Abstract
Currently, many industrial dyes are discharged into the environment in China, leading to serious water pollution. However, synthetic organic dyes in industrial effluents cannot be degraded by conventional wastewater treatment methods. Consequently, it is necessary to develop new environmentally friendly technologies to completely mineralize these non-biodegradable compounds. In this study, 300 mg/L typical Color Index (CI) Direct Blue 15 (benzidine disazo) in simulated dye wastewater was degraded by iron-carbon micro-electrolysis coupled with H2O2 to explore its decolorization, total organic carbon (TOC) removal rate, and degradation characteristics. Under the optimal degradation conditions (Fe/C = 2:1, pH = 3, 60-min reaction, 2 mL/L H2O2 (added in three aliquots), 300 mg/L dye), the TOC removal rate and the level of dye decolorization attained 40% and 98%, respectively. In addition, the degradation kinetics indicated that the iron-carbon micro-electrolysis process coupled with H2O2 followed first-order reaction kinetics. A degradation pathway for CI Direct Blue 15 was proposed based on the analysis results of treated wastewater obtained using UV-Vis spectrophotometry and gas chromatography–mass spectrometry (GC-MS). This study provides an efficient and economical system for the degradation of non-biodegradable pollutants.
Highlights
A large amount of synthetic organic dyes are applied in many fields, such as textiles, plastics, food, paper, printing, leather, cosmetics, pharmaceuticals, coatings, and others [1,2,3]
Under optimal conditions for the iron-carbon micro-electrolysis coupled with H2O2 addition, the total organic carbon (TOC) removal rate and the decolorization of Color Index (CI) Direct Blue 15 dye reached levels of 40% and 98%, respectively, after 60 min of treatment
The degradation pathway of CI Direct Blue 15 dye seems to include the main intermediates of 1-amino-8-naphthol and 3,3′-dimethylbenzidine. These compounds were completely broken into anti-pentenoic acid and phenol, which are speculated to degrade into CO2 and H2O through a series of oxidation reactions
Summary
A large amount of synthetic organic dyes are applied in many fields, such as textiles, plastics, food, paper, printing, leather, cosmetics, pharmaceuticals, coatings, and others [1,2,3]. It was proven that most azo dyes and their metabolites can generate toxic, carcinogenic, mutagenic, and teratogenic effects on human health and the environment [7,8,9,10]. Various advanced electrochemical oxidation processes are applied in China, including electro oxidation (EO, known as electrochemical oxidation or anodic oxidation), electrocoagulation, and electro-Fenton-based (EF) methods, to treat dye wastewater. These electrochemical processes achieved good results; they are expensive [18,19,20,21]. This study provided a basis for estimating the feasibility of this technique for the treatment of printing and dye wastewaters
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