Assessment of the Raceway Pond Reactor for Degradation of Methylene Blue Dye in Different Types of Water: A Systematic Kinetics Study under Natural Solar Light

The Atacama Desert (AD), known for its extreme aridity and abundant solar irradiance, presents an opportunity for innovative solar-based environmental research. Raceway pond reactors (RPRs), characterized by their shallow, circular design, offer a scalable solution for pollutant degradation in aqueous environments, known for their versatility and eco-friendliness. This study explores the effectiveness of RPRs under the intense solar radiation of the AD in degrading Methylene blue (MB) dye across different water types: deionized water (DW), tap water (TW), and seawater (SW) with natural pH levels of 5.7, 7.1, and 8.5, respectively. Zinc oxide (ZnO) synthesized via the sol-gel method was used as the photocatalyst with average crystallite size 42.38 and 80.14 nm determined by the Scherrer and the Williamson-Hall equations, respectively. Results demonstrate the successful removal of 100%, 98.54%, and 84.64% of 20 mg/L of MB dye using 0.4 g/L ZnO photocatalysts in 10 L of DW, TW, and SW, respectively. Kinetic analysis favors a pseudo-first-order model, and the degradation order follows DW > TW > SW based on pseudo-first-order constants (0.03902, 0.03217, and 0.00969 min^-1), highlighting the potential of solar energy and RPRs for environmental remediation in sun-rich regions.