Improvement of the Textile Industry Wastewater Decolorization Process Using Capillary Microreactor Technology

Dyes are an important class of pollutants because large amounts are often found in the environment as a result of their extensive industrial use. Traditional wastewater treatment methods often lead to high energy costs, formation of by-products, and the production of sludge. This paper analyzes the possibility of using a new, sustainable approach to water decolorization with reduced consumption of chemicals. In microreactor experiments, reactant molar ratios, volumetric flow rate, and microreactor length and diameter were varied. The obtained results showed that batch decolorization required 250–500 times higher molar ratios to achieve comparable decolorization (70–90%) and at least three times longer residence time. Microreactor experiments demonstrated that higher microreactor lengths and molar ratios influence positively the decolorization process, although satisfactory results are also achieved with medium microreactor lengths and lower molar ratios. Higher fluids velocities contribute to the decolorization process, but the best results were obtained using a medium velocity (in a 5.8 m microreactor system) to achieve the highest possible mixing intensity and long enough residence time. Microreactor systems have achieved significantly better decolorization results, considering any combination of microreactor length, molar ratio, diameter, flow rate, and residence time, than a batch system. Thus, a medium length microreactor system, with a low concentration of NaOCl, low flow rate, small diameter, and medium residence time can achieve satisfactory decolorization results, but with a lower consumption of chemicals, energy, equipment, and better environmental impact.