration in the liquid phase until adsorption equilibrium is approached. The rate of dye adsorption must be estimated and ruled out in the kinetic assessment. 

In general, the mechanism for azo dyes removal by adsorption on an adsorbent material may be assumed to involve the following four steps ... 

Another important factor to evaluate is the initial dye concentration of the azo dye-containing wastewaters. Swshadri and Bishop drew a conclusion that dye concentration may cause a drop in the percentage of dye removal. Furthermore, the inhibition may be directly related to the effects of increased dye metabolite formation due to higher dye concentrations. Cariell et al. [96] found that C.I. Reactive Red 141 was inhibitory to anaerobic organisms at concentrations greater than 100 mg/L. 

Nitrate and oxygen also may play an important role in determining the rate of azo dyes reduction. Wuhrmann et al. demonstrated that obligate aerobes might actually decolorize azo dye compounds under temporary anoxic conditions. However, high nitrite concentrations in the mixed liquor of activated sludge plants could significantly inhibit dye removal. 

The above work indicated that the combined processes for the treatment of azo dye-containing wastewater have become promising alternatives to replace conventional technologies used for the purposes of decolorization. These processes are efficient in azo dyes removal with advantages of being cheap, nontoxic, and biocompatible. 

Reaction mechanism of azo dyes removal Limited study has focused on the reaction mechanism of azo dyes removal. The research of mechanistic and mathematical models to optimize the integrated process and to characterize the interaction between the reactant and azo dyes should be carried out in the future. 

Crini G, Badot PM (2008) Application of chitosan, a natural aminopolysaccharide, for dye removal from aqueous solutions by adsorption processes using batch studies a review of recent literature. Prog Polym Sci 33 399 447... 

Complex mycelium pellets of Trametes versicolor with activated carbon powder were investigated for decolorization of Acid Violet 7 [49]. The complex pellets showed the best dye removal. The dye was almost completely removed in 6 h. For complex pellets, maximum decolorization rate (Vmax mg/L h) and half velocity concentration (Ks mg/L) was calculated 130.5 and 345.0 in batch system, respectively. 

Using nonviable cellular biomass for azo dye removal has some advantages, namely the ability to function under extreme conditions of temperature and pH, and without addition of growth nutrients [10]. Also, waste yeast biomass, which is a by-product of industrial fermentations such as beer production, can be used as a relatively cheap source for biosorption of azo dyes. An important setback is the fact that the use of biomass for dye removal leads to an increase in the sludge amount, which requires further removal and treatment. 

Keywords green synthesis, sunlight, TMO nanoparticles, morphology, dyes removal. 

The presence of color in many industrial effluent streams is highly undesirable. LDHs have been found to be particiflarly effective at removing various synthetic dyes (Table 1) [158]. For example. Acid Blue 29 could be adsorbed on the surface or enter the interlayer region of the LDH by anion exchange an equilibrium time of 1 h with 99 % dye removal was obtained. Furthermore,... 

Wang, S Li, H Xu, L. Application of zeolite MCM-22 for basic dye removal from wastewater. Journal of Colloid and Interface Science, 2006 295,71-78. 

Perhaps the most convincing series of measurements are those of Paneth and Vorwerk, made, however, with solutions. The true molecular surface of a specimen of lead sulphate powder was determined by the radio-active indicator method, and this powder was then used as an adsorbent for dye-stuffs. The amount of dye removed from solution by the powder was determined colorimetri-cally. The results obtained by this method supported the theory of the single layer very well. 

The cationic compounds precipitate the (anionic) dyes from their aqueous solutions and on the fiber form higher molecular mass, sparingly soluble, saltlike compounds with the dyes. Removal of the latter from the fiber is thus made more difficult. A number of companies have compiled their own ranges of this type of aftertreatment agent. 

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