Azo dyes are an important class of environmental contaminants and are characterized by the presence of one or more azo bonds (-N=N-) in their molecular structure. Effluents containing these compounds resist many types of treatments due to their molecular complexity. Therefore, alternative treatments, such as biosorption and biodegradation, have been widely studied to solve the problems caused by these substances, such as their harmful effects on the environment and organisms. The aim of the present study was to evaluate biosorption and biodegradation of the azo dye Procion Red MX-5B in solutions with the filamentous fungi Aspergillus niger and Aspergillus terreus. Decolorization tests were performed, followed by acute toxicity tests using Lactuca sativa seeds and Artemia salina larvae. Thirty percent dye removal of the solutions was achieved after 3 h of biosorption. UV-Vis spectroscopy revealed that removal of the dye molecules occurred without major molecular changes. The acute toxicity tests confirmed lack of molecular degradation following biosorption with A. niger, as toxicity to L. sativa seed reduced from 5% to 0%. For A. salina larvae, the solutions were nontoxic before and after treatment. In the biodegradation study with the fungus A. terreus, UV-Vis and FTIR spectroscopy revealed molecular degradation and the formation of secondary metabolites, such as primary and secondary amines. The biodegradation of the dye molecules was evaluated after 24, 240 and 336 h of treatment. The fungal biomass demonstrated considerable affinity for Procion Red MX-5B, achieving approximately 100% decolorization of the solutions by the end of treatment. However, the solutions resulting from this treatment exhibited a significant increase in toxicity, inhibiting the growth of L. sativa seeds by 43% and leading to a 100% mortality rate among the A. salina larvae. Based on the present findings, biodegradation was effective in the decolorization of the samples, but generated toxic metabolites, while biosorption was effective in both decolorization and reducing the toxicity of the solutions.

Industrialization and other human impacts have placed increasing pressure on aquatic environments, with the generation of large quantities of toxic aqueous effluents containing different substances, such as synthetic dyes and other organic pollutants. It is estimated that between 10 and 15% of all dyes used in textile processes and other industries are discharged into wastewater, causing extensive aquatic pollution. Biological methods have been employed for the removal of color and toxicity from effluents containing azo dyes. Therefore, biosorption tests were performed with the dyes Acid Blue 161 e Procion Red MX-5B in simple and binary solutions, whereas biodegradation treatment was performed with the dyes only in binary solution. For biosorption, the dyes were removed by the fungi Aspergillus niger, Aspergillus terreus and Rhizopus oligosporus. The fungal biomass demonstrated good adsorption capacity to these compounds. The elimination of the toxicity of the solution after biosorption demonstrated the effectiveness of the treatment. Intense molecular changes after biodegradation treatment with the A. terreus fungus were demonstrated by the FTIR analysis. However, toxicity tests with Lactuca sativa seeds and Artemia salina nauplii indicated the presence of highly toxic metabolites in the reaction medium at the end of the treatment. Based on the findings, biosorption is more suitable for this type of treatment, since it was also capable of removing the molecules from the medium, with the advantage of impeding the formation of highly toxic by-products.

The aim of the present work was to observe microbial decolorization and biodegradation of the Direct Violet 51 azo dye by Candida albicans isolated from industrial effluents and study the metabolites formed after degradation. C. albicans was used in the removal of the dye in order to further biosorption and biodegradation at different pH values in aqueous solutions. A comparative study of biodegradation analysis was carried out using UV-vis and FTIR spectroscopy, which revealed significant changes in peak positions when compared to the dye spectrum. Theses changes in dye structure appeared after 72 h at pH 2.50; after 240 h at pH 4.50; and after 280 h at pH 6.50, indicating the different by-products formed during the biodegradation process. Hence, the yeast C. albicans was able to remove the color substance, demonstrating a potential enzymatic capacity to modify the chemical structure of pigments found in industrial effluents.

ELECTROLYSIS OF POLLUTING WASTES. I -WASTEWATER FROM A SEASONING FREEZE-DRYING INDUSTRY.Wastewater from a seasoning freeze-drying industry was electrolysed to increase its biodegradability. Stainless-steel electrodes were used at 9.09 A/m 2 , for up to 80 min. Conductivity, pH, biochemical (BOD) and chemical (COD) oxygen demands, Daphnia similis acute toxicity bioassays, and bacteria counting through the plate count agar method were determined after different times of electrolysis. The results (e.g. higher BOD and lower COD) showed that the biodegradability of the wastewater was significantly increased; furthermore, Fe 2+ ions liberated by the electrodes cause microorganisms to die and, when oxidised to Fe 3+ , contribute for the flocculation and sedimentation of solid residues.Keywords: electrolysis; seasoning wastewater; wastewater treatment. ARTIGO INTRODUÇÃOO simples ato de viver implica que seres humanos gerarão resíduos (2ª lei da Termodinâmica). Isto sempre foi verdade, mas só mais recentemente passou a causar problemas. Anteriormente o processo de tratamento de resíduos da própria natureza (dispersão, diluição e degradação) garantia que o equilíbrio natural não fosse alterado. Mais modernamente, em decorrência de mudanças tanto qualitativas quanto quantitativas nos resíduos gerados, a situação deixou de ser tão simples. Muitos materiais modernos (plásticos, substâncias agroquímicas etc.) não degradam facilmente e a taxa de geração de resíduos é hoje muito maior que a de sua degradação natural. Assim, não resta outra alternativa a não ser minimizar a entrada de resíduos na atmosfera, na hidrosfera e na litosfera, bem como minimizar a geração de resíduos sólidos. Para evitar que resíduos poluidores adentrem o ambiente, eles devem ser purificados a ponto de permitir que a natureza tome conta do resto: este é o problema de tratamento de resíduos 1 , no que se insere este artigo. A Eletroquímica pode contribuir muito para a solução deste problema 1-4 , seja por si só ou acoplada aos métodos biológicos, como discutido abaixo. Entre as características que tornam atrativo o tratamento eletroquímico, destacam-se 3 : versatilidade, eficiência de energia, facilidade de automação, compatibilidade ambiental e baixo custo efetivo.Águas industriais poluídas por compostos orgânicos são tratadas, mais comumente, através de sistemas biológicos, amplamente utilizados para o tratamento de efluentes lançados nos sistemas fluviais e marinhos. O tratamento biológico possui, entretanto, algumas desvantagens que levam à investigação de novos métodos ou, até mesmo, ao desenvolvimento de tratamentos alternativos. Entre as desvantagens destacam-se a grande área ocupada pelos sistemas convencionais de tratamento biológico (várias lagoas aeróbias, anaeróbias e facultativas), a exalação de odores desagradáveis e sua total inutilidade no caso da presença de alguns resíduos que contêm substâncias tóxicas ao processo (pouco biodegradáveis ou não biodegradáveis). Materiais não biodegradáveis são, em geral, compostos contendo anéis aromáti...

The use of synthetic dyes is commonplace in many industries, and the effluent is often dumped into the environment with no prior treatment. The aim of the present study was to analyze the use of an industrial strain of Saccharomyces cerevisiae (Meyen) for the removal of the textile dye Acid Blue 161 from an aqueous solution. Kinetic, isotherm, and thermodynamic models were created to evaluate the biosorption mechanisms. Fourier transfer infrared (FT-IR) spectroscopy was used to characterize and identify possible binding sites. A toxicity test was also performed using Artemia salina to analyze the degree of toxicity of the dye following treatment. The kinetic results demonstrated the occurrence of intraparticle diffusion in the yeast cells as the controlling mechanism of the sorption process. Biosorption followed the Langmuir model, except at pH 8.50, when it fit the Freundlich model. The thermodynamic results demonstrate that the biosorption process is spontaneous and endothermic. The FT-IR analyses confirmed the occurrence of a chemical reaction in acid pH, but physical adsorption only occurred at pH 8.50. The toxicity test showed that the use of the yeast biomass led to the complete removal of toxicity from the dye solution, demonstrating the effectiveness of the biosorption process in the treatment of effluents contaminated with these compounds.