Removal of azo dye effluents generated by textile photography industries is a main issue in wastewater treatment. Enzymatic treatment of dyes appears to be one of the most efficient processes for their degradation. The elucidation of degradation pathways is of special interest considering health and environmental priorities. Ex situ nuclear magnetic resonance (NMR) spectroscopy and electrospray ionization (ESI)-ion trap mass spectrometry performed directly on incubation medium have been used for the first time to follow kinetics of sulfonated azo dye Orange II enzymatic degradation. Nine transformation products were identified using these complementary analyses performed ex situ without any prior treatment. Three types of cleavage are proposed for the degradation pathway: (i) a symmetrical splitting of the azo linkage that leads to the formation of 4-aminobenzenesulfonate (and 1-amino-2-naphthol, not detected); (ii) an asymmetrical cleavage on the naphthalene side that generates 1,2-naphthoquinone and 4-diazoniumbenzenesulfonate as products, with the latter one being transformed into 4-hydroxybenzensulfonate; and (iii) a third degradation pathway that leads to 2-naphthol and 4-hydroxybenzenesulfonate. Moreover, three other intermediates have been identified. This study, which constitutes the first concomitant use of (1)H NMR spectroscopy and ESI-ion trap mass spectrometry in this field, illustrates the indubitable interest of the ex situ approach.

The application of enzyme-based systems in waste treatment is unusual, given that many drawbacks are derived from their use, including low efficiency, high costs and easy deactivation of the enzyme. The goal of this study is the development of a degradation system based on the use of the ligninolytic enzyme manganese peroxidase (MnP) for the degradation of azo dyes. The experimental work also includes the optimization of the process, with the objective of determining the influence of specific physicochemical factors, such as organic acids, H(2)O(2) addition, Mn(2+) concentration, pH, temperature, enzyme activity and dye concentration. A nearly total decolorization was possible at very low reaction times (10 min) and at high dye concentration (up to 1500 mg L(-)(1)). A specific oxidation capacity as high as 10 mg dye degraded per unit of MnP consumed was attained for a decolorization higher than 90%. Among all, the main factor affecting process efficiency was the strategy of H(2)O(2) addition. The continuous addition at a controlled flow permitted the progressive participation of H(2)O(2) in the catalytic cycle through a suitable regeneration of the oxidized form of the enzyme, which enhanced both the extent and the rate of decolorization. It was also found that, in this particular case, the presence of a chelating organic acid (e.g., malonic) was not required for an effective operation. Probably, Mn(3+) was chelated by the dye itself. The simplicity and high efficiency of the process open an interesting possibility of using of MnP for solving other environmental problems.

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The aim of this study is the evaluation of the enzymatic action of the ligninolytic enzyme manganese peroxidase (MnP), through a suitable addition of H(2)O(2), as a feasible system for the in vitro degradation of complex structures. For this purpose, a highly recalcitrant polymeric dye (Poly R-478) was selected as a model compound. An amperometric technique was used to determine the H(2)O(2) requirement in the decolorization by nonpurified MnP. Two H(2)O(2) supply strategies-fed-batch (every hour) or semicontinuous (every 5 min)-were applied. The addition of H(2)O(2) in pulses led to a limited decolorization after the pulses and the instantaneous consumption or decomposition of H(2)O(2). Therefore, this way of addition may limit the actual H(2)O(2) concentration in the reaction mixture. In contrast, the semicontinuous strategy maintained lower and prolonged concentrations of H(2)O(2), which allowed a clearly greater decolorization (48% after 2 h). In addition, the effect of Mn(+2) concentration on the decolorization efficiency was investigated to establish the optimal application of the MnP-oxidative system. The enzymatic treatment provoked not only the destruction of the chromophoric groups but also a noticeable breakdown of the chemical structure of the dye. In experiments with pure enzyme, MnP proved to be the main factor responsible for the dye decolorization.