Dyes, decolorization, mineralization

Direct Fast Scarlet 4BS Consortium of a white-rot fungus and Pseudomonas 1-10 isolated from wastewater The microbial consortium showed a significant improvement in dye decolorization rates under either static or shaking culture. The 4BS was mineralized completely [89]... 

For the sonochemical mineralization of reactive dye Cl Reactive Black 5 with 20, 279 and 817 kHz irradiation, the discoloration and radical formation both are directly dependent upon ultrasonic frequency, acoustic power and irradiation time and indirectly on the number of free radicals thus generated, as their suppression decreased the discoloration rate due to radical scavenging effect. Although ultrasound alone is capable of decolorizing Reactive Black 5 but inefficient in mineralization as only 50% degradation was observed after 6 h of ultrasonic irradiation [121]. The sonochemical... 

There are several chemical compounds found in the waste waters of a wide variety of industries that must be removed because of the danger they represent to human health. Among the major classes of contaminants, several aromatic molecules, including phenols and aromatic amines, have been reported. Enzymatic treatment has been proposed by many researchers as an alternative to conventional methods. In this respect, PX has the ability to coprecipitate certain difficult-to-remove contaminants by inducing the formation of mixed polymers that behave similarly to the polymeric products of easily removable contaminants. Thus, several types of PX, including HRP C, LiP, and a number of other PXs from different sources, have been used for treatment of aqueous aromatic contaminants and decolorization of dyes. Thus, LiP was shown to mineralize a variety of recalcitrant aromatic compounds and to oxidize a number of polycyclic aromatic and phenolic compounds. Furthermore, MnP and a microbial PX from Coprinus macrorhizus have also been observed to catalyze the oxidation of several monoaromatic phenols and aromatic dyes (Hamid and Khalil-ur-Rehman 2009). 

Acid Orange 7 Sludge originally collected from a pulp and paper wastewater treatment plants Color removal of 96% was achieved in the presence of liposomes that facilitated uptake of dyes by anaerobic biomass, leading to a fast decolorization. Amines such as sulfanilic acid and aniline were mineralized by inocula with high microbiological diversity, even with domestic effluent. Orthanilic and metanilic acids and 1-amino-2-naphtol were persistent under tested conditions [176]... 

In anaerobic environment, the aromatic compounds can mineralize through hydrox-ylation, carboxylation, and redox reactions due to enzymatic reactions. Many of the amines that are formed during the anaerobic decolorization of azo dyes are known... 

The yeast-mediated enzymatic biodegradation of azo dyes can be accomplished either by reductive reactions or by oxidative reactions. In general, reductive reactions led to cleavage of azo dyes into aromatic amines, which are further mineralized by yeasts. Enzymes putatively involved in this process are NADH-dependent reductases [24] and an azoreductase [16], which is dependent on the extracellular activity of a component of the plasma membrane redox system, identified as a ferric reductase [19]. Recently, significant increase in the activities of NADH-dependent reductase and azoreductase was observed in the cells of Trichosporon beigelii obtained at the end of the decolorization process [25]. 

M. Neamtu, I. Siminiceanu, A. Yediler and A. Kettrup, Kinetics of decolorization and mineralization of reactive azo dyes in aqueous solution by the UV/H202 oxidation. Dyes Pigm., 53 (2002) 93-99. 

The efficiency of UV/O3 process (pH 8) for decolorization and mineralization of RB137 was investigated at higher dye loading of model wastewater, 80 mgL" (Figure 13). It can be seen that complete bleaching was achieved after 20 minutes of treatment, while final extent of partial mineralization after a one-hour treatment is 64.4% TOC removal. Trend of the curve that connects points of TOC removal extents measured during the treatment is almost linear, i.e. very different than that... 

Many dyes are decolorized and ultimately mineralized by photocatalysis. In the degradation of azo dye,18 21) the degradation rate decreases in the order monoazo > diazo > triazo.1819) Three processes including oxidation and reduction are considered to occur simultaneously in the photocatalytic degradation of dye. These are illustrated in Fig. 9.9. Process 1 is the common photocatalytic degradation process of organic compounds. Process 2 is spectral sensitization as observed in a wet-type solar cell. In process 3 one moiety of dye molecule serves as the electron acceptor, suppressing recombination between electron and positive hole. 

Whereas non-azo dyes are almost resistant to bacterial decolorization, azo dyes can be decolorized by bacteria under anaerobic conditions to form aromatic amines which show both toxic and carcinogenic potential [18]. Further aerobic mineralization can therefore only be initiated by additional chemical oxidation, for example, by partial ozonation, as reported by Krull et al. [19]. 

---