Photolytic Degradation of Methylene Blue: The Effect of Various Factors on Wastewater Treatment Efficiency

Abstract

In Ivory Coast, dyes are widely used in traditional textile dyeing. It's a lucrative business that is attracting more and more people. Unfortunately, the wastewater from these textile dyeing units is discharged directly and continuously into the immediate environment. This poses a risk to human health and the environment. Among these dyes, the frequently used methylene blue (MB) can disrupt the balance of aquatic ecosystems by affecting the survival of aquatic organisms, inhibit photosynthesis in exposed plants, and cause irritation or toxic effects in humans in the event of prolonged exposure. This work investigated the degradation of methylene blue (MB), a model dye, by photolysis. The effects of the following parameters were studied: initial dye concentration, pH, H2O2, NaI, NaCl, and NaCl combined with H2O2 or NaI. The experiments were monitored using a UV-visible spectrophotometer. The results showed that MB can be effectively degraded by direct photolysis in a basic medium and at very low concentrations. Additionally, NaI and H2O2 had a very significant positive effect (83.77 % and 92 %) in contrast to NaCl (6.23 %). Furthermore, the treatment of MB solution was enhanced when NaCl was combined with NaI or H2O2 with a degradation rate of 88.1 and 84.9 %, respectively. The kinetic study revealed that the UV irradiation of MB can be described by both zero-order and first or second-order kinetics. In conclusion, the UV/H2O2, UV/NaI, UV/NaCl+ H2O2, and UV/NaCl+NaI systems represent very interesting alternative processes for the treatment of wastewater containing dyes at neutral pH. These methods are particularly suitable for industries involved in textile dyeing and other activities generating dye-contaminated effluents, offering an efficient and environmentally friendly solution for mitigating water pollution and meeting regulatory standards.